Question 98 5.7 vortec swap to LM7 5.3l need wiring help

I'm having trouble finding exactly what wiring is required for the modified LM7 harness to swap into a 98 sierra with a 5.7 vortec.
I have followed lt1 swap's guide and removed all the emmisions etc. I'm keeping the 98's 4l60e so those wires are staying.

-will I have to make up an obdII connection for the LM7 ecu?
-what other modifications will i have to make to the LM7's wiring harness?
-what can i remove from the 98 vortec wiring harness?
-is there anyway to use the LM7 a/c compressor?

I also need some help with deciding on which water-meth injection to get. It's going to be a turbo-ed engine and it should make about 650hp. I'm not sure how many cc's I should be looking for in a kit. I'm not looking at spending alot on the kit either.

Any help would be greatly appreciated. Thanks

LT1swap.com Plenty of wiring info. Or you can do what I am planning on doing which is using my stock harness to run my LQ4.

Been lurking since 09 and I finally have my kickass 6.0 LQ4


There are a lot of videos on youtube about de-pinning the main plugs for the PCM which will make it a whole lot easier to do the harness swap. Follow the diagrams carefully on LT1swap.com and you cant go wrong.

Been lurking since 09 and I finally have my kickass 6.0 LQ4


I am certainly no expert on this, but will the 98 fuel pump handle the required pressure of the later engine? You may have to run the later pump, which would mean running that off the later computer. I think you will need the obd11 wired to suit the newer engine also, as you will be reading codes from the new engine.

1978 C20 short bed pickup, GEN111, 4L60E trans.

The '98 fuel pump is more than up to the task for a stock engine. The fuel pump relay can also be used but must get it's actuating power from the new PCM. I found this out by mistake. I used my existing relay/computer and when I started the engine, it died in about 10 seconds. Turns out, the old PCM would power the relay and the system would prime for start. After it started, the old computer powering the relay didn't "see" any information coming from the engine(crank signal, rpm, etc), so it would de-engergize the relay. I simply used the fuel pump relay wire from the new PCM to energize the existing relay. It worked like a charm.

Your new PCM should power the alternator, but I would retain the existing battery idiot light wire(if equipped).

As for keeping things simple as possible, you need to power the new PCM. You will also need to get it flashed to remove the VATS(Vehicle Anti Theft System).
You need to retain all your wires for the instruments(oil pressure, voltage, rpm, water temp,).

As for soldering connections, there will be some of that required. I don't rely on crimped and taped connections on something that I will be driving. Nothing is worse that being stranded somewhere due to a loose connection. Solder them and shrink wrap them.

Not sure if you can use the LS type compressor in these trucks. I read something about it and it requires frame notching.

Since you already have an OBDII system, only one wire is required to run to the new PCM. This way you can read any codes that may pop up.

Last edited by Mickeymotormount; 03-10-2013 at 07:26 AM.

'93 Chevy 1500 4X4 ECLB with a '99 Silverado LQ4 6.0 and '99 Escalade 4L60E. SOLD IT!!

New toy: 2001 2500 HD 4X4 Extended Cab Long Bed

John

By using the original fuel pump relay, alot of your wiring is already in place. Simply remove the actuating wire coming from the old PCM(ECU), and attach the fuel pump relay wire from the new PCM in it's place.

Reflashing of the computer requires special software. Not sure what's involved, but I sent mine to Brendan Patton on LT1swap.com. Turnaround time was about 1-1/2 weeks. He'll need to know everything about your truck, from tire size to transmission used to gear ratio. He can also program to actuate electric fans if the original donor vehicle did not have them. Cost was $75 and shipping to him. His shipping is included with the cost.

http://lt1swap.com/programming.htm

Nelson also provides these services and can also modify the programming for engine modifications. Since my engine is stock, I did not need any additional programming.

The single wire for the OBDII is only to read codes that may come up.
Reflashing of the old PCM is not required. I don't think the the old PCM is required at all. I still have mine but it is not used for any of the functions of vehicle running or driving.

The PCM wire for OBDII may depend on what year harness/engine you're using.
http://lt1swap.com/wiringharness.htm

Last edited by Mickeymotormount; 03-10-2013 at 03:05 PM.

'93 Chevy 1500 4X4 ECLB with a '99 Silverado LQ4 6.0 and '99 Escalade 4L60E. SOLD IT!!

New toy: 2001 2500 HD 4X4 Extended Cab Long Bed

John

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Source: http://www.ls1truck.com/forums/lsx-truck-conversions/45620-98-5-7-vortec-swap-lm7-5-3l-need-wiring-help-5Array.html