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View Full Version : Follow-up: My DB2 conversion, 96 K2500 burb - Sorry it is long



neo
09-02-2013, 07:51
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/rosbrughjb/library/Suburban%20Conversion) here is a link to the pic of the APP: http://i1048.photobucket.com/albums/s376/rosbrughjb/Suburban%20Conversion/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!)

phantom309
09-02-2013, 14:09
IIRC,.. the 93 only 6.5 auto, had a stand alone trans controller that worked off a simple tps setup,.??

Robyn
09-02-2013, 16:32
Thank you for sharing.

This conversion has been tried by several with varying successes.

Keep us posted on how it does over the long haul.


Missy

benaustic
01-06-2015, 08:36
Neo- Thanks for taking the time with all this. I'm new here... working on a '96 K2500 w/6.5 td vin F. Bought it cheap not in running condition. Has rebuilt 4l80e and new torque converter, new ball joints, decent body and 125000 miles. No brainer, right? What could go wrong!

When I bought it I noticed a lot of spaghetti under the hood... wires running everywhere, but I thought... eh, no big deal. It's cheap enough.

Then I set in to figure out what was wrong with the motor... put a new starter on and a new fuel pump, primed her up and she started... haaaaarrrd. But, she ran. With lots of black smoke and no power. Discovered the wastegate was wired open. Went looking for the vacuum pump to hook up the vacuum line to the wastegate. There was no vacuum pump. Perplexed, I ordered one. Went to put it on and (please don't think less of me) that's when I noticed this motor didn't have a serpentine belt. It had 3 Vee belts. WTH?!

Turns out I have a 1996 K2500 with a P.O.S. 6.2 that some dummie thought would be better than a 6.5. I have no compression, but I have a new-ish turbo and a new DB2 pump... which means that I have a throttle cable instead of the fly-by-wire.

Fast forward. Today, I have a 2000 6.5 turbo vin F out of an Express van sitting in my shop. The old 6.2 will be out today. I'm going to switch my intake/exhaust etc to the new 6.5 but I'm discovering that the wiring is very different than what's under the hood of my truck.

Here's the bottom line: Do I swap out the DB4 with my old DB2 and use the throttle cable? Or do I find the right throttle for the truck?

Sorry for the long story. I'm just misery looking for good company.

Yukon6.2
01-06-2015, 19:14
Hi benustic
Welcome to the Page
Sounds like you have your hands full.And i believe you have a few more issues to deal with than you know.There is a diferance between the heads on your van engin and the one that is supposed to be in your truck.
You should start a thread of your own so you can get maximum exposure to your problems.All of which can be overcome once you get a direction to go.
I converted my truck to a manual pump this summer and have a bunch of the electronic stuff you may need,like throttle pedal ect.
If you can post some pic's of the engines you have and of the wiring that is left in the truck,the pumps ect.That will help for people to give you advice.
Thomas