1987 BMW 325 warm start runs rough

[mccallas]

Here is a hard one to solve.

My problem started about 6 months ago in the late summer and early fall time. My BMW start spewing black smoke out of the exhaust and the engine would die out and have a difficult time restarting.

I have replaced the spark plugs, rotar cap and spark plug wires, air filter, fuel filter, and the O2 sensor. The fuel injectors have already been cleaned.

When I start my BMW cold, it warms up fine and I can drive it around. If I turn off the engine, wait a little bit and restart the engine...it runs really rough. Sometimes I have to put the gas pedal down half way to start the engine when it is already warmed up.

 

[Doughnut]

Your problem sounds like a TPS (throttle position sensor) problem, Or the ICV (idle control valve) could be playing up too... maybe ecu?
It's kinda hard to diagnose from the description you have given us.

If at all possible, try swapping out these parts with known good parts to narrow down the problem.

Peace.

 

[mccallas]

Your problem sounds like a TPS (throttle position sensor) problem, Or the ICV (idle control valve) could be playing up too... maybe ecu?
It's kinda hard to diagnose from the description you have given us.

If at all possible, try swapping out these parts with known good parts to narrow down the problem.

Peace.

Doughut and Tom,

I read some more of the threads titled "rough" and "idle" and I found what I was looking for. Several other Beamers were describing the exact problems I was having. My 325 was running fine, then it would run rough occasionally with black smoke. I didn't mess with the TPS, but was considering that option. I cleaned out the ICV with TPS spray cleaner. I tried swapping out a clean, spare ICV, but that didn't improve the rough idle/black smoke issue. Then I decided to swap out the ECU because I had a good working spare ECU. By the process of elimination it came down to a defective/damaged Engine Control Unit (ECU) which I replaced with my spare ECU. Bentley's and Chilton's also calls it the Digital Motor Electronic (DME). I know you probably already know this, but I hope it helps some poor soul who is searching the BMWboard forum and ready to get rid of their classic BMW. The rough idle and black smoke issue seems to be a common problem as the 1980s BMW get older. My BMW is going on 21 years and I would like to keep it running smoothly. The following websites educated me on ECUs and DMEs. Thankfully, I didn't have to pay the Mafia, I mean the BMW Service Shop to run the diagnostic test on my car. I am cheap. PEACE has arrived and my BMW is running smooth again! Time to celebrate, good times!!!

http://autorepair.about.com/library/illustrations/bl688a-lib.htm

http://www.usautoparts.net/bmw/technology/dme.htm

http://www.goingfaster.com/spo/electronic_engine_management_sys.html

http://www.data.bmrparts.com/

 

[Tom]

Glad you figure out the issue and thanks for posting an update.

 

[redshield3]

Similar problem

I just picked up a sweet 87 325es on a trade yesterday, and I'm trying to get it running smoothly. I found this thread in google so I figured I'd run it by you guys. I'm hoping it's NOT the ECU/DME as an ICV or TPS would be a whole lot cheaper.

Basically, to start it, I have to give it gas for it to 'catch' and let it warm up with my foot on the accelerator to have a chance for it to move after i put it in gear (Automatic). During this time the exhaust smokes pretty bad, but after it gets going the visual smoke will clear (but the smell still remains). If I am stopped at a light it will die unless i keep a foot on the gas the whole time.

However - I've noticed that if I take it on the highway, after I exit the problem goes away and it runs like it should, very occasionally hesitating from a stop after I give it some gas. When I park it after letting it run at highway speeds for a while, it will not die but the idle speed seems to go up and down (the tachometer isn't working - but that's a seperate issue. Someone told me that it needed a battery? Maybe they're blowing smoke up my ass.)

The guy I got it from showed me something in the glove compartment and he said that's what would get it fixed... He didn't know what it was called though.

Am I going to get away without replacing the DME? Any and all help would be appreciated.

EDIT: So I got in the car which had been sitting in the 90 degree weather - started up just fine. Idle speed fluctuates though.

 

[cliff]

sounds to me as though your fuel pressure regulator is shot. had the same symptoms on an 85 535. engine burns alot of fuel upon cold start but requires much less upon warm up so you don't notice it at first. black smoke is the key, unburned fuel...mine was pushing around 110 psi through the injectors, they weren't even closing apparently. i'd check the FPR before proceding forth...good luck

 

[cliff]

sounds to me as though your fuel pressure regulator is shot. had the same symptoms on an 85 535. engine burns alot of fuel upon cold start but requires much less upon warm up so you don't notice it at first. black smoke is the key, unburned fuel...mine was pushing around 110 psi through the injectors, they weren't even closing apparently. i'd check the FPR before proceding forth...good luck

. They run around 60 beans from Bavarian
Autosport and are pretty easy to replace....again....good luck with this one

 

[Doughnut]

sounds to me as though your fuel pressure regulator is shot. had the same symptoms on an 85 535. engine burns alot of fuel upon cold start but requires much less upon warm up so you don't notice it at first. black smoke is the key, unburned fuel...mine was pushing around 110 psi through the injectors, they weren't even closing apparently. i'd check the FPR before proceding forth...good luck

+1
Remove the vacuum hose on the fpr side, when the diaphram fails fuel is present inside the hole. Least thats what happened to mine.