Help - Motor Won't Fire

[RedDog]

1998 Mercruiser 502 Mag MPI

Last weekend I was motoring out of the cove I launch at and as I accelerated the engine just died. It was just like I had pulled the lanyard kill switch. I fiddled around with the kill switch and the circuit breaker on the ECU (???) for a while and after about 10 minutes she fired up. It would crank over just fine but wouldn't fire. When turning the key to the on position the "alarm" buzzer wouldn't sound.

Today the same thing happened. After running about 10 miles at 3200 RPMs she just died. No "alarm" when turning the key on. While getting a tow and continuing to fiddle with the circuit breaker, shifter lever, kill switch, the alarm sounded and she fired up. Dropped the tow line and started toward home. Half mile later running at 4000 RPM she died again and I could never get it to start again. Tow again.

So what is my problem?

Remember the bolt I posted about last week that I couldn't find a spot for? Related or coincidence?

[mrfixxall]

1998 Mercruiser 502 Mag MPI
Last weekend I was motoring out of the cove I launch at and as I accelerated the engine just died. It was just like I had pulled the lanyard kill switch. I fiddled around with the kill switch and the circuit breaker on the ECU (???) for a while and after about 10 minutes she fired up. It would crank over just fine but wouldn't fire. When turning the key to the on position the "alarm" buzzer wouldn't sound.
Today the same thing happened. After running about 10 miles at 3200 RPMs she just died. No "alarm" when turning the key on. While getting a tow and continuing to fiddle with the circuit breaker, shifter lever, kill switch, the alarm sounded and she fired up. Dropped the tow line and started toward home. Half mile later running at 4000 RPM she died again and I could never get it to start again. Tow again.
So what is my problem?
Remember the bolt I posted about last week that I couldn't find a spot for? Related or coincidence?


Try by passing the kill switch,after 19 yrs and all the power going through it it may have takin a crap:)

and what poodle said

[RedDog]

Try by passing the kill switch,after 19 yrs and all the power going through it it may have takin a crap:)
and what poodle said

that would 9 instead of 19 years, but I'll try it. If not the main connector as Poodle says, how do you by pass the kill switch?

[MOP]

Mine did not want to fire off last fall to put it to bed, it ran fine on a jumper so I finished up winterizing. Did not bother with it last fall to cold, this spring I found my pretty new kill switch was dead. I slapped a new one in and in fiddling with the old it started worked but dove into the trash can.

[roadtrip se]

must have been about this. I'll call you today.

But if we keep playing phone tag, the wiring harness is a good place to start.
I would also make sure that once you pull it apart that you tie wrap or hose clamp it back together. I fought this one for awhile with the 500 swap.

I would also look at the viewing tube on the fuel pump. When was the last time you had the fuel pump serviced or checked out? There is also a filter in the fuel line that could be clogged. Before I took it to the shop, I hate messing around with fuel system stuff and let the pros do it, I would also change out your water separator as you could have water in there that could cause these kinds of symptoms.

Talk to you later...

[MOP]

When you pull the main plug apart if you look closely you will see the prongs have a split, using a very small sharp blade it is a good idea to open the splits very slightly to insure good contact within the plug. All you need is a hairs width at the tips!

Phil

[RedDog]

I pulled the connector and it looked cleaned. I squirted it with some WD-40 and hit each prong with a file. It is held in place with a hose clamp.

I also by-passed the kill switch.

No luck on either account.

I really don't think it is the fuel system. When you turn the key to ON, there is NO warning alarm buzzer. That alarm always sounds when starting the boat. It behaves just like the kill switch lanyard has been pulled - except now I have clipped the kill switch wires and connected them to by-pass

MOP - I'll try your suggestion about spreading the prongs.

Back to the boat....

[RedDog]

spreading the prongs - hard to do - didn't help. The connection seems solid

[gcarter]

Phil Reed had a bad connector (where has he been lately?), it was internal inside the molding. Determined which wire was broken internally and bypassed that wire around the plug.
I suppose that could take awhile, but not beyond the abilities of anyone here w/ a continuity meter.

[Dave_N]

Turn the key on and go back to the engine compartment. wiggle the connection at the starter, engine breaker, engine fuses, cannon plug, ect. when you hear the alarm buzzer, you found the problem.

[mrfixxall]

that would 9 instead of 19 years, but I'll try it. If not the main connector as Poodle says, how do you by pass the kill switch?

OOPs!:bonk: i never finished my math class:)

BTW that 1/4 20 bolt! ccheck your starter solenoid, they use a small bolt like that too!

[RedDog]

using Dave N's suggestion, I am narrowing in on my problem. I opened the box where the Mercathode (sp?) is and other electrical thingys. When I closed it the alarm sounded and I could hear the fuel pump prime/pressure up. I open the box, the power shuts down. Close it, it powers. I don't see any loose / abraded wires yet but the problem is there somewhere.

[Dave_N]

Inside that box (usually attached to the lid) are the engine fuses. They are the blade type fuses with little black covers over them. That may be where the problem is.

[RedDog]

Inside that box (usually attached to the lid) are the engine fuses. They are the blade type fuses with little black covers over them. That may be where the problem is.

Yep - I narrowed it down to one of those fuses. I can't see anything amiss but I cleaned up the wire routing so less stress / pulling is applied and it seems to work fine now. I know that is not really a true fix but at least if the problem reoccurs I know where to start trouble shooting.

Thanks!

[BigGrizzly]

RD That same thing happened to me after I rewired the dash-I though I had made a mistake! A light bulb and a pointer solved the issue, boy did I feel stupid, nothing wrong with the wiring at all.

[osur866]

Hmm, this one sounds simialer to what I went through the weekend after AOTH, boat ran great there next weekend went LOTO ran great thur, and friday then came Friday night same kind of symtoms, turned out to be a bad fuse in the harness that controls the fuel pump, checked it with a volt meter checked ok but as soon as a load was put against it it dropped, the fuse was making contact enough to supply voltage some of the time, even after taking the fuse out it was hard to see where the problem was, the fuse had a straight line almost like a crack against one side of the mold very strange. Take the fuses out and hold them up to light to see if they might have a brake that might cause what happened to me, I lost the rest of the mermoial day weekend because of it, Good Luck Steve