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View Full Version : At wits end - Mercury 240EFI



jeffhtg
04-23-2013, 04:56 PM
I'm posing in the outboard section because every inboard mechanic that has looked at this has suggested going to an outboard master tech.

I have a 2003 sugar sand tango with the Mercury 240EFI option.

It has been sitting for a year trying to get running. After years of being a great boat it stopped one day - we think due to fouling from insulation foam disintegrating and entering the intake.

We cleaned out the engine, replaced plugs, and a bigger problem developed.

The engine will start and idle fine for a minute or two when cold.. then it will start sputtering like it is misfiring or on bad gas and usually die. It seems to not want to run good when its hot after this and only starts up great when it has cooled off several hours later.

New Plugs
Cleaned the fuel system / filter / pumps / lines / etc
Drained the fuel tank and replaced with 10 gallons high octane fresh gas (the gas was a year old - but was stabilized with sea foam)
Checked compression - all above 115
Checked spark / sparkboard - wierd stuff happened here will explain below but all had spark.
Checked system on computer - not throwing any faults.

Now there was a moment the ignition 20amp fuse on the block was getting blown (started when we were doing sparkboard). And for a while it was randomly blowing this fuse after it died). We THINK its a intermittent problem in the ignition harness.. we used a keyswitch and the engine still died but never blew a fuse. When I re connected the ignition harness it has not since blown a fuse. The sparkboard test with computer was causing the computer to reboot with any more than 3 plugs in any combination.. but i really think this may have been something with the computer. Was unable to test current at the time of this but I think it is irrelevant and we get no ignition errors from the computer when not doing sparkboard test.

The overheat sensor still works -because I just had it go off when running it on land for a tad bit too long (with water of course).

We did not test the coils - but suspect one of them may be off.. However swapping coils around or removing a plug wire does not change the way the motor is running really. (at $125+ im not to keen on blindly replacing parts anymore).

Any suggestions?

Docksidemarineservices
04-23-2013, 05:29 PM
Hook up a fuel pressure gauge. See what the fuel pressure is doing when the engine begins to die.

guyjg
04-24-2013, 11:45 AM
We did not test the coils - but suspect one of them may be off.. However swapping coils around or removing a plug wire does not change the way the motor is running really. It won't if one or more are not working properly. Pull each coil and inspect for phycial damage, clean all ground connections and test each coil w/an ohmmeter then compare. Do you have a factory manual? You need one for reference.

faztbullet
04-24-2013, 09:30 PM
Was unable to test current at the time of this but I think it is irrelevant and we get no ignition errors from the computer when not doing sparkboard test.
You testing with a DDT or CDS tool?

However swapping coils around or removing a plug wire does not change the way the motor is running really.
Check the harness to injectors and coils at PCM....

Now there was a moment the ignition 20amp fuse on the block was getting blown
There are (3) 20 amp fuses...(1) for the harness/power relay,(1) for the coils and (1) for the FI harness/oil/fuel pumps. Check your voltage as over charging can overheat fuel pump. It sounds like you have a fuel pressure regulator acting up. Check fuel pressure as suggested...

jeffhtg
04-29-2013, 07:03 PM
I forgot to mention this:

The engine seemed to start up and run nice when it was cold. After it heated up or ran for 2 minutes or so it would then start the symptoms in the op.

We ended up replacing the crank shaft positioning sensor and it seemed to fix the problem. The sensor was not throwing a code but it still seemed to be bad.

Not sure if I will trip a fuse again.. going to do an extensive lake test in the next few days - and will check your suggestions if we end up having to go for a swim.