dieseling

[dieselman123]

Hey everyone. i need some help. i have a 83 swb silverado with a  305 sbc. the problem im having is that when i go to shut off my truck after driving, it diesels and act like it wants to continue running after the key has been turned off then smoke comes back up through the carb. i have checked my timing and its at 5 degrees btc, all my spark plugs are gapped correct and everything. could a bad timing chain cause this issue??? i had the engine advanced 8 degrees before and it does it still. now i put back at 5 and it still does. i doesnt do it all the time just sometimes. any advice yall can give me to help solve this problem???

[zieg85]

Causes could vary but to high of an idle will cause that to happen

[dieselman123]

my idle screw is backed all the way off but it still seems to idle a little high. only time it idles low is when the truck is in gear. when i take it out of gear it goes right back up. any suggestions

[zieg85]

High idle like you describe is probably from a vacuum leak

[bd]

Causes could vary but to high of an idle will cause that to happen

X2

Dieseling is most often caused by base idle set too high, and/or a vacuum leak, and/or excessive wear around the throttle shafts that inhibits throttle plate closing.

Begin by checking for vacuum leaks.  Look for unplugged vacuum hoses, spray around the manifold and carb base with Berrymans B12.  (If you haven't used B12 before, be careful.  It's quite flammable).

Regarding wear...  http://forum.73-87chevytrucks.com/smforum/index.php/topic,22304.msg184228.html#msg184228

Open and look at the attached sketch.  The unworn plate is on the left; the worn plate on the right.  Gaps caused by wear can result in uncontrolled air flow.  The greater the "gap" the greater the amount of air that passes uncontrolled past the throttle valves.  The result is dieseling.  In the long run you may have to bush the base.  And, if your throttle plates look anything like the drawing at right, the plates will need to be replaced too.  Kits are available to "bush" the throttle base...  http://forum.73-87chevytrucks.com/smforum/index.php/topic,25139.msg210085.html#msg210085

[LITTLE BLACK TRUCK]

I have been fighting this problem on my truck for months. Things that cause dieseling are High idle, vaccume leak, incorrect timeing, improperly adjusted valves, carbon deposits on pistons and overheating. My dieseling problem went away when I adjusted my valves. But you can hook up an anti-diesel switch to help/stop you problem. Its an electric solenoid and it extends to base idle when the power is turned out and it drops the idle to around 300 when the power is shut off. they are mainly used when you have A/C to avoid dieseling from the increased idle.

[bake74]

I have been fighting this problem on my truck for months. Things that cause dieseling are High idle, vaccume leak, incorrect timeing, improperly adjusted valves, carbon deposits on pistons and overheating. My dieseling problem went away when I adjusted my valves. But you can hook up an anti-diesel switch to help/stop you problem. Its an electric solenoid and it extends to base idle when the power is turned out and it drops the idle to around 300 when the power is shut off. they are mainly used when you have A/C to avoid dieseling from the increased idle.

    1 thing you forgot, cheap gas.  I have had several vehicles that did not like the "cheap" gas around hear, and on top of that it can cause carbon build up like you mentioned.

[LITTLE BLACK TRUCK]

I have been fighting this problem on my truck for months. Things that cause dieseling are High idle, vaccume leak, incorrect timeing, improperly adjusted valves, carbon deposits on pistons and overheating. My dieseling problem went away when I adjusted my valves. But you can hook up an anti-diesel switch to help/stop you problem. Its an electric solenoid and it extends to base idle when the power is turned out and it drops the idle to around 300 when the power is shut off. they are mainly used when you have A/C to avoid dieseling from the increased idle.

    1 thing you forgot, cheap gas.  I have had several vehicles that did not like the "cheap" gas around hear, and on top of that it can cause carbon build up like you mentioned.

Thank you I did forget to mention that, the higher octane of the fuel helps/stops the dieseling because its harder to ignite. I also forgot to mention that you can just shut it off in gear and that will kill it sooner but I dont know if that would have any ill effects to your transmission. Ive done it with no problems....