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hatella
03-11-2012, 12:59 AM
Need help!! I have a 02 grand am gt, 125,000miles. Runs fine cold, but when it gets to normal operating temp. (200) the car starts sputtering and misfiring really bad. Very noticeable while cruising on the highway, the car makes like a hiccup or almost backfires? Sometimes it will stall when I come to a complete stop. Car started acting like this just after I had the harmonic balancer replaced. Had the balancer done by The Muffler Shop. I called the next day to see if they had done the case learn and they did not, said it wasn't necessary? This was about two weeks ago since then I replaced plugs, wires, coil packs, fuel pump, fuel filter, fuel pressure regulator, cleaned MAF sensor, and added lucas fuel injector cleaner. Problem is still there, oil is good and coolant is good. Before I do anything else I just wanted to chime in here and see if anyone has had a problem related to this? or if I simply just need the relearn done? Also this has not triggered an SES light. Any advice would be great! Thanks!

MMGT1
03-11-2012, 06:02 AM
No case learn on the 3400, you have two crank sensors. A 7x and a 24x. Check wiring to the 24x sensor behind the balancer. You are describing the the exact issue though as when the 7x goes bad. Check the 24x first, if its not there you may need the 7x sensor replaced or the harness to it. The harness to the 7x is exposed to a lot of heat and it can fuse the two wires inside the lead and cause this issue

hatella
03-11-2012, 12:02 PM
Thank you! I'll check it out

MMGT1
03-18-2012, 09:13 AM
Ok, finally found this.... could not remember where I posted this, so I am sorry for the delay on fixing the info here.

There most certainly is a crank learn procedure for the 3400's. I work at a GM dealer and had half a dozen of our mechanics say exactly what I posted there and turns out they are dead wrong on this one. Using a TEC II I found the relearn procedure for the 3400 and sucessfully ran it on mine. DHP and HP tuners has the ability to do it too, but the write up on how to do it is very vague. Before you even start the car, depress brake pedal and do not take your foot off it until the entire procedure is done and car is turned off again. Coolant MUST be above 158* for the test to run as well. Other than that it's a pretty straight forward procedure.