7060 PCM - - DRAC is Current Sensor

[b65cuda]

I have an intermittent issue that come and goes with ignition cycle. When reading live data ($85, A138) if the "DRAC is Current Sensor" = No/Magnetic, then my PCM reads the vehicle speed and the TOSS as about 1/2 causing it to

1)Shift at very high RPM and
2)Think the TISS/TOSS ratio is >4 and maxes out line pressure causing hard shifts.

On the rare occasion that DRAC is Current Sensor = Yes, TISS/TOSS and ratio read correct, pcm vehicle speed seems correct (a little lower than speedo like 40 vs 45).

The speedo always looks good.

Looking at o-scope signals
The AC signals from TISS, TOSS, and VSS look good and freq/amplitude tracks with speed.
The DRAC to PCM signal look like a clean sq wave at 5v that freqency tracs with speed.

So how does the PCM decide to use the drac or not, and when it decides no and uses magnetic, why does it seem to half all of the values of the TOSS and vehicle speed?

Appreciate any insight anyone might have, or any other troubleshooting steps I might be able to take.

Thanks,

Tony

[dave w]

I'm unable to answer the question; "how does the PCM decide to use the drac or not, and when it decides no and uses magnetic".

One would expect the .bin file "Switches" to define DRAC or Magnetic. Possibly the DRAC or Magnetic option is an undefined parameter?

The 7060 uses two different definition files, $85 & $D8.

http://www.gearhead-efi.com/Fuel-Inj...Information-85

http://www.gearhead-efi.com/Fuel-Inj...erceeded-to-D8

I've noticed $D8 .bin files error codes 24 (Vehicle Speed Diagonostic), 72 (Output Speed Loss Diagonostic), and 74 (Input Speed Sensor Diagonostic) are not selected or enabled.

It appears $D8 definitions start with Letter "B" and $85 definitions start with "A".
Example $85 "AWYN"
Example $D8 "BAJW"

I'm left wondering why $85 was superseded with $D8

[b65cuda]

I decided to pull the PCM out. Once the cover was off, i saw a memcal adapter and chip labeled AXXZ from The Turbo Shop, INC. Removed it and just installed the original AWBP memcal alone and so far so good. It was an intermittent issue, so I won't know for sure until I get a few drives on her.

[dave w]

I decided to pull the PCM out. Once the cover was off, i saw a memcal adapter and chip labeled AXXZ from The Turbo Shop, INC. Removed it and just installed the original AWBP memcal alone and so far so good. It was an intermittent issue, so I won't know for sure until I get a few drives on her.

It appears AWBP has been superseded AWBP --> AXXZ ---> BAJW ----> BDPN

I attached a Read Original BDPN .bin ($D8) from my library.

AWBP 01.JPG

AXXZ.JPG

BAJW.JPG

BDPN.JPG

[b65cuda]

Well, it came back so it is still intermittent. The "DRAC is current sensor" isn't set in the bin, but it sets right after the vehicle starts moving. It's like it looks for a signal and sets it if it exists. It doesn't check again until you cycle the ignition and drive again.

The PCM supplies 5v to the drac and the drac switches to ground at the same frequency as the VSS. The VSS being a sine wave that increases in amplitude and frequency with speed and the drac being a 5v square wave that matches the VSS frequency.

I've hooked the o-scope up to both VSS and drac and always see the expected results. I hate just replacing parts, but without being able to see or know what the computers logic is for setting that flag, I don't know what else I can do. Everything else seems to be working.

I'm studying a hacked bin and it looks like it has a timer to switch between magnetic and drac and look for valid input. Once it finds a valid input, it sets that as the vss to use.

So now I am thinking that sometime in its past someone hooked up too many speed sensors. I have found a lot of conflicting information for this model suburban. I have both TISS and TOSS as well as a Transfer case VSS. Maybe the TOSS was never hooked up from the factory? I'll have to try and unplug it and see what happens.

[dave w]

The $D8 definition file I use is from TunerCats, which does not have a defined Constant for DRAC vs. Magnetic.

Possibly TunerCats can provide an updated $D8 definition file with a defined Constant for DRAC vs. Magnetic?

Recently TunerCats helped me with an updated $4E definition which now defines parameters for Air Diverter.

TunerCats is not freeware.