armybyrd

Truck balancer yes and the water pump is from an f-body with spacers to work with the truck balancer.

Steve85

Hey, I wasn't sure how to respond to your PM, I can't really follow, since we (ch@os and I) followed different paths on this part. Unfortunately I'm a forgetful SOB and never came back with this info to try and help. I did the swap 5 years ago and it was probably 3 years before that that I actually ditched the original ECM and wiring so I'm a bit foggy on the details.

WVZR1 may be right (usually is) about 88 vs 85 so I will talk in general. For an 85, there is no connection between the ECM and the digi-dash except one thing for "Avg MPG" (and I don't remember what that link was). I was able to take all wires from the ECM and remove them, all the MAF, injectors, coolant sensor wire, distributor, etc.

The new PCM (your truck PCM) will talk to different sensors, it has it's own injector and coil wiring, a separate coolant sensor it will monitor, etc.

I'm not sure if you've seen my project thread, link here:
https://www.corvetteforum.com/forums...mond-6spd.html

Post #42 starts getting into the wiring. While I did go with aftermarket, your approach should be similar. If you have a complete truck harness, there is no need to try and tap into the existing 88 engine harness. What the new PCM needs is mainly power and ground and access to certain ground circuits to turn things on/off. The PSI harness guide in my thread might help identify the key circuits for you and you'll need a pin-out chart for the new PCM.

We'll get you wired up, and hopefully keep all the smoke in the wires!

armybyrd

appreciate the input. I think I was most likely just overthinking it all. For some reason I had it in my head that certain wires from the L98 were needed to make the new ls engine run but now that I think about it that wouldn't make sense seeing how the truck harness is what was used to run the 5.3. I've been pretty busy with work and can't find my '88s electrical manual but hopefully the fsm has some useful schematics.

Mike Holmen

Just wanted to share some info with you. My car was having an O2 sensor fault and throwing codes into my Fast LS computer. I didn't have my newly installed alternator plugged in at that time. I'm using my 85 vette two wire alternator connector and the LS has a 4 wire connect. I'm using the GM 2005 corvette accessory front kit.

I ran the red wire into the number one and the other one uses a resistor into the third wire on the connector. The car voltage was dropping below 12 volts and throwing codes. The car was also popping/studdering thru the intake when I was free reving the engine. I can take a picture for you if you want.

I now have a steady 14.5 volts. The engine rev's up pretty cleanly now.

armybyrd

I've been way too busy working and commuting 60 miles but only have about a week left of that. Messing with my c-beam my holes were about an inch off so I'm thinking a d36's c-beam may work out for me. From what I've read the d36 c-beam is about 1-1.5 inches longer than the d44 c-beam. With that being said am I right in thinking it may work since that's about the distance my
holes are from lining up on the tranny end?

Mike Holmen

My car should be on the road this weekend, I just have to build a cold air intake for mine. Just finished up wiring in my autometer gauges last night.

armybyrd

I figured that's how it would be. Now I just need to get a good schematic of the '88 so I can see what wires are for the lights, heater and fan and remove all of the engine harness.
On another thought-where did you guys mount your pcms? The engine bay is already tight and I really don't want to put it above the battery.

Mike Holmen

Well my car still isn't a driver yet. My parts didn't come in for my air intake. I'm probably going to just red neck an intake till all my parts come in. I'm still tweaking my exhaust and finishing up my wiring.

I installed most of my relays for the fuel pump, radiator. I have to add coolant. Very close. I had one exhaust pipe sitting to low and adjusted it last night.

I've heard the engine run and it sounds good. I'm 60psi of fuel pressure, not sure on how much fuel your using.

Steve85

I wanted to put the PCM where the original one was but there just wasn't room so it ended up under the passenger seat.

Mike Holmen

My ecm is under the driver side head light. Where you guys running your relay's?

I've already added a bunch of fuel to my maps, as my engine didn't want to accelerate and pops a bunch. What timing you guys using? I'm 10 deg's at idle and 31 at 3500 rpm.

armybyrd

did you lay it flat? I thought about that but wasn't sure if there would be Enough room.
did your aftermarket harness replace all of the stock relays by the battery?

armybyrd

sounds simple but how did you get it to fit under the seat? Mines a power seat and doesn't seem like it has a chance of fitting.

Mike Holmen

Ya my ecms are laying flat. The fast ecms are smaller than the GM ecm.

I using one relay for the pusher fan and another for the fuel pump. I'm using the stock GM relay for the main fan. I'm also installing a over ride switch to turn on both fans.

I've installed alarm system and stereo system into my car. Most of the wiring is almost done. Just have to make some exhaust hangers and add some coolant.

I also need to install my lokar throttle cable, trans TV cable and cruise cable. Figure out a cold air intake. The build list to get the car to running state seems to never stop.

Armybrd, you get your turbo locations figured out?

armybyrd

Waiting on my C4 electrical manual to arrive.
In the meantime maybe someone can help me out with a few questions..
is the stock junction area needed for the lsx swap? Anyone know about the stock relays can be removed?

Mike Holmen

Which relays are you planning on removing? If you want you could reuse the factory relays. If your trying to figure out what the relay are for, you could just run a ground to the relay and see what turns on.

I'm going to run a manually switch to turn on my coolant fans from inside the car.

Armybrd, Have you run a new cable for the throttle yet? What a pain, had to remove half the dash to get that done.

armybyrd

going dbw. Waiting on my electrical manual and d36 c-beam to get here so I can move forward.

Mike Holmen

Hey armybrd, I've drove my bone stock LQ9 85 vette on the weekend. Works awesome. The power comes on stronger from idle all the way to 6000 rpm than my L98 ever did.

Been impressed on well the street manors are. Not sure if the car is better on fuel yet. I seem to have a heavier foot than I did with the L98 engine.

Steve85

Ah, yeah I got rid of the power seats.

As far as relays and junction box, I don't think there is a set answer.

It depends on what you have from the new engine and how you want to integrate. If I had to guess, that junction block goes to more than just engine harness and will have to remain. If those are fan and/or fuel relays, you can keep them and just tie the ground of the relay control circuit into the new PCM control circuit. That way (keeping the existing relays) all the wiring from the relay to the actual fan and fuel pump, power to the relays, etc. doesn't have to be redone.

Mike Holmen

I finally got a chance to put some 3/4 open throttle pulls in this weekend. I just can say is wow these LS motor's put out some decent power.

I can't even imagine what a turbo LS engine would do in a manual car. Probably just blow the tires off any time you start to put some power into it.

I'm running LQ9 (6.0 stock), headers, intake and 103 mm throttle body, 700r and dana 36 with 2.73 gears. My car pulls pretty decent from stop to 80 mph.

knikula

I think we need some video....