Help..... my boat would not start. I replaced the fuel pump, wrapped the fuel lines, new ECM, distributor, plugs, and gas. The wire set was not replaced yet, as 1/2 of them were too short. Boat started up, however, once warmed up, when I went to dock, the boat dies at idle, in or out of gear. The timing was bouncing between 8 degrees, at 6, not staying steady in place at 8. '95 Powerquest, 454 Mag, EFI. I'm stumped where to look.

Have you checked the IAC valve ?

I have not. Retried to do the timing this a.m., however my timing light must of shot craps. I'm lowering boat shortly and hitting the local marina. Bad apart about being at LOTO, to far into town......

Timing will bounce around on an EFI engine.

I was wondering. I don't work on cars or boats much as I've gotten a tad older. I was wondering if that might have been the case.

Give it very slight throttle. If it runs fine at 1000 rpms and then dies when you go to idle, its the IAC.

Thanks Griff. Marina wasn't sure. So I'll run with the IAC, an see what happens next weekend.

+1. Been there before.

Not saying never but GM IAC rarely a problem. This is not the Ford style IAC used on ECM / PCM 555. But not saying never - Have the techs look into clear flood mode and that starting procedure. What is your rpm idle fully warmed up engine ?

Also they can OHM test the IAC within OHM range to see if it bad or not along with other sensors

Do you have fuel at the fuel rail after engine stalled ? DO the fuel injectors fire right after the stall ? Will they flow fuel upon restart ??

Did any one spark check the ignition properly and safely ???

fuel pressure is ? Vaccum hg testing the fuel system --- Run engine on a portable gas tank to see what happens .

That's a lot of parts changing man - marine techs have done all those changes ? or ?

Are they Merc trained ?

Think Griff's got you on the issue