Fuel pressure troubles???

[DON-Z-26ZX]

I've been chasing this problem for a few weeks now....I stress the "chasing" part....:(
99 454 mag mpi, starts & idles just fine. Problem is, after running hard for a while, (wot), it just drops back to idle, it doesn't die, but it struggles to get over 3000 rpms, really cuts out. After sitting for a couple of hours at the island, I only pushed it to 3500 rpms on the way home & it ran fine.
I just replaced the map sensor after a code 34. It now seems to be much "snappier" on the throttle, & it revs just fine, but this issue is still there when under a full load.
I haven't checked the fuel pressure, but I do plan on doing that this evening.
Does this seem like it could be a fuel pressure problem? I did check the pump to see if it seemed to be over-heating, but it felt normal to the touch.
Where is the best place to check the pressure?
After doing a search on fuel pressure issues, & reading many posts, I'm really thinking that my troubles is definetly fuel related. I do have to ask, if I had either hi-pressure, or low-pressure, wouldn't I have a trouble code indicating that? Or does it take something else to set that code? This is very nerve racking, I feel as though I'm "chasing my tail" with this. One other thing I noticed right about the same time this happened. The engine labored to get to 4800 rpms, & my top speed dropped down to 55. I had figured at the time I had 4 adults, coolers, & full fuel, so I just ignored it. Yesterday, it was just myself & wife, & about 3/4 fuel, still only 55, & then it falls off....I'm really baffled with this whole thing...Thanks for any input with this.

[VetteLT193]

I am thinking it could be something more sensor related. I assume the 454 mpi has a throttle position sensor. I'd start there... if that sends the wrong information you will get the symptoms as described. And, it could happen in an instant. It could also not be sending the right data for WOT, so the computer may not be injecting enough gas because it thinks it's only at 3/4 throttle...

It could be fuel pressure, but I doubt it... it seems too 'instant' of a problem.

[VetteLT193]

And by the way, if your TPS is out of whack, the computer could throw a MAP code...

Basically, if you are running at WOT, but the TPS is only telling the computer it's running at 75% throttle (or some other number less than full throttle) it would make the computer think it's running below sea level because the MAP will show a pressure that is ridiculously high (throttle is letting more air in than the computer thinks, so pressure is higher)

I am guessing that if the TPS data seems 'good' to the computer (i.e. within the acceptable range from 0-100%) but the MAP is sending data that is out of range based on the TPS, it will throw the MAP code.

[DON-Z-26ZX]

That's an approach I had not thought of, it definetly sounds like a good direction to look into. I've seen methods of testing a TPS, but I don't remember how it is. Do you have the specs on testing one?

[mrfixxall]

That's an approach I had not thought of, it definetly sounds like a good direction to look into. I've seen methods of testing a TPS, but I don't remember how it is. Do you have the specs on testing one?


First check that all the fuel lines from the tank are tight including the steel lines going to the fuel seperator and the fuel fuel filter...it wont leak but it will suck air and cause it to die and lack power....

second if your down on fuel pressure you will get a back fire through the intake..

third if your tps wasnt giving you the 4.5 to 5.0 volt referance at wot then their would be some kind of a boug.....tps is usually .5 volts or under at idle and at wot it should be between 4.5 to 5.0 volts....all you need is a multimeter to check it and check it at the tps wires...

last check your motor mounts (lower nuts) they have a tendcy to come loose on mercs and you loose your drive aleignment and that will bring your rpm down..

[MOP]

I usually stay out of FI posts being a bit old for it, it may be delivery related. When it comes to fuel it is always a good practice to start at the source, tank pickups, anti siphon valves, tank vents all could add to your problem. Many times it is the root and not the branches!

Phil

[VetteLT193]

I had to google for details, and piece this together. please verifiy this, or hopefully someone else here will. The details on the Merc TPS are hard to find:bonk:

Generally, TPS run from 0-5 volts 0 = idle and 5 = WOT, you should get a smooth sweep from 0-5 as you roll the throttle open... It looks like Merc uses this same voltage sweep.

It sounds like the merc TPS has 3 wires. Black, Blue, and Gray.

The black one is the one you need, connect the black to Pos. (red) and ground out the neg. (black) terminal on your voltage meeter. sweep it open and see if it goes to 5 volts.

Also pay attention if you hold it open that it stays consistent, and check as you run a smooth sweep that the voltage is smoothly increasing with no 'blips' in voltage.

[VetteLT193]

I think I might have misread your first post... to clarify: did it run great, then suddenly not run right and since that time it has not run right? Or, does it intermittently run good / bad?

If it all was fine, then it has run like crap after, it probably is the fuel system. First thing I'd guess there is a vac. leak. you maybe hit a big wave or something and a line popped off. This of could kill your fuel pressure (basically kicking it back to idle pressure) which would kill performance. the line popping off isn't all that likely, but still a possibility.

[DON-Z-26ZX]

First check that all the fuel lines from the tank are tight including the steel lines going to the fuel seperator and the fuel fuel filter...it wont leak but it will suck air and cause it to die and lack power....
second if your down on fuel pressure you will get a back fire through the intake..
third if your tps wasnt giving you the 4.5 to 5.0 volt referance at wot then their would be some kind of a boug.....tps is usually .5 volts or under at idle and at wot it should be between 4.5 to 5.0 volts....all you need is a multimeter to check it and check it at the tps wires...
last check your motor mounts (lower nuts) they have a tendcy to come loose on mercs and you loose your drive aleignment and that will bring your rpm down..

Thanks Jim, I was hoping you would chime in on this, I actually wanted to give you a call today, but once again, your number rolled off my phone & I didn't save it. I thought I had this thing figured out, but I was wrong...LOL...
I will be changing my filter this evening, & going thru all the connections, but I'm not thinking I'll find any loose, because it would lose prime & be hard to start back up if that was the case, am I correct with that?
Do I just prob thru the wires going to the TPS, to check voltage? Do you know what the wire color refrence is for the TPS connector?
You mentioned the back fire thing....I didn't think about it until I read your post...when the rpms fall off, I pumped the throttle a couple of times to try & get it going again, & it would back fire, & drop back to idle. Is that sounding more like a pressure thing? I hate just guessing & installing a new pump, that is a $300 guess....LOL...Again, thanks for your input.

[DON-Z-26ZX]

I had to google for details, and piece this together. please verifiy this, or hopefully someone else here will. The details on the Merc TPS are hard to find:bonk:
Generally, TPS run from 0-5 volts 0 = idle and 5 = WOT, you should get a smooth sweep from 0-5 as you roll the throttle open... It looks like Merc uses this same voltage sweep.
It sounds like the merc TPS has 3 wires. Black, Blue, and Gray.
The black one is the one you need, connect the black to Pos. (red) and ground out the neg. (black) terminal on your voltage meeter. sweep it open and see if it goes to 5 volts.
Also pay attention if you hold it open that it stays consistent, and check as you run a smooth sweep that the voltage is smoothly increasing with no 'blips' in voltage.

Thanks, I was trying to find that info....

[DON-Z-26ZX]

I think I might have misread your first post... to clarify: did it run great, then suddenly not run right and since that time it has not run right? Or, does it intermittently run good / bad?
If it all was fine, then it has run like crap after, it probably is the fuel system. First thing I'd guess there is a vac. leak. you maybe hit a big wave or something and a line popped off. This of could kill your fuel pressure (basically kicking it back to idle pressure) which would kill performance. the line popping off isn't all that likely, but still a possibility.

Yes exactly, it was running great, & this started about 3 weekends ago, & I've been chasing it since. Since then the RPMs are tough to get above 4000, & the speed has dropped off. I was able to run WOT for about 5 mins & then it fell back to idle. I tried it a couple of times & couldn't even get 2000 without it stumbling. I let it sit for a few mins, started it back up & ran it the rest of the way to the island not going over 3000. After a few hours, we left & it ran fine all the way home, but I didn't push it over 3800....I'm lost...I do appreciate any & all input on this. I think it would be easier if it was more consistant with the troubles. The only thing that is consistant, is the trouble reaching max rpm, & the loss of about 8 mph.

[mrfixxall]

Thanks Jim, I was hoping you would chime in on this, I actually wanted to give you a call today, but once again, your number rolled off my phone & I didn't save it. I thought I had this thing figured out, but I was wrong...LOL...
I will be changing my filter this evening, & going thru all the connections, but I'm not thinking I'll find any loose, because it would lose prime & be hard to start back up if that was the case, am I correct with that?
Do I just prob thru the wires going to the TPS, to check voltage? Do you know what the wire color refrence is for the TPS connector?
You mentioned the back fire thing....I didn't think about it until I read your post...when the rpms fall off, I pumped the throttle a couple of times to try & get it going again, & it would back fire, & drop back to idle. Is that sounding more like a pressure thing? I hate just guessing & installing a new pump, that is a $300 guess....LOL...Again, thanks for your input.


My brother is jim,,im mike lol.. dont poke the wires slide a paper clip into the back side of the connector and check it that way...vette has the wireing for you....i sounde fuel related tho,,,,you have a mec fuel pump on the side of the engine that feeds fuel to the high pressure fuel pump that is on the back of the intake which is a assembly that costs around 800.00:eek!:

[RickSE]

I've been going through something similar on a 500EFI. I chased a lot of gremlins and finally determined that I did in fact have a fuel pressure problem. Mine would cut out under heavy load, usually over 4,000 RPM's, and would not recover unless I backed off on the throttle. After trying a remote fuel pressure gauge out of the engine compartment I finally just bit the bullet and installed one on the dash. What I found when I have this issue is that my fuel pressure will run consistent for a while then bounce a few times, dropping a few pounds, then go to zero.

Why??

Mine seems to be vapor lock and related to the fuel filters but I've yet to determine the main cause. I'm either trapping air in the fuel lines when I change the filters or something in the winter fuel is clogging the filters when I store the boat over the winter. Mine will crap out when I use it after winter storage but after a few trips out the problem will go away and won't reappear until the following spring.

So I did something different this year and have not had the problem at all.

1) I left the fuel tank low last winter, almost empty with no fuel stabilizer.

2) I did not change the fuel filters this spring, still running the same filters from last summer.

I did this as a test so I can hopefully start narrowing down what is causing the problem. I'll probably leave the fuel tank low again this winter with no stabilizer but change the filters next spring and see what happens. If that works then I'll move on from there.

Have you changed your filters?

[VetteLT193]

Yes exactly, it was running great, & this started about 3 weekends ago, & I've been chasing it since. Since then the RPMs are tough to get above 4000, & the speed has dropped off. I was able to run WOT for about 5 mins & then it fell back to idle. I tried it a couple of times & couldn't even get 2000 without it stumbling. I let it sit for a few mins, started it back up & ran it the rest of the way to the island not going over 3000. After a few hours, we left & it ran fine all the way home, but I didn't push it over 3800....I'm lost...I do appreciate any & all input on this. I think it would be easier if it was more consistant with the troubles. The only thing that is consistant, is the trouble reaching max rpm, & the loss of about 8 mph.


Ok... with that info, it's probably not a vac. leak. Generally speaking, That would have given very consistent results once the leak started, and your point about trouble getting over 2000 rpm's a couple times, then sitting/restarting and it getting better means it's something less consistent.

I've had problems before with algae in a fuel tank, you'd run for a while and life would be good... then, you'd lose power. Shut off the engine, let it sit, fire back up and things are better, etc. Turns out there was clumps of algae getting sucked up to the pick up tube. By shutting down, the fuel system would lose pressure and the crap would fall off. In this case, I dumped some fuel system algae eater in the tank and I think went through 20 filters after that with all the crap that had to be filtered out of the tank.

The thing is, with MPI, the fuel system should be able to 'catch up' at idle if it's not totally blocked... This should make the boat feel normal getting onto a plane, etc.

If I were you, I'd check the TPS first (with the paperclip trick!) to at least rule it out. After that you can have 'fun' with the fuel system.:eek!:

[DON-Z-26ZX]

Ok... with that info, it's probably not a vac. leak. Generally speaking, That would have given very consistent results once the leak started, and your point about trouble getting over 2000 rpm's a couple times, then sitting/restarting and it getting better means it's something less consistent.
I've had problems before with algae in a fuel tank, you'd run for a while and life would be good... then, you'd lose power. Shut off the engine, let it sit, fire back up and things are better, etc. Turns out there was clumps of algae getting sucked up to the pick up tube. By shutting down, the fuel system would lose pressure and the crap would fall off. In this case, I dumped some fuel system algae eater in the tank and I think went through 20 filters after that with all the crap that had to be filtered out of the tank.
The thing is, with MPI, the fuel system should be able to 'catch up' at idle if it's not totally blocked... This should make the boat feel normal getting onto a plane, etc.
If I were you, I'd check the TPS first (with the paperclip trick!) to at least rule it out. After that you can have 'fun' with the fuel system.:eek!:

That sounds like something that should be easy enuff to check. I'll be changing the filter this evening, & I will dump the fuel into a container to see if there is any debris that may be causing troubles. I will also check the TPS, like you said, at least rule it out, & also do a pressure check. I know I won't get a good reading until I put it under full load, hopefully I can get time later in the week to put it in the water.....Whew!!! beyond that....:confused:...Thanks again.

[DON-Z-26ZX]

My brother is jim,,im mike lol.. dont poke the wires slide a paper clip into the back side of the connector and check it that way...vette has the wireing for you....i sounde fuel related tho,,,,you have a mec fuel pump on the side of the engine that feeds fuel to the high pressure fuel pump that is on the back of the intake which is a assembly that costs around 800.00:eek!:

I'll check the TPS this evening....
I wasn't aware of a second fuel pump, I'm not sure where that is located. The only one I've seen is the hi-pressure on the Cool fuel system located on the lower port side. You say it is on the back of the intake? I'll look to see if I can find it, thanks.

[mrfixxall]

I'll check the TPS this evening....
I wasn't aware of a second fuel pump, I'm not sure where that is located. The only one I've seen is the hi-pressure on the Cool fuel system located on the lower port side. You say it is on the back of the intake? I'll look to see if I can find it, thanks.

385 hp mpi efi? follow the fuel rails from the injectors,,i believe its called VST..(vapor seperator tank)
I know their was problems with them when they first came outand theirs a revised version of it...it a black square box lookin thang with two float level assemblies.If the floats stick it wont build pressure.


EDIT,,MERC HAS A SERVICE BULLITON ON IT..

[VetteLT193]

Also, is your 'filter' a fuel/water separator, or just a regular fuel filter? This could also be a case of water in the gas. (I keep thinking of more stuff to add to this thread!)

[DON-Z-26ZX]

385 hp mpi efi? follow the fuel rails from the injectors,,i believe its called VST..(vapor seperator tank)
I know their was problems with them when they first came outand theirs a revised version of it...it a black square box lookin thang with two float level assemblies.If the floats stick it wont build pressure.
EDIT,,MERC HAS A SERVICE BULLITON ON IT..

I don't believe I have the VST. I looked up on mercruiserparts.com, & it only shows the one located on my cool fuel system, but I will look a little harder for it.

[DON-Z-26ZX]

Also, is your 'filter' a fuel/water separator, or just a regular fuel filter? This could also be a case of water in the gas. (I keep thinking of more stuff to add to this thread!)

It's the spin on mercrury type, I don't have the number handy, but it's the one the dealer had on the shelf. I do hope that it's a simple as that....keep thinking, I really want to get on top of this....

[The Hedgehog]

I am thinking that you could use a mechanical gauge to check the fuel pressure off the shrader valve on the fuel rail. That would be pretty simple.

[MOP]

That sounds like something that should be easy enuff to check. I'll be changing the filter this evening, & I will dump the fuel into a container to see if there is any debris that may be causing troubles. I will also check the TPS, like you said, at least rule it out, & also do a pressure check. I know I won't get a good reading until I put it under full load, hopefully I can get time later in the week to put it in the water.....Whew!!! beyond that....:confused:...Thanks again.

You can take the filter issue one step farther by cutting it open like you would an oil filter, look for brownish slime. If found run a bunch of injector cleaner through, that crap has claimed a couple fuel pumps on our boats. We think it may have been the new Alky treatment stuff not sure.

Phil

[VetteLT193]

It's the spin on mercrury type, I don't have the number handy, but it's the one the dealer had on the shelf. I do hope that it's a simple as that....keep thinking, I really want to get on top of this....

I think that kind is water separating, but you can tell for sure because it should say water separating right on the filter... even if it is, and the gas is loaded with water you could still have a problem. those filters aren't very big for the amount of water that could get in the tank.

When you change it, dump it into a glass jar, let it settle, and see if you can see water in it. if it's a significant amount you might be on to something.

[DON-Z-26ZX]

I do appreciate all the input & suggestions, you folks are great. I don't know how things got done before Al Gore invented the ole internet :boggled:....I got plenty of things to check over the next day or so, I'll certainly keep ya updated with what I find out....It just is very baffling, I told my wife that I wish it would be more defineitive with what it does, it would be a bit easier to troubleshoot.....Ahhhh, the joy of owning a boat :boat:

[DON-Z-26ZX]

Ok, here is what I found this evening....Changed fuel filter, fuel was clean & no sign of water or anything. TPS checked out perfect, IAC checked out perfect. Checked all fuel lines, & hooked a pressure gauge to the schrader valve on front of the engine. Turned the key on, 22 psi, repeated this several times & each time pressure went down, finally bottomed out at 10 psi. I tried to crank the engine, hoping to get it to at least prime back up (new filter). The engine hit a few times but that was it. So, I have pretty much accepted that I have narrowed it down to the fuel pump. Before I order a $300 fuel pump & cool fuel (only way I mercruiser sells it), I have to ask, did I miss something on the repriming the engine with a new filter. I've always just let the pump cycle a few times & the system is primed. If there is a different way, please let me in on it, but I'm thinking with the extreme low pressures, it has to be the fuel pump, someone chime in if I've missed something with this.....

[VetteLT193]

Ok, here is what I found this evening....Changed fuel filter, fuel was clean & no sign of water or anything. TPS checked out perfect, IAC checked out perfect. Checked all fuel lines, & hooked a pressure gauge to the schrader valve on front of the engine. Turned the key on, 22 psi, repeated this several times & each time pressure went down, finally bottomed out at 10 psi. I tried to crank the engine, hoping to get it to at least prime back up (new filter). The engine hit a few times but that was it. So, I have pretty much accepted that I have narrowed it down to the fuel pump. Before I order a $300 fuel pump & cool fuel (only way I mercruiser sells it), I have to ask, did I miss something on the repriming the engine with a new filter. I've always just let the pump cycle a few times & the system is primed. If there is a different way, please let me in on it, but I'm thinking with the extreme low pressures, it has to be the fuel pump, someone chime in if I've missed something with this.....

I'd check the flow first. Even if you just hook up a hand pump to it and pump away, make sure the fuel is flowing.

I had another boat with a crack in the top of the fuel pickup, where it was welded to the plate that screws into the top of the tank. When the boat was full of fuel it would run great... It would run great as long as it was going fast (enough suction to keep enough fuel moving), but when you would slow down it would run like crap because of air in the line. We were on a trip, and it was standard practice to re-fill the tank for the next run... So, it was that much harder to troubleshoot.

If you have an air leak somewhere, it's gonna pull that air in first just because it's easier to suck air than gas.

Also, did you fill your filter with gas before installing it?

[DON-Z-26ZX]

I'd check the flow first. Even if you just hook up a hand pump to it and pump away, make sure the fuel is flowing.
I had another boat with a crack in the top of the fuel pickup, where it was welded to the plate that screws into the top of the tank. When the boat was full of fuel it would run great... It would run great as long as it was going fast (enough suction to keep enough fuel moving), but when you would slow down it would run like crap because of air in the line. We were on a trip, and it was standard practice to re-fill the tank for the next run... So, it was that much harder to troubleshoot.
If you have an air leak somewhere, it's gonna pull that air in first just because it's easier to suck air than gas.
Also, did you fill your filter with gas before installing it?

Thanks, I will check that....No, I didn't prefill the filter, I've not done that in the past, but perhaps I'll try that when I get home to see if that makes a difference. I definetly want to be as close to 100% sure it is the pump, as possible....

[mrfixxall]

[QUOTE=VetteLT193;420148]I'd check the flow first. Even if you just hook up a hand pump to it and pump away, make sure the fuel is flowing.
I had another boat with a crack in the top of the fuel pickup, where it was welded to the plate that screws into the top of the tank. When the boat was full of fuel it would run great... It would run great as long as it was going fast (enough suction to keep enough fuel moving), but when you would slow down it would run like crap because of air in the line. We were on a trip, and it was standard practice to re-fill the tank for the next run... So, it was that much harder to troubleshoot.
If you have an air leak somewhere, it's gonna pull that air in first just because it's easier to suck air than gas.
Also, did you fill your filter with gas before installing it?[/QUOT

Diddo!! you took the words rite out of my mouth,,I had a boat in my shop last month that did the same thing....

D26 unscrew the fuel p/u and check if the tube is cracked,, the new tude i got from the mfr of the tank sent me a new one but the tube was nylon insted of alunimum..

[VetteLT193]

Thanks, I will check that....No, I didn't prefill the filter, I've not done that in the past, but perhaps I'll try that when I get home to see if that makes a difference. I definetly want to be as close to 100% sure it is the pump, as possible....

Normally you don't need to, but it's worth a shot at this point:wink:

[DON-Z-26ZX]

WOW, that gives me even more to check...LOL. I would've never thought of the pick-up tube, but it's easy enuff to check & rule out. Thanks

[mrfixxall]

WOW, that gives me even more to check...LOL. I would've never thought of the pick-up tube, but it's easy enuff to check & rule out. Thanks


Be vary careful taking it out,,i got lucky with this one,,it fell apart in my hand and i didnt have to go fishing in the fuel tank for the other piece..

[VetteLT193]

Be vary careful taking it out,,i got lucky with this one,,it fell apart in my hand and i didnt have to go fishing in the fuel tank for the other piece..


That is a great piece of advice:yes:

Also, if it is put together, carefully inspect it. What I tried to explain earlier is regarding the same piece the MrFixxall showed the picture of, except instead of totally broken it just had a slit/crack on one side in the same location where his was totally broken.

[mrfixxall]

That is a great piece of advice:yes:
Also, if it is put together, carefully inspect it. What I tried to explain earlier is regarding the same piece the MrFixxall showed the picture of, except instead of totally broken it just had a slit/crack on one side in the same location where his was totally broken.


It came out in one piece but upon inspection it broke in my hand..


D26,,dont attempt to have it welded because it will brake again,,replace it with the nylon one,,it flex's with the waves you hit..it was around 25 bucks with shipping and make sure you use the nipple with the anti flo valve in it too..

[DON-Z-26ZX]

It came out in one piece but upon inspection it broke in my hand..
D26,,dont attempt to have it welded because it will brake again,,replace it with the nylon one,,it flex's with the waves you hit..it was around 25 bucks with shipping and make sure you use the nipple with the anti flo valve in it too..

Thanks for the tips, I will check that, hopefully that is not my problem, but the pick-up tube is easy enuff to get to. If it is damaged, I will definetly replace, don't want to go thru this again.

[VetteLT193]

So, what did you find?

[DON-Z-26ZX]

Ok, here's the update....Still nothing definitive...
I managed to get it to prime & start, with gauge hooked up & vaccum hooked to regulator, I had 35 psi & the needle was very eratic. I ran it up to 2000 rpms, pressure dropped to 30, & needle was still eratic. I then removed & plugged off the vaccum line, pressure went to 42 & eratic, I ran it up to 2000 rpms, & no change, but needle was eratic.
Shouldn't the needle be stable, & not eratic? By the way, the regulator is new, but I was reading thru the service manual, & it refered to a damper. I've not been able to locate a damper, does this engine have one (99 454 mag mpi) ?
Additionally, I removed the pick-up tube from the tank, & had planned on checking the anti-siphon valve. Well, there is no anti-siphon valve, just a small shut-off valve, & the pick-up tube is the nylon type, & it's not stopped up or restricted, & the shut-off valve is working fine, no leaks.
So, what does all this add up to? Being the the issue is so inconsistant, could this just be an issue of a pump either going out, or just having a "bad spot" so to speak? In which case, I should just bite the bullet & replace the pump / cooler (only way it can be purchased now)????
I do appreciate everyone's help on this matter, it's always good to hear from folks with much more knowledge than myself, it does help....

[BUIZILLA]

had the same thing happen to me on my MPI....

the damper is located on the port rear of the engine below the fuel rail, there is a vacuum source hose going to it... that's not your problem...

the fuel pump is probably suspect, and can be bought individually, also under the fuel pressure regulator, mounted to the cool fuel manifold, is a tiny hidden screen, this will play hell with your readings, take the damn thing out and leave it out...

I would install a new fuel pump, leave out the screwy and needless screen, and see what happens.

[VetteLT193]

Ok, here's the update....Still nothing definitive...
I managed to get it to prime & start, with gauge hooked up & vaccum hooked to regulator, I had 35 psi & the needle was very eratic. I ran it up to 2000 rpms, pressure dropped to 30, & needle was still eratic. I then removed & plugged off the vaccum line, pressure went to 42 & eratic, I ran it up to 2000 rpms, & no change, but needle was eratic.
Shouldn't the needle be stable, & not eratic? By the way, the regulator is new, but I was reading thru the service manual, & it refered to a damper. I've not been able to locate a damper, does this engine have one (99 454 mag mpi) ?
Additionally, I removed the pick-up tube from the tank, & had planned on checking the anti-siphon valve. Well, there is no anti-siphon valve, just a small shut-off valve, & the pick-up tube is the nylon type, & it's not stopped up or restricted, & the shut-off valve is working fine, no leaks.
So, what does all this add up to? Being the the issue is so inconsistant, could this just be an issue of a pump either going out, or just having a "bad spot" so to speak? In which case, I should just bite the bullet & replace the pump / cooler (only way it can be purchased now)????
I do appreciate everyone's help on this matter, it's always good to hear from folks with much more knowledge than myself, it does help....

Again, I don't know this exact setup, but usually the fuel damper is located @ the fuel inlet on the rail.

A) I don't see how this system wouldn't have one

B) The damper should stop the pressure "pulsing" you are talking about... that is it's purpose in the system. A messed up damper could be the root of your problem. They normally don't break, but when they do the symptoms can be erratic and basically as you described. Runs great going slow, but like crap going fast because the damper can just slam shut off of a sudden cutting off fuel pressure.

C) I think you might have a 2nd regulator on that crazy fuel pump/cooler combination package... did you see one there? I don't know if there is another check point for pressure there or not, etc. etc. but hopefully someone else will chime in.

[DON-Z-26ZX]

Went to mercruiserparts. com....

http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=804807%2099&ivar=images/CRUISER/804807.99/8.png&inbr=4854&bnbr=90&bdesc=FUEL+FILTER+AND+RAIL

The number 3, pressure valve, is this the damper I need to look for?
I just took a better look at it, I think this is the schrader valve I've been doing my pressure testing from. I'm confused, I can't find the damper in the parts listing. Am I looking at the wrong schematic?

[BUIZILLA]

that's the schrader your looking at.....

go to the fuel pump pic > the screen is #16, the regulator is #15, the regulator takes an o-ring where it mounts to the fuel manifold, but it's not shown in that pic, get rid of the #16 screen...

then go to the intake manifold pic > you'll see the dampner and vacuum hoses thereof...

the pic's are actually somewhat backwards..

also get rid of the factory Mercruiser fuel filter and get a Racor spin on in it's place, the stock Merc filters only keep the rocks and boulder's out...

[mrfixxall]

EM me your serial # for the engine so i can se what we are working with,,ill look it up on the fish...if that screen is plugged that buis is talking about then you may have to remove the injectors too and have them back flushed to clean all the little screens in the inlet of the injectors..

[DON-Z-26ZX]

that's the schrader your looking at.....
go to the fuel pump pic > the screen is #16, the regulator is #15, the regulator takes an o-ring where it mounts to the fuel manifold, but it's not shown in that pic, get rid of the #16 screen...
then go to the intake manifold pic > you'll see the dampner and vacuum hoses thereof...
the pic's are actually somewhat backwards..
also get rid of the factory Mercruiser fuel filter and get a Racor spin on in it's place, the stock Merc filters only keep the rocks and boulder's out...

I'm still not seeing the damper pic, what refrence number is it? It's odd, the parts listing doesn't cover the 1999 version, it only goes to 98. Could that be the problem, am I looking at the wrong engine? That wouldn't suprise me....LOL...

[DON-Z-26ZX]

EM me your serial # for the engine so i can se what we are working with,,ill look it up on the fish...if that screen is plugged that buis is talking about then you may have to remove the injectors too and have them back flushed to clean all the little screens in the inlet of the injectors..

Thanks Mike, I'll have to get that over to ya this evening when I get home. I've looked for the serial number in the past & had trouble finding it. The number I did find on the block (in front of the head) did not cross to anything. This is a quicksilver replacement long block, original owner had it replaced under warranty, the Quicksilver data tag is on the block. I'll look again this evening.

[BUIZILLA]

http://www.mercruiserparts.com/Show_pictures3.asp?dnbr=809994%2098&ivar=IMAGES/CRUISER/809994.98/11.png&inbr=2705&bnbr=130&bdesc=INTAKE+MANIFOLD+AND+INTAKE+PLENUM

[mrfixxall]

Thanks Mike, I'll have to get that over to ya this evening when I get home. I've looked for the serial number in the past & had trouble finding it. The number I did find on the block (in front of the head) did not cross to anything. This is a quicksilver replacement long block, original owner had it replaced under warranty, the Quicksilver data tag is on the block. I'll look again this evening.


look on the black box where the circuit breaker is and the ecu is in,,,their may be one stampped on their..

[BUIZILLA]

#5 is the damper, if this is the MPI engine you have...

does your intake look like this?? the shrader valve sticks up in that little nipple at the front on this version, on some versions the valve is in the aluminum fuel rail block itself

[DON-Z-26ZX]

#5 is the damper, if this is the MPI engine you have...
does your intake look like this?? the shrader valve sticks up in that little nipple at the front on this version, on some versions the valve is in the aluminum fuel rail block itself

http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=804807%2099&ivar=images/CRUISER/804807.99/10.png&inbr=4854&bnbr=110&bdesc=INTAKE+MANIFOLD+AND+INTAKE+PLENUM

This is the version I have....I read back thru the service manual, it says that the damper is "in" the fuel rail, & the removal directions state that the rail has to be removed, in order to change this. Does that sound right?

[BUIZILLA]

that version does not use a damper

[DON-Z-26ZX]

look on the black box where the circuit breaker is and the ecu is in,,,their may be one stampped on their..

I'll take a peek there, hopefully it will be, that will be a big help....

[DON-Z-26ZX]

that version does not use a damper

Outstanding...something else ruled out...LOL...I've ordered my pump, it should be in this afternoon...hopefully that is my problem, thanks for all your help, you folks are great...

[VetteLT193]

that version does not use a damper

That's good info, I didn't know they were 'optional'.

Do you know if fuel pumps are built better and smooth enough to eliminate the need, or is this just an odd setup? I'm Just curious:lookaroun:

[DON-Z-26ZX]

That's good info, I didn't know they were 'optional'.
Do you know if fuel pumps are built better and smooth enough to eliminate the need, or is this just an odd setup? I'm Just curious:lookaroun:

Just knowing the way things have gone with this boat, & it being "MY BOAT"....it's definetly an "odd setup"....I can't have "easy" :boggled:

[BUIZILLA]

I think the setup you have is a 1 year only deal, no more than 2 years... I also think (pretty darn sure) there is a replacement for that pump, I don't remember getting a Merc specific part for mine, it was something else and 1/2 the price...

[DON-Z-26ZX]

Here is the latest on my dilema with my Donzi's fuel woes....Last nite, I traced the fuel lines from start to finish. I have no additional regulators, or dampers on the fuel rail. I did remove the pump/cooler....all screens (under regulator, & pump inlet) are clean, no signs of debris at all. I went ahead & orderd a fuel pump...what the hell, lol...but I was talking with a friend last nite about this whole thing, he asked me if I've checked the vent for the tank fill. He says that there is suppose to be a check ball in the vent, & he said that if it were stuck, I would have trouble getting fuel. Well, I agree...but wouldn't I have trouble filling the boat? When I am filling the boat, I do feel air coming out of the vent...am I thinking wrong or is that correct? I am able to get to the vent, but it will definetly be some work to do it, I just don't want to go on a wild goose chase....hmmmm.....I suppose I've already been chasing the goose....:boggled: .... Has anyone ever heard of that being a problem?

[DON-Z-26ZX]

Check ball on a vent line?? :boggled::bonk:

He said there is some C.G. reg that says there is suppose to be one. I've never heard of it, but hey, I'm open for any & all suggestions at this point....:confused:

[VetteLT193]

anti siphon valve is probably what he's talking about. required if the fuel lines run lower than the top of the tank (I think).

I think if that were screwed up, you wouldn't see as much pressure as you are getting, but who the heck knows:bonk:

[DON-Z-26ZX]

FINALLY!!!!:yes:
Got my new fuel pump/ cooler in & installed it, also replaced the fuel line from the tank to the filter, & vacuum line to the regulator.
Third turn of the key, & pressure jumped up to 40 psi, started the boat....42 psi & needle is rock steady. Took it out for a run....much better....ran wot for a bit, & never missed a beat...still not a speed demon, only saw 58, but the rpms were there at 4800, perhaps I'll play with the prop, but I'm just happy it stays running :)...

I really want to thank all that gave me input on this, it definetly helped, I learned quite a bit thru this whole troubleshooting delima....You folks are great...

[VetteLT193]

FINALLY!!!!:yes:
Got my new fuel pump/ cooler in & installed it, also replaced the fuel line from the tank to the filter, & vacuum line to the regulator.
Third turn of the key, & pressure jumped up to 40 psi, started the boat....42 psi & needle is rock steady. Took it out for a run....much better....ran wot for a bit, & never missed a beat...still not a speed demon, only saw 58, but the rpms were there at 4800, perhaps I'll play with the prop, but I'm just happy it stays running :)...
I really want to thank all that gave me input on this, it definetly helped, I learned quite a bit thru this whole troubleshooting delima....You folks are great...


I am sure you are glad to be back on the water. sucks it was such a high dollar part, but it is a BOAT, and that == Break Out Another Thousand :)