Advice regarding a car that “diesels”

Question:

I received the June issue and read about what to do when your car “diesels.” I have worked on forklift trucks for many years and anytime my customer complained of this problem, I would take a soda can, rinse it out with water and fill it up with water. After the motor was warmed up, I would slowly dribble the water into the intake while revving the engine to keep it running. It would cough and sputter and sometimes the exhaust would get really hot and I would back off for a short time.

After pouring the 12 oz. can of water into the intake I would have them test it again. The motor stopped when they turned off the key and it would run better when running.

The problem is carbon build-up in the combustion chamber. When it gets hot spots from running, the fuel/air mixture is ignited, causing the run-on. The water turns to steam in an explosive way and breaks up the carbon and sometimes gets stuck in the exhaust valve making the motor stumble. The exhaust temperature gets hot enough to burn the carbon, but I have only tried this on one car with catalytic converters. I didn’t have any problems with that one.

Answer:

I have never tried the age-old home remedy of slowly pouring water into a running engine to break up carbon deposits so I can’t comment on that from my own experience.

There are various commercial products and procedures available to reduce carbon deposits inside an engine and I would use one of these before trying the water method. GM Top Engine Cleaner is a popular carbon reducing chemical that does a good job. Whether using the GM cleaner or another brand it is advisable to temporarily disconnect the catalytic converter if your car is equipped with one.