What Causes Run-on / Dieseling?
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Thread Starter
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
I've been using the clutch a little to shut it off, yes. That does it but the car hasn't always dieseled. I just moved it from Calgary to the east coast, so it stands to reason that it is now running richer than before by virtue of the major decrease in altitude. I'm tempted to pull my intake and reinstall, the car hasn't run as well since I did that job to stop an oil lek back in the spring. Stock manifold. I've checked for vac leaks and haven't found any, but maybe there's something I can't find with the WD.
No MSD here, completely stock, all major components original to the car.
No MSD here, completely stock, all major components original to the car.
Tech Contributor
Joined: Jun 2004
Posts: 20,931
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Hey partner, maybe you can get some more kick with this, too.
Improper timing (ie: retarded from the advance point that yields a LPP of 15-20* ATDC) causes a reduced efficiency of the combustion process. When the combustion process is made inefficient the engine will require more fuel and air to maintain the same engine speed. The only way to get more air and fuel is to open the throttle blades further. Upon shutdown coastdown the engine is drawing in a larger amount of air and fuel with this larger throttle opening, causing a higher compression pressure and temperature than it would if the throttle blades had been closed further. This higher temp can enhance the chances of the air/fuel to self ignite (ie: diesel). This problem occurs in a lot of engines that have improper timing advance.
Am I wrong?
Improper timing (ie: retarded from the advance point that yields a LPP of 15-20* ATDC) causes a reduced efficiency of the combustion process. When the combustion process is made inefficient the engine will require more fuel and air to maintain the same engine speed. The only way to get more air and fuel is to open the throttle blades further. Upon shutdown coastdown the engine is drawing in a larger amount of air and fuel with this larger throttle opening, causing a higher compression pressure and temperature than it would if the throttle blades had been closed further. This higher temp can enhance the chances of the air/fuel to self ignite (ie: diesel). This problem occurs in a lot of engines that have improper timing advance.
Am I wrong?
Melting Slicks
Joined: Feb 2004
Posts: 2,111
Likes: 32
From: Damascus MD
Run on
Like I said. It runs flawlessly if I add 3-4 gallons of CAM2 110.
Bill
Melting Slicks
Joined: Feb 2004
Posts: 2,111
Likes: 32
From: Damascus MD
Okay guys.
I think I am getting closer to solving the mystery based on input here and from another site.
The simple answer is it WILL NOT run properly on todays pump gas based on how the factory originally set up the L46 back in the day with all emissions hooked up.
I am told by extremely knowledgeable folks that it can be made to run properly on todays gas with a different vacuum advance, bypassing the TCS using manifold vacuum to the distributor and some other adjustments. I will report back at some point to share the results.
Obviously all other systems must be working too.
I must confess I get very frustrated when comments are made that there is automatically a problem when it won't run on todays pump gas and that more octane is not needed. The L46 at 11:1 compression WILL NOT run right on todays pump gas if set up exactly as it was new with all emissions stuff hooked up. Adjustments have to be made and parts replaced to run on today's gas.
The good news is that it can be made to run on todays pump gas.
Bill
I think I am getting closer to solving the mystery based on input here and from another site.
The simple answer is it WILL NOT run properly on todays pump gas based on how the factory originally set up the L46 back in the day with all emissions hooked up.
I am told by extremely knowledgeable folks that it can be made to run properly on todays gas with a different vacuum advance, bypassing the TCS using manifold vacuum to the distributor and some other adjustments. I will report back at some point to share the results.
Obviously all other systems must be working too.
I must confess I get very frustrated when comments are made that there is automatically a problem when it won't run on todays pump gas and that more octane is not needed. The L46 at 11:1 compression WILL NOT run right on todays pump gas if set up exactly as it was new with all emissions stuff hooked up. Adjustments have to be made and parts replaced to run on today's gas.
The good news is that it can be made to run on todays pump gas.
Bill
Melting Slicks
Joined: Aug 2012
Posts: 2,548
Likes: 379
From: Woodinville WA
your post was great until you got to the above quoted sentence. I have no idea who made the comment that lit you up; however, I do know that you're entitled to all your money back - just the moment you return all the nice people's time who tried to help you solve your problem.
Racer
Joined: Feb 2013
Posts: 386
Likes: 3
From: Clifton Virginia
Hey partner, maybe you can get some more kick with this, too.
Improper timing (ie: retarded from the advance point that yields a LPP of 15-20* ATDC) causes a reduced efficiency of the combustion process. When the combustion process is made inefficient the engine will require more fuel and air to maintain the same engine speed. The only way to get more air and fuel is to open the throttle blades further. Upon shutdown coastdown the engine is drawing in a larger amount of air and fuel with this larger throttle opening, causing a higher compression pressure and temperature than it would if the throttle blades had been closed further. This higher temp can enhance the chances of the air/fuel to self ignite (ie: diesel). This problem occurs in a lot of engines that have improper timing advance.
Am I wrong?
Improper timing (ie: retarded from the advance point that yields a LPP of 15-20* ATDC) causes a reduced efficiency of the combustion process. When the combustion process is made inefficient the engine will require more fuel and air to maintain the same engine speed. The only way to get more air and fuel is to open the throttle blades further. Upon shutdown coastdown the engine is drawing in a larger amount of air and fuel with this larger throttle opening, causing a higher compression pressure and temperature than it would if the throttle blades had been closed further. This higher temp can enhance the chances of the air/fuel to self ignite (ie: diesel). This problem occurs in a lot of engines that have improper timing advance.
Am I wrong?
I completely agree that with dieseling issues, TIMING is first thing you should check and work with. It saved me bunch of headaches and time.
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Intermediate
Joined: Jul 2011
Posts: 31
Likes: 0
From: Zernovka
I would agree with Solid. I had the same problem with stroker 11:1 compression. Sometimes just changing a gas station helps. As you know higher octane number = mixture will ignite exactly when it should. I think that if you have carbon buildups higher octave will not help much. So this could be a way to find out.
Drifting
Joined: Jul 2006
Posts: 1,259
Likes: 154
From: Deplorableville Nebraska
I'm headed down this path soon myself. My state (Nebraska) was one of the last in this great union to still offer 100% real gasoline at 91 octane. The evening news this week said that's all coming to an end, and in order to meet the federal mandate, our regular will now be blended.
I pull up to the pump today, and the PREMIUM is now 10% ethanol!
I also wonder if anyone with an original L46 11:1 compression engine has this trouble with their engine timed using Lar's timing paper?
I pull up to the pump today, and the PREMIUM is now 10% ethanol!
I also wonder if anyone with an original L46 11:1 compression engine has this trouble with their engine timed using Lar's timing paper?
Melting Slicks
Joined: Feb 2004
Posts: 2,111
Likes: 32
From: Damascus MD
comment
your post was great until you got to the above quoted sentence. I have no idea who made the comment that lit you up; however, I do know that you're entitled to all your money back - just the moment you return all the nice people's time who tried to help you solve your problem.
Please don't take the comment the wrong way superbuickguy. I REALLY appreciate all the input. No offense intended. Just a little frustrated.
This has been invaluable as a learning experience. I hope I can return the kindness one day.
For now I will continue to run factory specs and put a little octane booster in the tank.
I wish I could take all you guys for a ride with the top down and CAM2 in the tank.
Bill
Race Director
Joined: Sep 2005
Posts: 18,640
Likes: 121
From: Farragut,TN
Please don't take the comment the wrong way superbuickguy. I REALLY appreciate all the input. No offense intended. Just a little frustrated.
This has been invaluable as a learning experience. I hope I can return the kindness one day.
For now I will continue to run factory specs and put a little octane booster in the tank.
I wish I could take all you guys for a ride with the top down and CAM2 in the tank.
Bill
This has been invaluable as a learning experience. I hope I can return the kindness one day.
For now I will continue to run factory specs and put a little octane booster in the tank.
I wish I could take all you guys for a ride with the top down and CAM2 in the tank.
Bill
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Sometimes it can be very simple. I built a high compression motor and right off the bat it started doing the run on, dieseling.
The spark plugs were the wrong heat range extended tip design. If your plugs get so hot that they have glowing tips it causes this problem.
If you have to add race gas, the fix is a higher duration cam. It might only take a cam with 4-8 degrees more duration to run fine on 91 or 93 octane.
My two present motors are both over 11:1. True compression not some factory claim
The spark plugs were the wrong heat range extended tip design. If your plugs get so hot that they have glowing tips it causes this problem.
If you have to add race gas, the fix is a higher duration cam. It might only take a cam with 4-8 degrees more duration to run fine on 91 or 93 octane.
My two present motors are both over 11:1. True compression not some factory claim
Intermediate
Joined: Jan 2014
Posts: 45
Likes: 7
It can be #1 idle solinoid not deengerizeing as key is turned off,idle to high,timming too advanced,,check all elements ,inside dist cap,point setting fouled plugs causing hot spots proper plug range. It’s a crap shot
Melting Slicks
Joined: Dec 2009
Posts: 3,233
Likes: 657
From: Thunder Bay
I have to agree with the fuel being the problem. I have never had a dieseling problem with my engine (427 small block 10.5:1) until this spring. First few times I ran it I had to keep it in gear when I shut it down. I only run premium which around here is contaminated with alcohol. I managed to get some alcohol free 91 octane and the problem went away. Normally it runs fine on the gasohol but I suspect the problem was the gas was stale after the car sat all winter.
