Taurus Car Club of America : Ford Taurus Forum banner
1 - 7 of 7 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
What the heck could cause an engine to "diesel" after turning the key off?
I've run into it a few times over the years but I never knew the cause. Bad gas? After that I got nuthin. Maybe someone has some insight for me. Thanks.
 

·
Registered
Joined
·
3 Posts
Discussion Starter · #2 ·
So I guess I'm gonna answer my own thread here. After looking around, I've found that apparently dieseling is caused by several things, but basically it is the air/fuel in the cyl. igniting after the spark has been shut off. One cause of this could be carbon buildup, another one I found was the wrong spark plugs. Apparently there are cleaning solutions for the carbon buildup. Hope this helps someone.
 

·
Registered
Joined
·
10,929 Posts
Run On

So I guess I'm gonna answer my own thread here. After looking around, I've found that apparently dieseling is caused by several things, but basically it is the air/fuel in the cyl. igniting after the spark has been shut off. One cause of this could be carbon buildup, another one I found was the wrong spark plugs. Apparently there are cleaning solutions for the carbon buildup. Hope this helps someone.
When you shut the key off, the spark and the fuel should shut off, no fuel, no run.

So the question is, if the ign if off, why would you still have fuel?

I do not know.

-chart-
 

·
Premium Member
Joined
·
1,523 Posts
I would suspect a leaky injector is supplying fuel for the dieseling.
Carbon and plugs where a igniton source back in the carburetor days when we even had anti dieseling throttle stops to close off air to stop the diesling.
This was common on the early lean burn or lower emission engines with carbs that ran too lean.
The hot spots on plugs or carbon would ignite fuel , a FI car should NOT be getting fuel key off.
Leaking injector or fuel regulator is my choice of fuel source
 

·
Super Moderator
Joined
·
8,732 Posts
^^^^^ +1

Injectors have no power with key off, so the only way for fuel to get into the engine are leaking injectors or via the FPR.
 

·
Registered
Joined
·
3 Posts
Discussion Starter · #6 ·
All the subsequent suggestions make sense to me. I did a quick (and easy) carbon burn off today via a spray can of seafoam, dieseling seems to have ceased. I will keep an eye on it. That takes care (hopefully) of the ignition source but there still may be fuel there via (as stated above) possibly a dripping injector and/or the FPR. In the absence of codes, poor idle, etc. though I won't have anything to fix, will I? Anybody care to add to this? Like to learn something, as always. Thanks.
 

·
Registered
Joined
·
1,365 Posts
Well you can check fuel pressure leakdown with an EFI gauge after shutting off the motor. It should hold for at least a few minutes. If it drops, check the pressure regulator diaphragm for leakage. Then you can always remove the injector rail, with the lines and injectors attached, and cycle the key on/off (without starting). You'll see a leaking injector if there is one.
 
1 - 7 of 7 Posts
Top