My Olds Cutlass “diesels”

Question:

I am restoring a 1986 Oldsmobile Cutlass 442. I reconditioned the motor back to stock but replaced the computer-controlled engine components with manual ones like an Edelbrock 600 cfm carburetor and intake, a Summit EFI distributor, and headers with dual exhaust.

The problem I am having is that after a run I shut off the engine but the engine keeps running for another one or two seconds before finally shutting off.

I have replaced the ignition switch but it didn’t help. I retarded the timing 1-2 degrees from the stock setting, which is 20-degrees BTDC but that didn’t solve the problem either. The transmission has been rebuilt with all new cables including the one running from the shifter to the steering wheel column.

I am also having a problem finding the back retainer clip for the power wires that go on the back of the driver’s side window switch and the female clips that get crimped on the power wires.

I have the clip but there is no back to it to safely encase the wires. Any suggestions would help.

Answer:

Engine run-on or “dieseling” can be caused by a number of different things. One possible cause is excessive engine operating temperature, which can cause fuel to ignite without spark from the plugs. In a similar vein, significant carbon deposits in a combustion chamber will usually glow red hot and serve as an ignition source for fuel even after the ignition switch is turned off. Try retarding your ignition timing a little bit more and lower the idle speed, if feasible.

The fuel you’re using can also increase the engine’s propensity to run after it’s shut down. Gasoline formulated for winter use in cold weather areas and gas with a high alcohol content will both make dieseling more likely. Poor quality (low octane) fuel is also more likely to cause or contribute to a run-on problem.

Spark plugs that are the wrong temperature range for your car can cause runon because the tips can be way too hot.

A defective carburetor that leaks fuel into the engine after it’s shut off can be the source of your problem. If your Cutlass is equipped with an “anti-dieseling solenoid” that’s not working as it should, the result will likely be run-on. This is because the throttle remains partially open when the ignition is killed, and this delivers enough fuel to the hot engine for it to continue running for several seconds more.