The schematic shows that the LO side of the distributor reference pulse is ground. However, I get about 80 ohms resistance to ground when I check it.

Is this a problem?

 

The DRP is pulled lo by a transistor. I guess I would be measuring the V rather than R... AFAIK, the lo side should be within like 0.25 v of ground and the ECM should read it OK.

 

Kaiser, thanks. I'll check that.

I guess the larger issue for me, which I'm trying to figure out, is why my capacitor (condenser) in the distributor keeps failing. I've replaced it three times and each one runs fine for a few minutes and then fails.

It's easy to tell since I get a lot of noise in my radio after it fails. It fails open rather than short (if that helps the diagnosis any). Any ideas?

 

Ahhh, maybe we are talking about two different things.

DRP is a 5v sq wave sent to the ECM from the ign module. ECM uses it to calc timing and dwell.

The capacitor in an HEI is on the + side of the coil switching power transistor. It's usually protected by a ~250+ v zener inside the module.

If you are blowing out the cap, I'd look for a bad ground connection (back of the module) or an open plug or coil wire. Could also be a coil with an internal short on the primary side.

HTH

 

Kaiser,

I'm glad you replied. You seem to be knowledgeable about ignitions. I usually get blank stares when I ask people about the problem.

Anyway the module and coil are new. How is the module grounded? Through the body? I usually slober dielectric grease between it and the distributor housing to aide in heat transfer.

When I opened up the old capacitor assembly, the lead to the cap is hooked up to the +12V ignition feed to the coil. The body is obviously grounded. I replaced them because of this problem and then put a new capacitor in, but the same thing happened.

 

If you have a GM HEI distributor (of some sort), the ign module grounds through its back plate & the screws that secure the module to the body of the distrib.

The cap should be hooked up as you said. Assume you are using an automotive cap, rather than something from RadioShack?

I can't fathom what would blow out a cap without also blowing out the module(???).

Check the wire & coil continuities as previously suggested.

Coil primary R should be less than an ohm or so, secondary several K ohm. There should be ~0 resistance between the batt + & the coil +.

The module should draw 5 or 6 amps when running (square wave signal on a 'scope).

Good Luck.

 

Back from the dead....

I'm trying to diagnose a no-fuel condition in my TPI L98. I'm getting spark but the injectors are not firing. ECM has power. Ignition module is new. If I get spark does that still mean that the ECM may not be getting a reference signal? Can I check for 5V with a dvom or do I need a 'scope?

 

YOu should be able to hear the pump energize when turn the key to the "on" position. Also, you can check the fuel pressure in the rails prior to cranking the engine.

 

I have fuel pressure (just checked with gage). The problem is that the injectors are not pulsing. I just found that my ECM is storing code 46, which is the VATS fault code. I made a separate post about it here: https://www.thirdgen.org/forums/diy-...-question.html

 

I would definitely try to fix that VATS issue before attempting to replace/repair anything else.