CAN SOMEONE EXPLAIN THE PURPOSE OF THE 180 DEGREE DISTRIBUTOR PULSES?
started diagnosing problem:
- checked for spark, had good spark on all 4 plugs
- thinking it was fuel problem, checked fuel pump fuse, was good
- checked fuel pump relay, was good
- checked voltage at fuel pump, was good
- installed fuel pressure guage between fuel filter and injector rail, fuel pressure was normal
- opened exhaust manifold ahead of muffler to check for obstruction to exhaust flow, found no obstruction
- rigged the equivalent of a "noid light" using analog voltmeter, to check for pulses at fuel injectors, found pulses at all 4 injectors
- read about trick using "starting fluid", sprayed into intake manifold while cranking, engine would not start, this suggested it was not a fuel problem
- thinking it was now an electrical problem, pulled ECM codes, found no error code, so ECM thinks emission system is normal
- removed valve cover to check for possible timing chain problem, found chains ok and cams were properly timed
- removed distributor, (a) checked coil resistances, were normal (b) back probed connector while turning, found all 1 degree pulses (c) found the two 180 degree pulses
- performed all tests on power transistor, were good
- THEN with a mirror, found pink/black wire dangling behind console near ECM. found a pin in ECM connector that had no wire attached. removed pin from connector and, with magnifying glass, found the ends of a broken wire (but no indication where the wire came from). soldered jumper wire to pin, installed pin back into connector, soldered pink/black wire to jumper, ENGINE NOW RUNS. this "too short" wire failed at the connector after 13 years, apparently from fatigue.
Haynes manual does not show purpose of this specific wire but found on internet, that it goes to "starting system". Possibly this broken wire has something to do with the 180 degree distributor pulses and possibly the distributor was firing at BDC instead of TDC.
another example of a rare wiring problem, IT HAPPENS. read about "ohms law" in this link:
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