Engine won't turn-over

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bking6677

Engine won't turn-over

Post by bking6677 »

I am a long-time owner of the eighty's 5's & 6's, but now face a dead end on what should be the easiest problem to solve: no spark! (no smiley face appropriate!) It is an '85 635CSi and I have substituted parts from my working daily driver '88 535 and other parts from previous sixes and fives. The battery is at 12.6 at rest & remains on trickle charging, and the starter robustly turns over. I have replaced/swapped coil (no spark at output), two ECUs I have on hand (same BMW pn as original), start relay and K2, air-flow meter, resistance on reference sensor ok. Checked voltage at output of main relay, but not able to get to inputs on ECU. I raised the fuse box and found nothing corroded or disconnected (car came from CA two years ago). First big Q: has anyone ever heard of the raised pin (for ref sensor) on the flywheel falling off? Better still, how could you see if it is still there? I haven't borrowed an oscilloscope yet to see if there is a pulse. Also I understand the TDC sensor in the front of the engine and the speed sensor are irrelevant to start-up -is that true? One last thing, this failure occurred suddenly, however, for the last dozen or two starts, during start-up the engine would "catch" when the key was backing out of the start mode, yet battery was fully charged.
BKing
Carnegie, PA
'85 635CSi (130K mi)
'88 535CSi (235K mi)
'07 328Xi (13K mi)
'64 110 John Deere (still mows 1 acre every week)
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hornhospital
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Re: Engine won't turn-over

Post by hornhospital »

Welcome to the insanity! I guess that's much-belated, since you've been wrenching on your 5s and 6s for a while, you surely understand we're all crazy, right?

Correct on the front sensor having nothing to do with start/run.

You can take out the rear sensor(s) and with a mirror and flashlight you can see if the pin is still in. It's unusual but not unheard of to have one come out.
Ken Kanne
'84 633CSi "Sylvia"; '85 635CSi "Katja";'85 325e "Hazel Ann"; '95 M3 "Ashlyn"
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