90 Pontiac Drivability Problems

When I first met Larry he had already been beating himself against the wall trying to fix an elusive problem which he describes below. I think Larry holds the record for working with me on one problem on one vehicle. Both Larry and I have learned a lot from his problem. I ran out of ideas a long time ago but Larry persisted and finally solved his problem. If you have an elusive performance problem with GM performance then read Larry's letter below.

Do you have a "90-"93 GM car with either the 3.1L or 3.4L engines that is having unexplainable engine performance problems? If so read on. Your car may be reacting to some of the new additives being added to today's gasoline. My '90 Pontiac Grand Prix with 3.1L engine was stalling out when I let off the gas pedal (completely) while going over 70 MPH. It also acted sluggish when I let off the gas pedal at lower speeds even though it didn't actually stall out.

I spent 6 months and over $1,000 working with Dealers and Independent mechanics trying to solve the problem. Then, quite by accident, I was referred to a GM (TSB) Technical Service Bulletin which seemed to address similar conditions. The TSB is #336506 and came out in October of 1993. It refers to problems caused by "Low volatility/high driveability index fuels currently in the marketplace. (GM Dealers have copies of this TSB). It recommends changing the PROM (Computer chip) in affected car models' ECM (Computer) to chips that are specified in the bulletin. THIS IS NOT AN UPGRADE OR NEW REVISION FOR EXISTING CHIPS. The cost of the new chip is about $50 and if you're at all handy you can install it in about 10 minutes using an open end wrench, a nut-driver, and your two thumbs. The chip is located on the bottom of the ECM behind an access plate.

Just release the side clips, pop out the old chip and pop in the new one (Make sure the new chip "snaps" in on each end). If you're not familiar with using the "Learn Procedure" the car will run rough for awhile while the new chip learns its program but will soon straighten out. If you have one of the cars affected and you are having any kind of un-explained performance problems, $50 is a small price to pay to eliminate this possibility. It could have saved me $1,000 and 6 months of aggravation.

Message me at BobHewitt@Misterfixit.com

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