Pcm ground

[Darrenmb]

Still working on my swap into the jag, thought I was ready to try to start it, turned key on, no fuel pump prime and no check engine light, I have 12 volts everywhere I am supposed to, however what about grounds? Where do the they come from? Just a quick glance on shoebox site. Shows 2 grounds on red pcm connector alone, where is the other end of those???? What am I missing????

[Darrenmb]

I see the ground wires by the coil.. is that all of them? Just two whites tied together and a black???

[Injuneer]

Remind us.... what year is the PCM and harness?

[Darrenmb]

Sorry, everything is from a 94 pontiac formula

[blkchevyz]

its down by the motor mount and starter.

[Injuneer]

See Shoebox’s photo of 94/95 harness. The black PCM ground has an eyelet to attach to the block as described above. It is bundled with the wire for the pass side O2 sensor, knock sensor, and purple starter wire.

http://shbox.com/1/harness.htm

http://shbox.com/1/harness3.jpg

[Darrenmb]

My post dissapeared... oh well, thank you guys, I know that wire is hooked up as it's one if last ones i did, however I put it on an Oil pan bolt as I had run out of spare bolts, wonder if thats my issue..

[Darrenmb]

Just an update, ground was fine, was the 12 switched ( pink wire ) was bad, had 12 volts, about an inch away from the connector and 2.7 volts at the connector, fixed that, now I get my check engine light and my fuel pump prime.. :) still wont start though but best I can tell that is fuel pressure related..

[Injuneer]

The PCM has 4 ground terminals. Two of them (A2, C32) have black/white wires that connect to the same large splice, where it joins grounds from:
- oil level sensor
- MAF sensor
- a single wire from another splice that includes:
— DLC connector
— theft deterrent module
— trans position switch (A4)
— fuel pump relay
— instrument cluster
— traction control switch

The above connects to ground G103, a stud on the block above the starter.

The other two terminals (A18, D1) have tan/white wires that connect to ground G102, the stud on the block below the driver side head that holds the ICM/coil bracket. That stud also has a black wire from a splice connecting grounds from:
- A/C compressor clutch
- ignition coil module
- O2 sensor, bank 1
- O2 sensor, bank 2.

There should also be a braided ground strap that connects to the driver side frame rail.

What's the code for the SES light?

[Darrenmb]

Ok, having issues with editing above post for spelling and autocorrect issues keeps telling me invalid page.. but whack is supposed to say eehack and other gobblygook word is check for spark... sorry, typing on phone

[Darrenmb]

Wow, my whole post is gone again... looks like the edit issue I am.having is actually deleting...

[Darrenmb]

Sorry, guess I said it wrong, I dont actually get an ses right, then ight comes on for bulb test when ignition is first turned on.
I have hooked up scan9495 and whack, I have no codes, however I am seeing no injector pulse width. Didnt check.dornapark as i ran out of daylight.
Internet can be a bit misleading as I have read in a couple of places that pcm need to see at least 4 psi to activate injectors etc, but from what I read on shoeboxes site, none of the connectors at pcm go to oil pressure sensor, I have an adapter screwed into op sensor port with jag sensor screwed in and the wire goes straight to the gauge. The original op wire ( tan) is tucked into the harness loom, so no big deal if I need to pull it out and hook it to something.
Other things I am reading are pointing to the opti, however I am pretty confident it's not the issue ( I could be wrong, wouldnt be the first time) as it was sent off to the optidoc guy on ebay and he refurbished it and sent video of it hooked up to oscilloscope and working..

Any further insight greatly appreciated

Thanks
Darren

[Darrenmb]

Kept hitting back and my post was still there that way, so copied and pasted, sorry if it's a duplicate now

[Darrenmb]

Additionally I am reading a vats issue, but pcm was tuned by Moe Bailey, supposed to have deleted vats, but I don't know how to double check that..

[Injuneer]

The 94/95 F-Body LT1 control does not have the low oil pressure interlock. The Corvette LT1 does.

What is the VATS issue? The PCM is looking for a 60Hz signal from the theft deterrent module (TDM). Doesn’t turn on the fuel system until it receives that signal. That requirement can be “programmed out”. Do you have DTC 46?

Do you have spark at the plugs? ...... at the coil wire? When the engine is cranking, does the tach needle move upwards 200-300 RPM? Did you interface the PCM signal with the Jag's tach?

Testing for Opti signals:

http://shbox.com/1/4th_gen_tech2.html#opti_test

Is the Opti possibly the second generation (95-97 F-Body) “vented” unit? That has a different socket for the harness connector, and doesn’t match the 93/94 “unvented” harness connector.

[Darrenmb]

I have no codes at all, (per scan94/95) , didnt get to check for spark as it was getting dark and I had no helper, that's on tonights checklist.
Only reason I mentioned vats was because I read that it can cause issue i am having, however like I said, it's supposed to be deleted in the tune. Is there a way to check for that?
I will also check the opti with the shoebox link, will post again when I have all that info.

Thanks for your time!

Darren

[Darrenmb]

Opti is 1st gen but was converted to vented by opticdoc.
Had no movement at all from tach, and yes I had to add a resistor and its tied into pcm output.

[Injuneer]

Ask Moe to confirm he deleted it. But if the PCM isn’t setting DTC 46 and you don’t have a TDM in the circuit, it sounds like it's been programmed out. How did you address the other part of the VATS system that runs the starter solenoid relay power through the TDM to the starter relay (TDR), so the TDM can verify the key resistance before it allows the starter to engage? I assume you just wired it to bypass, deleting the TDM.

As far as codes for the Opti pulse signals, if both high and low res pulses are missing, the PCM can’t set the DTC 16 code for the low res signal (the one required to allow the engine to start) because it has to count high res pulses to determine if the low res pulses are missing. Run the Shoebox checks.

[Darrenmb]

I simply brought the purple starter solenoid wire from the 4 wire black connector inside, back out and plugged onto existing jag starter relay. Do i need to add something else?

[Injuneer]

If it cranks the engine when you turn the key to “start” it’s done right.

[Darrenmb]

I am at work scanning shoeboxes site, and have yet another question... the dark blue wire that is labeled fuel enable thatbis supposed to be hooked to tdm... I am missing that wire altogether... is that ok? Or do I need to add it and connect it to something?
Sorry about so many questions, I'm just tired of my car being an garage ornament...

[Injuneer]

If you have a STOCK setup, when you put the key in the lock cylinder, and they key has the correct resistance, the theft deterrent module (TDM) passes 12 volts to the starter relay (TDR) so the starter can crank the engine. At the same time, the TDM sends a 60Hz square wave signal (called the “fuel enable signal”) to the PCM on the dark blue wire. The PCM will not turn on the injectors until it gets that signal

In your setup, you don’t have a TDM. So you connected 12 volts from the key in the “start” position directly to the starter relay. Then you had Moe delete the requirement for the fuel enable signal. If the PCM was not reprogrammed to delete the requirement or the fuel enable signal, you would have DTC 46.

The dark blue wire does not need to be connected to anything.

If the PCM is not receiving the low resolution pulse from the Opti, it will not turn on the injectors, and you will not have any spark.

[Darrenmb]

Didnt get home until late last night, got a few mins to do some tests before I ran out of daylight, its currently looking like the opti or its harness are the issue, more tests this afternoon ( time permitting), hoping it's just the harnesses

[Darrenmb]

Ok, it looks like all signs point to the opti, but before I pull it off, I have one more question..

The 4 wires to the opti, I have 5 volts 5 volts, 12 volts with key on, then on 4th wire, I have a good ground when key is off but when key on, it gets very weak! Is this normal? Or am.i dropping a ground??
Thanks in advance. Darren

[Injuneer]

Shoebox’s procedure emphasizes the D pin resistance is measured key OFF.

Follow up with the measurements at the ICM. The 1-4 volts AC on the white wire (pin B) is the key to determining if the Opti low resolution pulse is reaching the PCM and being sent to the ICM to fire the coil.

Testing the Opti harness with the connector off the Opti just tells you the wiring from the PCM to the Opti is good. To check for the actual pulse signals from the Opti itself, you have to reconnect the harness to the Opti. Then, if all you have is a multi-meter, rotate the Opti slowly, and measure the DC volts at terminal A and B. Easy to do if the Opti isn't installed. As the Opti rotates the voltage should switch back and forth between 0 volts and 5 volts. If you have access to an oscilloscope, you can observe the 0 to 5 volt square wave produced at pins A and B.

[Darrenmb]

Thanks, I pulled off the opti, so that test should be easy enough.

[Injuneer]

You will have to run a ground wire from the Opti case to the block.

[Darrenmb]

Thanks, glad you mentioned that or I would not have!

[Darrenmb]

Ok, I'm at a bit of a loss now, hooked up opti and spun by hand , fuel pump runs, Injectors clicking away... guess my multimeter just doesnt refresh quick enough to test for the pulses.. I do get the 10+ volts on the two wires ar icm, which shoebox says means wiring and coil.is good.. leads me to believe it's the icm? Is my reasoning sound??

[Injuneer]

Turn it SLOWLY. The low res circuit will produce 8 pulse for one revolution of the Opti. There are 4 varying space longer pulses, alternating with 4 short pulses. The high res circuit produces 360 tiny pulses for one rev of the Opti.

But if the PCM is pulsing the injectors as the Opti rotates, the PCM is receiving the low res pulse.

The key measurement at the ICM is the 1 to 4 AC volts on the white wire on pin B. That can be checked with the Opti installed and the starter cranking the engine.

Any decent auto parts store can test the ICM. They need to test it multiple times in sequence to make sure it gets hot. Heat soak can cause intermittent circuit problems.

Testing for 10+ volts at the ICM verifies the wiring, but not the coil itself.

http://shbox.com/1/coil_testing.jpg

[Darrenmb]

I have to be missing something.... new icm and coil, still no spark... think I need to double check my harness, something has to be awry somewhere...

[Injuneer]

Did you measure the AC voltage on the white wire to pin B of the ICM connector, as suggested in previous post?

[Darrenmb]

I did, I get the voltage when spinning opti by hand but cannot see it when ots on motor and using starter, tried with two multimeter, you still thinking its opti??

[Injuneer]

Are you saying that when you reinstalled the Opti, and tested for AC voltage on the white wire to pin B, there was no reading?

If the ICM is not getting that signal on the white wire to fire the coil, you aren't going to have any spark.

[Darrenmb]

That is what I am saying, however, when opti is not installed and spun by hand, i get 8, 4-5 volt spikes on the white wire per revolution and injectors pulse, and fuel pump runs... could it still be opti? Bad wiring? Thing that gets me is motor was running when pulled out of other vehicle... that in itself leads me to think I have something wired wrong.. but everything is per shoeboxes site and lt1 swap.. The opti guy on ebay said I can send it back and he will double check everything. Guess I should do that regardless at this point..

[Injuneer]

Still not clear in my mind.... guess old age is taking it's toll. When you had the Opti off, and spun it, you got the 5V DC pulse at the Opti harness, and injectors pulsed. The proves the Opti is producing the pulses, and the PCM is receiving them.

When you had the Opti off, did you also check the AC voltage on the white wire to the ICM?

At this point, the circuit for the white wire to the ICM is suspect. And you verified the DC volts on ICM connector pins A and D? And you verified the ground on pin C?

Note that the factory service manual, which is what Shoebox shows, shows the ICM pins in the order C - A - D - B. That is not the same order as on the connector, as Shoebox cautions in his writeup.

[Darrenmb]

You are following along well. Lol. I did take note of the acdb thing, noting the letters on the actual connector not the picture.. I will check the wires tonight if I get home early enough, car is still facing out in garage, hood opens backwards creating huge dark area in engine bay, as I have. O lights above the garage door area, oh well, will keep digging and post what I find, thank you for all your help, I swear I am not trying to monopolize your time! :)

[Darrenmb]

Oops, missed a question in your response, yes I tested white wire and had pulses while opti was off, and yes I checked for ground on c. You can see why I am pulling my hair out here!

[JOATMON]

Just a WAG but I went through all the same tests one time when mine just wouldn't start. After everything tested good I put in a spare coil I had and it fired right up. ????

[Injuneer]

Just a WAG but I went through all the same tests one time when mine just wouldn't start. After everything tested good I put in a spare coil I had and it fired right up. ????

He already swapped out the coil. But maybe the new one is defective.

Can't remember if I already posted this:

http://shbox.com/1/coil_testing.jpg

[Darrenmb]

Yes, you already posted that, everything looked good, I have been back through all the wiring and everything looks to be ok, no open wires, everything grounded as it should be. My current line of thinking is the pcm or opti. I put opti back on and tested again at icm and get 0.02 as the highest spike, however although i hear the injectors pulsing when spun by hand, when opti installed I obviously cant hear them due to starter cranking (i have no helper, wife wont even go in garage) but scan 9495 says I have no injector pulse width..
I will be sending opti back to the ebay guy as he will check it all out. Its currently my only option that doesnt involves throwing money at it...

[Darrenmb]

Ok small update, this time I hooked up laptop before anything else, and when cranking for first time I do have injector pulse width, but only for about 5 seconds then it goes away, inwould assume that's about when pcm sees a no start and cuts fuel.. but that's just an assumption..
Any feedback on that??

[Injuneer]

You keep mentioning the “pulse” and “spike” on the white wire. Have you ever actually measured the AC voltage with the engine cranking, as recommended several times?

[Darrenmb]

Yes, as mentioned in above post, ac volts while cranking are 0.02

[Darrenmb]

Sorry, hit send too soon.. 0.02 volts is as high as it goes which is why I said spike.

[Z28pr0jekt]

I didn't go back and read the whole thread but to confirm, the car isn't activating the security is it? I had an issue where the chip in my key was loose and sometimes when I went to start the car, the security light would activate and lock the ignition from activating for about 10-15 minutes.

[Darrenmb]

Vats is disabled in pcm, this is an engine swap into 83 jaguar.

[Injuneer]

At this point, it's beyond my ability to resolve. If you want to run a Scan9495 log showing the startup attempt, in .csv format, I'll see if there is anything in there that points to the problem.

[Darrenmb]

Thanks,, getting ready for a wedding now, will have to create the log tomorrow.

[Darrenmb]

I have emailed the file to you, assuming of course your listed email.here is still current

[Darrenmb]

I have been watching the playback a few times, is it normal of the 12 volts ignition to drop to zero while cranking?? Seens a bit odd..

[Darrenmb]

Another update.. I found that the circuit in had the 12 volt switched for pcm into inside car drops voltage when starter engaged, so I connected direct to battery and now no longer Drop to zero
Now I have a dtc 41 ignition control circuit open. The dropping of 12 volts explains why spinning opti by hand was giving me everything, but when cranking i had no pulsing at icm.. now to figure out the 41

[Darrenmb]

Shes alive!!! Whilst testing agin she fired up... scared the crap out of me.. open exaust.... lol

[Z28pr0jekt]

:) happy for you! I just want to tell Injuneer that I believe it is highly appreciated how much effort you put into and patience you have when working with people on situations like this!

[Injuneer]

Thanks for the positive feedback. Funny thing is, these issues are seldom the same, and every time I work on a new problem, like this one, I learn something new - win-win situation. In this case it has me thinking about the fact there are two sources each of battery 12V, switched 12V, and grounds. How is the PCM divided internally to utilize the dual circuits. Are there two “halves” to the controls?

And, the problem showed up in a scan of just a few seconds of cranking a non-starting engine. Never underestimate the power of a data log. Amazing what can be lurking in there.

[JOATMON]

Thanks for the positive feedback. Funny thing is, these issues are seldom the same, and every time I work on a new problem, like this one, I learn something new - win-win situation. In this case it has me thinking about the fact there are two sources each of battery 12V, switched 12V, and grounds. How is the PCM divided internally to utilize the dual circuits. Are there two “halves” to the controls?

And, the problem showed up in a scan of just a few seconds of cranking a non-starting engine. Never underestimate the power of a data log. Amazing what can be lurking in there.

Yes Sir, I think you are correct about the two halves in the early PCM's. I know a tuner who is pretty damned sharp who told me the LT1 PCM's are dinosaurs compared to the newer ones. When I was looking into some reading material to help me understand what he meant, I ran across this article which says alot. In the second paragraph it does indeed say that the early OBD1 PCM did have two processors referred to as Event and Time. See the link;
http://www.superchevy.com/how-to/0704gm-factory-pcms