Engine diesels
Melting Slicks
Joined: Jul 2004
Posts: 2,867
Likes: 195
From: Maryland
Over advanced initial timing and too high idle speed are the most common causes. Reducing the advance or idle speed might be helpful. If you wish not to fool with those settings you could also when shutting down the engine leave the trans in gear and release the clutch to where it barely engages and turn off the ignition.
Tech Contributor
Joined: Jun 2004
Posts: 20,905
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Usually caused by retarded timing and the throttle blades being opened up too far to compensate for the retarded timing. Do you have the vacuum advance hooked up to manifold vacuum?
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Idle speed? I gave up on REd and put a lightweight flywheel in. Not only does it spin up quicker, when you turn the key off, it's done. Dead stop right now.
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Tech Contributor
Joined: Jun 2004
Posts: 20,905
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
3rd Gear
Joined: Apr 2009
Posts: 3
Likes: 0
From: Illinois
there is a rubber diaphragm in the vacuum advance that can go bad. The vacuum advance wont work and cause a vacuum leak, mine did the same thing and dieseled. Pull a vac on it with a hand pump with the cap off and see.
Team Owner
Joined: Jul 2008
Posts: 23,419
Likes: 22
From: In limbo
St. Jude Donor '13-'15, '17 thru '22
12 degrees initial with the vacuum advance disconnected and plugged sounds like a lot to me for a big block. Spec on mine is like 6 degrees at 800 rpm IIRC. I know small blocks commonly run at 12 initial, but stock big blocks are usually less.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Sorry, I had to. My low idle is right at 1000 RPM.
Anyway, high idle is a real distinct cause of run-on, dieseling or whatever yu want to call it. It can be caused by adjustment, vacuum leak(s), timing incorrect just for a start. Another thing can be carbon in the cylinders- makes little hot spots that ignite the fuel air mix. And the gas we all get today is not what it used to be.
Anyway, high idle is a real distinct cause of run-on, dieseling or whatever yu want to call it. It can be caused by adjustment, vacuum leak(s), timing incorrect just for a start. Another thing can be carbon in the cylinders- makes little hot spots that ignite the fuel air mix. And the gas we all get today is not what it used to be.
Safety Car
Joined: Apr 2000
Posts: 3,802
Likes: 61
From: Wichita KS
Guys, that's why GM put idle stop solenoids on these cars. To ensure the throttle blades are completely shut when you turn the car off.
My bb had the same problem before I purchased an idle stop solenoid and set the idle speed up correctly.
I have not had any dieseling in the three years since.
cc
My bb had the same problem before I purchased an idle stop solenoid and set the idle speed up correctly.
I have not had any dieseling in the three years since.
cc
