2.8 "Dieseling" When Turning Off

[ford4wd08]

Hi Guys,

As of late when I cut off my Bronco with the 2.8 it will have a case of "dieseling".

It isn't every single time, but it is becoming more frequent.

Does anyone have any experience with this? I know it was a lot more common on carb'ed engines.

I did see where a fix could be an electric solenoid on the fuel line, or perhaps an electric fuel pump, but that was just a quick search.

From my understanding it happens from a hot spot in the engine that allows the gas to continue to ignite without the ignition system on, is there a way to isolate this?

I think the Bronco might be running warmer then I would like, but I need to confirm. I believe I'll install a 160 degree thermostat that I've had for a while (lower thermostat engine).

I do have a new two row radiator with a newer fan clutch, just seems to me it is operating a little warmer than maybe it should, but I'll have to get some temps and possibly check the tune to make sure I'm not running too lean.

Any other tips or things to check would be great.

Any advice @RonD or @19Walt93 ?

 

[ford4wd08]

Oh, and I forgot, my idle seems to be turned up maybe a little too high, I know that can impact it.

I idle with no load around 1100 - 1200 rpm. When I put the trans in gear it drops to around 900 or so.

I had to turn it up over the summer to deal with the AC begin on as I don't have a plunger or IAC solenoid on this vehicle, I could add one I guess when the AC kicks on that it would make it work.

 

[rusty ol ranger]

Set the carb back to spec and check your ignition timing. Advanced timing can cause dieseling as well as higher operating temps.

 

[ford4wd08]

Set the carb back to spec and check your ignition timing. Advanced timing can cause dieseling as well as higher operating temps.

Technically it is all in spec. Base timing when I checked last week was 10 degrees BTDC, Idle is supposed to be between 800-900 rpm curb idle (trans in gear).

I think retarded timing is more of the culprit of higher temps than advanced from what I am seeing.

 

[rusty ol ranger]

Technically it is all in spec. Base timing when I checked last week was 10 degrees BTDC, Idle is supposed to be between 800-900 rpm curb idle (trans in gear).

I think retarded timing is more of the culprit of higher temps than advanced from what I am seeing.

I had always heard advanced did it. Hmm..

Any vacuum leaks at the carb base?

 

[19Walt93]

Technically it is all in spec. Base timing when I checked last week was 10 degrees BTDC, Idle is supposed to be between 800-900 rpm curb idle (trans in gear).

I think retarded timing is more of the culprit of higher temps than advanced from what I am seeing.

If it's idling that fast it ain't in spec. High idle speed is the primary cause of dieseling, timing has nothing to do with it because dieseling occurs with the ignition turned off and no spark is produced. I would recommend adding a throttle kicker solenoid to boost the idle a little when the a/c is on. A cheaper solution might be to turn the key off while the trans is still in drive, but I'd get a solenoid.

 

[rusty ol ranger]

If it's idling that fast it ain't in spec. High idle speed is the primary cause of dieseling, timing has nothing to do with it because dieseling occurs with the ignition turned off and no spark is produced. I would recommend adding a throttle kicker solenoid to boost the idle a little when the a/c is on. A cheaper solution might be to turn the key off while the trans is still in drive, but I'd get a solenoid.

Dieseling is basically fumes in the cylinder being ignited due to high combustion temps or abnormally high compression (carbon on top of piston or bottom of valves or chamber)

Basically igniteing like a diesel...hence the name. I had a 300 that did it so bad id have to put it in 4th and drop the clutch.

Also why i asked about the carb base, lean causes higher then normal cylinder temps

 

[ford4wd08]

If it's idling that fast it ain't in spec. High idle speed is the primary cause of dieseling, timing has nothing to do with it because dieseling occurs with the ignition turned off and no spark is produced. I would recommend adding a throttle kicker solenoid to boost the idle a little when the a/c is on. A cheaper solution might be to turn the key off while the trans is still in drive, but I'd get a solenoid.

I'm going off of the sticker under the hood. I believe it says 800-900 curb idle. I'll check when I get home.

Have any suggestions on a solenoid to fab up? I can't imagine it being that hard, AC clutch engaged, solenoid should be as well.

 

[ford4wd08]

I had always heard advanced did it. Hmm..

Any vacuum leaks at the carb base?

I believe I'm good on vacuum, but I'll take a look around when I get a chance. That for sure can cause lean and raise the cylinder temps.

 

[ford4wd08]

I still have my original 2150A carb, I do believe it had a solenoid or something similar on the front of it. I can likely take it off and get it to work with my 2150 no feedback carb I have now. Just need to get some time to investigate.

 

[ford4wd08]

Also, could use this cheaper version of a Holley.

Standard Motor Products ES9 Standard Motor Carburetor Idle Stop Solenoids | Summit Racing

 

[rusty ol ranger]

Ive got no idea on the feedback stuff. But they did run idle solenoids on non feedback carbs too. Ive seen them. But not sure if theres a difference

 

[RonD]

A Diesel engine doesn't use spark plugs, its ignites diesel fuel by compression, which gets it HOT enough to self ignite
To shut off a diesel you shut off its fuel

"Dieseling" in a gasoline engine is caused from self ignition of the lower octane fuel, and is bad for the engine, it's the same thing as pinging/knocking so can cause pitting in the cylinders
Spark system is off with key off, so not the issue, but as said, if spark timing is off it can cause hotter cylinder temps

On a carb you have a big float bowl so cutting off the fuel will take a long while, lol

So best to address the root cause which is cylinder heat, lower octane fuel still needs HEAT to self ignite
I am assuming engine is NOT running hotter than usual, if it is address that FIRST, clean cooling system

Let engine idle for 20-30seconds, then shut it off, this allows for heat dissipation in cylinders that is built up when engine was under load(driving)

Run some Seafoam in the gas tank to help clean off carbon build up in the cylinders
Make sure spark plugs are correct heat range/model for the engine

Run some higher octane fuel that has "cleaners" in it, the higher octane will prevent dieseling for now but not a long term fix

Make sure EGR system is working if you have one, EGR system cools the cylinders when they are under a load, so less residual heat when you stop

 

[Uncle Gump]

Whew... I don't miss the days that this problem was lined up waiting to get in one of my service stalls.

 

[ford4wd08]

A Diesel engine doesn't use spark plugs, its ignites diesel fuel by compression, which gets it HOT enough to self ignite
To shut off a diesel you shut off its fuel

"Dieseling" in a gasoline engine is caused from self ignition of the lower octane fuel, and is bad for the engine, it's the same thing as pinging/knocking so can cause pitting in the cylinders
Spark system is off with key off, so not the issue, but as said, if spark timing is off it can cause hotter cylinder temps

On a carb you have a big float bowl so cutting off the fuel will take a long while, lol

So best to address the root cause which is cylinder heat, lower octane fuel still needs HEAT to self ignite
I am assuming engine is NOT running hotter than usual, if it is address that FIRST, clean cooling system

Let engine idle for 20-30seconds, then shut it off, this allows for heat dissipation in cylinders that is built up when engine was under load(driving)

Run some Seafoam in the gas tank to help clean off carbon build up in the cylinders
Make sure spark plugs are correct heat range/model for the engine

Run some higher octane fuel that has "cleaners" in it, the higher octane will prevent dieseling for now but not a long term fix

Make sure EGR system is working if you have one, EGR system cools the cylinders when they are under a load, so less residual heat when you stop

EGR has been deleted. I suspect that could be part of the problem as well.

I'm tempted to go back and add one for a lot of reason.

I'll review it things listed when I get a chance.