No Compression???

[greg12]

i have a 1999 Z3 with the 2.3 engine and am having problems with it. the car starts fine but when i start to drive it jerks and dose not go above 50mph. i can get it to about 80mph but then is slows down to 50mph almost right away. i brought it to a dealer and they did not know what to do. i talked to some people and they said it might be compression or electrical, i have no idea. if you guys have any suggestions or might know a fix i am open just about anything.

[drivinfaster]

compression would not be my first guess. in fact, if it is running at all i would rule compression out (unless it misfires and such, but that was not listed as a concern...)
i would suspect fuel delivery. have you checked fuel pressure?? i used to take the car in question out on the road with a fuel guage taped to the windshield down some back roads to check driving pressure. if it starts dropping when the speed starts dropping, then i would suggest a new pump assembly and filter. if the pressure stays the same, but slows down anyway, then you are looking at some other malfunction.
a good tech will be looking at vacuum reading while driving, and may even want to do a backpressure test. if you are so inclined, and have some diy, you could try this little trick to see if it is an exhaust issue. check to see if there are 2 cap bolts on the exhaust manifolds (1 for each 'bank'), and break them loose before you start the car. if you don't hae them, or if they don't budge, then this won't work. if they do, then loosen them, and then just snug them down again. drive the vehicle until it exhibits the afore mentioned symptoms, and then remove teh plugs and see if the vehicle will regain some speed. please keep in mind the exhaust will be HOT. VERY HOT. use leather gloves to remove the plugs once loosened to prevent getting burned. if the vehicle immediately regains some lost acceleration, then you are looking at a restriction in the exhaust, which could point to a faulty cat, but please make certainthere are no other heat sensitive items attatched to the exhaust (cut-out valves and such) that may be the culprit.
it may very well be something else, and without a way to interface with the modules to see what is going on, i would just be guessing, but this is where i would start based on the facts stated.
hope this helps, and good luck.

drivinfaster

[w00ht]

Likewise I would be extremely surprised if if was a compression issue since it runs like you say. If you need to, advance and autozone have compression testers that are inexpensive (They may even have a loaner program). Checking compression is as easy as disconnecting your plug wires (make note of the order) removing a spark plug and screwing in the gauge then turning the motor over a few times. Repeat for the other cylinders and compare notes.

I would guess you have a fuel delivery problem or a plugged catalytic converter. If your converter is plugged up it will be extremley hot, perhaps even slightly glowing. Take the car for a short drive and when the slow down happens pull over and have a look under the car. If the exhaust is slightly red or super hot feeling then look into it further. The spot on the floor above the cat will be extremely warm also.

When was the last time the fuel filter was changed?

Hope it helps.

[Pinecone]

A basic compression test is of little value. Better is a differential or leak down test.

But as has been said, it doubt it is compression. Compression would make it hard to start.

Lot os possibilities, but I agree, fuel pressure is one place to start.