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What would cause a motor to Diesel when turned off? #797995 09/10/10 02:55 PM 09/10/10 02:55 PM
Joined: Aug 2007 Posts: 134 Anchorage,AK A AK_JH27 OP member
AK_JH27 OP member A Joined: Aug 2007 Posts: 134 Anchorage,AK	helping a friend with his motor and we cant figure out why it Diesels so bad. as soon as you turn the key off, it continues to try and run. we changed fuel, tried a different carb, checked timing. He had someone tell him that due to his MSD system, that there is still power going to the coil which causes the run on. I think is unspent fuel still in the cyinders. could use some help here.

Re: What would cause a motor to Diesel when turned off? [Re: AK_JH27] #797996 09/10/10 03:07 PM 09/10/10 03:07 PM
Joined: Apr 2003 Posts: 12,234 Looking for a way out of Middl... IMGTX I Live Here
IMGTX I Live Here Joined: Apr 2003 Posts: 12,234 Looking for a way out of Middl...	Dieseling is caused by something hot in the combustion chambers igniting the gas. This causes the engine to turn over creating vacuum which draws more fuel out of the carb (just like it was running) which enters the combustion chamber ignites and continues. If the voltage to the MSD is switched off it has no effect. The most common fix from the factory is to use a solenoid to set the idle speed. When the ignition is turned off the solenoid de-energizes and the throttle plates completely close and it will stop dieseling. High combustion chamber heat can be caused by lean mixture, ignition timing, or high compression. An alternate is to shut the car off and then hold the throttle open. The dieseling will not allow fast rpm's (in most cases) so the vacuum drops and the fuel stops being drawn out of the carb. I prefer the solenoid option if available. or EFI

Re: What would cause a motor to Diesel when turned off? [Re: AK_JH27] #797997 09/10/10 03:07 PM 09/10/10 03:07 PM
Joined: Jan 2008 Posts: 553 DE Ply72rr mopar
Ply72rr mopar Joined: Jan 2008 Posts: 553 DE	Try lowering the idle speed.

Re: What would cause a motor to Diesel when turned off? [Re: Ply72rr] #797998 09/10/10 03:11 PM 09/10/10 03:11 PM
Joined: Apr 2003 Posts: 12,234 Looking for a way out of Middl... IMGTX I Live Here
IMGTX I Live Here Joined: Apr 2003 Posts: 12,234 Looking for a way out of Middl...	Quote: Try lowering the idle speed. DOH! I forgot that one.

Re: What would cause a motor to Diesel when turned off? [Re: IMGTX] #797999 09/10/10 03:26 PM 09/10/10 03:26 PM
Joined: Aug 2007 Posts: 134 Anchorage,AK A AK_JH27 OP member
AK_JH27 OP member A Joined: Aug 2007 Posts: 134 Anchorage,AK	Duh! Didnt think about the throttle plates. I'll try that

Re: What would cause a motor to Diesel when turned off? [Re: AK_JH27] #798000 09/10/10 03:32 PM 09/10/10 03:32 PM
Joined: Nov 2003 Posts: 2,715 closer to Canadian beer! torkrules I'm neurotic
torkrules I'm neurotic Joined: Nov 2003 Posts: 2,715 closer to Canadian beer!	Quote: helping a friend with his motor and we cant figure out why it Diesels so bad. as soon as you turn the key off, it continues to try and run. we changed fuel, tried a different carb, checked timing. He had someone tell him that due to his MSD system, that there is still power going to the coil which causes the run on. I think is unspent fuel still in the cyinders. could use some help here. I did read somewhere that in some cases the MSD can cause this. There is some sort of device that can be used to prevent this. Other causes could be as someone said, high idle speed, or the fuel not having enough octane, or too hot a plug.

Re: What would cause a motor to Diesel when turned off? [Re: torkrules] #798001 09/10/10 04:40 PM 09/10/10 04:40 PM
Joined: Jan 2003 Posts: 25,200 Upper Midwest M MoparforLife Too Many Posts
MoparforLife Too Many Posts M Joined: Jan 2003 Posts: 25,200 Upper Midwest	Ignition or timing cannot effect dieseling/run on other than in adjusting the timing it will a lot of times effect the idle speed. Ignition or timing need voltage to operate and create spark. When the key is turned off there is no longer power to the ignition.

Re: What would cause a motor to Diesel when turned off? [Re: MoparforLife] #798002 09/10/10 04:53 PM 09/10/10 04:53 PM
Joined: May 2005 Posts: 222 morrisville, pa S skajm enthusiast
skajm enthusiast S Joined: May 2005 Posts: 222 morrisville, pa	steam clean your chambers. get a dollar store spray bottle fill with water. remove air clean start motor and slowly spray water into carb. rev motor as you spray. this will clean chamber of carbon build up. joe

Re: What would cause a motor to Diesel when turned off? [Re: skajm] #798003 09/10/10 06:20 PM 09/10/10 06:20 PM
Joined: Jan 2003 Posts: 1,883 Northern OH R rapom top fuel
rapom top fuel R Joined: Jan 2003 Posts: 1,883 Northern OH	Running hot, idle set to high, low octane gas, carbon buildup in combustion camber, timing.

Re: What would cause a motor to Diesel when turned off? [Re: Ply72rr] #798004 09/10/10 06:39 PM 09/10/10 06:39 PM
Joined: Mar 2005 Posts: 2,060 Pendleton NY T terzmo top fuel
terzmo top fuel T Joined: Mar 2005 Posts: 2,060 Pendleton NY	Quote: Try lowering the idle speed.

Re: What would cause a motor to Diesel when turned off? [Re: rapom] #798005 09/10/10 07:04 PM 09/10/10 07:04 PM
Joined: Jan 2003 Posts: 25,200 Upper Midwest M MoparforLife Too Many Posts
MoparforLife Too Many Posts M Joined: Jan 2003 Posts: 25,200 Upper Midwest	Quote: Running hot, idle set to high, low octane gas, carbon buildup in combustion camber, timing. Once again not timing. Can't happen. Key off - no power.

Re: What would cause a motor to Diesel when turned off? [Re: MoparforLife] #798006 09/10/10 07:43 PM 09/10/10 07:43 PM
Joined: Apr 2007 Posts: 905 SD Z zrxkawboy super stock
zrxkawboy super stock Z Joined: Apr 2007 Posts: 905 SD	Quote: Ignition or timing cannot effect dieseling/run on disagree It's Swifty! Swifty, you toad sucker!

Re: What would cause a motor to Diesel when turned off? [Re: zrxkawboy] #798007 09/10/10 07:47 PM 09/10/10 07:47 PM
Joined: Jan 2003 Posts: 25,200 Upper Midwest M MoparforLife Too Many Posts
MoparforLife Too Many Posts M Joined: Jan 2003 Posts: 25,200 Upper Midwest	Like I said the only way timing can effect engine run on is by slowing the idle speed down with the timing adjustment. the timing itself CANNOT effect run on as spark needs voltage and the timing controls the when the spark occurs. With the ignition off spark is killed.

Re: What would cause a motor to Diesel when turned off? [Re: MoparforLife] #798008 09/10/10 08:15 PM 09/10/10 08:15 PM
Joined: Jul 2003 Posts: 6,167 Maryland GO_Fish master
GO_Fish master Joined: Jul 2003 Posts: 6,167 Maryland	timing can cause the engine to run hot, and the overly hot chamber temps can then cause dieseling, and that much easier if there is carbon or casting hot spot (burr)in a chamber also. But most common I think is excess idle speed. Last edited by GO_Fish; 09/10/10 08:16 PM. Scott B. "I'm a self-made man... I started with nothing, and I still have most of it!" 68 360 rusty B'cuda 'vert (GO Fish)13.59@ 98.72 mph 69 340 GTS stock 14.18@ 95.60 mph 01 5.9L Ram 1500 Quad Cab 4x4 01 3.5L 300M 16.23@ 86.97 mph

Re: What would cause a motor to Diesel when turned off? [Re: zrxkawboy] #798009 09/10/10 09:14 PM 09/10/10 09:14 PM
Joined: Feb 2005 Posts: 28,312 Cincinnati, Ohio Challenger 1 Too Many Posts
Challenger 1 Too Many Posts Joined: Feb 2005 Posts: 28,312 Cincinnati, Ohio	Quote: Quote: Ignition or timing cannot effect dieseling/run on disagree If you give it more intial timing, then you can close the throttle blades more at idle which often is enough to prevent run on. So I'm thinking timing can effect run on/dieseling...

Re: What would cause a motor to Diesel when turned off? [Re: torkrules] #798010 09/10/10 09:26 PM 09/10/10 09:26 PM
A Anonymous Unregistered
Anonymous Unregistered A	Quote: I did read somewhere that in some cases the MSD can cause this. There is some sort of device that can be used to prevent this. Other causes could be as someone said, high idle speed, or the fuel not having enough octane, or too hot a plug. thats only with GM's.. you need a one way diode to prevent it.

Re: What would cause a motor to Diesel when turned off? [Re: MoparforLife] #798011 09/10/10 10:44 PM 09/10/10 10:44 PM
Joined: Apr 2007 Posts: 905 SD Z zrxkawboy super stock
zrxkawboy super stock Z Joined: Apr 2007 Posts: 905 SD	Quote: the timing itself CANNOT effect run on as spark needs voltage and the timing controls the when the spark occurs. With the ignition off spark is killed. See reply by Go Fish above. It's Swifty! Swifty, you toad sucker!

Re: What would cause a motor to Diesel when turned off? #798012 09/11/10 10:36 AM 09/11/10 10:36 AM
Joined: Nov 2003 Posts: 2,715 closer to Canadian beer! torkrules I'm neurotic
torkrules I'm neurotic Joined: Nov 2003 Posts: 2,715 closer to Canadian beer!	Quote: Quote: I did read somewhere that in some cases the MSD can cause this. There is some sort of device that can be used to prevent this. Other causes could be as someone said, high idle speed, or the fuel not having enough octane, or too hot a plug. thats only with GM's.. you need a one way diode to prevent it. That was it.

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