2004 4.3L MPI Mercruiser not starting--Tough problem

[h20cali]

Went out fishing and boat motor quit while idling. Difficult to start but finally started, could not rev past 3K RPMs sounded like fuel starvation was able to get back to marina at slow speed. I put a fuel pressure guage and measured 10 PSI supposed to be at 40psi. So I replaced the fuel filter and it climbed back to 40psi. But engine still will not start. So I checked for spark and injector pulse on both banks which appear to be okay. Looked at the wiring connections and sensors and everything appears to be okay.

Came to back to it a couple days later and it started right up and ran well no bogging above 3K RPM. I tested it for 4 days at all RPMs at 30 minutes each to make sure problem would not come back. It never did of course when I tried to launch it and started having the same problem. It would not start.

Things I know so far:

1. Fuel pressure is at specs 40psi
2. I checked one injector on each bank and able to see pulse.
3. Swapped out coolant temp sensor with known good one.
4. Replaced distributor cap (dealer mentioned that internal arcing has occurred with this model)
5. Spark is seen
6. Disconnection of cam sensor disables spark. So it appears to be working.
7. Did not check compression. But since it ran well again, it is unlikely this would be the case.
8. Unable to check TPS since I don't have a code reader.
9. IAC valve appears to be working. I can see the internals moving when I ignition is on.

If I can't figure it out by next week, I will take it to the dealer and have him take a look at it. Trying to save a few bucks by troubleshooting it myself. I would appreciate any input. I spoke to dealer today and he said that it was unlikely the ECM555 is bad, but it is possible.

 

[JustJason]

Re: 2004 4.3L MPI Mercruiser not starting--Tough problem

All you can do is check compression, fuel pressure, and spark, everything else you will need a scan tool for. Not much point in giving advice unless you've already thrown the scanner on it and have a question about a particular item.

 

[EddiePetty]

Re: 2004 4.3L MPI Mercruiser not starting--Tough problem

...... So I replaced the fuel filter and it climbed back to 40psi........

.....just because ya' got pressure doesn't mean ya' got the volume.

More trouble shootin' required.

 

[h20cali]

Re: 2004 4.3L MPI Mercruiser not starting--Tough problem

Good point!.... I connected the pressure guage again and was planning to run it from the shrader valve into a one gallon container to prove you wrong and it was bone dry with 0 PSI. I could hear the fuel pump running so I think it takes me back to the originally fuel problem.

I did change out the fuel filter originally and saw the fuel pressure go to 40 psi. Did not think about volume. Next step is to hook up an external tank to see it is a fuel pump or tank problem. I will play around with some more tomorrow and will let you what it turns out to be.

Thanks for your suggestion, I am back on making some progress!!

 

[h20cali]

Re: 2004 4.3L MPI Mercruiser not starting--Tough problem

Still not out of the woods. I did find a bad FPR and a weak coil, amazing how more than one component failed.

Engine now starts instantly but runs rough and backfires. Will rev up to full range, but doesn't sound smooth like it use too. I hear a loud sucking sound coming out of the port where the IAC connects onto the mouth of the intake. I don't recall hearing that noise before. IAC appears to work piston moves up and down.

Anyone have thoughs what too look for. Thanks,


I also checked compression +-150 psi for all cylinders. All good there.