E30 dies at random intervals

[KaeKilo]

Hey all. I have a 1992 325i 5spd convertible that has been running solid until recently. I would be driving and the car would suddenly just kill itself at random intervals (maybe after driving 100 miles, maybe after 5). When it dies, the antilock light on the cluster comes on. After this, most times, it will not start unless I disconnect the battery and let it sit for 3-5 min. (side note: it may be unrelated but after the car dies, when I take the key out, put it back in, and push it to the 2nd click, the check engine light does not illuminate but everything else will. If I try to crank, it cranks but no start. is this the sign for a No Start condition?) When the engine is behaving, it runs smooth, starts quick, pulls fine, passes CA smog, but runs a little hot (which has never been a problem usually). Just a hair over the half way mark. My theory is that the Main Relay is going out (it gets HOT after a while.) I don't want to spam buy random parts so if anyone has had anything similar to my problem, please let me know. I really mean anything helps :) More side notes: things done/noticed around the car (maybe important idk) is that the AFM carbon track has usual ish wear and tear, FPR and O2 sensor were replaced within the last 400 miles, oil change in the last 600, brake pads may need to be serviced as they are starting to squeak, car has a welded Magnaflow muffler, Car has no AC, no washer fluid reservoir. If there is anything I should do/check let me know. Thank You! (also I hope this isn't some dumb 5min fix i'm overcomplicating/overthinking lol)

HAS BEEN RESOLVED, CHECK REPLY #6 :)

[ZeKahr]

Hey all. I have a 1992 325i 5spd convertible that has been running solid until recently. I would be driving and the car would suddenly just kill itself at random intervals (maybe after driving 100 miles, maybe after 5). When it dies, the antilock light on the cluster comes on. After this, most times, it will not start unless I disconnect the battery and let it sit for 3-5 min. (side note: it may be unrelated but after the car dies, when I take the key out, put it back in, and push it to the 2nd click, the check engine light does not illuminate but everything else will. If I try to crank, it cranks but no start. is this the sign for a No Start condition?) When the engine is behaving, it runs smooth, starts quick, pulls fine, passes CA smog, but runs a little hot (which has never been a problem usually). Just a hair over the half way mark. My theory is that the Main Relay is going out (it gets HOT after a while.) I don't want to spam buy random parts so if anyone has had anything similar to my problem, please let me know. I really mean anything helps :) More side notes: things done/noticed around the car (maybe important idk) is that the AFM carbon track has usual ish wear and tear, FPR and O2 sensor were replaced within the last 400 miles, oil change in the last 600, brake pads do need to be serviced as they are old and starting to squeak, car has a poorly welded (by me) Magnaflow muffler ( doesn't leak :P), Car has no AC or Heater (but its a convertible so thats ok ), no washer fluid reservoir. If there is anything I should do/check let me know. Thank You! (also I hope this isn't some dumb 5min fix i'm overcomplicating/overthinking lol)

Sounds to me like your crank position sensor is going out. Or could be a dying ignition system that needs a refresh. I would check if you’re getting fuel and spark. Get a multimeter and start checking the resistances on the engine sensors per the Bentley manual. Worst case scenario, you’re dealing with a weak spot in the engine wiring somewhere (the harnesses in these cars are now 30 years old so they’re going to start breaking down too)

[varg]

When it dies and will not restart is it getting spark? Is it getting fuel? Neither? To eliminate the main relay as a cause you'd check for voltage when it is dead. Get out the multimeter and get checking.

[Maddog]

Been in your situation on an intermittent stall; it started infrequently and when outside temperatures were >90, but became more frequent regardless of temperature.

I replaced every conceivable relays and checked grounds, as well as repairing severely corroded wires at my C190 connection, but it still stalled without warning; car would always restart after 5-10 minutes. The C190 connector corrosion was really bad; wire would crumble when I touch them. Worthwhile to inspect since it’s located underneath the intake manifold and exposed to moisture.

It became too dangerous to drive and after exhausting everything within my skills, I had it towed to my BMW expert. He said a common issue with E30s; he identified a broken shielded ground wire and replace the harness. This was done almost 7 years ago and no more stalls. My mechanic just gently tugged/twisted the harness and the engine stalled; a momentary break in the circuit disrupt the signal to the ECU causing a stall.

I decided it was either pay someone who has the means to diagnose the problem or sell my car as a parts car.

Good luck and hope your gremlin is simpler to find than mine.

[It's Soda Not Pop]

Check your fuel pump wiring. I just rewired mine with it's own relay and power directly from the battery. It still gets the signal from the FP relay though. So it starts like factory. I was having issues where I would have to wiggle the wires on the fuel pump to get mine to start sometimes.

[KaeKilo]

Hey everyone. I found the issue and I am finally posting the resolve after many months of "ill post it tomorrow." I simplified and re-wrote the symptoms and I hope the diagnosis helps someone in need. :)

• ISSUE SYMPTOMS: Power to all instrumentation and starter. Car appears normal when key is in position 2 (on); EXCEPT, check engine light is NOT illuminated before start. WILL CRANK, NO START. Assumed, main relay would be out (specified in TEST). Voltage reads -1 on main relay power via voltmeter. Also, no buzz in engine bay when engine off and key in position 2. Intermittently starts pretty much whenever it feels like starting. Kills itself when it wants to. When it wants to start, check engine light is illuminated when engine is off and key in position 2.

• FIX: Battery main fusible link is popped/out. Replace it. 50A fuse. I recommend buying an aftermarket replacement because Break My Wallet wants to run the wallet thin :/ There are a few YouTube videos on aftermarket replacements.

• TEST: IF main RELAY is out, there should be power to it regardless. In this case, THE FUSIBLE LINK by the battery was popped and the arm intermittently made contact causing the “starts when it feels like starting” notion. Disconnects if jiggled. One way to test if it really is the fusible link (if car has a rear mounted battery), leave key in position 2 and jiggle, shimmy, and tap on the fusible link and see if the check engine light comes on when manipulated. (stay at the battery and look at the light through the rear window.) That's what I did and I hope it helps someone in need