94 9C1 - No spark

[xxskullxx]

Hey all - I've got a 94 Caprice Police car with the 5.7L V8. It's got about 220k on it, but runs great. I drove it to work the other day and it ran great, as normal. I went to go home after work and it wouldn't start. It sounds like it's turning over fine, but I get no spark. I replaced the coil, but still no luck. Any ideas? Coil module?

[silicon212]

A bone of contention with the LT1 is the OptiSpark distributor - this might well be the culprit.

[hondahappy86]

yeah...sounds like the optispark....i also have a 94 chevy police car....mine is gone at 195000 miles....i have to replace it.....it is a 2 and a half hour job.....and requires some mechanical ability....and the new distributor is also about 300$

[xxskullxx]

I have no problem replacing it... aside from it being a bit of a PITA to get to. I just want to be confident that I'm going to down the right path. Here's some more info - tell me what you think.
My water pump has been leaking a small amount, I know that this can affect the distributor, but I was under the impression that the car would at least run rough for a day or two if this was the problem. If nothing else, I would hope that it would fire a couple times instead of going from running fine to no spark at all. Although, I have the feeling that the distributor will be my next step considering the coil is new and the coil module tested good at Advance Auto. BTW - the distributor has been replaced w/in the last 70k. Let me know what you think. Thanks for your help.

[silicon212]

Leaky waterpump = failed OptiSpark. The '94 units were a little bit less than watertight, so if the pump did leak, then it probably did cause the failure of the OptiSpark.

They have a tendency to abruptly quit, not fade.

[xxskullxx]

I'm still not convinced... I haven't changed the distributor out yet, but I'm not getting spark at the coil. Maybe I'm mistaken, but I should still get spark at the coil even if the distributor is shot. Let me know what you think, please.

[silicon212]

Originally Posted by xxskullxx

I'm still not convinced... I haven't changed the distributor out yet, but I'm not getting spark at the coil. Maybe I'm mistaken, but I should still get spark at the coil even if the distributor is shot. Let me know what you think, please.

The coil receives its reference pulses from the distributor. If the distributor is shot, there will be no spark at the coil. Think about bad points in an old school distributor - if the points are bad the coil won't fire. In any instance, running the coil to check for spark without a special spark gap checker, can lead to the death of the coil.

You're thinking rotor failure, but there is more to a distributor than a rotor and cap.

[xxskullxx]

Alright. I replaced the distributor and water pump. But still no spark. I'm at a loss as to where to go next. Could it be the computer? Ignition coil module?

[Blue Bowtie]

You should determine if the Opti is

1. Getting power via the red wire (C terminal);
2. Generating a low resolution square wave signal on the red/black wire (A terminal);
3. Generating a high resolution signal on the purple/white wire (B terminal);
4. Switching power to the pink/black wire (D terminal).

There should be a distributor test connector with those same wire colors at the left side of the intake plenum, adjacent to the oil filler cap.

If the Opti is signaling the PCM correctly, make sure the HEI switching module is getting the signal from the PCM and switching power to the coil primary.

[xxskullxx]

Distributor test connector wires check out. Ignition coil module is good. Distributor is new, coil is new. Is there something else that could be signaling the computer to shut down the ignition system? Am I missing some important piece to the puzzle? Thanks for the help so far, how about a little more?

Thanks

[Blue Bowtie]

Since the necessary signals are evidently present at the Opti while cranking, you should test for spark directly at the coil. If there is spark at the coil but not at the plugs, there may be a problem with the Opti cap or rotor (even new). If there is no spark at the coil, the rest of the system is under the complete control of the PCM.

One possibility is that the PassKey system is preventing ignition and/or injector pulses. Even if the "SECURITY" lamp acts normally, the circuit may have a problem.

Report back with results of the spark test at the coil, and we can progress into the PCM and anti-theft systems if necessary.

[xxskullxx]

no spark at the coil.

[Blue Bowtie]

With your meter, verify a constant 12VDC on the pink or pink/black wire on the ignition coil with the ignition on. If there is no power, check the 10A #11 fuse in the UEC (Underhood Electrical Center).

If there is power at the coil primary with KOEO, check the ignition coil for switching. If you have an oscilloscope, connect to the coil primary (pink/black and white/black wires) and watch for the relatively square wave while cranking. Lacking a scope, you may be able to get some indication with a dwell meter or duty cycle scale on a multimeter.

If there is switching at the coil primary, the coil should be producing spark. If there is no switching, verify a good ground at the 'C' terminal of the coil module (black wire) and use your scope to check for reference pulses at the 'B' terminal of the coil module (white wire). There should be four pulses per engine revolution at the 'B' terminal. If the pulses are present, the system should be working.

If there are no pulses at the ignition module 'B' terminal, check for the same signal or circuit continuity at the PCM terminal 'B5' in the passenger compartment. If pulses are present at the PCM but not at the ignition module, the white wire has lost continuity.

If there are no ignition pulses at the PCM terminal 'B5' check for continuity of the Opti harness to the PCM. That same test connector you checked before (on the right side of the plenum) should be wired to the PCM on the following terminals:

• Test connector 'A' terminal (red/black) to PCM B2;
• Test connector 'B' terminal (purple/white) to PCM B20;
• Test connector 'C' terminal (red) to PCM B14;
• Test connector 'D' terminal (pink/black) to PCM B3;

If the wires have continuity and/or the Opti high and low resolution signals can be read at the PCM terminals, the circuit is complete. If not, there are wire harness problems.

If all signals at the PCM are present, verify that there is a 30 or 50Hz signal on PCM pin 'A25' from the theft deterrent module. If thee is no signal from the Theft Deterrent Module, the PassKey system has a problem.