Mercruiser Alpha one Gen 2 4.3l MPI LOW Idle

[samseoane]

Hello Everyone,

I have A mercruiser 4.3l MPI with a low idle between 450 and 500. Here’s what I done so far.

2008 engine no alarms no beeps

1New Fuel Filter
2 New IAC and cleaning of the throttle area
3 fuel regulator on top with fuel rail checked for blockage no issues
4 new spark plug wires and spark plugs.
Took off all the spark plugs and checked
Compression all cylinders 120
5 checked for spark on all 6 holes of rotor cap with timing light no issues
6 fuel rail psi 40.
Thanks any ideas would be great

 

[achris]

You need to get the diagnostic software on the engine and find out what the sensors are telling the ECU, and what the ECU is doing to maintain the idle speed. If the ECU can't get enough response from the IAC valve it will start to advance or regards the timing. If it's doing that, the IAC valve driver circuit might be fried. If the IAC shorted and drew too much current, them even with a new IAC valve, it's going to still not be able to use the IAC.

Chris...

 

[alldodge]

Are you sure its idling that low as checked with another Tach?
Spec is 600

 

[samseoane]

Are you sure its idling that low as checked with another Tach?
Spec is 600

Yes I did. Use the boats tach and Mercury vessel view. I have twins so audibly sounds weaker than the other one.

thanks

 

[samseoane]

Are you sure its idling that low as checked with another Tach?
Spec is 600

You need to get the diagnostic software on the engine and find out what the sensors are telling the ECU, and what the ECU is doing to maintain the idle speed. If the ECU can't get enough response from the IAC valve it will start to advance or regards the timing. If it's doing that, the IAC valve driver circuit might be fried. If the IAC shorted and drew too much current, them even with a new IAC valve, it's going to still not be able to use the IAC.

Chris...

Thanks Chris.

unfortunately I don’t have a Mercury computer that would be the next step if I’m out of choices a mechanic

thanks
Sam

 

[alldodge]

Measure the voltage of the IAC MAP and TPS on both motors and compare

 

[achris]

Throw a timing light on and see if the timing is jumping around at idle. Should be a steady 8° BTDC. If it's jumping around, and you know the IAC valve is good (spindle moves freely and it's not open or short circuit) then it's possible the IAC valve driver in the ECU got fried. If that's the case, I would spend the money and buy the software and connection cable and verify it (the software will pay for itself after the second use. Shops like to charge a ridiculous fee to take 5 minutes to plug the cable in and read the codes). You can then can either replace the ECU for a new one ($pendy!) or get your ECU repaired (about 1/2 the price of a new one). I think Whipple are an authorized repairer.

Chris.......

 

[QBhoy]

Surely we should perhaps think about fuel quality first off, if we haven’t already ? Is she sitting steady at those low rpms or hunting ? What plugs do you have in her ? The plugs look like ? Wet or dry or coloured ? Proper iridium spec plugs ?