Thread: Can a diesel engine blow black smoke at idle.

Originally Posted by nice1guv

So if you turned up the "smoke" screw on the pump at idle the excess air would still compensate and you couldn't really produce smoke unless you turned it like a madman?

The "smoke" screws only change the upper limit of fuelling. At idle the governor only gives the engine enough fuel to maintain rpm, so that adjustment has no effect.

Originally Posted by Dougal

The "smoke" screws only change the upper limit of fuelling. At idle the governor only gives the engine enough fuel to maintain rpm, so that adjustment has no effect.

Rephrase: not the smoke screw then, but isn't there an internal adjustment in the injector pump that gives more off boost fuel?

If this was increased, could it smoke at idle or is there just too much excess air?

Originally Posted by nice1guv

Rephrase: not the smoke screw then, but isn't there an internal adjustment in the injector pump that gives more off boost fuel?

If this was increased, could it smoke at idle or is there just too much excess air?

If you could turn up idle fuelling it would have the same effect as pressing the accelerator (rpm would increase).

Since air is not metered on a diesel, the only thing keeping rpm where it is is the amount of fuel being injected.



On diesels which use a butterfly valve in the intake to produce vacuum, you may be able to make it smoky at idle by turning up the fuel.

Turbo is fingered. Had it on drill rigs running Cummins engines.

Yes. Incomplete combustion. Work it out from there. Bob

Actually, my wife made my work car smoke at idle.

It's the anti-stall feature which cranks up fuel and advances injection timing to try and stave off a stall. I was watching one day when she tried to start off in 3rd instead of 1st.

in that case its not idling, its working.

Originally Posted by Dougal

Actually, my wife made my work car smoke at idle.

It's the anti-stall feature which cranks up fuel and advances injection timing to try and stave off a stall. I was watching one day when she tried to start off in 3rd instead of 1st.

I hope you suitably re-educated her?

I find the phrase "you silly cow" works appropriately.....and is often the last phrase I use just before I find myself in a heap on the floor with sore genitalia!