, Salem, MA

April 20, 2013

Dieseling getting worse in 1969 Jeep

Auto Scanner
Larry Rubenstein

---- — Q: Please allow me to ask your assistance with an engine problem. A solution could save me some time and expense. I hope you find it interesting. The truck is a 1969 Jeep J2000 with the factory-installed Buick 350 V8 engine. I use it around my small farm doing chores. It has idled a lot picking up brush and other chores where you jump out, do something for a minute, jump back in move forward, over and over. It is not registered for the road and also has some body corrosion. It could not pass inspection. I have used the truck for 20 years, and it gradually developed dieseling when turning off the ignition. We use octane booster and buy 89/93 octane gasoline (it has helped a lot). The dieseling is getting worse. When I turn off the ignition, it will run for 30 seconds, sometimes more, and finally runs backward and blasts back through the carburetor.

The following has been done to try to correct the problem: Put in 160 thermostat (helps — if temperature goes over 160 degrees, dieseling is much worse; below 160, Jeep acts almost normal); put in a new timing chain (small change); tried changing the timing per distributor (no change or worse); sprayed water into carb to loosen cylinder carbon (helps some ,only temporarily) sprayed in 3 quarts of sea foam when running, smoked out the yard and let it sit overnight (no change at all — water did better). The two-barrel carburetor has original jets and runs on the rich side. I put in colder spark plugs, but there was no change. There is something hot in the combustion chamber/chambers that is igniting the fuel, carbon or hot metal. Can you suggest a solution or a reason for this? I plugged cooling; the coolant is always clean, but there are mineral deposits in the radiator. I heard you at one point say Cadillac has some carbon-removing solution at the dealerships used in the North Star engine. I would appreciate your help.

A: You have already tried a few cures that I would have suggested. But getting back to basics, to run on, a car needs fuel and ignition. Most likely, your carburetor is leaking. Further, your intake manifold has a hot spot that is causing ignition. The carburetor will be an easy fix. The manifold can be purchased online or at any speed shop. With correct timing, proper point dwell and no vacuum leaks, this should cure your dieseling problem. I do agree with you on using the water — I did that for years back in the day. You may also want to check that your distributor is moving internally when you apply vacuum to the distributor advance port. If you need any help locating parts, shoot me an email, and I will be happy to assist.

Car care tip: Do you fear that your son or daughter may be involved in drinking and driving? Lives can be saved with a simple install of an ignition interlock device. Voluntary installs of this device are exempt from the Massachusetts $30-a-month administration fee. Anyone wanting more information can send an email to or visit the Massachusetts Registry of Motor Vehicles website.


Larry Rubenstein is a master technician who owns a North Shore service station. His column appears every Saturday. Write to Larry at The Salem News, c/o Auto Scanner, 32 Dunham Road, Beverly, MA 01915, or send an email to