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Dieseling???

81K5GUY

81K5GUY

1/2 ton status
Joined
Jan 30, 2006
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Location
Rockingham ,N.C.
I get some dieseling from my engine from time to time which makes me think the timing may be advanced too high.Heres my problem though the previous owner replaced the original 305 with a built 350 but heres the catch they didnt bother to install a timing tab on the timing cover so I have no way to check the timing with a light.Since it has been years since I messed with any chevy engines(been playing with late model Mustangs for the past 1o years)I cant remember which way to turn the dist to retard it ,clockwise or counterclockwise.I know I could go out and play with it and figure it out but I figured someone here could help me out .Thanks!

Bill
 
Your Edelbrock card could be part of the problem. Try idling the engine down a little. Not sure what speed exactly because I don't know your cam specs. Normally from my experiences dieseling is usually caused by too high of idle or too hot of an engine at shutdown.
 
I have had the same problem with my Edelbrock, just turned down the idle and it was fine. As for the timing, I believe you need to go CCW with your dist.
 
I dont see how any amount of timing could possibly cause dieseling. Not to highjakc but mabey this will help. Why would it matter if the spark quits the second the ignition is shut off. It seems like it would make its last fire and quit rotating as soon as that explosion was done.
 
I have adjusted the idle as far down as I can go with my cam without it stalling in gear .The engine temps are nowhere near too hot ,the only other thing i figured on was the timing since it metioned the timing could be advanced too far in my chiltons manual as a possible cause of dieseling.One other thing I saw was the octane rating being too low so I may try some higher octane fuel since I have been running the lowest(87) grade.
 
81K5GUY said:
I have adjusted the idle as far down as I can go with my cam
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What cam brand & grind/part number are you running (and at what rpm is your warm idle set)?

The ignition advance could do it, since more advance increases octane requirement and enough added advance can cause preignition if the octane too low.
 
1985_K5_Silverado said:
What cam brand & grind/part number are you running (and at what rpm is your warm idle set)?

The ignition advance could do it, since more advance increases octane requirement and enough added advance can cause preignition if the octane too low.
Click to expand...


Thats just the thing I bought the truck as is and have no idea what cam is in it.It has a pretty fair idle .I am running a Edelbrock carb with a manual choke I dont even know the size of the carb .The previous owner bouhgt it from the guy that installed the engine so he was clueless also as to what parts are in it.I know it runs great and pulls hard but just runs on sometimes when you shut the engine off.It doesnt seem to matter if I have been driving an hour or just around the block .Sometimes it may go a day or 2 without doing it .
 
chevron additive

I had the same problem and started using BP high octane and the chevron additive to remove the carbon deposits and have had no more problems since.
 
so far it hasnt done it since I added the octane booster.Guess I need to start using a higher octane fuel.Think I will try the 89 octane first then if that doesnt do it I will switch to the 93.
 
81K5GUY said:
so far it hasnt done it since I added the octane booster.Guess I need to start using a higher octane fuel.Think I will try the 89 octane first then if that doesnt do it I will switch to the 93.
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Have you crunched the cost difference of just using premium fuel vs regular + octane booster?
 
haha you read my mind I was just figureing it up.It is a couple dollars cheaper to just put the octane booster in.Compared to a tank of premium.Around here 93 octane is around 20 cent more per gallon than 87.
 
thats what it is around here, 20 cents more for 93, 10 cents more for 89. i figured it up with my truck, it costs me $4 more for a full tank of premium, it costs me $4.49 plus tax (only place in town that sells it) for a bottle of octane booster that treats 20 gallons (full tank on my truck). and the premium got me better gas millage.
 
Dieseling ....

Engines usually diesel due to high idle speed,or high internal temps like a valve or piston top,or carbon deposits glowing red hot igniting the mixture after the spark stops..over advanced timing can cause it to run hot enough to make it diesel..turning the distributor towards the firewall (clockwise) retards the timing on a chevy motor..

What you probably really need is an "Idle Stop Solenoid" on the carbs throttle linkage..its an electrical solenoid with a plunger that extends when the ignition is turned on,and it contacts the throttle lever on the carb,and sets the idle speed...when the key is turned off,the solenoid plunger retracts,causing the butterflies in the carb to shut completely,thereby "smothering" the engine of air,so no way can it keep running..

You may very well need the higher octane fuel with the cam and other engine modifications you have...but if it ran well otherwise,with no pinging,you might just as well keep using regular gas and put an idle stop solenoid on the carb instead..remember, retarding the timing cuts power,increases engine temparature,and kills gas mileage to some degree..if it starts up hot without binding ,the timing probably is not too far advanced..timing that is too retarted can cause dieseling too..:crazy:
 
Thanks guys ,that idle stop solenoid doesnt seem like a bad idea .Would I need to adapt a oem piece or do they make one for the edelbrock carbs? I have been playing with the idea of buying a Holley Truck Avenger carb.I never really liked the Edlebrock carbs that much ,but it was what the previous owner had on it.For now though the octane booster seemed to solve my problem .I wouldnt doubt if there isnt alot of carbon buildup since the last owner never new what the choke cable was for and left it half shut the entire time he had it .And he wondered why it got such bad mileage lol.
 
solenoids..

I've seen Idle Stop Solenoids in Jegs and Summit catalogs..not sure if they fit one particular carb,or are "universal"...Edelbrock may make one too..your problem may fade away over time,if its due to carbon build up from the choke being left half closed!..hope your rings didn't get gas washed!--my friend's sister fried the rings in his 67 283 Impala when she drove it for three days with the hand choke 3/4 closed!..:doah: smoked like a chimmney after that!..:(
 
engine seems to run great .I have been driving it daily and the only issues I have found was the before mentioned dieseling.Now that I have that under control it time to start on the mods!!!!!Thanks alot guys!
 
I'm still confused. Is it dieseling or knocking? I suppose the octane booster would help both problems.

As for timing it, you could just retard it a bit (rotate dizzy clockwise) until it works better or you could make or buy a timing tab. I would rather lose a few degrees of timing than be forced into premium fuel, at least for a daily driver.

If the vehicle had a 305, it may still have the ESC box, which is supposed to detect knock and provide a retard signal to the ignition module. If this worked, it could help with knocking (assuming the timing is set reasonably), but likely wouldn't do anything for dieseling.
 
no its not knocking it "running on" when the ignition is turned off.Well it was but the higher octane seems to fix that.Looks like retardiing the timing would help too .I picked up a new timing cover form summit yesterday so soon I will be able to tell where im at with the timing.
 
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