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ky-donzi
04-24-2008, 12:03 PM
how much fuel pressure should I expect to see at idle on a 350 mag mpi engine? I supect that my gage is off some. I have a mechinacal type gage with a isolator diaphram. This set up had fuel on one side of the diaphram and antifreeze on the other, which travels down a hose to the gage. Anyone have a trick to bleed the line. I siphoned some threw the line, but still think there might be some air traped.

BTW antifreeze is a aquired taste....

The Hedgehog
04-24-2008, 12:48 PM
I would like to know that myself. It is around 37 psi on the big block.

I used a mechanical gauge that hooked onto the shrader valve on the fuel rail for dialing it in. Then I use the dash gauge to monitor it.

ky-donzi
04-24-2008, 12:56 PM
As soon as I turn on the ign. it shows 20 psi. Then it stays there no matter conditon. This is all on the trailer, not in the water yet. I would have expected to see higher numbers at idle and then slight fluctuion at different rpms.

The Hedgehog
04-24-2008, 01:49 PM
As soon as I turn on the ign. it shows 20 psi. Then it stays there no matter conditon. This is all on the trailer, not in the water yet. I would have expected to see higher numbers at idle and then slight fluctuion at different rpms.

That sounds low but I am no 350 mag expert. Are you using a boost reference regulator? I know that you are probably not pulling boost in the muffs but that can be the source of some issues.

ky-donzi
04-24-2008, 02:23 PM
Yea, using the stock procharger stuff.

I havn't water tested it yet nor even reved it up. My consern was how accurate the isolater was, or more so, how accurate my istallation of the isolator was, it is very difficult to remove the air from the gage line.

I found a tattle-tale gage here at work that I'm goin to plum into the fuel line before the isolator to compare reading. This will also be useful in checking high reading while on the throttle.

I'm still intrested in know the fuel pressure on a fuel injected 350 for comparasion if anybody knows

mrfixxall
04-24-2008, 04:33 PM
Ky what year is your engine? you can release the air by unscrewing the guage whyle the engine is running, can be a little messy just make sure you have plenty of rags around the the guage:wink:

ky-donzi
04-24-2008, 05:34 PM
Fixxall

It is a 98 mpi mag. I put a tatle tell gage on it this afternoon and it register 42lbs with the engine off while the key was on.
I like your idea but I assume the the diaphram is maxing out in the isolator so I'm going to have to get more antifreeze in it first before I bleed it. What do you think?

The Hedgehog
04-24-2008, 06:55 PM
Where is Tex when you need him? He spent days fighting this battle. Maybe he will chime in. Probably not though, I talked to him a couple hours ago and he was beat from a trip.

I did not really have any problems getting good readings. My only problems were with the regulator itself.

ky-donzi
04-24-2008, 07:06 PM
hedgehog

your dash gage is it a mech or electric? If mech do you have a isolator on it?

Last Real Texan
04-24-2008, 07:59 PM
hedgehog

your dash gage is it a mech or electric? If mech do you have a isolator on it?
give me about an hour.....posting from my phone, I'll have my computer available soon. I have some info for you ....

BUIZILLA
04-24-2008, 08:18 PM
what size is the hose or capillary tube?

Last Real Texan
04-24-2008, 08:45 PM
Fixxall
It is a 98 mpi mag. I put a tatle tell gage on it this afternoon and it register 42lbs with the engine off while the key was on.
I like your idea but I assume the the diaphram is maxing out in the isolator so I'm going to have to get more antifreeze in it first before I bleed it. What do you think?
Forgive my spelling and typo's still posting from my phone.......
Ok first things first...I will tell you what I know and then secondly I will tell you I hink is going on here.
First
When dialing in this set up on any fuel injected motor it is imparaitve that you get your readings directly from the rail! Do not rely on isolaters or electric guages etc....they are only useful once you get a base line with the true reading using a mechanical accurate guage from the rail, ( shrader valve or port on the rail) once you establish what the fuel preassure is make reference on your dash guage and remember it.
When plumbing the fuel system it is best to plumb the regulater after the fuel rail, in the front and then out the back to a regulator. make sense ? the injectors will like this much better and will react faster plumbed this way.
So I will now step down from my soap box and reemember I am only stating here what I know because I have been through this before and chased my tail forever...Go get an Automotive FP tester that hooks up to th Schrader valve, about $ 40 bucks
Second
As for stock fuel preassure on a 350 MPI I would venture to say that it will be pretty close to the same as a Big block...preassure is preassure and I would think a 350 most likely has a smaller injector that is lesser flow at the same preassure as a 502 injecter...ie, 37 LB or 30 lb or whatever it is....Base FP on a stock 500 EFI is 34-37 psi all the way up to 5400 rpms
I would start with the 350 @ 34 -35 PSI and check the plugs 2 idle and see where it goes....under boost I would say an increase of no less than 15 psi which means a 3-1 step up on the boost referencing...minimum. of coarse this is at 5 lbs of boost.
Lastly what does the manual say that you got with it?
hope this helps a bit.
Tex

ky-donzi
04-25-2008, 07:48 AM
Texan

All of that pretty much jives with the procharger manual. Although they don't list a stock F.P. I assume that it shouldn't have changed with anything that I have done (plumbing) the 15 psi that you said mirrors the manual too.
My rasing rate regulator is past the rail in the return line to the pump, this is how procharger recomended the istall, and the F.P. gage is at the regulator. My rails doesn't have a schrador valves on them. At the regulator Ive got 42lbs with key on, havn't ck it with the engine running since I installed two gages. I now have a mechancal gage before the isolator and a mech gage after the isolator. I'm getting two totally different reading 42 and before gage and 20 after gage, I believe that the diaphram is maxing out in the isolator before it reaches 42, so I have to get more antifreeze in the line.

Buizilla I've got an 1/8 hose. I tried the capil type tube twice and it kinked before I could fish it threw the hull. I think today I'm going to remove the gage and use a old air cylinder like a large syrenge to force antifreeze into the line. I'm going to add a schrador valve at the other end to bleede the air,,,,,, any thoughts?????????

BUIZILLA
04-25-2008, 08:00 AM
we have had a few of these remote isolators on my car's and my brother's dragsters, and we never found them to be long term reliable...

the smaller and more solid the tube, the quicker and more accurate the reading, I personally like 1/16" ID copper tubing for this, any bigger than that and the hose/tube becomes an unstable and sluggish accumulator

anyways, with the vacuum hose off the pressure should be 43-45#

hose on, about 35-37#

should never fall below 20-25 after shutdown

a quick key up usually won't bump the regulator setting the first time, you need to do the on-off, wait 6 seconds, on-off, 2 or 3 times...

as far as boost compensation, rule of thumb is 1# of fuel pressure for every # of boost rise, I have rarely seen it equal the 2# mark, and never seen it equal the 3# mark, but that's just me

your method may vary

ky-donzi
04-25-2008, 08:05 AM
"with the vacuum hose off the pressure should be 43-45#
hose on, about 35-37#"

I assume this is the vac/boost reference line?

BUIZILLA
04-25-2008, 08:11 AM
10-4

ky-donzi
04-25-2008, 08:25 AM
I'll let you know the out come tonite. Haven't ran the engine since I have added the mech non-isolated gage. key on not running at 42lbs, this might drop alittle when the engine is actually running.

I'm trying to get the gages to "match" before I water test the boat. I doubt I will get any volunteers to mointer the gage under the hatch while in motion..

Thanks Everybody for your help

The Hedgehog
04-25-2008, 08:25 AM
we have had a few of these remote isolators on my car's and my brother's dragsters, and we never found them to be long term reliable...
the smaller and more solid the tube, the quicker and more accurate the reading, I personally like 1/16" ID copper tubing for this, any bigger than that and the hose/tube becomes an unstable and sluggish accumulator
anyways, with the vacuum hose off the pressure should be 43-45#
hose on, about 35-37#
should never fall below 20-25 after shutdown
a quick key up usually won't bump the regulator setting the first time, you need to do the on-off, wait 6 seconds, on-off, 2 or 3 times...
as far as boost compensation, rule of thumb is 1# of fuel pressure for every # of boost rise, I have rarely seen it equal the 2# mark, and never seen it equal the 3# mark, but that's just me
your method may vary

I agree that 1-1 is best on the boost referencing. I am going to that and a 2 bar map sensor on mine.

At least from what I have learned. Procharger use a 3-1 on their stock systems to compensate for smaller injectors. Stick on a 1-1 and don't tune the ECU + use bigger injectors and you will make expensive noises. I ran a stock procharger setup for 3 years no problem (got the ECU tuned though).

The Hedgehog
04-25-2008, 08:27 AM
hedgehog

your dash gage is it a mech or electric? If mech do you have a isolator on it?

I use the electric and run it off the regulator. I go the same route as Tex for dialing in. Use the mechanical off the rail to benchmark the electric.

Last Real Texan
04-25-2008, 01:10 PM
OK
I'll add some more to this....
with the stock Procharger FMU and stock injectors in the motor you will need at least 15 lbs more FP @ 5 lbs of boost....you do not have the 2 bar map sensor so the rise in FP is only a band aid to the problem, it works but crudely. Guys think about it stock FP is 37-40 lbs and with the procharger @ 5 lbs you say it should onlyu be 1-1 in referencing...that would give a FP of 45 lbs @ 5 lbs of boost?
The 2 bar map sensor reads the boost and according to the program in the ECU it will widen the pulse width of the injector to let it flow more fuel ...it is still necessary to raise the fuel preassure some even running the 2 bar map sensor, it will vary from 5-20 lbs depending size of the injector...
AS far as the fuel rail dilema and reading preassure it is a simple fix, if there is no schrader valve then t off a fitting at the end before it enters the regulator , like I said before it is very important to get a reading @ the rail to do this right, only use a good mechanical guage to do this, if it was me I would run an electrical guage at the dash ( get a good one ) and bench mark it to the mechanical on the rail.
I am supride Jamie @ lakeside has not responded yet...he is most likely very busy this time of year but has set up a bunch of 350 set ups he will know for sure.
I agree with Buizilla on the remote isolater deal, finicky at best and do not provide a long term solution , Now if it is a set up that can easily be inspected just go with -4 braided to the dash and run the mechanical that way, ( i will take some heat for this i'm sure.....
keep at it and keep us posted
Tex

BUIZILLA
04-25-2008, 01:30 PM
Guys think about it stock FP is 37-40 lbs and with the procharger @ 5 lbs you say it should onlyu be 1-1 in referencing...that would give a FP of 45 lbs @ 5 lbs of boost? actually, that's not right, the boost/extra fuel reference starts at 0 base vacuum, at the point boost starts, or the same as line off pressure, in this case 42-43#, then boost vs pressure relevancy goes up from there exponentially. :wink:

Last Real Texan
04-25-2008, 01:48 PM
actually, that's not right, the boost/extra fuel reference starts at 0 base vacuum, at the point boost starts, or the same as line off pressure, in this case 42-43#, then boost vs pressure relevancy goes up from there exponentially. :wink:
so at 1-1 meaning for every lb of boost you get an additional 1 lb of fuel ...correct. So even at 43 lbs base you still only get 48 lbs at 5 lbs of boost...still not enough to make it run properly AFR on the top....

But back to the preassure readings being off from the rail to the reg. and the whole isolator thing. he needs to get the pressure correct before any of this even becomes relavent.

Tex

BUIZILLA
04-25-2008, 02:10 PM
so at 1-1 meaning for every lb of boost you get an additional 1 lb of fuel ...correct. So even at 43 lbs base you still only get 48 lbs at 5 lbs of boost...still not enough to make it run properly AFR on the top.... absolutely correct on all counts, however I think Catch 22 still has stock injectors in his setup and his seems to haul a$$...

The Hedgehog
04-25-2008, 05:01 PM
actually, that's not right, the boost/extra fuel reference starts at 0 base vacuum, at the point boost starts, or the same as line off pressure, in this case 42-43#, then boost vs pressure relevancy goes up from there exponentially. :wink:

You are both right. My discussion with Tex earlier today reminded me about the whole PSI and injector relationship. I would imagine that Buzilla knows the exact detail about the whole PSI/Injector Size/Pulse width to flow calc. I may in the end have more than 1-1 to get my injectors to flow 825+ hp.

We need to step back and remember that Ky's system is probably a #3 diaphram. I think that the most important point is to get a good base fuel psi reading.

If he tunes it right, it should work just fine. Now where is Jamie for those base fuel pressure levels? I know that he has done one of these before.

ky-donzi
04-28-2008, 02:31 PM
Ok.... finally got the two gages (mech and isolated) to read the same. I found the tatle-tale gage to be very helpful. I plan to wet test the boat Wednesday

The Hedgehog
04-28-2008, 03:02 PM
Ok.... finally got the two gages (mech and isolated) to read the same. I found the tatle-tale gage to be very helpful. I plan to wet test the boat Wednesday

Good deal. It should be one heck of a surge. Are putting a bigger wheel on yet?

ky-donzi
04-28-2008, 06:44 PM
Got a good deal on a 29p mirage +. I had a 25 mirage + on it stock so I figuared this is a good place to start.