Author Topic: Ignition acting up (Read 8829 times)

locknload · « **on:** February 23, 2012, 01:53:59 PM »

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.

DesktopDave · « **Reply #1 on:** February 23, 2012, 04:33:56 PM »

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.

locknload · « **Reply #2 on:** February 23, 2012, 11:42:00 PM »

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" ?

DesktopDave · « **Reply #3 on:** February 24, 2012, 07:00:53 AM »

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.

colin86325 · « **Reply #4 on:** February 24, 2012, 08:36:20 AM »

For a 3-letter search (for example, CPS), i suggest you use Google instead with the following query:

site:m42club.com cps

Wrench · « **Reply #5 on:** February 24, 2012, 11:53:17 AM »

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.

locknload · « **Reply #6 on:** February 25, 2012, 03:40:28 PM »

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?

DesktopDave · « **Reply #7 on:** February 25, 2012, 04:51:40 PM »

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.

locknload · « **Reply #8 on:** February 26, 2012, 09:32:12 PM »

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.

Wrench · « **Reply #9 on:** February 26, 2012, 09:43:55 PM »

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...

Wrench · « **Reply #10 on:** February 27, 2012, 06:00:28 PM »

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...

locknload · « **Reply #11 on:** February 29, 2012, 08:29:19 PM »

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.

colin86325 · « **Reply #12 on:** February 29, 2012, 09:27:35 PM »

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

Wrench · « **Reply #13 on:** March 01, 2012, 06:18:50 AM »

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!

locknload · « **Reply #14 on:** March 01, 2012, 07:14:31 PM »

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.