1992 Chevy P30

[boba]

I was pretty much just chasing down hunches and trying to verify the condition of things that may have been causing a problem, I don't know that the DRAC should draw any current with power connected or not, the output speed sensor will generate a AC voltage as it runs anyway - so that may be what really powers it up.
I'd found the UD and Harris tuning links the other day when looking, can't get the atracom link to work though. It would be nice to get an explanation of how the DRAC does it's job so I'd know what to look for.
I did use the Harris link to set jumpers on the DRAC I do have, the speedo has always read a little fast so it was worth doing and I'm curious to see if it makes a difference.
I honestly think this is going to end up being a 7060 with bad output drivers.
Nothing else makes sense to me after all I've looked over, the replacement ECU will be here early next week...and if it's the correct one I'll know more then.

[boba]

Replacement ECU showed up today, engine started right up & ran fine. Now for a road test & see if the trans will shift.
Edit - mixed success. Didn't work so well once I drove it, trans did shift which was a worry with an unknown PCM, but it still gave me an MIL after just a short time and idle rpm changed.
Looked through the driveability manual and found a reference to check the neutral switch, I did that and it was out of adjustment (how I don't know) but I reset it and things seemed to smooth out after that.
Took it out and ran errands in town all afternoon and it was fine in mixed driving, highway and in traffic. I was thinking once again it was good to go...and then it gave me another MIL and a high idle. (I've not been able to get a code out of this thing the whole time, when it goes bad I also get no-com with the scan tool.)
On the way out of town it went to neutral again but I was ready for it this time and got off the gas, the trans dropped back into gear without me having to stop this time and I got it back to camp Ok.
But I'm wondering if I've got a bad DRAC module and might be losing the VSS signal? To my mind that could do weird things to trans operation.
I can put a scope on it tomorrow and check a little further.
Pretty well frustrated with it for right now, but I'm not quite ready to give up on it just yet.

[MO LS Noobie]

Pretty well frustrated with it for right now, but I'm not quite ready to give up on it just yet.

Don't give up the fight. We're all pulling for you.

[In-Tech]

Hiya's
Have you tried the BAMM memcal? It's 3.73 vs your 4.10 rear end and probably a few other things. Once you lose scanner data stream, it means the eprom is no longer communicating. Those early 7060 memcals were notorious for pin problems.

[boba]

Thanks for the reply's - both.
@ In-Tech I'm running the BAMM now, It's on a Moates adapter with a custom prom for the trans from Sinister performance.
Honestly I had no idea what I was putting in there when I got it, but it works as well as the AWUM the rig came with, which is also the chip I had in the original ECU when these hicups started.
I didn't know there were pin problems with the memcal's, all I can say is I'm getting the same driveability weirdness with either one.
@MO LS - thanks for the support, I'm trying to get somebody to rocket-freight a DRAC (CBU 16124435 if anyone's interested) to me by Friday. (I need to be gone by Monday next week).
Reason being, I did the jumper re-calibration for tire size on the DRAC I have, and noticed it now "bumps" the speedometer needle at low speed, maybe related - one of the last times I drove it with with the old 7060 PCM the speedo needle flipped over all the way to the right.
My current working theory is that the trans going to neutral at 50~60 mph, the pulsing speedo needle at low speed, and the speedo flipping are all related, and all point to a bad DRAC. Also if the DRAC is passing 12v to an ECU pin that looks for a 5v square wave signal it could be the source of the electrical aneurysm this thing is having now.
I wish I could get an actual circuit board schematic for the DRAC, I'm thinking it may just have a bad diode and it's putting 12 volts to the ECU on the VSS input to the PCM.
I have diodes and a soldering iron.
I could fix that here and be done with this drama!
(sorry if my grammar and context are scrambled this morning, it's early and I'm pretty cranky over this...)

[In-Tech]

@ In-Tech I'm running the BAMM now, It's on a Moates adapter with a custom prom for the trans from Sinister performance.

First thing is get rid of that adapter and just try the memcal alone, Those are a HUGE failure point regardless of brand. Report back ;)

[boba]

I found and ordered a replacement DRAC, my testing approach today to start with will be to put my scope on both trans output speed and VSS input to see what I get.
Question on ditching the adapter though, you say the BAMM is for a 3.73 gear, so if I remove the adapter it will control the trans, I'll just be getting a different speed input?

[boba]

First thing is get rid of that adapter and just try the memcal alone, Those are a HUGE failure point regardless of brand. Report back ;)

I changed back to the original AWUM memcal, still had a MIL & low idle, re-seated the chip but didn't bottom it out in the receiver and it was suddenly all good.
I don't know what to think of this now, except it's going to be hard for me to trust it. I'd do more if I had a work environment where I could, but that isn't the case for me right now.
I should get the DRAC in a few days, I have no idea now if that will change anything.
Wasn't able to get any scope patterns out of the current DRAC today, but that might be my fault - I need some more working time with the scope I have.