Help Diesling.
- Thread starter tomythakat
- Start date
mudbilly
Member
Then it should be in the only valve cover.
That asside... I really doubt that a
PCV/vacum problem would cause this.
Since this is a straight 6, I'm going to assume that it's a factory spec engine.
So this points me to your carb. What RPM is the engine idleing at when warm? It should be around 600-800RPM. Also check the idle mixture. Basicaly I think the carb is dumping too much fuel into the engine at idle.
That asside... I really doubt that a
PCV/vacum problem would cause this.
Since this is a straight 6, I'm going to assume that it's a factory spec engine.
So this points me to your carb. What RPM is the engine idleing at when warm? It should be around 600-800RPM. Also check the idle mixture. Basicaly I think the carb is dumping too much fuel into the engine at idle.
Most likely: points are worn and/or out of adjustment. Check these first! Next, pull the spark plugs, check, and replace if necessray. Check and if needed replace the spark plug wires, dist. cap and rotor. 99% sure it is the points though. Carb. screws do not turn themselves out of adjustment.
It is a good idea to replace the cap and rotor when replacing points and they are all inexpensive.
It is a good idea to replace the cap and rotor when replacing points and they are all inexpensive.
Hmmmm see this is what I don't understand. Lots of people point to timing/spark problems when troubleshooting a dieseking problem but this makes absxolutely NO sence to me. Dieseling is called dieseling because the engine is acting like a diesel engine! Meaning the fuel is being ignited without the help of a spark.
When you turn the key off, you turn off power to your ignition circuit. Meaning no more spark... now if your not getting a spark in the 1st place how the heck could the problem be a timing or points issue????
When you turn the key off, you turn off power to your ignition circuit. Meaning no more spark... now if your not getting a spark in the 1st place how the heck could the problem be a timing or points issue????
Let me 'splain Lucy. Dieseling is caused by incorrect timing most often. If the points are worn or out of adjustment, they will be firing when they should not be. As the piston is trying to go up or down, there is a spark that should not be there forcing the piston the other direction and causing it to keep up an unatural cycle even after the key is off.
That being said, other causes as you pointed out are: idle too high, excessive carbon buildup, vaccuum leak at manifold or hose, valves sticking, overheating, wrong spark plug heat range,etc...
I'm assuming this is a stock engine and guessing the most likely cause from experience. Diesleing is very destructive to engines; it can break rods, cranks,etc...The absolute last thing I would advise a novice to do is to atrt turning screws on a carb. 9 times out of ten, that's not the problem anyway if the car has not been modded or wrenched on by a backyard mechanic.
That being said, other causes as you pointed out are: idle too high, excessive carbon buildup, vaccuum leak at manifold or hose, valves sticking, overheating, wrong spark plug heat range,etc...
I'm assuming this is a stock engine and guessing the most likely cause from experience. Diesleing is very destructive to engines; it can break rods, cranks,etc...The absolute last thing I would advise a novice to do is to atrt turning screws on a carb. 9 times out of ten, that's not the problem anyway if the car has not been modded or wrenched on by a backyard mechanic.
mustangdave said:
You missed my whole point.. with the key off there is NO SPARK. Timing doesn't matter when there is no spark...
I agree that hot spots can cause dieseling (carbon build up, poor cooling, etc)
Again.. it's called dieseling because the air/fuel mixture is being ignited without the help of a spark....just like a diesel engine.
65ShelbyClone
Founding Member
Yeah, when you turn the key off, it cuts power to the coil so theres no way for the ignition system to function. I would suspect carbon buildup or perhaps spark plugs with too high of a heat range. The spark plugs are easy to fix, but the carbon will either need a teardown & rebuild to remove or a helluva lot of hard driving to blow some out.
I see your point; just saying I have had it happen with points with the key off. The "spark" was there out of time when I turned the key off and carbon buldup or whatever kept it going for a few seconds. Replace and adjust points... no more deiseling.
You may be right in your diagnosis but I would check the easy, (and cheap), things first. I didn't mean to contradict you, just provide an alternate point of view. It may well turn out that you are 100% correct.
At first glance, it does seem stupid to think that it could be caused by a spark when there is no power to the ignition, but further analysis reveals that the spark could have already occurred and the effect is being spurred on by other factors. Wow, I sound like a math teacher or some crap. I am no expert on this subject but this has been my experience and would love to debate the subject more as long as it doesn't gey nasty.
Ultimately, my problem was worn dist. gear amd carbon buildup but the engine ran with fresh points (repaced periodically) for another 100,000 miles.
You may be right in your diagnosis but I would check the easy, (and cheap), things first. I didn't mean to contradict you, just provide an alternate point of view. It may well turn out that you are 100% correct.
At first glance, it does seem stupid to think that it could be caused by a spark when there is no power to the ignition, but further analysis reveals that the spark could have already occurred and the effect is being spurred on by other factors. Wow, I sound like a math teacher or some crap. I am no expert on this subject but this has been my experience and would love to debate the subject more as long as it doesn't gey nasty.
Ultimately, my problem was worn dist. gear amd carbon buildup but the engine ran with fresh points (repaced periodically) for another 100,000 miles.
If there is spark with the key turned off, then there is a wiring problem somewhere.
This is how the engine is turned off...buy cutting the spark. Could you have done anything else that fixed the problem while you were in there?
There are 4 causes of dieseling.
1) Too much heat. This could be from hot spots due to carbon buildup, wrong plugs, etc.
2)Too much compression. Unlikely the cause with a factory engine.
3) Too much fuel. Caused by poor carb tuning, or too high of an idle.
4) Poor fuel or wrong fuel. Higher octane fuels are more resistant to dieseling.
It's been my experience that of these 4 causes, "too much fuel" is the most common. Usually because the idle speed has been set too high.
This is how the engine is turned off...buy cutting the spark. Could you have done anything else that fixed the problem while you were in there?
There are 4 causes of dieseling.
1) Too much heat. This could be from hot spots due to carbon buildup, wrong plugs, etc.
2)Too much compression. Unlikely the cause with a factory engine.
3) Too much fuel. Caused by poor carb tuning, or too high of an idle.
4) Poor fuel or wrong fuel. Higher octane fuels are more resistant to dieseling.
It's been my experience that of these 4 causes, "too much fuel" is the most common. Usually because the idle speed has been set too high.
