94 Sentra "cranks but won't start", rare solution to wiring problem

CAN SOMEONE EXPLAIN THE PURPOSE OF THE 180 DEGREE
DISTRIBUTOR PULSES?

started diagnosing problem:
1. checked for spark, had good spark on all 4 plugs
2. thinking it was fuel problem, checked fuel pump fuse, was good
3. checked fuel pump relay, was good
4. checked voltage at fuel pump, was good
5. installed fuel pressure guage between fuel filter and injector
rail, fuel pressure was normal
6. opened exhaust manifold ahead of muffler to check for obstruction
to exhaust flow, found no obstruction
7. rigged the equivalent of a "noid light" using analog voltmeter, to
check for pulses at fuel injectors, found pulses at all 4
injectors
8. read about trick using "starting fluid", sprayed into intake
manifold
while cranking, engine would not start, this suggested it was not
a fuel problem
9. thinking it was now an electrical problem, pulled ECM codes, found
no error code, so ECM thinks emission system is normal
10. removed valve cover to check for possible timing chain problem,
found chains ok and cams were properly timed
11. 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
12. performed all tests on power transistor, were good
13. 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:
http://www.asashop.org/autoinc/feb97/techtips.htm

"nucleus" <rose122550 (AT) yahoo (DOT) com> wrote

CAN SOMEONE EXPLAIN THE PURPOSE OF THE 180 DEGREE
DISTRIBUTOR PULSES?

Do they create a spark at the plug?

If so, it is probably to burn off any remaining fuel and hopefully lower
emissions.
--


Joe in Northern, NJ - V#8013-R

Currently Riding The "Mother Ship"
http://yunx.com/valk.htm

Ride a motorcycle in or near NJ?
http://tinyurl.com/5apkg

On Mar 27, 6:29 am, "nucleus" <rose122... (AT) yahoo (DOT) com> wrote:

CAN SOMEONE EXPLAIN THE PURPOSE OF THE 180 DEGREE
DISTRIBUTOR PULSES?

started diagnosing problem:
1. checked for spark, had good spark on all 4 plugs
2. thinking it was fuel problem, checked fuel pump fuse, was good
3. checked fuel pump relay, was good
4. checked voltage at fuel pump, was good
5. installed fuel pressure guage between fuel filter and injector
rail, fuel pressure was normal
6. opened exhaust manifold ahead of muffler to check for obstruction
to exhaust flow, found no obstruction
7. rigged the equivalent of a "noid light" using analog voltmeter, to
check for pulses at fuel injectors, found pulses at all 4
injectors
8. read about trick using "starting fluid", sprayed into intake
manifold
while cranking, engine would not start, this suggested it was not
a fuel problem
9. thinking it was now an electrical problem, pulled ECM codes, found
no error code, so ECM thinks emission system is normal
10. removed valve cover to check for possible timing chain problem,
found chains ok and cams were properly timed
11. 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
12. performed all tests on power transistor, were good
13. 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:http://www.asashop.org/autoinc/feb97/techtips.htm

Here's what I would do now. Pull all spark plugs and perform
compression check. If compression check is normal.... stick a
screwdriver in one empty spark plug wire. Lay the screwdriver near
ground. Have an assistant crank engine while you hold your thumb over
the spark plug hole (now empty) of the coresponding plug wire. Watch
the spark and get the rhythm of when the spark hits... do you feel
your thumb being blown off the hole. This would be correct... and
would indicate that your spark timing is certainly in the ball park.

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