[adm750]

...and again, I'm going off the assumption that when PassLock intervenes, the vehicle will not crank at all.... This is what I've understood to be the norm if there is a PassLock / VATS issue. That's the only failure mode I've seen - no crank when it goes into protection. Please correct me if I am wrong...

 

[Bill58]

Have you tried a shot of starting fluid?

 

[adm750]

Have you tried a shot of starting fluid?

Hey Bill ! TBH, I have not. I'll snag a can on the way home tonight and give that a shot (pun intended...) and see what happens.

 

[Colt Hero]

@adm750 : two PCMs and no power at the Injectors ... probably not the PCM ... something common ... like wiring or fuses. Could you have missed a fuse ... like an in-line one?

...and again, I'm going off the assumption that when PassLock intervenes, the vehicle will not crank at all.... This is what I've understood to be the norm if there is a PassLock / VATS issue. That's the only failure mode I've seen - no crank when it goes into protection. Please correct me if I am wrong...

It sure feels like a SECURITY thing ... if the Injectors are not firing at all.

Can you verify the ECM(s) are trying to output a signal to fire the Injectors? Do you know which output(s) they are? Maybe something is blocking the signal(s) from reaching the Injectors? Does anyone know if these signals go directly to the Injectors from the ECM ... or do they go through one or more "gates" beforehand?

Do we have Wiring Diagrams?

 

[adm750]

@Colt Hero - I have power to the injectors but the PCM is not grounding them. The noid light will not come on at all when cranking but I do have spark. Looks like each individual injector is grounded inside the PCM. One common power feed to all of them but each one has an individual return line to the PCM.

I do not know of an inline fuse anywhere, but I do NOT have any worthwhile wiring diagrams.

I'm not familiar with the 'bypass mode' (or IC Mode ???) these engines operate in at start-up until the PCM takes over so I'm going to do a bit of research on that too when I get off work.
I think I understand that a 5v signal is sent from the PCM to the ICM that triggers the ICM to switch and allow the PCM to take over spark timing. I'm assuming that might also include injector timing but have NOT confirmed that.

this describes that operation for a 3.4 engine: 2004 Impala 3.4 No Injector pulse

I'm going to try to find the wiring diagrams for the 3.8 and check these 'signals'. I suspect maybe I have a broken wire that may be stopping this hand-over (??) or at least may be interrupting comms between the components in the system. (heck...maybe I have a bad ICM ???)

again...I'm assuming the PCM is getting all the proper data since I can read engine RPM when cranking via my scan tool. Now, what it's actually doing with it is becoming a prolonged agonizing mystery. LOL

*note: not sure if I posted this last night but I checked resistance of all injectors last night (to ensure one wasn't shorted and shutting them all down) and all six were mid 12 ohm range.

 

[Bill58]

GM 3.8L Ignition Control Module And Crank (3X, 18X) Sensor Test

GM 3.8L Index of Articles

easyautodiagnostics.com

A lot of reading but good info.

 

[adm750]

@Bill58 - thanks for that ..! I've done those test but reading that test page was a good refresher. This looks nearly identical to the test write-up I found but I manually turned the car over using the crank pully bolt to do the CMP and CKP signal tests. Works just the same and all components tested good, as did the powers and grounds.

But...and harking back to the GM Bypass ignition System signals,

, I need to find a way to find out where these wires below feed to the PCM, and how to test them:

• A- WHITEwire.
  • ECM control of ignition control module (after the 400 RPMs and above are achieved).
• B- TAN with BLACK stripewire.
  • 5 Volt BYPASS from ECM for Ignition Timing Control.
• C- LIGHT BLUE with BLACK stripewire.
  • CRANK Position Signal to ECM.
• D- PURPLE with WHITE stripewire.
  • Fuel Injection Control Signal to ECM.
• L- BLACK with RED stripewire.
  • Ground that ECM gets thru' the ignition control module.

I need to find out if the ICM is sending the reference signal(s?) back to the PCM so it will turn on the injectors.

I'm onto that next.

 

[Colt Hero]

Manual says you can view a “Scan Tool Data List” (using the Tech 2?) that will show the “Ignition Mode” as either “IC” or “Bypass”

And … what are the “Driver Module”s 1-4 used for? What do they do? The “Driver”s are solid-state devices used by (apparently by the PCM?) to ground the control circuit of each Fuel Injector. The Tech 2 can display their state(s) in real-time. Normally, they show “Enabled”, but they can also be “OFF” (High Volts or High Temp) or even “Invalid”

 

[adm750]

@Colt Hero - wow..! thank you !!!

I didn't have a lot of time tonight to get into the trouble shooting. I did get into it a bit but I need to ensure I clarify the terminology. Like what is the "multi-way harness connector of the fuel injectors" . Is that the ICM connector Term P ?? the 80-pin clear PCM connector Term 24 ?? the 2-pin conn at the injector itself..? or the 8-pin connector that looks to come off the ICM right at the manifold on the pass side of the engine ??. So I just need to familiarize myself a bit then will proceed with those test steps.

Just for grins I did get to pull the ICM / coil / bracket assembly off the block tonight just to make sure the ground surface between the ICM base and the bracket was clean. It was a bit of a mess with aluminum oxide. Not the worst, but not my face look for sure. I cleaned that all off and reassembled it. Tried to stat it but it made no change. Didn't expect it to, but at least I took that out of the equation.

thanks again for posting those pages. Even though for a 2002, it's still helpful.

cheers all !!

 

[Colt Hero]

Like what is the "multi-way harness connector of the fuel injectors" . Is that the ICM connector Term P ?? the 80-pin clear PCM connector Term 24 ?? the 2-pin conn at the injector itself..? or the 8-pin connector that looks to come off the ICM right at the manifold on the pass side of the engine ??

I think that’s their all-encompassing term for the harness with all the connectors serpentining between the ICM, Injectors, and PCM. The “P” pin is the “Ignition 1” Voltage from the ICM driving the three Coils.

Good thought cleaning that ICM … wonder if that thing could be failed internally? Not sure yet…

 

[adm750]

I think that’s their all-encompassing term for the harness with all the connectors serpentining between the ICM, Injectors, and PCM. The “P” pin is the “Ignition 1” Voltage from the ICM driving the three Coils.

gotcha .....

Good thought cleaning that ICM … wonder if that thing could be failed internally? Not sure yet…

yeah, I'm leaning towards that actually since this was such a rapid failure with ZERO prior symptoms of anything. I want to root into the signals between it and the PCM that tell the PCM to be at the ready with those injectors...LOL. The ICM may not be giving the PCM the ok signal. I think I might just get the ICM from the yard I got the PCM from just to test. Cheap test for the money.

So far all I have in it is $35 for a used PCM and $200 to update/program both, $30 in a cam sensor that was solely replaced as a preventive measure and because it's cheap, and a bit of time (which my wife would value at $0.00 some days. LOL )

 

[Colt Hero]

yeah, I'm leaning towards that actually since this was such a rapid failure with ZERO prior symptoms of anything. I want to root into the signals between it and the PCM that tell the PCM to be at the ready with those injectors...LOL. The ICM may not be giving the PCM the ok signal. I think I might just get the ICM from the yard I got the PCM from just to test. Cheap test for the money.

So far all I have in it is $35 for a used PCM and $200 to update/program both, $30 in a cam sensor that was solely replaced as a preventive measure and because it's cheap, and a bit of time (which my wife would value at $0.00 some days. LOL )

Hmmm ... $216 for a brand new GM ICM at RockAuto ... but look at this ... a (brand new) Standard Motor Products (SMP) knockoff on closeout for $75 (1 left, same GM# 19245558)! Not sure if I'd trust it, though ... I've seen people Post about using off-brand replacement sensors and having issues (Equinox Forum). Seems like Electrical replacement parts are hit-and-miss ... if they're not ACDelco.

Seems like you're right on top of the problem, though. I'd keep going to try to avoid buying any more unnecessary parts. What about that TECH-2? Do you still have access to that?

Huh! I totally missed that link @Bill58 posted. I had watched the video instead ... which was "OK" ... but not as good as the information in that link!

More Information for STANDARD MOTOR PRODUCTS LX364T

 

[Brhatweed]

Well square-one isn't a bad place to be at this moment. The 20mv differential is not enough to be noticed, the fact you don't have any injectors firing is so with that have you checked for +12v on the injectors themselves? They are all fired via grounded collector and should have a steady +12v available from the pink wire on all the injectors thru the 15 amp FUEL INJ fuse located in the underhood box. Do you have the factory wiring diagram for the 3800 VIN-K cars? It is different than whats found in the Chiltons and other aftermarket DIY books.

 

[adm750]

@Colt Hero - thanks for the suggestion on Square-One's closeout ICM. I'd like to avoid buying things I don't need, but thought a cheap yard part might help me continue to rule out stuff.

I consent it's not the most logical way to approach it, but $30 is worth delaying me tearing the tape and corrugation off a bunch of harness sections looking for broken wires in the chance the output signal from it to the PCM is bad. 😂

Good idea - I will probably ping my friend for that Tech 2 this weekend. Why have 4th of July fun when you can doink around fiddling with non-running cars. haha.

@Brhatweed - I do have steady voltage at each individual injector connector. Just can get the PCM to ground them when it's supposed to. As the one-liner states, they are all at 'G' waiting on 'O'....

This is why I think I am missing that reference signal from the ICM ----> PCM that tells the PCM that firing the injectors is a GO. Just haven't figured out if there is an RPM limit that allows it to be created, or if it's supposed to be there when cranking, or at ignition on. Have not found that test yet. Maybe the Tech2 can see that ? Dunno at this point.

I do NOT have the factory wiring diagram for this model car. Which is rough because I had the full factory GM set for my k1500 truck and for the Vette. Their invaluable. I've searched on-line a very little bit, but my google-fu has been weak and poorly applied. Will dedicate some time to that this weekend as well.

thanks again for everyone's suggestions and help. virtual cheers/beers to all of you !!

 

[adm750]

Interesting find tonight.

I've checked all the inputs to the PCM and ICM from the crank and cam position sensors during my prior adventures with this issue. With the scanner reading engine RPM during cranking, I'm going to say all the input signals from those two sensors to the ICM and PCM are good (this is also based on the test plan Bill58 added and others I've found).

So I go to check all the wiring from the ICM outputs to the PCM for continuity with both the ICM and the PCM connectors disconnected from their respective modules. Checked were ICM terminals:
B to C1 BLUE 53
C to C1 BLUE 9
D to C1 BLUE 8
F to C1 BLUE 7
L to C1 BLUE 48

These all had continuity....so all good.

Next I checked the grounds (which I have verified before), but this time I am strictly isolating the harness by itself.

K to C1 BLUE 56 - good (and good to engine block)
K to C1 BLUE 57 - good (and good to engine block)
K to C1 BLUE 61 - open circuit (no continuity)
K to C1 BLUE 16 - good (and good to engine block)

As noted, they all had continuity EXCEPT for terminal K to C1 (Blue) terminal 61. Now, again, I checked these before and ruled them all out as an issue.

aw damn....I just rechecked the diagram....I was supposed to check terminal 60. I thought I was on to something. 🤣 🤣 🤣

*puts tools away, grabs bourbon and makes stiff drink....

Tomorrow is another day

 

[Colt Hero]

@adm750 : have you verified your CKP inputs at the ICM yet? If the ICM isn’t receiving these, then they’ll be no Injector Pulses.

Also, you can probably force the System to stay in Bypass Mode (with ICM in control) if you can block the IC Timing Signal output from the PCM to ICM (or maybe it’s never getting set to 5V anyway)!

UPDATE: looks like you snuck a Post in just ahead of me … you think your CKP and CMP signals are good … but what if the ICM is “seeing” it but just not using it? I think it’s in control of the Injectors during initial Cranking, correct?

If you had the TECH 2 you could see all the status signals in real-time. I think it would make everything very clear to you … what state the system is in …

I’m no mechanic, but I’m leaning toward a bad ICM.

 

[adm750]

@Colt Hero - ha..! yeah quite a post I put up till you get to the end, right...! LOL.

got your message also. totally respect the concern you noted in the content.

I talked with my guy that has the Tech2 and we discussed forcing the system into bypass mode, we just weren't sure how to pull that off. More learning ahead

 

[Colt Hero]

@Colt Hero - ha..! yeah quite a post I put up till you get to the end, right...! LOL.

got your message also. totally respect the concern you noted in the content.

I talked with my guy that has the Tech2 and we discussed forcing the system into bypass mode, we just weren't sure how to pull that off. More learning ahead

I think you just have to block the PCM’s output on the “IC Timing Signal”. The PCM sets it to 5V as soon as it’s ready to take over Injector Timing (and everything else). Until the ICM sees this input, it stays in “Bypass Mode”.

So … you could cut the wire, or block the pin (if that’s possible).

 

[adm750]

… and let me know when I can take that stuff down…

go for it....! I'm all set
thank you again...those were super helpful

I think you just have to block the PCM’s output on the “IC Timing Signal”. The PCM sets it to 5V as soon as it’s ready to take over Injector Timing (and everything else). Until the ICM sees this input, it stays in “Bypass Mode”.

So … you could cut the wire, or block the pin (if that’s possible).

am going to look into this
needed to edit -
so, rethinking what you said, I understood the ICM to control ignition timing only, and the PCM always controls the injectors regardless of mode.
Back in the day, this is how we would set base timing....by removing that 5V reference signal from the PCM/ECM. This even goes back to the OBD1 days.
Even if I were to keep it bypass mode, that would mean that the timing only is still being controlled by the ICM. Fuel is still being controlled by the PCM. (I could be wrong here so please correct me if so....)
I don't know the RPM figure the PCM must see to send that 5V reference to the ICM, but I think it's somewhere around 400+rpm (ie...just after start-up).

This is why I'm leaning towards that reference signal from the ICM to the PCM being absent (or corrupt) so the PCM would never see that the injectors were being called for. With the harness connections for those pathways (ICM --> PCM) being "good" this is leading me to believe I have a failed output from the ICM. Or there is an output value that is not right...something that I haven't quite figured out how to determine yet. This might be where that Tech2 comes into play.

thoughts ?

 

[Colt Hero]

@adm750 : Oops! You’re correct! PCM is controlling Injectors … using the “Low Resolution 3X Reference Input” from the ICM. ICM isn’t passing it to the PCM … quite possibly (even though it’s seeing it on the Input side)

And it’s 1200 RPM that the PCM is waiting for (to take over Spark Timing) … at least, according to my 2002 Shop Manual. Seems kind of high to me …

Some of the things the TECH 2 can display:

1.) Injector Circuit History & Status (OK/Low/High)
2.) Driver Module 1-4 Status
3.) Ignition 1 Signal
4.) Ignition Mode (Bypass/IC)
5.) 3X Crank Sensor
6.) 18X Crank Sensor
7.) CMP Sensor Signal Present
8.) Misfire Counts
9.) Engine Speed

… but maybe not proving communication of these things between Modules, though…

Question: The ICM gets both CKP inputs directly. One is called “Sensor 1” and the other is “Sensor 2”. I can’t find anywhere in the Shop Manual where it says which is the 3X and which is the 18X. And could these pulses be jumpered directly into the PCM as the “Low” and “Medium” Resolution Signals? Are they, in fact, the same Signals … just being passed through to the PCM?