Hard Start / Stall Issue


Just looking for long-distance diagnosis of an intermittent problem – should be easy, right?

Bottom line up front: Car sometimes does not want to start, and occasionally cuts out or dies.

Shortish version:
Hard start: For quite a while now, the car has intermittently been difficult to start. Will crank like a champ, but no start. Appears to have been correctable by reseating the ECU.
Stall: More recently, the car has died a few times while running. Tach drops to zero, but I believe other gauges still had power. Don’t know if this is related to hard start issue or not.

Long version:
Car is an ’88 325is. First issue was this spring at Autobahn. We had a deluge right before our warm-up session. By the time we went out, it had slacked off to moderate rain, but the track had quite a bit of standing water. The car died on the outlap, and would not start at all afterward. All the electronics seemed to be dry, and finally punted and took it home. Eventually diagnosed it as a bad ECU, replaced, and all was well. May or may not have been related to the rain.

Next event was at Mid Ohio. Car ran fine during Friday’s test day, as well as Saturday’s warm-up and qual. During the race, I took a pretty decent hit to the passenger side – hard enough to cave in the rocker panel pretty nicely. I kept the car running and did one more lap, then pulled in and went to contact impound. Car started fine afterward, but died as I was just about back to my paddock spot. It restarted immediately, but died again as I was pulling into my spot and wouldn’t restart. Tried again an hour or two later and it started right up. The rest of that weekend and at the following race weekend (Gingerman), it occasionally would be very hard to start, but ran fine once started. I almost missed sessions a couple times because it took so long to start.

Next up (and most recent) was Road America. When I tried to load the car on the trailer, it wouldn’t start. For giggles, I disconnected and reconnected the ECU, and it fired right up. During Friday’s test day (just two sessions for me) and on Saturday, it failed to start almost every time, but always started immediately after reseating the ECU. Same thing Sunday morning, but then during the morning race I had an altercation with a Thunder Roadster (yes, it’s been an abusive season for my car). My left front rode up over his right rear tire, so I had a pretty substantial drop back onto the pavement. Car died immediately, and wouldn’t restart. Back in the paddock, it looked like one of the relays had come unseated. After popping it back in and reseating the ECU, it started. After replacing the bent control arm, I took it for a test drive in the paddock. It died once, and cut out a time or two more, which didn’t bode well. Sure enough, it died again just as I was pulling into grid for the afternoon race, and wouldn’t start even after reseating the ECU. This was a longer grid period because we were doing the national anthem, so I ran back to my trailer, grabbed my spare ECU and some zip ties, and slapped it in. Still wouldn’t start even after reseating the ECU a couple times. Finally gave it one last try as the field was pulling out, and it fired. Since I’d missed my group, I got to join the CMC guys at the back of the field and do a standing start. The car seemed to be running great, but on the first lap it died completely immediately after the apex curbing in the kink. I kept the clutch engaged and the gas pedal down, and after a few seconds it came back to life. Video shows that the tach went to zero when it died, then back to normal as soon as it refired. Difficult to be sure, but it looks like the rest of the dash stayed alive. Ran fine afterward, but I pulled in and went straight to the paddock so I wouldn’t screw up everyone’s race if it died again in a bad spot.

So, lots going on. I tend to think the initial problem at Autobahn was unrelated. The new ECU seemed to fix everything, and swapping the old ECU back in resulted in a no-start again.
The contact at Mid Ohio may have nothing to do with anything, but the current issues seem to have started immediately afterward. Interestingly, I’ve had intermittent no-start problems ever since, but the only times it ever stalled were shortly after the contact at Mid O, and then after contact at RA. When it died on track at RA, it may have been helped along by the curbing, but again, the timing may be coincidence. Curbing at the apex of the Kink is about the most benign at the whole track (although still noticeable).
Since I got back from RA, the car starts and runs great every time. I’ve wiggled all the grounds and connections I can think of, and can’t even make it stutter. I’ve not done any real troubleshooting when it fails to start, because it’s always as I’m suited up and ready to go on track. I thought I had found a smoking gun this morning when I found that the O2 sensor cable has worn and/or melted through – looks like it’s contacting the header during right-hand turns. But, when I touch the bare wire against the header, nothing happens – just keeps running right along.
Any suggestions on where to start? I realize there may be more than one problem here. The two things that I hope will help are the fact that reseating the ECU seemed to consistently solve the no-start problem until the contact at RA; and the fact that the tach went to zero when it died, which I assume means it’s not just a fuel delivery problem.

Thanks for any advice and assistance…


Remove and check the crank position sensor and look at the whole wire.


Well, I’ve made progress of sorts - now I’ve got the car to where it fails to start in my garage, rather than at the track.
I’ve been starting the car almost daily for the past couple weeks in hopes that it would fail so I could troubleshoot, but it fired right up every time - including earlier today. Following Brian’s suggestion, I pulled the CPS. It was new earlier this season, and apparently I missed one of the retaining clips when I installed it. There was no obvious sign that it had contacted the pulley, but I figured I’d try swapping it anyway. I had replaced it when the car died at Autobahn earlier this season, but it made no difference at the time. Turned out to be a faulty ECU, so I assumed the old CPS was good and hung on to it. I put the old one back on this afternoon, and the car took quite a while to start. After running for a couple minutes, I shut it off and tried again. Started reluctantly again, so I figured maybe the old CPS may have been iffy after all. So, I put the newer one back on again. Now it refuses to start altogether, and I finally managed to run the battery down. Got it on the charger now, and I guess I’ll order another CPS just for fun. Are the cables for these things particularly fragile or something? I didn’t think I was overly abusive when I R&Red the sensors, but maybe I damaged one or both.