I have a holley single plane multi-port intake and 4 barrel throttle body. I want to use the GM 730 ecm to control it.
Should I spend the money for a 90-92 TPI harness and change the TPS connector for the TBI style. Since I still have to wire up my T56, should I go with one for a 5 speed car or Auto...or does it really matter?
Or....should I just rewire the stock TBI harness to accomodate 8 injectors, repin for a 730 ecm, and modify for T56 wiring?

 

If your existing harness is in good shape I'd just modify it. All you really need to do is splice in the injector harness from a TPI car to where the harness went for the TBI injectors, since they are both bank to bank systems. This is what the Edelbrock conversion Multipoint kit for trucks has you do. You also need to change the TPS connector as mentioned, but your should be able to just swap the pins into a new body, so you don't even have to cut a single wire.

As long as your PROM is setup for the stick then you will be fine. Otherwise it may throw a trans related trouble code. The wiring for the T56 is pretty basic anyway. I had TPIS burn me a chip when I swapped in my T56, and it works fine.

 

Its easier to modify the existing harness, if you know what you're doing. That's what my dad did on his 92 Camaro.

 

I've been going over schematics and I agree with you guys. Anestes just posted recently about it and his info seems to confirm what I've found so far. I didn't take into account the resistor for the tpi knock sensor though, so props to him.

 

This is the type of advice that gets people in trouble.

1) Edelbrock ships a new prom fro their truck TBI to MPFI kit.
The injector fire time, and firing methods will at least have to
be modified. Not to mention VE changes.

2) Edelbrock ships new injectors with the kit, which are most likely
low impedance. I don't believe the '746 has a high impedance
driver.

Modify the harness, run a '730.

-- Joe

 

I know Edelbrock ships you a new chip. I did the conversion on my Blazer. Obviously with this type of conversion you are going to need a custom chip, because you will effectively be running a custom setup.

The firing method for the injectors doesn't change. All you're doing is going from TBI to a bank to bank system, which is basically the same thing, just with more injectors. A TBI only fires one injector at a time, so now the computer just fires one bank at a time using the stock injector drivers. Everything else besides the wiring is handled with revisiosn to the tables & equations stored on the chip.

The Edelbrock system uses regular injectors, otherwise the stock ECU couldn't fire them. Low impedance injectors require a totally different injector driver (hardware on the computer board, not software in the chip). The only way you can make low impedance injectors work with a high impedance ECU is with a signal conversion box. I've seen them for Fords, but never for Chevys.

I already said the system would require a custom PROM, so I don't see how this is going to get anyone in trouble...

 

I double checked. TBI fires once every rev. TPI fires twice each rev. So the BPW and firing logic would have to be changed, ad min. All those calculations for a TBI setup would be incorrect for TPI.

TBI injector for '746 = low impedance sat injector. Wouldn't fire right, would burn out the injectors/or the driver. I think the edelbrock setup comes with an "injector adapter" which has some resistors and other things inthere.

And no you said "As long as your PROM is setup for the stick then you will be fine.". The mods to the prom will be very extensive, my guess.

-- Joe

 

Obviously the PROMs will be very different. My reference to the PROM being set up for the stick was specifically related to his question about the T56 swap. I assumed that he was going to have a custom PROM burned from the get go, and figured that he ought to know to tell them that he has converted the car from auto to stick so he won't get a trouble code. I had that problem after swapping in my T56.

It goes without saying that the VE tables, equations, constants, and other entires in the PROMs logic are going to be very different. I never said "just use the TBI PROM and it will work fine". You'd have to be an idiot to make an assumption like that, and I figured that since he was talking about modifying his wiring harness and repinning it for a different ECU that he would know that he needed a custom PROM from the beginning.

I know that the injectors in my truck's TBI weren't low impedance, because I talked about this with Edelbrock. I had to run a DFI system, because their chip wouldn't work with my system because I used a better cam and bottom end than their "performer package". My system made a lot more power than theirs. I just used their EFI conversion because it was the cheapest option to get multipoint EFI.

 

Whats obvious to you and I, is not obvious to everyone else. Sometimes you have to spell it out. Its better than having someone come back and saying they listened to you, and everyone went wrong, and you gave bad advice.

Doing some basic searches on here, I find they they are low impednance peak and hold injectors. Perhaps the Edelbrock guy was a phone guy, and not a mechanic? I dunno. I know edelbrock ships an injector adapter with their kit. I dunno whats in it. I'm not a edelbrock, or a TBI expert. But I have more confidence in this *not* working, than working.

Besides, if your running MPFI, just run '730 like I stated above. I did a writeup a few days ago on repinning the harness. The '730 is a nice setup to tune, if you use tunercat it has online help, and a lot of the guys in diy_prom are running '730 setups.

If he manages to get this thing working with the '746, with some hacks and custom tuning, he's gonna get hardly any help from anyone - cuz noones using that code for a MPFI application. I doubt edelbrock is gonna give him tuning advice.

-- Joe

 

Yeah, I could have been clearer about the PROM issue. I don't like coming off as condescending, and I figured that he alaready knew that.

Well, it wouldn't suprsie me if the Edelbrock guy either lied to me or didn't know what he was talking about, because I was lied to about a bunch of things regarding the conversion. First, they said it would work with either old or new style heads. This was a lie, and I had to get the manifold altered for my old style heads. Second, they said they custom made chips to suit your individual engine. Lie, they make two chips. One for a stock engine, and the other for one with their performer heads and cam.

I never received any kind of "injector adapter", and the contents list didn't mention one. The kit I bought is to convert TBI trucks to Multi-point. It wasn't their Pro-Flow complete package EFI.

I never said he should stick with his stock ECU either. I always assumed he has going to repin for the 730, as he stated initially. I think it's a great idea.

 

If you still have the truck, you should try and copy the prom for us and post it. Even though its a '747, we can do a compare to a stock '747 truck prom and get an idea of how extensively it was changed. I still wouldn't recommend going this route for the reasons I listed before, but for the sake of education I'm sure some people would be curious.

-- Joe

 

I've still got the truck, and the stock PROM that came out of it, as well as the Edelbrock one. How would I go about copying it? I don't know much about chip burning and such, so I may not have the ability to do so.

 

You would need a prom burner. .SO I guess thats a no.

 

Yeah, I never got into burning my own PROMs. I usually convert to user programmable EFI, so I can just use my laptop.

Eventually I'll be doing that to my truck, at which point the chips will serve me very little use. If I send them to you can you see what makes them tick? If you I'll PM you when I no longer need them.

 

I already decided that I was gonna use a 730 ecm before I made the post. I assumed it was the clear cause that's the common one to use. With all the great advice available here and on the web, I've decided to get into doing my own proms. But that's another obstacle and I not to that point yet.