Well, I'm prety much at my wits end and the bottom of my wallet. I've been having an issue with my engine where is surges and stalls at idle.
Engine specs:
- 5.7 Mercruiser EFI Stern Drive, Bravo III.
- Engine serial number 0M033393
- Throttle body injection
The symptons are:
- When I start the engine from cold, I allow the engine to warm up at idle. This goes smoothly everytime. When I rev up the engine, either in neutral or under load, the engine works fine. It's when I bring the engine back into idle, the RPM's will drop and the engine will almost stall, and then catch itself and surge up to about 1500-2000 RPM's and then will drop back again to almost stall and then surge again and so on and so forth until it actually stalls out or I turn off the engine.
Diagnostic steps:
- Myself
- Replaced fuel filter and checked fuel for particulates. Fuel was clean. No water. Topped up engine with new fuel anyways.
- Replaced Idle Air Control. Made sure to re-learned IAC a few times to make sure it was adjusting properly. I even pulled IAC and turned the ignition to start to make sure the pintal was operating. IAC is not the problem. No change in symptoms.
- Took boat to mechanic 3 weeks ago. He went to working:
- Plugged up to the ECU to look for fault codes. None exist. All diagnostic outputs say engines is working fine.
- Rechecked IAC using computer. All works fine. No change in symptoms.
- Checked plugs and wires. Noticed one plug had a crack. Replaced all plugs on engine. No change in symptoms.
- Checked for Vacuum leak. None exist.
- Checked fuel pressure. Pressue within 1 lb of manufacturers spec. No issue there
- Replaced fuel regulator. No change in symtoms.
- Replaced fuel pump. No change in symptoms.
- Replaced map sensor. No change in symptoms.
- Checked for exhaust leak. None found.
- Checked timing. Timing was bang on.
- Mechanic sent ECU files over to Mercruiser for diagnosis. They couldn't find anything wrong, but suggested it might be injectors.
- Checked injectors at throttle body. They work fine. On chance, he had a second throttle body in the shop. He replaced mine with that one, including injectors. No change in symptoms.
- Mechanic also says he can trick the engine into thinking it's cold (even after warmup....unplugs a sensor I think, not sure which one). When he does this, the symptoms go away. So the issue seems to be related to warm engine.
Both my mechanic and I are both banging our heads. Last ditch effort is to have the ECU reflashed today or early next week. Beyond that, the mechanic and Mercruiser have no other ideas how to resolve this. This is why I am here. If anyone can throw out some other possibilites, I am all ears and open to suggestions.
