2.8 "Dieseling" When Turning Off

[RonD]

If EGR was deleted then does the engine ping/knock while accelerating, after its warmed up
If it doesn't then spark timing is OK and its most likely not your current issue

 

[19Walt93]

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.

That's what I'd do, it should bolt right on and you probably even still have the connector to plug into it.

 

[ford4wd08]

If EGR was deleted then does the engine ping/knock while accelerating, after its warmed up
If it doesn't then spark timing is OK and its most likely not your current issue

The engine is loud since it is a flat tappet mechanical lifter engine. So I don't believe it is marking any other noises?

I don't believe it is pinging, but I've honestly never had an engine ping that I'm aware of.

I believe it is more idle related. I can kill it in gear with no dieseling.

 

[ford4wd08]

That's what I'd do, it should bolt right on and you probably even still have the connector to plug into it.

It is a 4 prong connector. I'm not sure what all controlled it, but I'm sure I can figure it out.

I believe it's an a actual IAC or a stepper motor vs a solenoid like the one I linked.

 

[RonD]

I wouldn't worry about the EGR system then

 

[19Walt93]

It is a 4 prong connector. I'm not sure what all controlled it, but I'm sure I can figure it out.

I believe it's an a actual IAC or a stepper motor vs a solenoid like the one I linked.

It's not an IAC, that means idle air control and those didn't appear until port fuel injection. It may be a stepper motor but I don't think so, try feeding it 12 volts and see what it does. You already own it so if it'll do the job you're ahead.

 

[AndyB.]

It's not an IAC, that means idle air control and those didn't appear until port fuel injection. It may be a stepper motor but I don't think so, try feeding it 12 volts and see what it does. You already own it so if it'll do the job you're ahead.

Two wires are for the sensor that tells the ECM if the idle speed control motor is contacting the throttle arm, the other two connectors extend or retract the plunger, based upon ECM applied voltage. I don’t know how you’d make this work without an ECM,TPS, etc.

The solenoids being referenced by others were called dashpots—which I also don’t think would help you. The combustion chambers and piston tops are probably covered with carbon, causing the dieseling.

 

[ford4wd08]

Two wires are for the sensor that tells the ECM if the idle speed control motor is contacting the throttle arm, the other two connectors extend or retract the plunger, based upon ECM applied voltage. I don’t know how you’d make this work without an ECM,TPS, etc.

The solenoids being referenced by others were called dashpots—which I also don’t think would help you. The combustion chambers and piston tops are probably covered with carbon, causing the dieseling.

I thought a dashpot was more like a cushion for when he throttle closed and letting it decelerate too quickly. Used a lot with Auto trans to help with emissions and letting the engine speed and all mess better with throttle position on sudden changes.

>Carburetor Dashpot - Mikes Carburetor Parts (carburetor-blog.com)

GM did use a lot of solenoids like I liked for dieseling and the like from my research.

It is very possible that I need to run some seafoam etc. to help with carbon build up.

 

[alwaysFlOoReD]

I used to slowly pour water down the carb to clean out carbon. Keep the revs up as you pour.

 

[ford4wd08]

I used to slowly pour water down the carb to clean out carbon. Keep the revs up as you pour.

I saw that online. Heard just a little at a time.

 

[alwaysFlOoReD]

I saw that online. Heard just a little at a time.

As long as the revs are up you can pour as much as you want... until the revs start coming down. It's pretty easy to figure out once you start pouring it in.
One hand on the throttle, one pouring.

 

[19Walt93]

Two wires are for the sensor that tells the ECM if the idle speed control motor is contacting the throttle arm, the other two connectors extend or retract the plunger, based upon ECM applied voltage. I don’t know how you’d make this work without an ECM,TPS, etc.

The solenoids being referenced by others were called dashpots—which I also don’t think would help you. The combustion chambers and piston tops are probably covered with carbon, causing the dieseling.

The sensor that read closed throttle was an idle tracking switch- or ITS. ECM is GM speak, Ford called it a processor in the EEC I,II,III, IV days and it became a PCM when OBD II hit. An idle solenoid is electric, a dashpot was basically just a cushion that slows the return to the idle stop screw. A dashpot won't help- it would actually make the dieseling worse if you shut it off quickly after releasing the throttle. A throttle kicker solenoid would allow you to have a higher idle speed with the a/c on and let the throttle drop to base idle quickly when the key is turned off.

 

[19Walt93]

I used to slowly pour water down the carb to clean out carbon. Keep the revs up as you pour.

We did that a lot on 200 sixes to get rid of the carbon and cure spark knock. Make sure to disconnect the cat first or it will glow red, I once set the exhaust hose on fire when dosing a Fairmont with water. Ford carbon cleaner will do the same thing and stink worse. It won't fix dieseling, though.

 

[4x4prepper]

First off, DITTO, on everything RonD posted.

$0.02 - I have a well worn 2.8L that idles about 1500-1800 rpms, base 14+ degree timing, running duraspark ii, 160 or 180 thermostat (I forget), no fan shroud (yet), and I have no issues with dieseling. Since you did not have problems, but, now you do, I would look at what changed. Most likely a vacuum leak or carb base leak. I would not rule out the PCV. If you have vacuum caps, get rid of them, and use a hose with a bolt in the end and a hose clamp around the hose on the bolt end.

I would say it is about impossible to get a good quality vacuum cap anymore because now they all come from China and that is the only kind you will find at box stores. They get holes, they crack, they fall off, they do not seal, they are a headache waiting to happen. Rice racer silicon or rubber, they are all inferior to what was a simple reliable item 20 years ago.

If your 2.8L is still pretty much stock, you might have a problem with the charcoal vacuum system and the canister is loaded down with gas and the carb is not pulling fumes out or dumping them into the canister when the vehicle is shut off. Very easy to check, just remove it and see if it is loaded with gas vs. just fumes. Located on the driver's side next to the radiator.

Sometimes adding a 1" Phenolic Throttle Body Spacer can cure the dieseling without doing anything else. Though that will not fix the problem, just mask it. I run red pump QT (no alcohol) in my 2.8L and it makes a huge difference in drive-ability. My neighbor noticed improved performance once I convinced him to use it for his SHTF supply, which he then used it in his 2017 Expo with the twin turbo 3.5L a few months later.

 

[ford4wd08]

First off, DITTO, on everything RonD posted.

$0.02 - I have a well worn 2.8L that idles about 1500-1800 rpms, base 14+ degree timing, running duraspark ii, 160 or 180 thermostat (I forget), no fan shroud (yet), and I have no issues with dieseling. Since you did not have problems, but, now you do, I would look at what changed. Most likely a vacuum leak or carb base leak. I would not rule out the PCV. If you have vacuum caps, get rid of them, and use a hose with a bolt in the end and a hose clamp around the hose on the bolt end.

I would say it is about impossible to get a good quality vacuum cap anymore because now they all come from China and that is the only kind you will find at box stores. They get holes, they crack, they fall off, they do not seal, they are a headache waiting to happen. Rice racer silicon or rubber, they are all inferior to what was a simple reliable item 20 years ago.

If your 2.8L is still pretty much stock, you might have a problem with the charcoal vacuum system and the canister is loaded down with gas and the carb is not pulling fumes out or dumping them into the canister when the vehicle is shut off. Very easy to check, just remove it and see if it is loaded with gas vs. just fumes. Located on the driver's side next to the radiator.

Sometimes adding a 1" Phenolic Throttle Body Spacer can cure the dieseling without doing anything else. Though that will not fix the problem, just mask it. I run red pump QT (no alcohol) in my 2.8L and it makes a huge difference in drive-ability. My neighbor noticed improved performance once I convinced him to use it for his SHTF supply, which he then used it in his 2017 Expo with the twin turbo 3.5L a few months later.

My 2.8 has all emissions equipment removed and a duraspark distributor with HEI module running the ignition. I have a 2150 carb from a 2.8 pinto.

I will look for a vacuum leak today because I do suspect my idle changes once the engine is warm. I'll also confirm all the tuning, etc.