2001 Mercruiser EFI hard to start after engine off for a while

[Kentcb1972]

2001 Mercruiser EFI 5.0. Starts perfect when cold. Starts even better if it is hot, say within a few minutes after running to full temp. But if you sit for an hour or so,engine won’t start unless you apply slight throttle and crank a little longer than normal. Has never been an issue on this engine, as this has always been the quickest starting engine I’ve ever owned, at any temp. Thinking about checking the ecu temp sensor resistance both cold and hot. Any other ideas? Fuel system is clean, running marine stabile in every tank. New fuel filter this spring.

 

[alldodge]

The IAC might need cleaning along with IAC muffler

What is your serial number?

 

[Kentcb1972]

0M063131

 

[alldodge]

Your fuel pressure should be 30 psi
The issue is it does take a fitting to measure the pressure. Its connected in between the fuel line and throttle body. P/N 91-806901



Looks like it doesn't have a IAC muffler but does have an IAC (item 7). Remove it carefully and clean with soap and water. Don't use carb cleaner or other caustic cleaners. Clean the bore where the IAC sits.

If that doesn't fix the issue, you may need a IAC

 

[Kentcb1972]

Thanks for the advice. I was just looking at the IAC motor. I’m familiar with the IAC valve on the MPI engine and I know when that goes out, the engine will not idle at all. Mine idles fine once I get it started by opening the throttle as I described. I’ll look into it.

 

[alldodge]

Previous comment was IAC "muffler", which is a piece of foam that is in the TB that reduces some of the sucking sound.

If the tip of the IAC is dirty or its bore has crud build up, it can have difficulty doing its job. Might not be it, just thoughts to look at. It only happens when warmed up, and things expand with heat. Could also be that the IAC is failing when it gets heat. When the key turns ON it should retract and maybe its not