1990.. Been parked 2 yrs... No fuel to Tbi..Tia

[Schurkey]

The Ignition Control Module under the distributor cap actually controls the injectors too.

Not exactly. It's a link in the chain.

The Ignition module sends a signal to the ECM, the ECM controls the injectors.

If there's no signal from the ignition module, there's no injector firing. But you'd probably also lose spark, too.

 

[someotherguy]

Not exactly. It's a link in the chain.

The Ignition module sends a signal to the ECM, the ECM controls the injectors.

If there's no signal from the ignition module, there's no injector firing. But you'd probably also lose spark, too.

They can fail in either way; no spark OR no reference pulse for injectors to fire.

Definitely a suspect but not to be replaced until actual troubleshooting is performed. If there's sufficient fuel pressure, and spark, but injectors won't fire - yeah, the most likely suspect at that point would be the ignition module. There are certainly other possible causes but you've exhausted the overwhelmingly common ones. One could troubleshoot further before replacing the module but you're reaching the point of diminishing returns there. On some trucks, you'll find the harness going to the module has gotten brittle so the wiring has gone bad. Pickup coil in the distributor could be bad, too, and that's easy enough to test with a meter.

Richard

 

[Schurkey]

They can fail in either way; no spark OR no reference pulse for injectors to fire.

The module controls spark below 400 rpm. (Cranking speed, plus a bit more--but even at curb idle, in gear, the ECM should be controlling the spark.)

The ECM controls spark above 400 rpm, by sending a timing-advance signal to the module.

No RPM signal from module to ECM, no injector spray, and no spark, at least above 400 rpm.

Definitely a suspect but not to be replaced until actual troubleshooting is performed. If there's sufficient fuel pressure, and spark, but injectors won't fire - yeah, the most likely suspect at that point would be the ignition module. There are certainly other possible causes but you've exhausted the overwhelmingly common ones. One could troubleshoot further before replacing the module but you're reaching the point of diminishing returns there.

As a rule, the module failures take out the injector pulses AND spark.

On some trucks, you'll find the harness going to the module has gotten brittle so the wiring has gone bad.

Yup, that would do it, too. So many folks don't consider the wiring harness as part of the circuit.

Pickup coil in the distributor could be bad, too, and that's easy enough to test with a meter.

1. If the problem was the pickup coil, you'd have no spark and no injector pulse, because the module wouldn't have a reliable signal to trigger from.

2. Pickup coils can be tested with an ohmmeter, and the test can confirm the pickup coil is defective. The ohmmeter testing CANNOT confirm that the pickup coil is GOOD. Even if the pickup coil resistance is within spec, there are other possible failures that could prevent it from sending a proper signal.

 

[PlayingWithTBI]

I agree with both Schurkey and Richard. I would think it's very rare to lose one and not the other. If you disconnect the EST bypass wire, you'll eliminate the ECM from spark timing altogether but, it'll continue to control the injectors through the DRPs on pin "R", if the Pickup Coil, ICM, and wires/connectors, are still good.

FYI, here's a diagram of a typical GM ICM, YMMV (too many acronyms huh?)

You must be registered for see images attach

 

[someotherguy]

Regardless of your view on it, I think the moral to the story here is always troubleshoot before replacing parts.

Richard

 

[SuperSpore]

I had the same problem and was banging my head for a while before somebody on here pointed me in the oddly right direction.

The Ignition Control Module under the distributor cap actually controls the injectors too. Probably something to do with not feeding fuel if there is no spark. I replaced that and has been running fine since.

I also had this problem recently. Truck just died, crank no start. Swapped the ICM and it started right up. Dont forget to use real thermal paste that goes underneath the ICM before install. (Not what they offer you at autozone or oreillys) - you may have to order it online.
If in a pinch, use thermal grease from Bestbuy for computers. They have it in stock. Seems to hold up so far.

 

[someotherguy]

I also had this problem recently. Truck just died, crank no start. Swapped the ICM and it started right up. Dont forget to use real thermal paste that goes underneath the ICM before install. (Not what they offer you at autozone or oreillys) - you may have to order it online.
If in a pinch, use thermal grease from Bestbuy for computers. They have it in stock. Seems to hold up so far.

Same stuff. Most heat sink compounds are generally silicone dielectric grease, with ceramic (or other materials) added to help it conduct the heat while being eletrically non-conductive.

With that said, don't ever let anyone tell you that dielectric grease is a suitable product for the ignition module, or anything else requiring heat sink compound. It won't do the job.

Used to just be able to go down to Radio Shack and get a tube of heat sink compound, in a pinch. Or Fry's. Long gone now..

Richard

 

[SuperSpore]

Die electric grease is what they offer you at autozone and orielly's instead of thermal paste. I've pressed them on this, and they admit they don't know what I'm talking about.
That's a really bad situation for the customer. Those ICM's wont last long for the poor folks using die electric grease. But those parts people are repurposed from fast food, at least around here. They just parrot what they're told. Buyer beware.

This is what I got at best buy and available at amazon:

Corsair TM30 Performance Thermal Paste | Ultra-Low Thermal Impedance CPU/GPU | 3 Grams|w/applicator​

 

[PlayingWithTBI]

This is what I use...

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www.amazon.com/ARCTIC-MX-5-Incl-Spatula-Non-Conductive/dp/B08T5Q4J7H/ref=asc_df_B08T5Q4J7H?tag=bingshoppinga-20&linkCode=df0&hvadid=80676781093377&hvnetw=o&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4584276308403946&th=1

 

[Erik the Awful]

Die electric grease is what they offer you at autozone and orielly's instead of thermal paste. I've pressed them on this, and they admit they don't know what I'm talking about.
That's a really bad situation for the customer. Those ICM's wont last long for the poor folks using die electric grease. But those parts people are repurposed from fast food, at least around here. They just parrot what they're told. Buyer beware.

They really need an education program for their counter guys, and most of it could be taught through CBTs. Complete enough CBTs and you get a raise! But then they'd have to pay for the raise, and they'd rather the customer just eat their fail for them.