tbi harness

[Fireman605]

building an 85 k20 I have an 1995 5.7 tbi with complete donor truck harness ecm etc. I absolutely stink at electrical type stuff can someone tell me what the engine absolutely has to have to run correctly and what I could possibly eliminate to clean up the engine compartment. Thanks for any help

 

[Crispy]

Off the top of the head I would say you need to keep the following circuits:

Coolant temp sensor
Fuel pump relay
Electronic spark control
O2 sensors
EGR (unless you are going custom tune to remove it)
MAP
VSS
TPS
IAT
You'll also need a proper fuel pump for the TBI

What are you doing for the trans?

I'm sure I missed some stuff but I suggest getting a wiring diagram and labeling what is what on the harness connectors. Then you can go about stripping the harness down to whats necessary for your swap.

 

[Fireman605]

Ive got a 700r4 with a constant pressure valve body, suburban fuel tank in between frame rails and new pump for the tbi

 

[Crispy]

Alright, so hopefully someone will correct me if I'm wrong but in 1995 trucks used 4L60Es so you will almost certainly have to use a custom chip burned or some sort of VSS solution (maybe be able to delete it all together in your application). If you're going custom I would suggest contacting Harris TBI. He was very helpful and offers a bunch of options and he can probably tell you what sensors can be deleted and can also bump up performance a bit.


You may also need to source the TV cable mount for the TBI unit so your 700 shifts properly. You should be able to yank that from any tbi truck from 87-92 unless theres still a provision on the later tbi units.

 

[Fireman605]

Ill give him a try, yeah ive already had a bracket made for the tv cable. I appreciate the help

 

[Crispy]

Good luck man, post up what you find out. I'm sure it'll be of help to someone in the future.

 

[1987 GMC Jimmy]

I’m thinking that if you got an ECM from a manual transmission truck, you wouldn’t need to worry about the transmission stuff. That being said, the manual transmission ECMs did not have integrated electronic spark control so that would add a problem for you unless your donor was a manual. It’s probably gonna be best to reburn the MEMCAL in your PCM to get rid of the transmission provisions. The spark control is integrated in automatic transmission trucks post-‘92 so you’re good there. I wonder if the PCM would accept the VSS signal from the Hall Effect module that’s hooked up to your cluster. That would make things easier, too.

Add IAC, CTS, TCC, to the above list. I don’t know how the TCC lockup is gonna go since the later PCM was designed to control more than just that, but a pinout diagram for the model number PCM you have will make things more clear for you.

 

[Fireman605]

87 Jimmy you just scared the crap out of me haha! Thanks for the info electrical stuff scares me to death

 

[4WDKC]

Pretty sure the hall effect sensor wont work or the ls swap guys wouldnt be buying all the 91 speedos, in the older systems you just set the trans values to 0 and its a manual..not sure how it would work with newer ecm. why not use the 4l60e?

 

[1987 GMC Jimmy]

Damn, I didn’t think of that, but it makes sense. The later PCMs are trickier to me than the earlier ECMs. It’d be pretty clear to me what would need to happen there.

87 Jimmy you just scared the crap out of me haha! Thanks for the info electrical stuff scares me to death

It’s not that bad, and you have to start somewhere. The later TBI stuff is definitely trickier than say the ‘87-‘91 stuff. I could tell you everything you needed to do then, but once they updated the computers later on, things got more complicated, and fewer people are as well informed about them.

 

[Daveo91Burb]

Have you joined Gearhead EFI forum yet? You should definitely check it out that site is a wealth of info. One of the main users there is Dave W - he programs/burns custom chips and also builds GM harnesses. His chips are much more tailored for your specific setup than Harris. Harris will ask you questions and then build a chip based on answers but that’s just the starting point for Dave W. The downside is you may have to get into the data logging business with an ALDL to USB cable and laptop but you’ll end up with a much better setup.