Cylinders 2-4-6 Too Rich

My independent has had my car, a 1990 525i for too long. He has found that the cylinders 2-4-6 are getting way too much gas from the injectors. He originally put a new air mass meter on it, no change,
that wasn't it. He thought it was the computer that controlled the injectors, that wasn't it. Now he thinks it has something to do with the wiring harness. Has anyone had a problem like this before and how did you fix it? Any ideas?
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Tell us why you took the car to the shop.

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Took the car to the shop because it stalled 40 miles from home and I couldn't get it restarted. Had to get it towed. Just before it conked out, it would try to stall at stop lights, or in slow moving traffic. I would put it in neutral and then give it some gas. That seemed to keep it going. Tried to start it up after the last time it stalled and got a big gray smoke cloud out of the exhaust and that was it. The garage I had it towed to said it restarted the next day and couldn't figure out why I had it towed. I didn't believe him, but sure enough we went out and it started and seemed to run ok. He turned it off and then the next day, it wouldn't run. The independent asked me if it was cold out the day this happened and it was pretty cold, maybe high 20's. He thinks it could be some wire on the harness now. Any other ideas would be appreciated. My regular mechanic couldn't figure it out so he had it towed to an independent he knows who is supposed to be good with BMW's. He is the one who thought airmass meter, computer, etc. Does this thing sound like a crank sensor? Any ideas would be greatly appreciated.
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Once the fuel pressure regulator failed on my 318i and created somewhat similar symptoms to those you mentioned.. It seems that when the regulator fails that the result is very high fuel pressure that leads to a very rich mixture, especially at low rpms when the fuel usage should be very low. The other interesting thing about the fuel pressure regulator failure is that if you remove the pressure for a while, that the mechanism can kind of 'heal' itself for a while and the problem will go away for a short time. My car would stall at a stoplight if I didn't keep gunning it, but after it stalled I could start it back up and it would run OK for a while. The amount of time it would run OK was about 20 minutes when the problem first arose but kept getting shorter and shorter and was less than a minute by the time I finally figured it out. I think it would be worth checking the fuel pressure in your car. The cost of a fuel pressure regulator is a small fraction of these other items you mentioned. Be advised that the fuel pressure will be fine except when the car won't run at idle so you have to monitor it until it screws up.
I'd be glad to describe how the fuel pressure regulator can fail in this peculiar way but it's pretty long and I have to go now.

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I'll mention the fuel pressure regulator to the independent. But, wouldn't that cause all the cylinders to get too much fuel, vs. just 2-4-6? Thanks for your suggestion. Joe
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Yes it would but my speculation is based purely on your statement because I find that mechanics often add a few 'flowers' to enhance their actual findings especially if they aren't coming up with a cure. The deeper the mystery the more forgiveable is their failure.

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Upon further consideration, I noticed in my Bentley manual that the fuel injectors are fired in two banks 1,3,5 and 2,4,6. Now I can see how your mechanic would be led to suspect the wiring harness. There is a test for this condition in the Bentley manual where the injector wiring and action can be tested without the engine running by jumpering some terminals on the Motronic control unit connector after first disconnecting if from the computer. I'm sure your mechanic has access to this test and please apologize to him for me regarding my prior statement.

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Jack: I have the Bentley manual. What page is it on or what section is it in? No need to apologize for your prior statement as I wouldn't have told him and I also appreciate the words of wisdom.
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Jack: I have the Bentley manual. What page is it on or what section is it in? No need to apologize for your prior statement as I wouldn't have told him and I also appreciate the words of wisdom.
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Page 49 of the fuel system section. My manual is for the 3 series so it may be a different page number but it's for the same engine and Motronic fuel injection system.so the test should be the same.

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If you can get hold of a dwell meter - originally used for setting points on older ignition systems, you could compare the opening times of each injector. It's a useful device to have for EFI fault finding at a DIY level.
--
*Experience is something you don't get until just after you need it.*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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After 2 months of having my car (long story), the answer was, the connection from the computer to the injectors, somewhere near the bottom of the engine had oil, antifreeze in it causing the connections to short out. The mechanic cleaned the connections and scraped them and now the car works. What a pain the butt!!!!!!!!!
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After 2 months of having my car (long story), the answer was, the connection from the computer to the injectors, somewhere near the bottom of the engine had oil, antifreeze in it causing the connections to short out. The mechanic cleaned the connections and scraped them and now the car works. What a pain the butt!!!!!!!!!
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Thanks for the info. I was really curious as to how you ended up. I'm one of those guys who believe that the computer will be the last thing to fail and that connectors are the achilles heel of all things electronic so I am very grateful for the reinforcement. I wish more people would let us know when they arrive at the final solution.

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