dieseling

[markpro45]

new engine 2.3 punched to a 2480cc. new everything wiring, coil, switches. start it up run for a bit shut it down and (not a nice word)(not a nice word)(not a nice word)(not a nice word) thing will pop diesel and run backwards. Ive tried diffrent carb and have come to the end of my rope. Any help would be greatly appreciated.

[Headhunter]

What gas do you have in it?
What ignition is on the motor?
Do you have colder plugs in it? ie. Champion 304's
If it ran backwards have you checked the cam timing?
Does the alternator backfeed the ignition until the voltage gets low enough to shut it down?

[BVS40FL]

Something Headhunter said jogged my memory a bit.
Residual voltage. Are you running an electric fan ?
Had a car come into my shop once that had an electric fan wired into the harness and was getting it's voltage from the hot wire to the coil. When you would turn off the ignition the engine would run until the fan stopped spinning.
Disconnect your alternator and fan and then try to shut down the engine.

[that dude]

This may be wrong and not associated with what your problem really is...but its what i've learned and seen and you may find a helpful option:

Like BVS and Headhunter mentioned, electric motors or any type of coil for that matter will retain some voltage in it after power is removed.due to the magnetic energy (EMF) created and stored in the coil caused from current flowing through it.

When current is removed, it creates a saw tooth type discharge downward wave til completely discharged. if you have an LED indicator in your dash for your electric fan, you can actually see this slow discharge as the fan slows down after you flip the switch off....even after you've removed the 12VDC power source, the LED will stay lit for a second and slowly dim down...I don't know if that has a way of feeding back into your ignition somehow, but I would definitely weigh it in if all else fails...

.i can imagine that if the engine is spinning over trying to stop and slows down just enough, and you had enough advance timing in the motor, with rich enough mixture, then it would still detonate when induced voltage from a coil was discharged through the spark plug and cause piston to reverse its direction before reaching TDC. and make it go backwards a lil bit, but not far cause the intake valve would still open relieving the pressure and the exhaust valve would open next sucking only fresh air and whatever is left in the exhaust pipe...

If you are running an electric fan, I would suggest putting it on a separate DC circuit then you ignition, so it can't back feed induced current through your system. And make sure your fan has a really good ground to aid in pulling that induced current back to the battery as well. I don't know if your ignition coils in can store and discharge in the same fashion.. but i would keep any other type of coiled item (alternator or e-motor) away from your ignition circuit.

On my car: i pull two different leads from the hot side of the starter solenoid, and they go to three different switches..
1 lead to the fan switch that then goes to the fan, and from fan to ground..
the 2nd lead is ran parallel to my starter button switch (solenoid signal) and my ignition power switch (coil).

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The only other thing I could think of is fuel/combustion issues, as mentioned in the 3rd post on this thread of this jeep forum:
http://www.virtualjeepclub.com/archi...p/t-23517.html

kinda like rounds cooking of in a hot machine gun chamber, causing a 50 cal and 240's to run away from their operator. Too hot of a chamber, and combustible/rich material causes bang (why its called dieseling) like a diesel motor does without a spark plug.

try some easy stuff first, like a different carburetor which you've already done and next like they said, remove your lead going to the fan..if it helps, run it parallel on another switch which is not in series with the switch that does to your ignition. ....

[markpro45]

no electric fan running mechanical. i do have everything off one switch ignition, tach, lights and everything. i think im going to add a switch and leave the ign on its separate switch. thanks for the advise

[that dude]

one other thing, are you running an electric fuel pump or a mechanical pump?

also, make sure you read that jeep forum post. it covers mechanical causes of dieseling.

And has the car always done this or was something changed before it started dieseling (i.e. new carb, rebuilt carb, new head, etc.? )

Does it happen when engine is cold, or hot? In garage or after coming off of track? Just hunting for something that might point to a cause.

[Headhunter]

Also as a electric field colapses you get a voltage spike that can be in the thousands of volts backfeeding through the positive. it is possible that the spike happens when the motor is almost done rotating and firing the ignition that one last time.

Best thing to try first would be seperating all the circuts.

[Hiredgun]

I had a tach not allow the engine to shut down.

Also, try higher octane gas.