Why Can't I stop My 351w From Dieseling (Engine Runon)

[jikelly]

Something I have been trying to fix, but failed is once my engine is warmed up and I turn off the key it keeps running.

I have readjusted my timing, air fuel mixture, swapped distributor, installed a new electronic ignition, and just fooled around with stuff. The dieseling remains.

So I also bought a new carb replacing my carter/edelbrock 750 with a carter 625. Engine runs smoother now, but still runs on after the key is off.

Maybe the problem is electrical. Like the coil is still receiving power after the key is off. I can check that with my multimeter, I think.

Really I'm kinda just scratching my head on this one.

 

[golf4283]

is your ignition box hooked up to a keyed 12volt source? It might just be that it's hooked to an on all the time source and all it needs to go is the crank and when you do it gets stuck on. Make sure the box is properly connected to a switched 12v source so when the key is on the box is on.

Seems simple but It's hard to tell without knowing how everything is wired up.


EDIT: Keep in mind that an ignition box draws power from the battery/alternator BUT it needs a trigger from a keyed 12v source. It works like a relay basically.

 

[golf4283]

If you do have the voltmeter check the wire connecting to the ignition box that is supposed to be a switched 12v. If it's still giving you power after the car is off then there is your problem. If not then I'm sure someone can think of some other solutions.

 

[dodgestang]

Just turn it off in gear.

 

[Steve S]

Hi,

I had the same problem, with an auto you can't stall the motor so dodgestangs solution didn't work for me ....

I changed to premium gas and the problem disappeared.

Steve

 

[dennis112]

Try advancing the timing a few degrees and see what happens.

 

[zookeeper]

Hi,

I had the same problem, with an auto you can't stall the motor so dodgestangs solution didn't work for me ....

I changed to premium gas and the problem disappeared.

Steve

You most certainly can stall the motor with an auto. How do I know? Mine used to do it as well, so rather than shut it off in park and let it diesel, I started shutting it off in drive and it killed it instantly with no run-on. My problem was the carbs were too rich, once I fixed that, it fixed the problem.

 

[Rapid]

Carbon build up will cause the problem. Get a top end cleaner to fix it.

A rich mixture can cause the carbon problem.

 

[Wart]

Hi,
I changed to premium gas and the problem disappeared.

Carbon build up will cause the problem. Get a top end cleaner to fix it.

The best answers, more knock resistant fuel and/or removal of hot spots.

Dieseling is caused by hot spots (Usually carbon) and compression, the higher the compression (or hotter the engine) the 'fewer' hot spots needed.

My knee jerk response is to just get a jug of TEL ... Yeah, Right, I've been looking for years.

 

[stonecoldtx]

The best answers, more knock resistant fuel and/or removal of hot spots.

Dieseling is caused by hot spots (Usually carbon) and compression, the higher the compression (or hotter the engine) the 'fewer' hot spots needed.

My knee jerk response is to just get a jug of TEL ... Yeah, Right, I've been looking for years.

Well, there are actually a few more things that can contribute to or even cause runon

* Idle speed too high--this is why there were idle solenoids on some cars that did not have A/C

* Ignition timing too far advanced

As has already been mentioned, carbon building can cause this condition, because it can create a "hot spot" that basically acts like a glow plug, and ignites the fuel even when the spark plug isn't firing.

One "old school" way we used to remove carbon is to take a quart of water, and with the engine running at around 2000 RPM, pour it down through the carburetor; what this will do is basically "steam clean" the piston tops, because the water will instantly turn to steam and blast the carbon away.

I've also used Transmission fluid as well--and it's effective, but man, it really smokes up the place when you do that! Because of that, whenever I'm faced with removing carbon, I just use water these days.

So . . . if you have a stock or smooth idle camshaft, make sure that the idle speed is set to the shop manual specs--and if it has an idle solenoid, use that to adjust the speed, not the screw on the throttle blades.

With an idle solenoid that engages when you turn on the key (no A/C), the screw that adjusts the throttle blades should be set so that the engine just barely runs when it's at full operating temperature, and the idle solenoid is then used to adjust the idle speed to the specifications published in the manual.

If you have an aftermarket long duration camshaft, try to get it to idle as slowly as possible.

In either case, after you set the idle speed, you will probably want to make sure your timing is set to the correct specs as well--if you have to move it back, you'll also need to adjust the timing again (and repeat the idle speed adjustment . . .)

Then--I'd recommend the "water treatment" to remove any carbon on the tops of the pistons or in the combustion chambers. It certainly won't hurt anything if carbon buildup is minimal, and it could go a long way toward removing any that exists.

 

[dodgestang]

Then--I'd recommend the "water treatment" to remove any carbon on the tops of the pistons or in the combustion chambers. It certainly won't hurt anything if carbon buildup is minimal, and it could go a long way toward removing any that exists.

I wouldn't it may be old school and all....but if you do that little trick the wrong way you could bend a rod or worse. Water doesn't compress.

 

[stonecoldtx]

I wouldn't it may be old school and all....but if you do that little trick the wrong way you could bend a rod or worse. Water doesn't compress.

That's a good point there, and I should have been more descriptive with the details of how to do this . . . if you're not familiar with how to do it, it might not work out too well.

But--if you pour a little bit of the water at a time (a small stream), with the engine at a very high idle (like around the 2000RPM I mentioned in my previous post), you shouldn't have any problems--I never have.

One more tip--when pouring the water down through the carb, hold the container is such a way that if water comes out too quickly, it will go onto the engine instead of going into it. For example, leaning across the driver's fender, point the container away from you and pour into the venturi on the passenger side.

 

[Evan@ROUSHperf]

Check your timing, if you can spare a degree or two try and retard it. Does it run hot or is it hard to start when hot?

 

[jikelly]

Just turn it off in gear.

Yeah that works. I didn't get out to check the power to the coil last night but will find time tonight to check and let you know what I find.

 

[jikelly]

I can tell you that I have tried retarding the timing and that had no effect. I don't expect my engine to have much carbon in it at 6000 or so miles, but that could be it. I also have tried higher octane fuel and that seems to lessen the dieseling a bit.

Tried leaning out the fuel mixture and my engine ran like crap. (That might just be how it's supposed to run)

I've also readjusted my idle speed below 700 rpm and found my car dying at lights, but still dieseling. So I turned that back up. The engine is a bit hard to start when cold, but starts pretty quickly when warm. I check my spark plugs and the color tells me that the engine is just a bit on the lean side. No deposits, well some soot and dirt on the number 4 cylinder spark plug (I don't like that, but figure it is deposits from my dirty old carb.

 

[rbohm]

kelly, one more thing to look for is a small vacuum leak.

 

[Wart]

* Idle speed too high--this is why there were idle solenoids on some cars that did not have A/C

And cars with AC had 2 stage solenoids.

I'm trying to remember a car with a solenoid before unleaded fuel, only thing I know I saw was a dashpot.

* Ignition timing too far advanced

Or retarded. Both lead to excess engine heat.

One "old school" way we used to remove carbon is to take a quart of water, and with the engine running at around 2000 RPM, pour it down through the carburetor; what this will do is basically "steam clean" the piston tops, because the water will instantly turn to steam and blast the carbon away.

It's been mentioned how an engine can hydrolock if the water is applied to quickly.

A quart in at least a 5 minute period, 10 minutes would be better.

In either case, after you set the idle speed, you will probably want to make sure your timing is set to the correct specs as well--if you have to move it back, you'll also need to adjust the timing again (and repeat the idle speed adjustment . . .)

We use to set timing by going to a "country road", do acceleration runs at WOT in a higher gear and keep bumping the timing up till the engine pinged, and when it pinged back it off a hair.*

But then stock ford had funny chains and plastic cam gears ....

{edit} * Forgot to say, we use to check our main jets during these acceleration runs by shutting off the key while keeping the throttle open then reading the plugs. {/edit}

 

[Wart]

I can tell you that I have tried retarding the timing and that had no effect. I don't expect my engine to have much carbon in it at 6000 or so miles, but that could be it. I also have tried higher octane fuel and that seems to lessen the dieseling a bit.

I figured the engine was 'fresh', I figured it wouldn't have more than fluffy carbon from, say, idling rich.

Things I left out about hot spots, any kind of a raised edge in the combustion chamber can result in a hot spot. Way back when there were tails of detonation traced back to casting flash.

Worn valves will also lead to dieseling, knife edging or insuficent seat can lead to a glowing valve. At 6,000 miles that shouldn't be the problem.


There is an obvious answer, Your running too hot of a plug. Drop down a heat range or two. If you drop 2 ranges and the problem goes away you have nailed the problem, then you only have to find the right heat range in the right plug manufacturer. I'm sitting here laughing at my losing track of the number of sets of plugs I had laying around.

(plugs are like shoes, size 11B from one manufacturer is a 10EE from another, and just cause they look the same doesn't make them the same).

Tried leaning out the fuel mixture and my engine ran like crap. (That might just be how it's supposed to run)

Idle or main jet?

Concern yourself only with the idle circuit.

I've also readjusted my idle speed below 700 rpm and found my car dying at lights, but still dieseling. So I turned that back up. The engine is a bit hard to start when cold, but starts pretty quickly when warm. I check my spark plugs and the color tells me that the engine is just a bit on the lean side. No deposits, well some soot and dirt on the number 4 cylinder spark plug (I don't like that, but figure it is deposits from my dirty old carb.

Seems to me the most interesting things happen in #s 4 (and 8).

Thing is soon as the engine is ran up the fluffy carbon from idle should be gone (except for maybe the deepest recesses of the insulator).

If I were you my next move would be to set the timing where it's "suppose to be" and install a colder plug and see what happens.

 

[jikelly]

kelly, one more thing to look for is a small vacuum leak.

Yeah could be that too. I can't find one anywhere though. I do think my PCV valves need replacing though. I've got pressure coming out of the dipstick tube.

 

[jikelly]

We use to set timing by going to a "country road", do acceleration runs at WOT in a higher gear and keep bumping the timing up till the engine pinged, and when it pinged back it off a hair.*

But then stock ford had funny chains and plastic cam gears ....

{edit} * Forgot to say, we use to check our main jets during these acceleration runs by shutting off the key while keeping the throttle open then reading the plugs. {/edit}

Huh?

I thought that was the preferred method.