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1996 GP GTP with 3.4L. had timing belt, water pump, and plugs replaced at a local shop. car began missing at around 35 mph and had a lumpy idle. same shop then replaced MAF and idle control valve. no improvement. no service engine lite showing. replaced plug wires (ac delcos). no improvenent. went to pontiac dealer. they retimed engine. still no improvement. car started bogging down under light acceleration. went back to dealer, they couldn't make car duplicate symptons during driving. car was getting worse. slight miss at most all speeds, idle lumpy, bogging down getting worse. backpressure check on cat done. replaced cat. slight improvement, still has problems. going in for a fuel pressure check today (thursday 11th). anyone have a suggestion as to what to check next? just replacing parts and hopeing is expensive. any good 3.4 mechanics in the north alabama area? the car is bogging down under light acceleration and missing during driving. for some reason, it really misses at 35 to 40 mph, but doesn't do it all the time. read some other posts here. did anyone get their missing and bogging fixed? update; fuel pump pressure ok
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RE: 3.4 bogging and missing, short repair history given
I would almost say the timing is off. It's real easy to do with this engine. After doing mine wrong once I was able to pull the boots off all the rear plugs and noticed the engine sounded the same, weak and shitty. Then repeated it on the front wire boots and the car died. Basically I was running on 3 cylinders.
If it ran fine before I would say the timing is off. Make sure the shop knows what they are doing. If they don't take the instructions from this site and do it yourself or give it to them.
I am assuming the engine was fine before.
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