4L80e stock controller vs. aftermarket

[GMCJason]

I'm looking to pick up a 4L80e out of a '91 3/4 ton truck and would also have access to the computer, wiring harness and whatever else I'd need. I have a few questions related to that.

First, if the price was right, and I think it will be, would it make sense to go with the stock computer? The truck had the 4L80e and a TBI 350. It's going into a '90 3/4 ton Sub that currently has a TBI 350 but will have a TBI 454. I already have the computer that came out of the truck with the 454 and it had a SM 465 so the computer in it had no transmission knowledge. The TCI controllers are about $700ish which isn't too bad but would it be better to use my TBI 454 and the aftermarket tranny computer or the stock?

If I go with the stock what all do I need? I've searched but don't really understand how the set up works. As I understand it with the gas engine I'll need the ECM from behind the glove box and would need to have a chip burned that would control both the 454 and the 4L80e. Also, I'm assuming there is a wiring harness that'll be necessary. Anything else?

Any other input would be most appreciated. Thanks for your expertise.

 

[1-ton]

If both of these trucks are second-gen body style V or R series trucks, then you should go with the entire ECM control and wire harness (if wire harness is needed) out of the truck with the 4L80E trans and TBI 350 eng. The ECM used to control a 350 engine in the V/R series trucks, is the same ECM used to control a 454 in a V/R series truck. I am not sure about third-gen body style K/C series trucks of that same year.

As far as burning chips, the chip you will be burning for increased engine performance with an aftermarket camshaft (I believe) only controls the engine, and not the trans (the trans has its own EPROM also located in the same ECM encasing).

The nice thing about the aftermarket wire harness and computer set-up is you can adjust the computer to when the trans overdrive kicks in. You are also free to go with an aftermarket fuel injection system, which comes with its own ECM for engine control, but this is a lot of money.

 

[GMCJason]

Thanks 1-ton. I assume that they are both V series but I'm not sure. My truck is a 1990 3/4 ton Suburban so I'm pretty sure it's a V2500 but the other is a 1991 3/4 ton pick-up with the IFS and newer body style. Is that a V or K? Either way is it compatible?

If I understand correctly the TBI and Transmission each have their own EPROM so if I had the computer from the transmission donor truck it would have the capacity to control the 4L80e and the TBI 454 assuming I had a chip for the latter, is that correct?

I should mention that the TBI 454 came from a 1988 1-ton dually crew cab pickup so that's the computer that I currently have for the 454.

Thanks again for your help. I never have understood how the computer works with the engine and transmission

 

[dyeager535]

Did we already discuss this before? if so, apologies.

So the '7747 ECM wasn't used in '90-91 R/V with the 700R4?

I know the '7747 won't control an electronic trans, so I was thinking there were two different ECM's based on transmission for those years.

IFS trucks are referred to as C/K for '88+.

 

[GMCJason]

There have been numerous discussions of 4L80e controllers but none that directly help me, so thanks for your input.

I had a '90 1/2 ton sub a while back that did have the '7747 ECM and a 700r4. My current truck is a '90 3/4 ton sub with the TH400 and honestly I haven't looked at the number. I suppose I should as I'm trying to sort this out. As I see it I have a number of options and I just don't know which are feasible and of those which would be the preferred method.

1. Use the existing ECM in my sub replacing the 350 chip with either the stock 454 chip or a custom one as a tune for the engine I end up with and using an aftermarket controller for the tranny.
2. Replace my ECM for that of the TBI 454 and use the aftermarket controller.
3. Get the ECM from the tranny donor truck and use it but either get a custom 454 tune or use the 454 chip I have and use the stock tranny chip. (this is where I get confused. Is it the same computer with two chips? Two computers? One computer with one chip controlling both? It sounds like the last one is the case from what 1-ton said.)

Is there another choice?

I guess the biggest question is if I had the ECM from the donor truck ('91 with TBI 350 and 4L80e) could I use it in my Sub and get a custom tune for the 454 and that particular ECM? I'm leaning toward yes but am not sure.

 

[dyeager535]

I think we need to narrow down the focus a bit, sort out the ECM difference (if any) then go from there.

If the '7747 was used '90-91, then you can't even consider a non-4L80E application. I know for a fact that a 1991 4L80E R/V ECM for a TBI app. is not a '7747.

I doubt there is anything in a 4L80E ECM that you can remove that deals with the transmission. On the ECM I had, it was externally identical to all the other GM OBD1 ECM's from 1981-1995 (or so) and with the PROM cover off, looked the same inside as well. Now that I think about it more, the PROM cover/opening MIGHT have been a larger size. I got rid of it though, so I can't look.

A TH400 has no use of a transmission controller, therefore I doubt it's anything other than the '7747. Just check it and see.

Number three is the general direction I would head. A 350 and 454 PROBABLY used the same ECM part number if they both had 4L80E's attached to them. You'd need to confirm this somewhere. (GM, Napa, etc) As I recall, the 454 uses a different TPS connector wiring setup, which may or may not translate to different wiring pinout at the ECM. But again, if the ECM part number is the same, the wiring will be the same at the ECM.

The PROM is (typically) the only difference when dealing with different engines, transmissions, etc., in roughly the same vehicle. Early 90's was a transition period, so there isn't going to be a one size fits all answer.

 

[1-ton]

If the '7747 was used '90-91, then you can't even consider a non-4L80E application. I know for a fact that a 1991 4L80E R/V ECM for a TBI app. is not a '7747.

Yes you are correct. The part # for the above mentioned truck is 7702. This ECM controles both a Big-Block and Small-Block with a 4L80E.

 

[dyeager535]

So along these lines, he'd *likely* need the '7702, with a 454 PROM. Still want to confirm wiring and what not, but I suspect there will be no differences on the ECM side.

I wonder what Brian at TBIchips.com says about the 4L80E controls, (shift points, timing, TCC, etc) and whether that is something he has messed with in the past.

 

[GMCJason]

OK, this is great stuff guys; I think it's starting to make sense.

So, a related question would be if I had the 350/4L80e ECM from the '91 truck could I use it as is in my '90 by replacing my ECM with it and my TH400 for the 4L80e. I don't see why it wouldn't work as long as the ECMs are a direct swap as far as wiring and the like. It would be an intermediate step and would essentially create the combo that's in the donor truck

If I did this, which is likely since it looks like the big block will come later, I could then just get a chip burned for my BBC specs for the '7702 ECM, correct?

Anybody have any comments on why I should do this over just using the TCI 4L80e stand-alone computer, other than cost?

 

[1-ton]

So, a related question would be if I had the 350/4L80e ECM from the '91 truck could I use it as is in my '90 by replacing my ECM with it and my TH400 for the 4L80e. I don't see why it wouldn't work as long as the ECMs are a direct swap as far as wiring and the like. It would be an intermediate step and would essentially create the combo that's in the donor truck

Yes, this would work. The only thing you need to do is make sure your Suburban's engine has the same sensor inputs (i.e. MAP, BARRO, O2, coolant, etc, etc) as the trucks engine you get the 4L80E from.