gustagen

1990 Honda Prelude 2.1 Injected Auto - NO SPARK

I am helping my friend troubleshoot his car that has no spark. He bought the vehicle

not running and upon doing a compression test found that the headgasket was blown. It

also had some bent valves so he replaced the cylinder head, head gasket, timing belt

and water pump and put the motor back together. After everything was back together,

he put a jump box on it and started it up. The motor ran fine for ~10 seconds and cut

out. The car's shutting off seemed to correspond with him moving the connections/jump

box. I suspect either the + and - cables touched each other, or he simply lost

connection with one of the cables. The car would not re-start and it was found that

no spark was coming from the coil. The ECU fuse and the clock fuse (both in the

underhood fusebox) were both found blown. The fuses were replaced and have not blown

again. Still no spark.

We have several repair manuals for this car, and we've gone through the "no spark"

troubleshooting they suggest.

Since then, we have tested/swapped:

ignition coil (resistances)
distributor
ECU power and ground sources
ALL fuses
main relay and wiring
ignition switch and wiring
coil/plug wire resistances
TDC/CYL/Crank sensor resistances and wiring to ECU
wiring from ECU to other sensors (intake air temp, coolant temp, etc)
swapped ECU for another from 1990 2.1 auto

One component we couldn't test is the radio condenser, a small square device mounted

to the ignition coil with two wires leading off of it. It prevents ignition system

signals from creating unwanted noise on the radio. The repair manual says if this is

shorting internally that it will cause a no-spark symptom. Unfortunately, a

capacitance tester is needed and we don't have access to one. We do have a spare

radio condenser (from the junkyard) and swapped that with no luck though.

After all of this, we took the car to the local Honda dealer to have them

troubleshoot it. They called and said they reconfirmed our tests and determined that

our components were good, and it must be a faulty/shorting wire. We brought the car

back and began more wiring tests.

We peeled back the insulation and inspected the wires and connections inside the

engine compartment and leading into the firewall and to the ECU. We found no damaged

wiring and re-wrapped the wiring.

At some point we noticed a "hot electric" odor from the engine bay and sniffed around

and found that the alternator was hot to the touch with the key off. We re-checked

the alternator wiring and found that the BLK/YEL wire to the alternator, which should

be hot when key is ON or START, had continuity to ground when the key is off. We then

found that the positive battery cable has continuity to ground when the battery is

unhooked. Does it seem our system has a hot wire shorting to ground? BTW, the car

still gets no spark even with alternator unhooked.

STRANGE BEHAVIOR

The car is now back together with most of the original parts. We have noticed some

strange things during the last few days of testing:

Car has no spark, however if key is turned to ON, then off (never to START) a single

spark is produced from the coil wire when the key goes to OFF. This was observed many

times seems to happen only with one out of three igniters we swapped.

We took each engine bay fuse out one a time and tested each side of the circuit for

continuity to the positive battery cable (with the battery out). Each gave continuity

only to one side, except for the headlight fuses. There is one for left, one for

right. However, when the headlights are on and we pull one side's fuse, that side

dims but does not go completely out. If both headlight fuses are pulled, both go

completely off. We tried the test of a 1991 Accord and each headlight goes out

totally when its fuse is pulled.

Another test we performed was to pull each fuse and replace it while checking for

continuity between + battery cable and ground (with the battery disconnected). The

meter changed very slightly for some fuses, but for the most part stayed near 0. We

found that the meter jumped to about 600 when we pulled just the "seat belt

retractor" fuse from the underdash fusebox. The car has regualar seatbelts, not the

kind that move when you open/shut the door. Does this mean something?

OTHER CONCERNS

What would happen if you touched + and - battery terminals while the car is running?

What caused the ECU fuse and clock fuse to blow? (Perhaps the clock fuse was blown

before we started work on the car, but obviously the ECU fuse had to be good for

those 10 seconds when the car was running.)


We are near our wits' ends with this car. We don't have a superb understanding of

electrical circuits, but we can read a schematic and (sort of) use a multimeter. Can

you think of anything we haven't yet?

Thanks for any help you can offer!