My cavalier is a Z24 with the original 3.1L V6. When cool, the engine runs fine for about 20 miles and then I can feel a change. The whole car begins to viberate as I am driving. More pronounced under engine load. I can feel the vibration in the steering wheel, floor, seats, even the inside rear view mirror shakes so bad you can see anything in it. The exhaust smells very rich at that point. The catalytic converter glows and the fuel mileage drops in half. The exhaust is so hot the left rear tail light has melted from the heat of the muffler. I pulled the coils expecting one bad, but they test out fine. The car has a DIS system and MFI.
Have you had the exhaust system pressure tested excessive back pressure?ALso any codes?
November, 5, 2012 AT 4:13 AM
Check the fuel pressure for leak down; it could be fuel pressure too high or a leaking injector o-rings causing a high fuel rate
November, 6, 2012 AT 3:09 AM
I pulled the cat, it was fried. The guts were like a rock flopping around inside the housing. Replaced the cat, muffler, and tailpipe. The engine still runs horribly. Like it is running on 3 cylinders. Rotten egg smell. Fuel pressure 40 psi at startup, 35 psi while running. No codes, no check engine light.
November, 6, 2012 AT 7:02 AM
Do you have a nice blue spark to all the cylinders?Also have you done a compression test yet?
November, 7, 2012 AT 11:33 PM
No codes Hmmm. Well if your fuel pressure STAY at 35 after the engine is off and you have no codes check the EGR to see if its sticking open, make sure your ign modules are grounded, and do a compression test. It seem like you should be getting some codes if your fuel/air mixture is that rich, so if you have a scanner try to see what your o2 sensors are doing.
November, 8, 2012 AT 7:05 AM
Its obd1 not obd2 system I have seen them run pretty bad and not set codes there is no miss fire codes etc it could set a system rich code 45.I would really check and make sure all the cylinders have a nice blue spark and do a compression test on all the cylinders. Could also pull one spark wire at a time and put them back on to see if pulling any off makes it run worse?To see which cylinders arent running.
November, 11, 2012 AT 2:31 AM
O.K. Guys, I spent a few days with it and found that it had a few problems coming together at the same time. First, the new cat, muffler, and tailpipe fixed the hot exhaust problem. Like I said before, the cat was toast, that is why it was glowing red. And the tailpipe had a hole in the top side directing hot exhaust at the left rear corner, that is why the taillight melted. Probably running rich on top of it didn't help. I found a couple of weak plug wires contributing to the engine running issue. But after reading your replies, along with articles on 2carpros website, I bought an IR Thermometer. Aiming the thermometer at each exhaust port and taking a reading, I found that the #1 and #4 cylinders were running about 60 degrees cooler than the rest. Since the #1 and #4 cylinders are connected to the same coil, I swapped out that coil. The car runs like new now. I am planning to do a complete tune up soon with all new coils, plugs, and wires. Big thank you to 2carpros, saturntech9 and jay4cars1 for your help diagnosing my car and getting me back on the road!
November, 11, 2012 AT 4:43 AM
Glad to hear you got it running well again your very welcome thats what were here for.I only replace coils when they fail not for any kind of tune up I think thats over kill. But if you want to you can.