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TBI to TPI conversion

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77crewcab

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Okay been thinking about this for a while and have finally decided to do it. I am going to swap my 90 GMC burb to TPI. I will be using a MAP TPI, I have a harness from a 90 Trans Am and the burb has an electric speedo.

The big question comes in merging the two harnesses. Before when I had considered the swap it was to a vehicle with a cable speedo and I would use an adapter for the TPI ECM to get the right speed sensor input. As I understand the TBI uses the electric speedo sendor in the tranny to replace the speed sensor at the speedo guage.

Also the burb has an extra black box mounted to the brake master cylinder and it is wired into the TBI harness. What is this?

What am I looking at when it comes to combining the harnesses? Is there a company/reputable individual that can do the work for me?
 
You should be able to install the TPI wiring as a stand alone harness seperate from the rest of the truck. like you said, you will have to tie into the VSS somehow for the reference that the ECM will be looking for. Do you have to deal with emissions testing where you are? If not it would be easy.

These people were very helpful when i did a TPI conversion years ago, granted i went from a carbed blazer to TPI but still they were very helpful. Mark is who i dealt with back them. http://www.hotrodlane.cc/
 
No emissions to deal with. I have read that there is a way to re-pin the the tbi harness to the tpi harness connections and use the tpi ecm. just not sure if that is the right way to do it or if I should just use the tpi ecm/harness and merge in the dash harness part of the tbi. Other than the speedo and maybe cruise, what would be control in the dash on a 90 tbi? Any idea what the black box on the master is?
 
The only thing near the master cylinder that i'm aware of would be the anti lock brake controller that was optional starting in 1990. The link i posted above, somewhere (if they still offer it) have an intergrator harness to go from TBI to TPI without hacking any wiring. Just type TBI to TPI into the search and it will come up.
 
I see the article on the "interceptor" but no other mention of it on their site. I need to try and get ahold of detailed wiring diagrams for the 90 GMC burb with antilock and a 90 Trans Am GTA to compare them. You think I would have to change the actual speed sensor in the trans, or would it be the same signal for tbi and tpi?
 
I'm pretty sure it is the same reference signal. You might want to ask Dorian.

Ok, looking through their old catalog i found the integrator TPI harness with integrator box and it was 545.00. This is in a catalog that i believe to be from 2000. There is a footnote that you would also need to purchase the electric VSS if you're running a 700R4 with the integrator.
 
i have thought about doing this many times, but for me it wasnt worth it, but i also just swapped my truck to tbi, with the painless wiring and everything, thats probably why, but none the less im interested in this thread.
 
i bought a TPI system but never got around to installing it. post some pics when ur done. its an awesome set-up
 
Well it seems I'll have to swap the speed sensor since the VSS for the tbi is 2k ppm and the tpi requires 4k ppm. I think I am going to just merge the two harnesses rather than try to run it as a stand alone tpi. Anyone have any detailed wiring diagrams for a 90 GMC 5.7 tbi? Would it be possible to retain the abs with the tpi ecm? Or is it possible to remove the abs?
 
77crewcab said:
Also the burb has an extra black box mounted to the brake master cylinder and it is wired into the TBI harness. What is this?
Click to expand...


The ABS module isnt tied into the ECM.
If you cut the wire loom apart, the ECM and ABS should be seperate.

I would recommend against converting your current TBI harness.
And suggest you use the TPI harness and ECM...thats what I have done in the past and has always made the conversion easier.
 
I am thinking of using the tpi harness as the main harness and tie into the underdash harness of the burb for things like the speedo etc. and then work out what I need to do for the abs.

Odin have you converted a tbi to tpi. If so how did you deal with these issues?
 
Maybe. When I swapped the engine in to the burb the abs harness was bundled with the tbi harness so I assumed they were all connected. But under the dash there were the typical ecm plugs plus a couple extra plugs which I assumed just went to the guages and ALDL plug, but they could also be part of the abs system. I'll have to look more into it once I get the truck back from the tranny shop.
 
The DRAC on your truck should feed the right signal to the TPI ECM, just have to use the right terminal on the connector. Shouldn't be an issue.

Don't know much about the truck DRAC, but everything else GM used them in (Astro's, C/K's, etc) had multiple outputs, 2k, 4k, 128k, so even if it involved grabbing another DRAC it's not a big deal as they are all interchangeable in regards to the connectors AFAIK.
 
im finally going to do it found a camaro with a tpi setup w/maf, getting the whole car for 350 cus he dont have a title.
 
What year? Stay away from the '85's, and '88(?)+ needs a chip burn to even run to get around VATS.
 
i can wire in a resistor to get around that as well. but im not quite sure on the year yet, im not going to get it till this weekend, worse case scenario, i go get a junkyard computer
 
Has the resistor workaround ever been "published"? I know it shouldn't be that hard to workaround, but people act like some of this stuff will somehow give thieves a leg up, which it won't unless they've got hours to work on your vehicle.
 
So you are saying that the sendor can send different signals or that the ecm can read it differently. If so that would definatly make it easier. I am just curious what else the 90 trucks used that signal for if anything.
 
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