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I'd throw a dart at this,,look at the distributor shaft,,see if it has excessive wear.also the pick up coil.

Quote:

Originally Posted by ziemer (Post 4607297)

Worked on the motor again this weekend and had a DDT. Ran on both motors and didn't see anything glaringly different between the two. Fuel flow rates were varying between .77-.95 with injector pulses around 3.41 +/-. IAC readings were different between the 2, but my guess is the bad side is compensating for the weird idle pattern. MAP sensor readings were around 18 on both motors. Fuel pressure matched on both also. And the bad motor did not bleed down with the key off.

No codes in either. As soon as I pull the bad side up to 1000 rpms, it goes away completely. Back off to dead idle and it comes and goes.

The only feedback for diagnosis you are not gettting is AFR and what the injectors are actually doing. I know you have commanded BPW but that doesn't mean the injector is actually doing that. It is likely you have a stuck/bad injector. IAC's will dance all over the place trying to control the idle, so I believe your analysis on that front is correct. In other words the IAC is likely fine.

Idle conditions your describe on those particular motors are typically fuel related from my experience.

Well, what ever happened? What was the diagnoses and fix?

Yes, finally got it fixed. Was the stupid coil. Ugh... Changed everything else on the motor, and finally ran it on the lake one day pretty hard until it finally quit. The coils on my boat take a beating because they sit right under the lip of the engine hatch, so they regularly get dowsed with water.

COIL -- had that Indmar small block EFI as I mentioned in POST # 9 somewhat the same issue. Thought it over for an bit and yes the est coil fixed the surging / hunting idle. - maybe a a good read for some in post # 9. . Have to determine what side the issue(s) is on the fuel side or ignition .

Surprised you did not follow in the post # 9 first line of reply - " Coil and cap and rotor and plugs -- OHM test the spark plug wires "

Quote:

Originally Posted by BUP (Post 4601944)

After the tune up, it still had a fluctuating idle - but seemed even worse than before. After thinking about it, I decided it prob was the est ignition coil. Yep the coil fixed the issue. Weak spark causing for the idle rpm issues plus the efi system / ecm compensating from the received inputs and basically trying to correctly compensate the signal outputs for engine running (for a short jist of an explanation )

Quote:

Originally Posted by BUP

Surprised you did not follow in the post # 9 first line of reply - " Coil and cap and rotor and plugs -- OHM test the spark plug wires "

I know... Sometimes, the mind doesn't like to accept what's right in front of you. :P