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Truck is dieseling

Babaganoosh

Babaganoosh

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Could it be because my idle is up around 900 to 1000?

Its got fresh ac delco plugs and cap and rotor. Doesn't burn and oil at all, surprised for a 70K motor.


Thanks guys.
 
General causes for dieseling are too high an idle, or timing off.

I gather that carbon buildup in the heads, from prolonged running hot, can also do this.

-- A
 
Hmm, forgot to say in park it idles at 900- 1000, Is that correct? Also it only does it when it runs more then 30mins. Just runs for a few seconds then clunks to a stop.
 
Babaganoosh said:
Hmm, forgot to say in park it idles at 900- 1000, Is that correct? Also it only does it when it runs more then 30mins. Just runs for a few seconds then clunks to a stop.
Click to expand...

Well, it IS bad for the motor, so while it's doing it, turn your engine off in gear, then move to Park.

Idle is specified in Drive, so if you're at 900-1K in Park, you're prolly in the ballpark while in Drive.

I'd check the timing -- heat is a cause, so the extended running would make sense. Possible that you've got the carbon thing going on, but dang if I know what to do about it :dunno:

-- A
 
I believe my timming is correct, allthough im not positive. I have no trouble starting it. Carbon build up could be the case, it scored 23 out of 40 allowed on emissions.

maybe it wouldn't be a bad idea to try some seafoam.
 
What is your engine combo ?

Stock , you should follow your emissions sticker . I idle super low , like 500 in gear , and 600 in park .
 
I have a 82 truck with the original 305 stuff on a 78 crate 350. While in drive with my foot on it idles about 6 to 700.
 
SO by 78 crate 350 you mean an over the counter stock 350 replacement , like an old GM Targetmaster or Goodwrench motor .

Then you better set it to the emissions sticker :thumb:
 
Yes direct stock motor from autozone. Would I set it to my 1982 305 specs? Its never had this problem before, and nothing has been changed.
 
Here is the sticker on the truck. I have nothing to do tomorrow so I may fiddle fart with it.

sticker.jpg


sticker2.jpg


not bad for 25 year old stickers.
 
mine, in gear idles just under 500...it's where the motor likes it the best. no dieseling at all, and it neve dies, even when it's cold. i lowered it to cure dieseling and "clunking" into gear when i shift. it's perfect now.
 
Mine diesels every once and awhile I think its a combo of timing and carbon going to look at it next week when I have some more time, post up if you figure it out.
 
My '77 would diesel on cheap gas, so I always use premium. They will also diesel if you get any little bit of water in there, but that will burn off.
 
Stock , you should follow your emissions sticker . I idle super low , like 500 in gear , and 600 in park .
Click to expand...

mine used to idle that low, but it would miss really badly at lights and stuff. now, i have it around 750rpms and it's smoooooth.

My '77 would diesel on cheap gas, so I always use premium
Click to expand...

my 94 pickup diesels sometimes in very hot or very cold weather, but going from cheap gas (QT) to chevron or exxon seems to clear it up. i tend to think the tiny amounts of additives and stuff they put in don't do much, but maybe it's just enough to make a difference. either way, running MMO can help clean out the carbon.
 
My 400sbc would diesel when I turned it off also. When I replace the old carb to the avenger carb I messed with the idle for awhile and found that when the idle was high it would diesel and when I turned it down to normal (500rpm) or so it stopped dieseling and the problem fixed.
 
Well, I got to lazy today and I havn't even steped outside today.:haha: Most likely tomorrow i'll get out there and do something.
 
Babaganoosh said:
Well, I got to lazy today and I havn't even steped outside today.:haha: Most likely tomorrow i'll get out there and do something.
Click to expand...

Uummmm! Your last post was at 4:26pm and you hadn't stepped outside yet?:screwy: You lazy fock, at least if you are not going to go to work, go and wrench on your rig.:D J/k bro good luck with the job search and your dieseling problem.
Hoby
 
Ok, this has got to be the lamest question ever. I can't seem to find the idle adjustment screw for my quadrajet on the drivers side. :confused: If anyone has a picture pointing out the screw, that would be very helpfull.
 
Babaganoosh said:
Ok, this has got to be the lamest question ever. I can't seem to find the idle adjustment screw for my quadrajet on the drivers side. :confused: If anyone has a picture pointing out the screw, that would be very helpfull.
Click to expand...

Follow the throttle cable from the firewall to the carb. The idle screw will be just inside (towards the center of the truck) of where the cable attaches to the carb. It's basically a stop screw, that stops the throttle mechanism from rotating any further down.

Once you know where it is, it's easy, but the first time, take the air cleaner off. BTDT.

-- A
 
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