Need help with 4l80E swap!!!

[blueburb]

Hi there, I am new to this forum and I am new to Chevys (mostly a Ford guy, GASP!). But I have a very nice 89 suburban with a tbi 350 and a TH400, and a complete 91 suburban (still a square body) with a tbi 350 and a 4l80e. I would love to swap the 4L80E from the 91 to the 89, what do I need to do to do this swap? I understand about crossmember and driveline differences, and I will just switch them from the 91, but what about wiring? Can I just take the ecm out of the 91 along with the wiring harness for the transmission? Or would I have to replace the entire vehicle harness? Is this a can of worms that I don't even want to open, or is it gonna be well worth the pain?

 

[marks86]

if I was you I would take the entire wiring harness from the 91, and I mean the entire harness, and swap it into your 89. If the 91 was a diesel then the 4l80e would have a separate computer(which I have for sale btw) but since its a gas motor the trans computer is built into the ECM of the truck

 

[MadOgre]

Is there a difference in the harness from ecm to ecm aside from the transmission?

 

[marks86]

Is there a difference in the harness from ecm to ecm aside from the transmission?

your asking from an 89 suburban to a 91 suburban?

 

[MadOgre]

YA the harness not the ecm.

 

[marks86]

YA the harness not the ecm.

sorry dude im confused. when you say harness I think of under the dash wiring like gauges etc, and when you say ECM I think of what controls the engine, but on these trucks its all connected together, I mean you can unplug engine harness to under dash harness, but it reality its all the same thing

 

[MadOgre]

Well I was thinking all he really needs to do is replace the ECM and add the transmission to ECM harness

 

[MadOgre]

But that only works if the harness to the engine is the same

 

[marks86]

you might be on to something, because I dont see why a 89 ecm would be different from a 91 ecm, Im not a TBI guy though hopefully someone will chime in, but if it is different hes gonna have hard time figure out why its not working, thats why I said just use the entire harness, electronic speedometer and all

 

[blueburb]

yeah it looks like the engine harness is the same to look at it. I know I will have to switch over to the electronic dash and harness, I just really don't wanna swap or splice the entire body harness

 

[marks86]

yeah it looks like the engine harness is the same to look at it. I know I will have to switch over to the electronic dash and harness, I just really don't wanna swap or splice the entire body harness

ive swapped a ton of harnesses, its really not that hard

 

[oneluckypops]

Ok hold on let me try to help you out here. Your wanting to swap a 4l80e in to an 89 suburban correct?

I am not sure what Transmission you have in the burb as of right now, but most likely either a TH350, or a 700R4. It doesn't really make a lot of differences neither of them are electronically controlled Transmissions.

you would need to change the engine/transmission harness, as well as the under dash harness to match up to the 91 burban ECM. Kind of goes with out saying you would also have to use the ECM from the 91 burb as well.

This type of swap is rather common and IMO pretty easy to do in later models that are originally equipped with 4l60e, but of course these are not square bodies.

Your looking at a lot of swapping in this situation, so IMO your probably not going to gain enough to go thru all the work involved.

 

[89Suburban]

OLP is in Da house

 

[bucket]

Your looking at a lot of swapping in this situation, so IMO your probably not going to gain enough to go thru all the work involved.

You really think so? He apparently has the complete donor, so besides the trans swap itself, it's just and engine and dash harness swap. No tracking down any parts and the body harness should stay. Seems time consuming, yet simple to me.

 

[MadOgre]

And a good working 4L80E is a big time improvement over a 700r4 or th350