still rumbling once i shut her down

[NJBattleWagon334]

hey guys quick qeustion. when i drive the waggy short or long trip when coming to the end. i park and shut it off it rumbles for a second or two as if its still burning gas... dieseling? its called... what causes this and is it bad....

[joe]

Not a good thing but not instantly terminal either. There are other causes but most common cause is just idle speed set too high.

[rockrollin]

Typically carbon build up will cause deiseling. If you still have the idle solinoid, check that it's working, it's supposed to prevent deiseling. A slightly open throttle blade and hot combustion chamber (like glowing carbon) will cause it.

[Carnuck]

Vacuum leaks will do it too. If the motor is hot enough to "diesel" fire fuel and has a hot spot it will, unless there isn't enough air to do so.

[NJBattleWagon334]

Yes joe I think you got it. It seems to idle pretty high in park, around. 1000 rpm, how can I lower the idle speed correctly.

[joe]

Don't know the specs for an 89 but with trans in N on a fully warmed up motor, solenoid wire disconnected should be ballpark around the 500-600rpm range? Use the curb idle set screw on the linkage.

[deckside]

Bumping really old thread

I started deiseling about a month back. Tried Se Foam with no improvement. Setting timing again. 14 sound about right for a 360 with HEI ignition? Was going to check the idle on my 4 barrel Edlebrock carb after that.

[tgreese]

For now, suggest you leave it in drive when you shut it off, then go to park. Probably enough drag to prevent dieseling.

I would start by leaning out the idle mixture (best lean idle) and making sure your idle RPM is in spec. Also move the vacuum advance from manifold to ported vacuum for less advance at idle. The original carb may have had an idle stop solenoid that closed the throttle fully when the key is off. This was intended to prevent run-on.

[deckside]

Got rid of the deiseling by bumping initial timing to 17....picked up some pinging under load/ uphill though

[67GMC]

I like TGREESE's comment. See what port your vacuum advance on distributor is attached to. If you've changed from the stock set up, you won't be using the CTO or Non-Linear valve thing. If you have the stock setup, might be more complicated.

I have never had luck with ported vacuum on vac advance. Always used manifold vac. The CTO controls what is sent to the vac advance on the distributor depending on coolant temp. I think if it's cold, it lets manifold vac go to vac advance. If warm, it lets the ported vac go to vac advance.

Others could chime in. It's a Jeep thing and I don't understand!

[deckside]

I like TGREESE's comment. See what port your vacuum advance on distributor is attached to. If you've changed from the stock set up, you won't be using the CTO or Non-Linear valve thing. If you have the stock setup, might be more complicated.

I have never had luck with ported vacuum on vac advance. Always used manifold vac. The CTO controls what is sent to the vac advance on the distributor depending on coolant temp. I think if it's cold, it lets manifold vac go to vac advance. If warm, it lets the ported vac go to vac advance.

Others could chime in. It's a Jeep thing and I don't understand!

I hear ya, Im using manifold vac. Running HEI distributer and Eddelbrock 1406 Carb.

[deckside]

Premium gas seems to have sorted it out but this is a relatively new development and I sure would not mind going back to regular.