I'm stumped...truck no worky.

[907 Chevy]

That's true, but if it was a PCM/wiring issue I'd still have spark at least, right?

[1project2many]

Possibly no. 5V applied to bypass line will cause icm to look for pulses from ecm. You could try with 4 wire connector disconnected.

You're running around in circles with this. Roundy roundy round. Even if you make the distributor spark, the engine still won't run without an ecm/pcm to control it. I mentioned the "cranks but won't start" tree from the FSM which walks you through each and every test needed to determine what's at fault. You still have time to follow it.

The distributor spins at 1/2 crank speed. If you're cranking at 800 rpm then the dizzy is spinning at 400 rpm. Your drill spins at what... 2k, 3500?? That's equivalent to the engine runnning at 4000 to 7000 rpm. The pickup coil voltage gets greater as the distributor shaft spins faster so it's no surprise you're seeing voltage at that speed. Pickup coil voltage can be near 8-10V at high speed so maybe you saw a problem right from the start?

You said you had fuel then you said no fuel. The fuel pump is engaged by the pcm for a few seconds after key on, then it will be powered again if the pcm sees a distributor pulse. There's a second circuit which can power the pump... the oil pressure switch. If the engine is cranked long enough the switch will close and the pump will engage. This is not pcm controlled. But if the pcm is not powering the pump on with initial key on then you have yet another clue that the pcm is faulty.

Two former GM techs and a pretty smart guy are all saying you should focus on the pcm. No communications, no CEL, no spark, no injector pulses, and maybe no fuel pump prime all point to a problem with the computer.

BTW, if you have access to the FSM you can read about everythig I've described in section 6E

[907 Chevy]

Possibly no. 5V applied to bypass line will cause icm to look for pulses from ecm. You could try with 4 wire connector disconnected.

You're running around in circles with this. Roundy roundy round. Even if you make the distributor spark, the engine still won't run without an ecm/pcm to control it. I mentioned the "cranks but won't start" tree from the FSM which walks you through each and every test needed to determine what's at fault. You still have time to follow it.

The distributor spins at 1/2 crank speed. If you're cranking at 800 rpm then the dizzy is spinning at 400 rpm. Your drill spins at what... 2k, 3500?? That's equivalent to the engine runnning at 4000 to 7000 rpm. The pickup coil voltage gets greater as the distributor shaft spins faster so it's no surprise you're seeing voltage at that speed. Pickup coil voltage can be near 8-10V at high speed so maybe you saw a problem right from the start?

You said you had fuel then you said no fuel. The fuel pump is engaged by the pcm for a few seconds after key on, then it will be powered again if the pcm sees a distributor pulse. There's a second circuit which can power the pump... the oil pressure switch. If the engine is cranked long enough the switch will close and the pump will engage. This is not pcm controlled. But if the pcm is not powering the pump on with initial key on then you have yet another clue that the pcm is faulty.

Two former GM techs and a pretty smart guy are all saying you should focus on the pcm. No communications, no CEL, no spark, no injector pulses, and maybe no fuel pump prime all point to a problem with the computer.

BTW, if you have access to the FSM you can read about everythig I've described in section 6E

I don't have access to the FSM unfortunately. I've also had the 5v bypass wire unhooked since I put everything back together and tried to fire it up.

To recap...

The PCM is not commanding the injectors to fire.
All 12v inputs and PCM grounds checked out.
Fuel pump primes with key on.
When I probed the IC Ref High terminal at the 4 pin connector with a test light wired to 12v the injectors fired. This tells me that there's nothing wrong with the PCM...please correct me if I'm wrong.
I back probed the IC Ref High/Low terminals at the PCM connector with a DVOM and had no distributor reference pulse. I know we already discussed that, but I think there'd at least be some signal at the IC Ref High pin no matter the cranking speed.
I have a brand new ICM that tested good at the parts store before I left.

The thing with the lack of ALDL/CEL is I can't pinpoint exactly when that issue began, whether it was recently or if it's existed for a while now. I've driven the truck two times in the past year and that was only when I needed to relocate it. I don't even remember the last time I logged data.

I appreciate all the help and advice you guys have given me and yeah, I'm definitely going around in circles with this. About the only variable that's changed between the truck running and this present no start issue has been the distributor...I encountered a no start condition a year and a half ago that wound up being due to the distributor so I bought a cheap replacement dizzy at the parts store and it solved that issue. However, since it was a cheap chinese made distributor I decided to clean up the old stock distributor that had failed, install a new AC Delco pickup coil, use that instead and tossed the chinese one in the trash...that may have been a bad idea.

[1project2many]

The cranks but won't run chart begins at the check engine light. If the light doesn't light, diagnose that first. If the light does work, plug in scan tool. If no data, diagnose that problem. If you have data, look at TPS voltage and CTS for correct readings. If those are good, key off for ten seconds, key on, listen for pump operation. If that test passes, check for spark. There are three other tests before spark and yours fails the first two.

The test for no check engine light is simple. Disconnect pcm connectors and check for power on circuits 439 and 440 with key on. If power present, problem is either the grounds or the pcm. If power is not present repair the faulty circuits.

[907 Chevy]

Okay, I'll do that. I'm not sure what circuits 439 and 440 are though...which pins in the PCM connectors do I check for power?

Thanks

[EagleMark]

Circuits are listed on same diagram you used to check pins.

[907 Chevy]

Oh gotcha, thanks. Yeah both of those circuits have power and all grounds for the PCM are good.

[EagleMark]

The test for no check engine light is simple. Disconnect pcm connectors and check for power on circuits 439 and 440 with key on. If power present, problem is either the grounds or the pcm. If power is not present repair the faulty circuits.

I would also turn key on and ground E6, CEL should come on!

[907 Chevy]

I would also turn key on and ground E6, CEL should come on!

Okay, I'll try that and let ya know the results. Thanks

[907 Chevy]

Check engine light does not illuminate when E6 is grounded.

[EagleMark]

Then it is not getting power! And likely something else is not getting power.

Or the very unlikely possibility that the bulb is burned out...

[907 Chevy]

Then it is not getting power! And likely something else is not getting power.

Or the very unlikely possibility that the bulb is burned out...

Is the CEL on the cigarette lighter fuse?

[907 Chevy]

Update: I swapped my PCM into a coworkers truck and it fired right up so the PCM isn't the cause of this issue. I also looked for the pink wire at pin F15 (iirc) that was shown in the wiring diagram in his harness and it was not present so that's a non issue.
Does anyone have a copy of Diagnostic Chart A-1? I've looked online and haven't been able to locate it...

[907 Chevy]

Well, I think I found the issue...

While cleaning up the wiring harness and removing the transmission wires and pins, I cut the FWD Low Range Signal wire at pin F8 by mistake...SMH. Anyways, I repaired the wire and put it back in the PCM connector, turned the key on, and voila...functioning SES light and the injectors are firing. I don't know why no signal from this wire would keep the PCM from functioning though. Weird

Thanks for all the help guys