why does my motor keep running when i shut my truck off - The 1947 - Present Chevrolet & GMC Truck Message Board Network

OlBlue85 · 08-02-2011, 05:05 PM

i have a 350 in my truck and when i shut it off it sounds like a diesel truck or tractor and runs for about10 seconds after you shut the truck off< ive took it to 2 different poeple and it still does it sick of getting ripped off any body have any idea what it could be i put new wires plugs distributer and cap timing chain and set the timing and thats what i get still any idea?

rwhit57 · 08-02-2011, 05:47 PM

A few things can cause dieseling as it's called. Timing is one, low grade fuel, and carbon buildup. Try some fuel additive, mess with the timing, and there are a couple of ways to blow out carbon. My favorite is a little trans fluid down the carb keeping the rpms up, then go drive it till the smoke is gone.

Dalaigh · 08-02-2011, 05:51 PM

I'm going to guess you have an electric choke. Check the wires going to it, if they are fine then chances are the choke has gone bad.

tucsonjwt · 08-02-2011, 06:15 PM

High idle was my cause. When the truck is dieseling, remove the top of the air cleaner and see if the choke valve is partially closed or if jerking the throttle bracket back quickly stops the problem. You may need an assistant to do this. If you have a stuck choke you can replace your stock choke with a manual choke - I have done this to all my squares and is the best way to make sure your choke is open (or closed) when you want it to be - a $12 experiment. If your throttle is sticking, you will need someone familiar with Q-jets to fix it, unless you can spot the source of the hangup external to the carburetor and fix it yourself.

bigwheel15 · 08-02-2011, 09:28 PM

Check for any vacuum leaks.

383Chevy · 08-02-2011, 11:00 PM

I had the same problem mine was timing

BigRed76 · 08-03-2011, 12:54 PM

If the centrifugal advance in the distributor gets stuck it will cause the timing to stay advanced causing it to diesel...happened to me.

kezark31 · 08-03-2011, 01:26 PM

ive seen a bad alt cause dieseling as well it back feeds in to the ignition.

njlimbaugh · 08-03-2011, 01:34 PM

You didn't mention if you had a fast idle solenoid connected to the throttle linkage. These were used on the pre-computer carbs. It's designed to hold the throttle plates slightly open when the ignition is on, but allow them to close completely when the ignition is cut off. If it's not closing all the way, it could be allowing your engine to diesel for a few seconds.

texasfunk · 08-03-2011, 07:39 PM

Mine was high idle as well at one point

Dan1969 · 08-03-2011, 10:30 PM

Quote:

Originally Posted by texasfunk

Mine was high idle as well at one point

this

true74enduro · 08-04-2011, 02:11 PM

vacume could cause it deffinetly. and that wouldnt shock me if all you guys and gals have one and dont know. gm made a mess of vacume lines on my 85 k10 350. ugh my machanic said i can aliminate atleast 99% of you vacume problem with outout effecting the emmisions. becuase basically as long as if you have an 85 and have a cat on it will pass. 84 no need for a cat. ill have to take pictures of all the vacume lines i removed. i could basically supply checker or autozone for years.

08-02-2011, 05:05 PM	#1
OlBlue85 Registered User Join Date: Jan 2011 Location: Norwich Ontario Posts: 25	why does my motor keep running when i shut my truck off i have a 350 in my truck and when i shut it off it sounds like a diesel truck or tractor and runs for about10 seconds after you shut the truck off< ive took it to 2 different poeple and it still does it sick of getting ripped off any body have any idea what it could be i put new wires plugs distributer and cap timing chain and set the timing and thats what i get still any idea?

08-02-2011, 05:47 PM	#2
rwhit57 Registered User Join Date: Jan 2011 Location: Tulsa,Okla Posts: 590	Re: why does my motor keep running when i shut my truck off A few things can cause dieseling as it's called. Timing is one, low grade fuel, and carbon buildup. Try some fuel additive, mess with the timing, and there are a couple of ways to blow out carbon. My favorite is a little trans fluid down the carb keeping the rpms up, then go drive it till the smoke is gone.

08-02-2011, 05:51 PM	#3
Dalaigh Canadian Trucker Join Date: Nov 2010 Location: Sarnia, ont canada Posts: 648	Re: why does my motor keep running when i shut my truck off I'm going to guess you have an electric choke. Check the wires going to it, if they are fine then chances are the choke has gone bad. __________________ 2020 Silverado Trail Boss - 6.2/10spd

08-02-2011, 06:15 PM	#4
tucsonjwt Registered User Join Date: Jul 2007 Location: Tucson, AZ Posts: 3,189	Re: why does my motor keep running when i shut my truck off High idle was my cause. When the truck is dieseling, remove the top of the air cleaner and see if the choke valve is partially closed or if jerking the throttle bracket back quickly stops the problem. You may need an assistant to do this. If you have a stuck choke you can replace your stock choke with a manual choke - I have done this to all my squares and is the best way to make sure your choke is open (or closed) when you want it to be - a $12 experiment. If your throttle is sticking, you will need someone familiar with Q-jets to fix it, unless you can spot the source of the hangup external to the carburetor and fix it yourself.

08-02-2011, 09:28 PM	#5
bigwheel15 Registered User Join Date: Feb 2010 Location: Fort Worth, TX Posts: 727	Re: why does my motor keep running when i shut my truck off Check for any vacuum leaks.

08-02-2011, 11:00 PM	#6
383Chevy [><]Sofa King Dirty 4x4[><] Join Date: Jul 2009 Location: Englewood, Fl Posts: 353	Re: why does my motor keep running when i shut my truck off I had the same problem mine was timing __________________ 00' Chevy Silverado 1500 z71 33"s 3" lift 5-speed Past trucks 85' Chevy C10 Step side 388 stroker 33" bfg a/t's holley 670cfm world product heads 14.80@92mph 92' S10/Tahoe sbc swap

08-03-2011, 12:54 PM	#7
BigRed76 Registered User Join Date: Jan 2010 Location: Loveland, CO Posts: 1,921	Re: why does my motor keep running when i shut my truck off If the centrifugal advance in the distributor gets stuck it will cause the timing to stay advanced causing it to diesel...happened to me. __________________ Zach 1970 Chevrolet Custom Camper K20 1971 GMC Super K2500, 12V/NV4500 swap in progress 1971 Chevrolet Custom C10 1972 Chevrolet Custom Deluxe C20, 5.3/4L60E 1972 Oldsmobile Cutlass Supreme, 455/TH400, 3.73 posi 2004 GMC Sierra 2500HD, LB7/Allison, CCSB 2005 GMC Sierra 1500, 5.3/4L60E, CCSB

08-03-2011, 01:26 PM	#8
kezark31 Registered User Join Date: Jul 2011 Location: lebanon,or Posts: 7	Re: why does my motor keep running when i shut my truck off ive seen a bad alt cause dieseling as well it back feeds in to the ignition.

08-03-2011, 01:34 PM	#9
njlimbaugh Registered User Join Date: Jun 2011 Location: LaFayette GA Posts: 111	Re: why does my motor keep running when i shut my truck off You didn't mention if you had a fast idle solenoid connected to the throttle linkage. These were used on the pre-computer carbs. It's designed to hold the throttle plates slightly open when the ignition is on, but allow them to close completely when the ignition is cut off. If it's not closing all the way, it could be allowing your engine to diesel for a few seconds.

08-03-2011, 07:39 PM	#10
texasfunk Registered User Join Date: Jun 2009 Location: Lubbock, TX Posts: 1,671	Re: why does my motor keep running when i shut my truck off Mine was high idle as well at one point

08-04-2011, 02:11 PM	#12
true74enduro Registered User Join Date: Jun 2011 Location: riverton,ut Posts: 233	Re: why does my motor keep running when i shut my truck off vacume could cause it deffinetly. and that wouldnt shock me if all you guys and gals have one and dont know. gm made a mess of vacume lines on my 85 k10 350. ugh my machanic said i can aliminate atleast 99% of you vacume problem with outout effecting the emmisions. becuase basically as long as if you have an 85 and have a cat on it will pass. 84 no need for a cat. ill have to take pictures of all the vacume lines i removed. i could basically supply checker or autozone for years.



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