Follow-up: My DB2 conversion, 96 K2500 burb - Sorry it is long
Hi Folks,
I feel compelled to follow-up and give back to a community that has helped me out. I am closing in on the conversion of my 96 K2500 Burb to a DB2 and feel I may be able to share some info and help someone challenged with the same.
I finally made the jump to rid myself of the DS4 when it left my wife, kids and dog stranded in traffic on a hot June day. I had done considerable research to learn the best avenue to go down, but ended up learning some other tid-bits I had not read about. I read Bobbie Martins excellent reference a dozen times, but chose to use a standalone TCI TCU after a referral from a guy I met at the Charlotte Autofair back in April. He had done many of these (95's) and had been successful with the TCI controller. The fact it was 4wd added the obvious concerns.
I wont go into detail regarding the tons of time t/sing this, trying different things, complaining to everyone and my dog and filing tech support notes at TCI. Here is what I found:
The weirdest thing is the fact the original wiring harness for the 4L80E definitely used the Transmission Output Speed Sensor (rear most sensor on the 4L80E, NOT THE T-CASE SENSOR) for the speed input. Now there are many folks MUCH smarter and more knowledgeable that me that told me this was not the case, but when I disconnect the plug that originally went into the TOSS, I loose the speedo. Nothing to do (surprising) with the t-case sensor, this is the rear most sensor on the trans. Now, that said, to make this even weirder, once I unhooked it, plugged the TCI "vehicle speed" wire (correct plug and everything) into the sensor, I got half speed on the TCI and no dashboard speedo signal. The trans would not shift correctly in this configuration, but the TCI literature said to use this sensor. There is indeed a reluctor in there, but it is 20 tooth. I have a photobucket folder with pictures of the signals I got off the sensors (T-case and TOSS) on my oscilloscope, and the TOSS is definitely half speed, and half tooth count. REALLY WEIRD! I really wish I understood this part.
I was able to find another connector that was tapped to the OEM harness that had the same type of connector shape as the TOSS, so I plugged in the TCI to that and it read correct speed. I plugged the original OEM plug back into the TOSS and it reads half speed and triggers the Anti-Lock backs due to the speed mismatch.
Since I used the DS4 fuel shut-off solenoid for triggering a relay that I use to feed the "run" signal (12V) to the DB2, what ended up happening is the relay would cut on/off because there was no APP signal and the CKP was showing the engine running. I could disconnect the CKP and it would not do this, but I wanted to use the CKP for my RPM signal to the TCI. So, I disassembled the APP (security torx bit needed and you have to twist off - by filing some flats onto it - the conical shaped not holding the accelerator pedal shaft onto the spring assembly of the APP) to remove the potentiometer set and the pedal bracket. I then fabricated a new mount for the APP so it would be two pieces, one that bolts to the floor, then allows the APP to bolt to it. THis put the center of rotation of the APP where the center of rotation of a standard cable pedal would be. I felt this was important. I then used a standard cable pedal and fabricated a lever arm that would pull the cable at the SAME rate as the APP turns and a normal cable pull would use.
I should have pictures included, but they are all in my Photobucket folder (http://s1048.photobucket.com/user/ro...n%20Conversion) here is a link to the pic of the APP: http://i1048.photobucket.com/albums/...n/DSCN1810.jpg
Hopefully that will work and you can navigate through the pics and see them all.
ANyway, this eliminated the "runaway" condition since the APP was not back in the circuit. I continued to try and use the TCI. I could not get the true speed to the dash and the TCI. I tried splitting the signal, that did nto work. I bought a Dakota Digital SGI-5 to "massage" the signal, still no luck. There were two issues in my opinion: 1. the dash reads half speed and 2. the TCI would never know I was in 4Lo and shift correctly. The true cure to the TCI is either use the TOSS and then it is insensitive to 4Lo, use the connector I found on top of the trans to drive the dash speedo, or TCI programs in a "4Lo" condition and I somehow split the t-case signal for both dash and TCI inputs. That said, I could also plug the OEM back to the TOSS and change my VSSB to accommodate 20 tooth.
I STILL FIND THIS REALLY STRANGE CAUSE I KNOW THIS IS HOW IT WAS ORIGINALLY SET-UP: USING THE TOSS.
Finally, Saturday, I realized it was just simply not going to work with the 4wd. I decided on a whim to plug the OEM harness completely back in and see what it would do. I did this with the exception of I plugged the OEM harness plug that was connected to the TOSS to the connector I cut off the harness.
Believe it or not, it works GREAT! The OEM PCM is now controlling the 4L80E perfectly.
The ONLY things I had to do to make this happen was:
1. Fabricate a reasonably convoluted pedal assembly - of which I will try and take more photos to it is a little clearer as to what I did. I can even take measurements if someone is truly interested.
2. Moved the plug that was connected to the TOSS up to a connector that was taped to the harness located on top of the transmission.
3. Fabricate a throttle bracket for my set-up (D/S A/C compressor and single t-stat) This is shown in the photobucket and I think I attached one here too.
4Lo works, she shifts like factory. If I hold the pedal down, she will hold off on shifts till about 2500/3000 rpm. If I am accelerating lightly, she will shift in the 15-1800 rpm range. You can hear it go though all the gears and even lock up the TC.
Now I will try and attach photos. Please feel free to let me know what you think. I am so happy to finally have it running close to right. And a BIG thanks to RustyK for what will soon become a new engine for this burb. I am going to keep it on the road as long as I possibly can, cause honestly, I can't think of any vehicle I could replace it with!
Neo
(the one with no knuckle skin left on either hand!)
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