My car has had a slight problem in the past with engine run-on after I turn off the ignition, but it's worse than normal. I know this could be carbon deposit or a bad head gasket, but are there any other suggestions to eliminate this? Will timing make a difference at all? As it is, she's been idling a little strange recently. I'd just like some suggestions...

 

check your timing, if it's too far advanced it'll diesel also carbon will do that but have an H engine code and that compresson is too low for that to happen unless you have a s**tload of carbon buildup

 

Fast idle speed and excessivley hot engine temp will do it too.

And yes, it could definitely be the timing--My car was dieseling for a while... i replaced the coil, cap & rotor (wires too) and it hasn't since.

good luck...

 

Idle speed and ignition timing are usually the reason for dieseling. The 86' LG4 had 9.5:1 compression, so that is part of the reason that it does that. Make sure your idle is set to 750RPM, and set the base timing to 6 degrees BTDC. You might be able to go a little more on the base timing, but start at 6 and work up from there.

 

I've had my initial timing advanced up to 14*, so the good LG4 can take a lot! And that was on 87 octane.

Try the carb cleaners that goes through the gas tank. They should help burn off any carbon in the combustion chamber.

 

Doesn't anyone but me find it odd that someone using the name "Hummer" is complaining about diesels? Just an observation...

Presuming you have the stock Rochester E4ME, you'll need to check the idle speed, high idle cam adjustment, idle solenoid adjustment, and mixture control solenoid.

As mentioned, the ignition timing can create hot combustion chambers, as well as cooling system problems, lack or EGR, and excessively lean mixture.

Hot chambers, carbon deposits, low octane fuel, and high heat range spark plugs can contribute to run-on.

 

Well, HUMMWVs certainly do a lot of odd crap, but I am not aware of a problem with run on.... lol. Or at least none of ours do..... 'course, we are a maintenance unit and actually take care of ours. No, PMCS definately does not stand for "Park the Mother and Call the Shop" ....

I agree with the usual suspects all pointed out above... Also, dunno if this applies to you, but if you have an MSD box (maybe some other brands too) you might have to install a diode on the Alternator voltage regulator wire to prevent residual power from causing run-on. I know that little bit had a friend of mine chasing his tail for a few hours/days... I believe it is in the instruction sheet though, so..... .