1986 LS swap
Thread Starter
Racer
Joined: Aug 2007
Posts: 370
Likes: 6
1986 LS swap
Hi everyone, I’m in the process of ls swapping a lq9 in my 1986 and have some questions and hoping someone can help. I have searched on here and google and can’t find much. I want to retain my factory digital gauges and use the harness that came with my ls out of the 2003 Escalade. What do I need to do to make factory gauges work? I did find that I can by the sensor adaptors for oil pressure , temperature sensor but do I keep my original computer in the car to send this to dash or can I make the ls harness work with it and also what do I do for tach and speedo?
Pro
Joined: May 2025
Posts: 614
Likes: 147
From: OK
Wiring diagrams are you friend. I've LS'd a few GM vehicles of this era and other than the MPG readouts I suspect you can retain the oil temp and pressure and engine temp just by physically adapting the senders and wiring them as needed.
The ecu and gauge temp senders I know off hand are separate on an early 86, the oil pressure likely is as well but they tied it into the starting circuit such that it has to see 4psi or so from one sender to trigger the fuel pump or something
along those lines. It's all pretty straight fwd in the FSM. You need the manual for the car and the manual for the doner vehicle/harness or you're going to have a headache.
The ecu and gauge temp senders I know off hand are separate on an early 86, the oil pressure likely is as well but they tied it into the starting circuit such that it has to see 4psi or so from one sender to trigger the fuel pump or something
along those lines. It's all pretty straight fwd in the FSM. You need the manual for the car and the manual for the doner vehicle/harness or you're going to have a headache.
Intermediate
Joined: Jun 2018
Posts: 43
Likes: 16
I'm currently putting an LS6 into my 1986 C4 and the factory service manual is definitely your friend, bonus points if you get an actual hard copy with color wiring diagrams. Also I can confirm that the gauge cluster gauges are standalone from the ECM, So far I only have the oil pressure gauge hooked up but I also plan on running a coolant gauge probably in the upper rad hose with a coupler. Also your best bet is to either ditch the stock Escalade harness for an aftermarket one or prune it for just what's needed. Can't comment on transmission control for the car though as I'm running a T56 in mine, not an auto.
Melting Slicks
Joined: Mar 2002
Posts: 2,876
Likes: 764
From: Sligo PA
I swapped an LQ9 and a 4L80e in mine with a big Summit cam and TEA 243 heads. Basically making an iron block LS2 at 10.9:1 compression.
The best advice I can give you is to not use the factory gauges. I know you said you want to keep them. But it makes the swap much harder. Before you say for sure you want to keep the factory stuff take a look at some aftermarket options. Remember you can sell off the factory cluster to help offset the cost of new gauges.
The second thing I would recommend is to not use the 86 transmission. I'm assuming yours is an automatic. If it's a standard then skip this part. It's fairly easy to fit a 4L80e or a 4L60e in these cars. You just need to weld together a C beam adapter. Lots of threads here about how to make them. You just need to order a piece of 4 1/2" box steel that's around 1/4" thick. And again if you go that route you get to sell the old trans to help pay for the project.
I made a video a long time ago about how I did mine. I'll post a link. The video was back with my old Chinese gauges and the old exhaust. But you can see my other videos for updates to the car if you want.
The best advice I can give you is to not use the factory gauges. I know you said you want to keep them. But it makes the swap much harder. Before you say for sure you want to keep the factory stuff take a look at some aftermarket options. Remember you can sell off the factory cluster to help offset the cost of new gauges.
The second thing I would recommend is to not use the 86 transmission. I'm assuming yours is an automatic. If it's a standard then skip this part. It's fairly easy to fit a 4L80e or a 4L60e in these cars. You just need to weld together a C beam adapter. Lots of threads here about how to make them. You just need to order a piece of 4 1/2" box steel that's around 1/4" thick. And again if you go that route you get to sell the old trans to help pay for the project.
I made a video a long time ago about how I did mine. I'll post a link. The video was back with my old Chinese gauges and the old exhaust. But you can see my other videos for updates to the car if you want.
Intermediate
Joined: Jun 2018
Posts: 43
Likes: 16
I swapped an LQ9 and a 4L80e in mine with a big Summit cam and TEA 243 heads. Basically making an iron block LS2 at 10.9:1 compression.
The best advice I can give you is to not use the factory gauges. I know you said you want to keep them. But it makes the swap much harder. Before you say for sure you want to keep the factory stuff take a look at some aftermarket options. Remember you can sell off the factory cluster to help offset the cost of new gauges.
The second thing I would recommend is to not use the 86 transmission. I'm assuming yours is an automatic. If it's a standard then skip this part. It's fairly easy to fit a 4L80e or a 4L60e in these cars. You just need to weld together a C beam adapter. Lots of threads here about how to make them. You just need to order a piece of 4 1/2" box steel that's around 1/4" thick. And again if you go that route you get to sell the old trans to help pay for the project.
I made a video a long time ago about how I did mine. I'll post a link. The video was back with my old Chinese gauges and the old exhaust. But you can see my other videos for updates to the car if you want.
https://youtu.be/rDLhoTz5zjc?si=tQhWtFHfqcpxmEyP
The best advice I can give you is to not use the factory gauges. I know you said you want to keep them. But it makes the swap much harder. Before you say for sure you want to keep the factory stuff take a look at some aftermarket options. Remember you can sell off the factory cluster to help offset the cost of new gauges.
The second thing I would recommend is to not use the 86 transmission. I'm assuming yours is an automatic. If it's a standard then skip this part. It's fairly easy to fit a 4L80e or a 4L60e in these cars. You just need to weld together a C beam adapter. Lots of threads here about how to make them. You just need to order a piece of 4 1/2" box steel that's around 1/4" thick. And again if you go that route you get to sell the old trans to help pay for the project.
I made a video a long time ago about how I did mine. I'll post a link. The video was back with my old Chinese gauges and the old exhaust. But you can see my other videos for updates to the car if you want.
https://youtu.be/rDLhoTz5zjc?si=tQhWtFHfqcpxmEyP
Melting Slicks
Joined: Mar 2002
Posts: 2,876
Likes: 764
From: Sligo PA
Use a C6 Vette LS3 water pump. Then get ICT Billet spacers. This will give you two threaded ports for gauge sending units or a steam line.
You can put a sender on the passenger side. I think the ohm range of the LS temp sender is the same as the C4 's. I would try a LS temp sensor on the passenger side and see if it will run the gauge. If it won't you could add some resistors to the harness to get it in range.
You can put a sender on the passenger side. I think the ohm range of the LS temp sender is the same as the C4 's. I would try a LS temp sensor on the passenger side and see if it will run the gauge. If it won't you could add some resistors to the harness to get it in range.
Melting Slicks
Joined: Mar 2002
Posts: 2,876
Likes: 764
From: Sligo PA
That and you can get a reasonably low mileage 4L80e or 60e in a local salvage yard with a warranty for around $200. So if you do ever scatter the thing you can just grab another one.
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