LQ4 into a 3rd Gen/1972 Nova
on a plane to Germany. Need to try new PCM when I get back
I've been procrastinating making a how-to instruction on my mini-tub. I did take pics of everything.
I essentially cut all the way thru the framerail, leaving about 1/4" of thickness left, or about 1/8" gap between the inside of the inner frame rail vertical wall and the backside of where the reinforcement gusset plate wall would end up. I can't find the photos on my phone so will check my desktop when I get home tonight.



What a good buddy, Mark came by to help out..

The MAP sensor on the harness side wasn't getting a ground, so I checked all engine/body/PCM grounds and found this block-to-subframe ground that I had "soldered", at least so I thought..

After verifying all hard grounds were good, the MAP plug was still not getting a ground, giving the PCM (as read thru HPTuners) an inconsistent signal and more often than not a max-MAP reading regardless of all other conditions. This (I'm hoping) is the reason for why the injector pulse width was maxed out for cranking, and was flooding the cylinders so bad that the plugs were dripping wet and wouldn't even spark.
I've always had a suspicion that my PCM has voodoo devils of fuckitude in it, and so cracked it open..

Found this guy. Again, supposed to be soldered but it obviously isn't. Conveniently, it's the ground reference pin for the MAP sensor plug..

Investigating the plug pins, found some more screwy stuff. All pins that are pushed out/charred are for PCM grounds. I think there was a weird back charge early on that fried the ground pin connections, so that during one of the several times that I unplugged/re-plugged the harness-PCM plugs, the pins wouldn't re-insert in the plugs and got pushed out..


Adding to this, when I check ground connectivity when HPTuners is linked up, and force-on the MIL light, the output pin does not get a ground, so I'm just going to junk this PCM and start over. Hopefully that allows it to start, as well as fixes my no-TACH-output, no-speedo-output, and no-MIL-light-ouput from the PCM.
I found a known-good PCM locally and am going to try to run it as-is, not flashed, this weekend, to see if it gives a correct injector pulse width during start-up cranking. Also going to check all the harness plug pins and re-pin the charred ground ones from the spare truck harness I have lying around. If HPtuners reads a correct (for stock truck tune) cranking injector pulse width, then I'll buy extra HPtuners credits, load my last known-good tune onto it, and hope for the best. Wish me luck.
Last edited by frojoe; Jul 3, 2013 at 12:58 PM.
The Best V8 Stories One Small Block at Time
99% most likely would have never found that PCM Issue..
Good work on the problem isolation, Hope a another PCM is the fix !
BC
If you mean swap, here is the link to the pdf..
https://ls1tech.com/forums/attachmen...osts-tally.pdf
Here's my parts list for the CAR..






