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Old 03-28-2011, 10:38 AM   #1 (permalink)
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Can CPS be bad when resistance test is in spec?

I have a 1989 BMW e34 M20 that I can not get to start. No fuel or spark after a rebuild. My question: Can the CPS be bad even though when tested it shows to be within resistance specs.
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Old 03-28-2011, 10:52 AM   #2 (permalink)
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I'm not sure the answer to your question , but I believe when the CPS fails the ECU does not send a signal for the injectors to fire or send spark to the engine. If your CPS is within specs, you dont have spark, and your getting fuel to the engine but not igniting... I would see the ECU as suspect.

Did you pull your plugs to see if they are wet perhaps? Fuel? Oil?
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Old 03-29-2011, 12:42 AM   #3 (permalink)
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I am not getting fuel at all to the rail when the engine is turned over. I also do not hear the fuel pump prime when the ignition is in the on position. The fuel pump is not faulty as I jumpered 30 and 87 on the pump relay socket and the fuel pump runs strongly. I think it may be the CPS, but the one on the car tests out at 540 ohms which is in spec. I don't want to buy a new CPS if it is not the problem. This is why I asked the question if the CPS can be faulty even though the resistance is within spec. I also purchased a brand new main relay and installed it. I also swapped out the fuel pump relay with a known good one with the same no start result. I'm pulling my hair out at this point. I have put it up for sale since I can't figure it out even though I'd like to keep it.....soooo frustrating --> http://www.onlinedealsplus.com/myclassifieds/list/385
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Old 04-02-2011, 06:52 PM   #4 (permalink)
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Found out what the problem was. Wanted to follow-up just in case this solution might help someone with similar issues.

1989 BMW 525i e34 w/ m20 5spd.

Symptoms: No start condition - w/ no fuel or spark. (The engine will turn over)

Did full battery of tests including check of main and fuel pump relay.

CPS was in spec for resistance.

Checked inputs to ECM for grounds and voltage on appropriate pins all were correct

Checked voltage to coil and it was fine.

The problem ended up being the OEM theft/security system. I pulled the fuse to the theft system and the engine fired right up.

So if you have the OEM theft system on your e34 or other model BMW and you have a no start condition w/ no fuel or spark, perform the appropriate fuel, relay, and CPS tests. If all checks out, it might be your theft system.

Some will tell you that the car will not turn over at all if the theft system is tripped. I am proof that this is not the case. My car turned over great, just would not start.

Hope this helps someone. Boy it feels good to finally have this figured out. I was pulling my hair out. Took 2 months and it ended up being a simple fuse. Glad I didn't take the car to a dealer. Might have ended up being a $500 fuse.
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