Help needed ASAP: CPS question

[mr walker]

Here's what's going on.

1987 325is

Intermittent no start, engine will crank. After running for a while it will buck/stall, but again intermittent. No CEL. Stomp test yields nothing.

Known issues: the battery is done. I left an interior light on just the other day and I had to jump it. Prior to this I haven't had any issues with no starts or bucking/stalling. I'm picking a battery up tomorrow.

I feel that it could likely be the crankshaft position sensor. I'm willing to roll the dice on this as I'm driving the car across the country on Monday and I would strongly prefer not to get stranded.

For part ordering, is there a difference between the front CPS that reads the wheel behind the crank pulley, and the one that mounts to the bell housing?

Is there anyone out there that thinks this could all be related to the dead battery (wishful thinking, yes. But I have seen cars do weird shit when running on a dead battery)?

Scroll down for repair

Any and all help is much appreciated.

TIA

[MR 325]

The battery should have nothing to do with it if it's running and the battery light is not on. There is definitely a chance it could be the CPS but it's hard to be sure over the internet.

The M20B25 cars only have the front crank sensor, not the bellhousing sensors. They do not interchange.

[jlevie]

If the battery is bad and the alternator is weak, the system voltage may be low enough to cause the DME to misbehave. So that could be a cause.

[MR 325]

If the battery is bad and the alternator is weak, the system voltage may be low enough to cause the DME to misbehave. So that could be a cause.

If the alternator is not working properly, that's a different story.

[mr walker]

Great, thanks for the help. I will update this thread when I get a chance to fully diagnose this with a multimeter...if I make it back to GA where my multimeter is.

Just to clear things up, was it only the eta engines that had two CPS?

[jlevie]

Yes, only the ETA engines had the twin bell housing mounted timing sensors.

[riceh8r]

there is no stomp test for this model. turn on key, cel will light up then go off. count the blinks after that. there are only four possibilities. you will have to search for them...i cannot remember.

[mr walker]

Noted. Thanks for the info, when I looked up the stomp test it did say it was only for 88+ e30's. I thought there could be a typo, but it's good to know not to use that in the future.

***Update and fix***



FIRST: I had read on the forums that the symptoms I was experiencing could be several different problems such as the DME relay, fuel pump relay, 02 sensor, CPS, fuel pump itself, grounds, etc. There was one problem with all of these "diagnoses"...it seemed like most people were just throwing parts at the car without any real reason to. I HATE doing this.

Here's how I fixed it: I first purchased a new battery with hopes that the car would start and run (remember this was an intermittent problem). Fortunately it fired right up. With the car now running I popped the hood. I don't have my multimeter with me, so I was strictly limited to visually inspecting the wires, sensors, and relays mentioned above, as well as moving them around and tapping on them.

I started with the CPS which I thought (well, assumed) was at fault. Nothing (not that you should EVER deem a part good because you wiggled it...it's just all I could go on). I kept doing this for all the connectors, sensors and wiring. Eventually I picked up the whole relay block for the DME, fuel pump, and horn. The engine stuttered. JACKPOT, problem duplicated. I did it again and the engine stalled. To get to the point, after prodding around all the wiring in the area I determined that when I poked the injector harness even the slightest bit the engine would stall. The harness is two pieces: one is basically attached to the body or engine harness, and the other is what I believe is called the injector loom and goes straight to the injectors. These two attach via one of those screw together type connectors. They're screwed together sandwiching their mount plate. I unscrewed them from the mount plate, and reattached them so the plate was no longer being sandwiched. I could now poke, bend, flex, and literally yank on the connector without any engine issues.

I do know the PO had the injector loom repaired at some point. I believe the connector was reinstalled incorrectly afterwards, and probably not screwed together all the way.

I am reasonably confident that this problem is fixed.

Thanks for your help!