95 Sunfire Jerking/Bucking

In the middle of Feb., the oil pump on my daughter's 1995 Sunfire Convertible (130,000 miles) went out. Two mechanics agreed that a new engine was required, and we had one put in, along with a new clutch pack ($3,650, plus $950 for a rental car, and $300 for taxis/shuttle).

After 600 miles, daughter took it in for the warranty-required oil change, etc., and Pontiac dealership noticed that it was unable to get any computer diagnostics--the message was "computer not connecting to (or communicating with) scanner," or something like that. They said they had no idea what the problem was, that it would take an unknown number of days to diagnose and repair. Since she wasn't having trouble with it, she decided not to pursue it at that time.

After 2,000 more miles, the car started to jerk violently in all gears. She took it to PepBoys, who first thought it was (1) ???, but jerking persisted; (2) the flywheel (it hadn't been turned when the clutch pack was replaced, and was badly pitted) - PB had it professionally done, but jerking persisted; (3) the O2 sensor (which appeared to be new to PB, altho not a normal part of the engine replacement effort, and was putting out readings in the thousands) - PB replaced the sensor and the readings became normal, but jerking persisted, and (4) the computer ($1,300 total to PepBoys, plus $350 for a rental car).

After replacing the computer, it still wouldn't connect to the scanner, but the car reputedly "drove like a dream." PepBoys test drove it three times however, for 20 - 25 minutes each, and no jerking. (In the test drives following the ???, flywheel, and O2 sensor, they said 10 - 15 minutes into the drive, when it got "warmed up," it started jerking/bucking in all gears. Daughter and mechanic both described the jerking as feeling like when you're first learning to drive a stick shift.)

Three hours after daughter picked it up, and 30 - 35 minutes after starting to drive it, daughter had it on the highway, shifted the manual transmission into 5th gear, and it started the violent jerking/bucking again. IT IS **CURRENTLY** NOT JERKING IN ANY GEAR OTHER THAN 5TH.

Other than thinking there might be "a short," which they indicate could take days to locate, PB is out of ideas. They are confident that it is not the fuel system--I believe the fuel filter was changed somewhere in this saga--and I believe they said they tried a new control module without success as well (assuming that is the "little computer, that's not exactly a computer" the mechanic referred to).

Daughter thinks it's the clutch because, when the clutch went out on a Mazda she had previously, it acted like this--first problematic only in 5th, then in 5th and 4th, etc. She recalls that she didn't have clutch problems before the new engine/clutch pack--we just replaced the clutch pack because it was convenient to do while the engine was being replaced--and recognizes that two mechanics have now worked on the clutch - when the new engine was put in a month and a half ago, and when PepBoys worked on the flywheel.

Daughter's boyfriend thinks its the transmission, but I ran that by PepBoys early on and they dismissed it, as did the two local mechanics we've been discussing the problem with, primarily, I believe, because its a manual transmission.

Daughter is attending college over 1,000 miles away, and parents have now invested $6,250 in this (old) car in the past six weeks, and are OUT of money! We simply don't have the money to buy a replacement car, or continue to pay for repairs that may, or may not, be needed. OUT OF IDEAS AND $$$ - DIAGNOSTIC HELP/IDEAS/ADVICE NEEDED DESPERATELY!!

does the car have cruise control?

what all was replaced with the new motor? did it have a full tuneup? was the fuel pump replaced? fuel filter? when exactly does the bucking occur, when changing gears, or after its already in gear and you put it under load by giving it some gas in a high gear like 5th? a bad clutch will usually just slip and the rpms will go up. could be anything from needing a tuneup to bad motor mounts/trans mount, fuel related, ignition related etc. my best guess is since it did drastically improve with a new computer, that some sensors are bad, (map, o2, tps, coolant temp, etc) causing the car to hesitate under a load(5th gear acceleration), that probably combined with a bad motor mount or something gives it that violent jerking/bucking.

Its got to be in the tranny is the engine has been replaced. First of all, I would tell your daughter to ride the bus or train, or hitch a ride for a while.

After that, take it somewhere other than Pepboys. I for one would never trust a Pepboys with my car. And from what you described, these knuckleheads don't have any idea what the hell they are doing. And it sounds like they are getting every penny they can from you for nothing but half-assed work. The car is bucking in each gear so they replace the motor?

Finally, I think its the clutch. I think that because my clutch was on the fritz a few months after I bought my car, and I experienced the same bucking (we called it chugging for some reason) in the first 3, sometimes 4 gears. Replaced the clutch and it was perfect.

If you have no major attachments to this car, I would say stop spending money on it. Pouring $6300 into a car that worth maybe $3,000 in mint condition is not worth it at all. If you can't have the problem fixed for next to nothing, I would suggest bite the bullet and sell it.

KustmAce, good answer there, it very well could be the clutch, she probably didnt break the clutch in right and glased it over or something. but, it was bucking in every gear until they changed the computer then it was just in fifth. figured it was probably ignition/fuel related because of this. also just cuz some dealer put a new motor in a car doesnt mean they replace everything, could need new mounts, fuel filter, fuel pump, etc. they coulda just replaced the short block and reused everything else, i know i would.

that just sucks to have over $6k in a car that bluebooks for half that.