Engine "dieseling" after shut down.

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cudaspaz

cudaspaz

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I have noticed that once the weather got really hot out that my engine will diesel or start to want to run again after I shut it down.
The motor will shut off, then all of the sudden come back to life for a second then die off.

Yesterday I overheated after sitting in traffic.

I was running a pusher fan on the bumper side of the radiator so i decided to get a universal flex fan and bolt it on to help cool the engine as I have been meaning to do this but I never saw the need to since I was running at 180 and maybe approaching 200 at long red lights, but last night it finally overheated in 85 degree weather.

I drove the car home after the sun went down and it ran perfectly at 180 degrees even at red lights so I'm sure the combination of ambient temperature and the new flex fan helped.

I am running an electric fuel pump and just converted to pump gas from race fuel and backed my timing off 5 degrees.

The car did over run or diesel once on me on a hot day before I converted to pump gas.


What normally causes this and how do I fix it.

I am not running a fuel return line to the tank and I am going to try to kill the fuel pump with the cut off switch prior to shutting the car down.

I will also pull my plugs and check my compression.

You can see some of my previous posts for engine specs while I was asking about pump gas conversions.

The only thing I did differently before my trip yesterday was changed the oil with valvoline 20w50 racing oil per several recommendations and added hughes high zinc cam break in lube.
I hope this did not screw things up, but like I said, it ran really well on the trip home with the flex fan and cooler weather.
 
Most of the time, it's due to the idle speed being set just a little high. OR a vacuum leak that allows too much air into the manifold after the key's been turned off.

Try adjusting the idle speed down a bit and see if that helps; I'll bet it does.
 
I actualy had to bump the idle up a bit to keep it from stalling after I retarded the timing 5 deg.

With my big cam it seems to only want to idle at 1100 rpm without stalling so my idle was a little lower after timing retard.

I was thinking if I killed the electric fuel pump prior to shut down and let it basically run out of fuel it just may help....or not???
 
High combustion chamber temps usually due to carbon or high compression. Something's still lighting off the air/fuel mixture, most likely the spark plugs are red hot. I know your engine is new, so it's not carbon although there could be a sharp edge somewhere on the pistons or chambers.

I would try a set of plugs that were one or two steps cooler.
 
If you have a big cam and the idle mixture screws won't let you idle it down, the throttle blades are open too much. When you shut the ignition off, the engine can still suck enough air in to (barely) run and this pulls some gas thru the jets and engine heat sets off the mixture just like a diesel. The easist fix is an idle stop (anti-dieseling) solenoid that Chrysler installed on the mid 70s cars that held the throttle blades open at the the preferred idle speed. When you shut off the ignition, it de-energized the solenoid and let the throttle close completely.

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You can also use an A/C idle kick-up switch from a GM 2 or 4 bbl. They were used to kick the idle speed up when the A/C compressor engaged. Most Qaudrajets have them.
Hope this helps. And you can always kill the ignition with it in gear and drag the clutch just a bit.
 
Spaz,

I just changed my thermostat to 160* and it really helped drop the temperature down. This was suggested to me by a old radiator shop guy. He said since I wasn't running a heater anyways that he would try to gun a 160* first. Then I could start spending money on expensive radiator,etc... down the road if the 160* doesn't help. My motor wasn't running hot but I stopped in to talk to him about the hot approaching weather and wanted to be ready. I haven't however drove it in stop and go traffic at 85* weather with the 160* thermostat.

I had the dieseling motor effect going on awhile back. Turns out my distributor was on the loose side and must have turned. I changed the timing to all in (I don't run vacuum advance) to 34* at 3000 RPM. This helped a lot! lol!

If you still have problems with it and the motor is running fine you can always let the clutch out just a little to slow the RPMS down and cut the switch off. I did this numerous times before I found out that my timing was off. It won't diesel if you do that.
 
I'm gonna go straight to the horses mouth and talk to the guy that built this motor and see what he thinks.
So far I have made all the timing and fuel adjustments to his recommendations allthough I am no pro at carb adjustments.

I may run it over to his place and see if he wants to tinker with it a bit.
 
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