1999 7.4mpi cold start won't idle

[1990dtgl98]

Hey guys,

This will be a little winded backstop but might be helpful.

New question. I bought a 1999 sea ray with a 7.4 mpi mercruiser (l29) from a guy that had issues getting it run. Replaced the iac and got it running last year enough to winterize it since it was already mid October.

Fast forward to this year and it wouldn't even crank. Siphoned some gas and it was rusty colored and smelled off. Figured he said it sat it had bad gas. Took all the gas out, refilled it with ethanol free, replaced the fuel filter and hoses to the filter (as well as the pickup), and tried to start it. No go. Replaced the plugs figuring they were coated. Fired right off.

Finally got a nice day to see if the thing even floats or has any leaks, got it to the river and it was blowing like crazy. Would up idling it in the water on the trailer. No leaks. No issues. Came up to temp and idled fine.

Fast forward to this weekend... I went to clean everything off, put ears on it to idle and get any residual gas out of the rails and the river water out of the engine. It started, ran for about 30 seconds, then died out. Every restart it would rev then die unless I opened the throttle. Noticed after revving it to 2500rpm it would surge between 2_3k rpms. Also noticed there wasn't water running through the exhaust and the risers were HOT. So I shut her down, figuring something is bad with the impeller and just bought a replacement since who knows when it was last changed.

But up until that point it with no throttle it would fire right off on the key, rev up, then instantly die. 5 or 6 times I did that. All the same result. At the river it idled 600rpms perfectly at temperature.

Any idea where to start looking? Tps sensor? Fuel pressure regulator (I hope not. It has cool fuel and looks impossible to get to).

Thanks everyone in advance!

 

[tpenfield]

You will probably need either the scanner or the computer diagnostics for the engine to really see what is going on.

During cranking the engine control unit (MEFI) sets the injector pulse very high to provide plenty of gas. Once the engine starts the injector pulse drops down and then continually lowers as the engine reaches its operating temperature. It would be good to know what the TPS and IAC readings are, as well as the injector pulse, during the initial start-up and as the engine warms up.

Fuel pressure would be good to check, both before starting and as the engine runs. The fact that you had contaminated fuel (rust) would be of concern if any contaminants made it past the fuel filter(s).

Also, an air leak in the plenum (loose hose or loose throttle plate housing) will result in high revs of the engine and possibly a stall from a lean fuel condition. Check that sort of thing out as well.

 

[1990dtgl98]

That's unfortunate. I really thought it running perfectly on the trailer every would be good.

Now we're back to square one. Maybe replace the impeller, get water through her and see if she'll idle warm again?

Does anyone rent those scanners? 600 dollars and only being compatible with that mefi system is kinda pricey for me. Should've went with a carb setup. Ha!

 

[tpenfield]

Yes, that is the thing about fuel injection and the computer controlled engines. They run great until they don't. Often folks will throw $600 in parts at the engine and not get anywhere, so the computer diag. can pay for itself, if you plan on doing work on your engine.

Otherwise, a repair shop may charge you similar money just to look at the engine.

I'd get the cooling back in working order, then see what you can do.