I'm stumped...truck no worky.

**EagleMark** · 03-06-2013

Originally Posted by 907 Chevy

I'll try that, although I'm wondering why the PCM would need two 12v ignition sources? It seems more than a little redundant...hmm

We had better let GM know they have been wasting money all this time!

B5 has how many volts at EST/ICM?

**helo** · 03-08-2013

HEI ICM is supposedly prone to (permanent) failure from ground faults. Heat would be the other concern, with deteriorated heat sink grease being the primary cause.. Kind of a hack-job commitment to remote mount the ICM, but it sure makes troubleshooting and/or replacement much less painful; From experience, I would not advise trying to splice your harness for this without removing it from vehicle, or get a spare JY harness for $20. Even then it's a hack job, there's no great way to splice the pickup coil wire leads and safely route them out of the distributor.

I don't think that would explain your OBD serial not working, though. I still say quadruple check your 5v wires, _especially_ since you admit to messing with them =). Though, after reviewing the 7427 docs, 5v to ICM doesn't matter for no-start, because it only goes to 5v when PCM wants control of the timing. We start with the 5v wire unplugged to set base timing, afterall (EST bypass).

The troubleshooting chart in the link Mark provided says I should be getting around 1.2v with engine running.

Well, your engine isn't "running," so that's not a concern... I might know what I'm talking about; the low/high IC ref input pins are for the square wave DRP input. You can use a low power LED with test leads (OR, O-SCOPE) to see if anything is coming from the ICM, but at cranking rpms you won't have any measurable "voltage." 12v-rated LED can be hooked up to TACH wire output off the coil, too, with other LED lead to 12v (led will flash on during coil's dwell period). When running, IC input (DRP) is not a constant 1.2v, it's a square wave that happens to measure as ~1.2v on multimeter, at idle (probably slightly higher at 3500rpm..).

The DRP square wave (IC high/low pins) comes from the ICM, which is producing it based on the A/C signal from distributor pickup coil. ICM also triggers the coil with timing coming from the dwell signal on pin F11. Your problem could definitely be the ICM is not passing the square wave anymore, but it could also be that your A/C pickup coil signal is not strong enough or wire is broken (rebuild dizzy with new delco pickup coil from amazon/wherever).

I think you said you tested the pickup coil with a drill and it was "good"? There is a specification for this and you will get some a/c voltage even with a "bad" pickup coil, but I'm not sure what the official specs are.. Though, I'm pretty sure under 1v (a/c) is no bueno and anything over that should be fine, voltage will be higher the faster you spin the shaft...

**EagleMark** · 03-08-2013

The troubleshooting chart in the link Mark provided says I should be getting around 1.2v with engine running.

Well, your engine isn't "running," so that's not a concern...

I just re read this, wasn't really looking with the one ignition wire missing?

That chart is Key On Engine Off. So this may be the concern? Some of those numbers change, but should be close...

I don't think that would explain your OBD serial not working, though. I still say quadruple check your 5v wires, _especially_ since you admit to messing with them =). Though, after reviewing the 7427 docs, 5v to ICM doesn't matter for no-start, because it only goes to 5v when PCM wants control of the timing. We start with the 5v wire unplugged to set base timing, afterall (EST bypass).

Pretty sure the 5 volt reference and ByPass are 2 differant wires?

Did you ever say if you had spark? Are injectors firing when cranked?

**907 Chevy** · 03-08-2013

Originally Posted by helo

HEI ICM is supposedly prone to (permanent) failure from ground faults. Heat would be the other concern, with deteriorated heat sink grease being the primary cause.. Kind of a hack-job commitment to remote mount the ICM, but it sure makes troubleshooting and/or replacement much less painful; From experience, I would not advise trying to splice your harness for this without removing it from vehicle, or get a spare JY harness for $20. Even then it's a hack job, there's no great way to splice the pickup coil wire leads and safely route them out of the distributor.

I don't think that would explain your OBD serial not working, though. I still say quadruple check your 5v wires, _especially_ since you admit to messing with them =). Though, after reviewing the 7427 docs, 5v to ICM doesn't matter for no-start, because it only goes to 5v when PCM wants control of the timing. We start with the 5v wire unplugged to set base timing, afterall (EST bypass).

Well, your engine isn't "running," so that's not a concern... I might know what I'm talking about; the low/high IC ref input pins are for the square wave DRP input. You can use a low power LED with test leads (OR, O-SCOPE) to see if anything is coming from the ICM, but at cranking rpms you won't have any measurable "voltage." 12v-rated LED can be hooked up to TACH wire output off the coil, too, with other LED lead to 12v (led will flash on during coil's dwell period). When running, IC input (DRP) is not a constant 1.2v, it's a square wave that happens to measure as ~1.2v on multimeter, at idle (probably slightly higher at 3500rpm..).

The DRP square wave (IC high/low pins) comes from the ICM, which is producing it based on the A/C signal from distributor pickup coil. ICM also triggers the coil with timing coming from the dwell signal on pin F11. Your problem could definitely be the ICM is not passing the square wave anymore, but it could also be that your A/C pickup coil signal is not strong enough or wire is broken (rebuild dizzy with new delco pickup coil from amazon/wherever).

I think you said you tested the pickup coil with a drill and it was "good"? There is a specification for this and you will get some a/c voltage even with a "bad" pickup coil, but I'm not sure what the official specs are.. Though, I'm pretty sure under 1v (a/c) is no bueno and anything over that should be fine, voltage will be higher the faster you spin the shaft...

Well, I was supposed to be back in town today, but my flight was cancelled due to bad weather...gotta love Prudhoe Bay. Okay, to begin with...I did rebuild the dizzy with a new AC Delco pickup coil while I was doing the intake. AC voltage read ~3v while testing it with a hand drill.
I see what you're saying about the voltage reading on the IC Ref High pin during cranking so I'll test the circuit with a test light like is outlined in the flow chart below to see if I can isolate the ICM as the issue. I'll also check all the wires running to the diagnostic connector for continuity...

Originally Posted by EagleMark

Pretty sure the 5 volt reference and ByPass are 2 differant wires?

Did you ever say if you had spark? Are injectors firing when cranked?

Yeah, I think the 5 volt wire is just to put the ICM into bypass...

Still haven't checked for spark, which now I'm realizing I should've tested for a while ago. I tested the injector circuit with a noid light and no, the PCM isn't commanding the injectors to fire.

Originally Posted by EagleMark

We had better let GM know they have been wasting money all this time!

B5 has how many volts at EST/ICM?

B5? I show that as being a transmission signal wire...??

And I'll be sure to let the CEO of GM know next time we play golf :P

Thanks for all the help guys.

**1project2many** · 03-08-2013

I have to a *lot* of diagnosis and I generally have to do it fairly quickly. If you were in the shop where I worked, I'd advise you to start with the area you last worked. Do a thorough and complete visual inspection. Check all your ground connections, check for loose wires, check for wires connected to wrong places, etc. Chances are high that you'll find the problem that way.

Did you pull wires from the junction block on the firewall? Everything go back the same? Both connectors attached at the distributor? Any chance you accidentally plugged the 4 wire distributor connector into the IAC and vice-versa? (Hint, I'd double check this where you seem to have both a dead ICM and PCM that occurred at the same time). Did you accidentally try to connect the battery backwards? Is there a power wire from the starter that is not connected? Is the small ground strap between body and engine intact and connected? Did you pinch a power wire under the intake during the swap?

If the pcm is not behaving properly, confirm the connections are correct and that the pcm has a fighting chance. The check engine light will only do the blink test if the key has been off for more than thirty seconds. If this test does not occur or does not pass suspect the memcal / adapter / calibration / pcm but don't hesitate to check circuits connected to the pcm to ensure they are good and to prevent a replacement part from being damaged. You obviously have some ignition power at the pcm but what about battery power? When you checked fuses, did you do it with a test light to confirm power on both sides of the fuse? Check for voltage on 5V lines with the pcm disconnected... maybe one of the sensor wires got plugged into the wrong connection.

Something that probably doesn't matter, but I've been wondering about...I relocated the ignition coil to the fire wall, does the coil need to be grounded to the engine to work?

No. It needs +12 and the white wire from the ICM for primary side negative. The spark actually "grounds" through the +12V wire, through the battery, and back to the block so make sure you're using the OEM or better 12V feed. Really.

considering all present symptoms it points to something pcm related like wiring, fuses, relays, terminals, ignition switch, etc...... Since the ignition operates in bypass mode during cranking it should still have spark while cranking.

I agree with this guy!

When I jumped the injectors no fuel came out, but there was no pressure in the system when I jumped them. I had considered a fuel delivery issue as well, but fuel pressure is right where I set it, which tells me that fuel is reaching the regulator just fine...right?

Aiee!!! You jumped the injectors? These are TBI injectors? And you just attached a wire between ground and the ground side of the injector? That's often a death blow to TBI injectors.

I checked for voltage at pin A5 IC Ref High as jim_in_dorris suggested while my friend cranked the engine over and got no voltage to that pin.

You should check that voltage between B5 and the black/red REF LO signal. REF LO is the ground link between pcm and icm.

I'm wondering why the PCM would need two 12v ignition sources? It seems more than a little redundant...hmm

Because the traces on the circuit board cannot carry enough current to place all the demand on one 12V source. And / or because it's redundant.

In all honesty, you could get the factory service manual and start with the "cranks but won't run" trouble tree in section "6E3-A". It's usually very fast about pinpointing the system that has a problem. But you have to follow the tests and you can't cheat the results because you might miss an important detail.

HTH

**907 Chevy** · 03-08-2013

Originally Posted by 1project2many

I have to a *lot* of diagnosis and I generally have to do it fairly quickly. If you were in the shop where I worked, I'd advise you to start with the area you last worked. Do a thorough and complete visual inspection. Check all your ground connections, check for loose wires, check for wires connected to wrong places, etc. Chances are high that you'll find the problem that way.

Did you pull wires from the junction block on the firewall? Everything go back the same? Both connectors attached at the distributor? Any chance you accidentally plugged the 4 wire distributor connector into the IAC and vice-versa? (Hint, I'd double check this where you seem to have both a dead ICM and PCM that occurred at the same time). Did you accidentally try to connect the battery backwards? Is there a power wire from the starter that is not connected? Is the small ground strap between body and engine intact and connected? Did you pinch a power wire under the intake during the swap?

Grounds are good, I did the big 3 upgrade so I have good frame-body, frame-engine, and engine-frame grounds. I didn't remove any wires from the firewall, nor did I touch the starter. PCM grounds checked out.
I spliced in a 4 way flat connector for the IAC since I swapped to a 454 throttle body so I know for sure which connector is which. I didn't hook up the battery backwards...I'll check along the back of the intake to see if I pinched any wires back there.

Originally Posted by 1project2many

If the pcm is not behaving properly, confirm the connections are correct and that the pcm has a fighting chance. The check engine light will only do the blink test if the key has been off for more than thirty seconds. If this test does not occur or does not pass suspect the memcal / adapter / calibration / pcm but don't hesitate to check circuits connected to the pcm to ensure they are good and to prevent a replacement part from being damaged. You obviously have some ignition power at the pcm but what about battery power? When you checked fuses, did you do it with a test light to confirm power on both sides of the fuse? Check for voltage on 5V lines with the pcm disconnected... maybe one of the sensor wires got plugged into the wrong connection.

I checked the fuses for continuity with a multimeter, both ECM-1 and ENG-1 fuses checked out. Is there any other fuses I need to be checking? I have battery power at pin E16, I think I mislabeled it as ignition feed in a previous post though.

Originally Posted by 1project2many

Aiee!!! You jumped the injectors? These are TBI injectors? And you just attached a wire between ground and the ground side of the injector? That's often a death blow to TBI injectors.

...oops. Yeah, they're TBI injectors and I jumped them directly from the battery. Hopefully I didn't just smoke my injectors...

Originally Posted by 1project2many

You should check that voltage between B5 and the black/red REF LO signal. REF LO is the ground link between pcm and icm.

Ah, when I checked IC Ref High I was using the PCM ground and not the IC Ref low. I'll check that again...

Thanks

**907 Chevy** · 03-09-2013

Alright, I just got into town tonight and figured I'd post a quick update... I have good continuity between ground and the distributor base and I checked again for DRP at pins A4 & A5 while cranking and got nada; no surprise there, but figured I'd check just for sh!ts and grins.
I need to buy a test light tomorrow and and I'll start testing things according to that injector circuit diagnosis chart.

**907 Chevy** · 03-09-2013

Update: I picked up a test light this AM and probed the IC Ref High terminal in the 4 pin dizzy connector with the test light hooked up to 12v and the noid light flashed, so it appears my ICM that I assumed was good, has failed. How's that saying go about making assumptions? lol

I'll pickup a new ICM today...now I just need to figure out why I can't datalog or pull codes...

**907 Chevy** · 03-11-2013

Uhhh, so I went out and bought a new ICM and installed it and it didn't change anything. The injectors are STILL not firing. I did notice that the SES light does not illuminate with key on, so I was mistaken when I said it was working as it should. So no SES light with key on, SES light does not illuminate when I attempt to pull codes, I can't connect with TunerPro...wtf.

**EagleMark** · 03-11-2013

E15 Pink ignition power = batt voltage. If not, it causes no start and no CEL.

E16 Orange batt power = batt voltage. If not causes no start and no CEL.

F15 Pink Ignition Feed...was not found in my harness...?? Not sure if this is important or not?

F15 Pink ignition power... all the diagrams show this?

CEL is fused. Check all fuses again...

**907 Chevy** · 03-11-2013

Originally Posted by EagleMark

E15 Pink ignition power = batt voltage. If not, it causes no start and no CEL.

E16 Orange batt power = batt voltage. If not causes no start and no CEL.

F15 Pink ignition power... all the diagrams show this?

CEL is fused. Check all fuses again...

Okay, so E15 and E16 check within specs for voltage. I ran a jumper wire from E15 to F15 and nothing changed so far as the no start issue was concerned. I'll look over the fuses again...

**907 Chevy** · 03-13-2013

So it turns out I have no spark as well as no fuel. That pretty much only leaves the pickup coil as the cause of this, which makes no sense since it's brand spankin new. I tested the voltage output of the pickup coil while my friend cranked the engine and it was only producing about 2 tenths of a volt, although when I pulled the dizzy and tested it again with a hand drill it was producing 5 volts. I do have an O scope at work, maybe I should hook it up and make sure it's putting out the proper signal...??
The distributor itself seems fine; there's no play in the shaft, it turns freely, doesn't bind, and I don't believe that the stator hits the pole piece anywhere (although the magnets do come VERY close to touching one part of the pole piece...). Or maybe I should just pull a dizzy at a junk yard and swap it in? I really don't want to throw parts at this, but the distributor is really the last thing it could be.