Author Topic: Ignition acting up (Read 8809 times)

DesktopDave · « **Reply #15 on:** March 01, 2012, 07:33:08 PM »

I believe that the AFM going up/down/up is normal. It's just a general test. IIRC the only perfect test is with a 5v power supply on a bench.

Not sure if you've seen this page, but here's FR Wilk's info:
http://www.the944.com/afm.htm

Excellent info on the Motronic...just ignore all the Porsche retentiveness.

DanOKC · « **Reply #16 on:** March 02, 2012, 02:01:07 AM »

I agree with Dave, AFM going up down on resistance test is normal, I have two cars, one parts car & one I bought about 7 months ago that had several 'issues'. Working through the issues, I had swapped the AFM with the parts car AFM, both tested the same way, it's not a linear resistance change, it does go up & down. My TPS was bad though, Stomp test didn't work before I replaced it. Mine had a 'dead spot' in the middle. Made it run rough or jump rpm in the 2K to 3K RPM range. Made it hard to cruise steady anywhere in that range, made the motor buck & pull. Cleaning the TPS with contact cleaner didn't help. Had to replace it.

locknload · « **Reply #17 on:** March 02, 2012, 08:38:13 PM »

Thanks dave, I had seen that and had it bookmarked in case I need it, which seems to be now. I tried unplugging the O2 sensor which didn't change anything. I did notice though the CEL didn't come on at all while the O2 sensor was unplugged. It seems it would have come on & stayed on while it was unplugged. This morning I disconnected the O2 sensor, the TPS and the AFM. Had to learn heel & toe all over again at the stoplights, but other than that it ran, albeit miserably. Happily though, the initial symptoms and the associated bucking had subsided. Plugged in the O2 sensor & drove a few miles with no change. Plugged in the TPS, stayed the same, so it looks like it may be the AFM. While the AFM is unplugged, the acceleration and idle stink, but there's no off/on with the ignition and almost no bucking and kicking while driving under 2500 RPM.

Will do the TPS swap out as planned and will put the 5V on the AFM to see what's what. Will report back. Thank you to those who are responding with suggestions/encouragement.

One other thing I noticed, the fuel pump runs continuously when the ignition is in the run (Pos II) position. I thought I had read somewhere that the ECM checks the CPS first to make sure the engine is rotating before activating the pump. Is this true for M42 cars or just the other versions?

Wrench · « **Reply #18 on:** March 04, 2012, 10:22:43 AM »

Looks like your making progress.... I'm minutes away from swapping out the TPS on my car this morning. It's a 10/1990 318is, M42. I have installed a new AFM, fuel pump, CPS and all air hoses.

My fuel pump only runs when the engine is cranking or running.

Re. O2 sensor, sometimes the control unit has to "see" that a sensor is unplugged over time and varying driving conditions to set a code. I drove mine with the O2 sensor unplugged and the CEL would come on after about 10 seconds of cruise. If I let off the pedal momentarily the CEL would go out and the engine would continue to run ok but with some misfires.

We both have the exact same problem with the bucking and cut out at the same RPM range. Sooner or later one of us will find the "gremlin"!

Good luck...

locknload · « **Reply #19 on:** March 06, 2012, 08:41:55 PM »

Some things that it's (probably) NOT:

AFM. Popped the top, retracked the swing arm per suggestion. Cleaned up the air temp sensor connector. No change.

Coolant temp sensor. Ohmed at 3500 on a brisk 40 deg. morning.

Fuel pressure regulator. Tried this on a hunch based on the problem's disappearance above 2700 RPM, plugs looking like they were running lean, a little detonation noise is audible when accelerating and everytime it "burps", the MPG gauge spikes to the high side. Replaced the badly deteriorated vacuum line on the FPR. No change. (Note to self: Order parts for the mess under the intake fix ASAP).

Weather kept me from swapping out the TPS this weekend. Need to secretly disable wifey's E38 so I can grab one of her TPS's for my car.

Wrench · « **Reply #20 on:** March 06, 2012, 08:47:22 PM »

My TPS swap did nothing to improve the situation. I ordered some new coils today.

locknload · « **Reply #21 on:** March 06, 2012, 10:11:01 PM »

One other thing. I checked the 5v wire in the AFM harness connector. When I checked it against chassis ground, I got exactly 5v. When I checked it against the ground socket in the connector, it was 4.75. Is this significant?

Wrench · « **Reply #22 on:** March 06, 2012, 10:17:31 PM »

Significant enough to be wondering about supply busses and grounds like I am. I have my harness at the fire wall all exposed. There are about five splices in that bundle that have to do with ground and power. I'll be checking those out while I'm waiting for my coils to arrive.

Another suspect spot is the junction box under the intake. That one has ten or more splices with crimps that could be faulty.

DanOKC · « **Reply #23 on:** March 06, 2012, 11:18:11 PM »

NO, that's only 250 mV & is normal for the different ground points you mentioned.

locknload · « **Reply #24 on:** March 08, 2012, 07:38:48 PM »

Thinking this is fuel related somehow, but electrical in nature. On bad days, car bucks & jerks several times a minute at 2500 RPM & below. As soon as the tach hits 2800, problem disappears completely. Also have not noticed anything when decelerating in gear below 2700. Fuel pump hums rock solid continuously. Are there any better (i.e. more complete) electrical diagrams other than this one:

http://wedophones.com/Manuals/BMW/1991%20BMW%20318i%20-%20318is%20-%20318ic%20Electrical%20Troubleshooting%20Manual.pdf

It's helpful, but missing almost every second & third page of most systems, like 1360-2.

Wrench · « **Reply #25 on:** March 12, 2012, 06:53:27 PM »

Replace the crank position sensor. It worked for me and a few other people. They seem to go flakey and intermittently fail around 3k.

locknload · « **Reply #26 on:** March 14, 2012, 08:15:03 PM »

problem is, th car sings like a bird above 3k. I wish I could keep it there all day.

Finally did the MUTI and was sooo hopeful this would solve it as every hose was cracked and based on all the the coffee colored goop in the two hybrid hoses, I think I've finally eliminated a pesky coolant leak that has been eluding me for 7 years. Cleaned up the injectors and the ICV and the inside of the intake. Also OHM'd the joints in the injector harness (3.1) which is within the tolerance of the meter. Car seems to run better, but still burps occasionally, although it seems not as violently. Something I did seems to have had an effect, but not 100%. One thing I did today was re-disconnect the O2 sensor. It didn't affect the problem I've been working on, but it didn't illuminate the CEL either, which I think it should have done. Even the stomp test says there are no codes in memory.

I guess I'm at the point where I have to start spending $$ on parts. Intermittent CPS sounds plausible & it is the cheapest part on the list of suspects. Would be nice to be able to borrow an ECU, AFM & ICV to see if that changes anything. Of course, I'd pay the postage both ways if anyone out there has them available.

Wrench · « **Reply #27 on:** March 14, 2012, 09:54:22 PM »

I would suggest cam and crank sensors. How old are they? So far I've learned that this car is fairly strict about the signals coming from these sensors. Nearly all of the fixes I found in my research involved replacing one or both..

A scope would tell you a lot.

locknload · « **Reply #28 on:** April 02, 2012, 10:27:52 PM »

Ok, I'm going to call this resolved. The problem it seems, was with my COP conversion. I haven't done any investigation yet to see exactly where the failure lies, but it is definitely with the COP. I removed the COP's and reconnected the original plug wires and coils about 4 days ago. Since then, not a burp, not a skip not a stumble. Drives like a dream once again (new O2 sensor probably helps with the running smooth part, but had nothing to do with the original problem). I suspect I either have a bad coil or one of them was shorting intermittently. Will post the exact cause when I nail it down.

Final answer, it was indeed, a bad coil, although the DME never detected it. I suspect it has something to do with the infant stage of OBD hardware/firmware development at the time. Got a spare coil & started swapping; was fortunate enough to hit it on the second one.