M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Engine + Driveline => Topic started by: locknload on February 23, 2012, 01:53:59 PM
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Car is a 91 E30,5sp w/COP, 250k+ miles. Normally, runs like a top. Today, it started acting up. At idle, it will on rare occasions behave like I switched the engine off and then quickly on, so it would stop running for a milisecond but then start back up again before it dies. Today, it started doing that while driving. It's like the ignition grounds for a split second and then reconnects again. This also causes the check engine light to come on, but as soon as the engine catches again, the light is gone. The instantaneous nature of the symptom leads me to the ignition rather than the fuel system. Any disagreement there?
I have tried the stomp test, but the check engine light does not flash at all, not even to show no codes set. Do I have to have codes set for the stomp test to work?
Could this be Crank position sensor? Does the Cam sensor have anything to do with ignition? Any other possibilities for investigation?
Problem resolved. See final post.
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Cam sensor does help with timing. I'd suspect it's something simpler though. If the CEL comes on but you can't get the stomp test to display, it's either that you're not stomping the right way or the TPS isn't adjusted correctly.
I'd be temped to check the main relay and ignition switch for wear & tear. Or just replace it, they're not that expensive yet critical for a running engine.
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Pretty sure it's not the ignition switch, but will put it on the list of things to check. Where's the main relay located?
Also, OHM'd out the CPS, crank was 600, cam was (I believe) 1200 (possibly 1400, idr).
Will also check the TPS. It seems I've had trouble with it in the past.
If my TPS is bad, can I just wire in a simple ON/OFF switch to simulate the 5 stomps?
Here's a MOD question: Why won't Search look for "CPS" or "ohm" ?
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Yeah, it should be possible to wire the WOT wires with a momentary on-off. It might just need rotated a bit though, no big deal. It's important for developing maximum power and durability though...I'd definitely check it for continuity. At WOT the DME disables the O2 sensor and the engine goes rich for an added safety margin.
I had the same problem with the "cps ohm" but "crank sensor ohm" pulled up a lot of hits.
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For a 3-letter search (for example, CPS), i suggest you use Google instead with the following query:
site:m42club.com cps
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Try replacing the main relay. If it goes out you loose spark and fuel. It's in the middle of the firewall at the back of the engine, under a black plastic cover about 18 inches long. The cover is next to the big round diagnostic connector. Just pull the cover off and you'll see three relays. Main relay is to the left, passenger side. Next relay is fuel pump, next is O2 sensor heater.
Make sure when you do the stomp test to press the gas pedal all the way 5 times within 5 seconds after key is turned on.
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Closer, maybe. Swapped out the main relay, no change. Stomp test has me befuddled. I ohmed my TPS as well as the 2 on my E38 just to get a comparison, and they were close. M42 were 200-500 ohm higher than the E38. Closed throttle on the M42 I got: pin1/pin2:4500 ohm, pin1/pin3:4100 ohm, pin2/pin3:1490 ohm. At WOT the readings were 1770, 4110, and 4260. Unless that 200-500 ohm difference is out of spec, it looks like the TPS is working fine.
Last thing I did was to disconnect the ICV just on a whim. That seems to have made an improvement, but only because it makes the idle higher and causes more of a cushion when the engine flames out for that brief half second. Also caused the CEL to illuminate steady. Intermittent fail problem still there, just less disruptive to my sanity.
So, where to from here? I realize without codes, it's an exercise in replace this, replace that. Any thoughts?
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That is a puzzling one. I'd check & clean the car's grounds, especially the straps off the motor. It starts though, so no biggie there.
What kind of plugs are you using?
I might also ohm out the other terminals on the crank & cam position sensors to see if you have troubles with the insulation. Should be very high resistance between pins 2-3 and pins 1-3.
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Will try more suggestions tomorrow. Funny thing, I remember last week saying out loud to myself after a particularly gratifying 3-4 upshift how really well the car has been running lately.
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Check fuse # 21. Among other things it feeds power to the computer. Should be a 7.5 amp fuse. Pull it out and look for corrosion or a hot spot on the terminals. If it's OK push it in and out of it's socket a few times then install it and see if the problem persists. It's a process of elimination...
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Wow it seems that I have the same issue with my 91 318is. I just bought it, not running, a couple weeks ago. I work at a European service shop and a guy just walked in one day wanting to sell it. I bought it for $500. So enough of that...
I got it running this evening. I had bad gas, lots of cracked air hoses, needed a fuel pump and a AFM. All that is done. It will start but it idles about 2 - 3K and hunts. It also pops and snorts like it's running rich... when you try to rev it, it climbs a few hundred RPMs and then it cuts off and comes back down to 1K then starts running again. Check engine light comes on with enough time. If I turn the key off then back on quick the CEL resets.
Plugs are a bit questionable, injectors too. Bad gas really screws things up.
Anyway, I'll keep you posted on what I find out...
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Checked the fuse, it's fine. Opened the top of the AFM today, it looks ok, but the resistance values don't steadily increase as the vane is opened. They increase, then decrease, then increase again as it opens. Also discovered that the problem is almost non-existant above 2800 RPM. Cleaned ground connection and unplugged every connection I could find under the hood, including the ECM, to clean connector contacts. Will check plugs in the AM just to make sure they aren't pooling oil or something.
Barring any discoveries with the plugs, it looks like I have 3 possible courses:
1. Replace the AFM. It's the most expensive part, but the easiest to replace.
2. Replace the TPS. Seems to work ok, but OHM's are a bit low & maybe I'd get my stomp test to work.
3. Replace CPS. Cheapest part that could be faulty given the symptoms, but could be a bear to R&R. Not sure though if the newly discovered RPM parameter supports this theory.
Since I have a pair of TPS's available in the E38, that seems to be the logical course of action. Condition is getting worse & the bucking & kicking at speed is driving me insane.
If anyone else has any ideas for things to check while I'm in there, I'm all ears.
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Other stuff you can check:
Ground point near ECU
Fusible link near battery has been know to have tiny cracks that are not noticeable at first
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locknload, I'm troubleshooting a 91 I bought with the exact same issues. I've started a thread I call a repair log in the General discussion forum if you would like to see what I've done so far.
I had some progress yesterday when I started messing with the O2 sensor. I unplugged it and plugged it back in a few times and it suddenly started to run right but with a misfire here and there. I've ordered a new O2 sensor so check out that thread for the results.
If you'd like to check the O2 sensor plug on your car, it's just about the exhaust header pipe on the wheel well near the firewall. It's kind of hidden under a lip of metal there. Black round plug that you turn to release like the one on the AFM.
I know what you mean about the bucking issue! Wow... talk about pilot induced oscillation! :)
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Pulled the plugs today. Had a little oil in #1 well, but not enough to reach the coil boot. All plugs had that brown ring around the base of the ceramic that looks like rust but is really oil residue. I thought I had cleaned them up when I replaced the cam cover gasket, but maybe not. Other than looking like its running a little hot (NGK Iridium plugs), the looked ok. Regapped & reinstalled. No change. I did clean the O2 connector while I was on that side of the car, but didn't think about leaving it disconnected. Will try that tomorrow & report back. Beyond that, TPS swap out scheduled for saturday.
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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. :D
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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.
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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?
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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...
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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.
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My TPS swap did nothing to improve the situation. I ordered some new coils today.
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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?
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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.
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NO, that's only 250 mV & is normal for the different ground points you mentioned.
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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.
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Replace the crank position sensor. It worked for me and a few other people. They seem to go flakey and intermittently fail around 3k.
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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.
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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.
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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.