this has been going on for the past month, but recently its gotten worse. i started off by replacing the battery, then the starter went out, so i replaced that, which didnt help. i then noticed that the fuel pump wasnt priming the system all the time, so i replaced that the other day. that didnt solve the problem, so i said screw it and took it to a repair shop. the fuel pump relay is good.

since the relays are good, i wanted them to figure out why the fuel system wasnt being primed. the owner of the shop thought that it sounded like i had low compression when it kept cranking when he tried to start it. he did a compression test and you wont believe what he found. 70, 90, 90, and 150 lol....while i dont doubt the compression(the gauge doesnt lie), i find it hard to believe that once started, my car runs as good as it does. my car does have a hard time idleing, but it does idle sometimes. the only engine related code its throwing is throttle position sensor, but would that affect starting so much? the mechanic didnt think it would...any help is appreciated, as it could save me from doing my engine swap too soon. -grant

A couple of things come to mind here. Let me start with you asking yourself some questions. Does it always start with difficulty or does it start easier when it's been run within a few hours? This would define cold-start or semi-operating temps. Let me also say that I've never owned your model but it may be similar to the 84 733i or the 98 328is that I have. There is a cold start injector under the manifold that sometimes goes bad or the fuel line loses pressure. Check for a wet fuel line on this injector.

There are also two temp sensors in the thermostat housing. One is for below a certain temp, the other is for above a certain temp. These feed signals back to the ECU for things like the cold start injector and regular injector pulse width. Failure of either of these can affect the starting/running condition. Find the values for these as well as the temperatures these values are set for (open/closed) and test with a VOM.

There is a fuel regulator on the fuel return line. This ensures a set fuel pressure in the line, bleeding off the excess to return to the tank. It also holds pressure in the line when the motor is shut off. There is a pressure value over a given time it should hold (P/T) and this should be tested. If it's gone bad and allows fuel to simply bleed back into the tank then you would have to crank the motor a lot to get fuel back up into the fuel rail.

Compression low? I can't say if it's low or not but I seldom benefit from the opinion of somebody seeking my cash. I've seen many an operator try to scam me with some meter that he's rigged. Sort of like the butcher that puts his thumb on the scales. Get your own meter and do your own testing if you don't know this guy or his reputation. I'm a toolmaker by trade and I've had several shops I took work to try to scam me. I would go home and take my own readings and find what they were up to. If nothing else, taking your own readings will confirm whether somebody is honest or not. You can spend the money on getting taken or spend the money on confirming that repair does need doing. All you have to do is spot ONE scam for the tools to pay for itself whether you do the work or allow a shop to. It's also mandatory that you own a proper manual (Bentley is good) if you intend to understand what the specs are to be. I still buy a manual for every vehicle I own, it's easier than guessing and pays for itself. Hope this helped.

thanks a lot for your reply!

it is typically harder to start after its been running for 5+ minutes. if i let it sit for an hour or so, it will usually be "easier" to start. sometimes it was start right up like normal after sitting for a while, other times it will crank for a while before it finally fires up. if it is push-started, it will start up with no problems what-so-ever. i was thinking about renting a compression tester from autozone on my day off this tuesday and seeing what it says. i originally took it to the mechanic to diagnose why the fuel pump wasnt priming the system sometimes, instead he decided to do a compression test. i have a manual and dmm, so i will also check on the fuel line for the cold start injector, as well as the ct sensors.

i wish this problem would have occured while i was in school so i could have used the scopes and whatnot to check out the waveforms.

Hmmm....not the symptoms I would have expected. Perhaps I'm suggesting the wrong culprits. Do the tests and post what you find.