where are you guys mounting your PCM? PSI Conversion harness with PCM

[paradigm]

I bought a 5.3 LM7 swapped 86 Monte Carlo SS, and the prior owner left all the wiring in the driver front fender area. The car is an incomplete project, still needs fans wired up, tachometer, speedometer, some other gauges, and not sure what else. The car runs and drives (though somewhat rough, and rich so it needs a tune at the very least).

The wiring and PCM were supplied by PSI Conversion. According to PSI Conversion a lot of the wiring should have been inside the cabin, underneath the passenger side dash / glovebox area circled in red on the image below.

I feel kind of inclined to leave the PCM wiring section of the harness in the engine bay becasue running it back into the intended area under the dash will either require me unplugging the rest of the engine harness to route it through the firewall from the interior, or having me cut a large enough hole in the firewall to route the PCM harness through.

Where do you guys mount your PCM? OBDII port? I would try to run the engine light back to the dash.

Currently how the engine wiring sits:

 

[Rt Jam]

If PSI Conversion said it's supposed to be inside the car. They would have made the wires long enough to reach inside. This is a big factor in determining where things get mounted when using a terminated harness.

Mine is a Holley Terminator Xmax. I ran all the wires through the factory 2" hole just behind the right front wheel and mounted my ECU under the glove box.

 

[64nailhead]

Inside the dash in the center under the radio. But it's alot easier if you don't have a radio.

Definitely not in the engine bay if you want it to be 'nice' appearing.

 

[paradigm]

If PSI Conversion said it's supposed to be inside the car. They would have made the wires long enough to reach inside. This is a big factor in determining where things get mounted when using a terminated harness.

Mine is a Holley Terminator Xmax. I ran all the wires through the factory 2" hole just behind the right front wheel and mounted my ECU under the glove box.



View attachment 248383View attachment 248384

That looks clean, I may end up going this route too and putting it in the car. I need to find the 2" hole in the firewall to see if I can pass the PCM connectors through, otherwise I will have to keep it in the engine bay if its too small.

 

[paradigm]

Anyone know if the LS PCM connectors can pass from inside the engine bay to the passenger compartment through the factory ECU harness hole behind the front passenger inner fender?
Also how hard is it to remove the front passenger inner fender?

 

[64nailhead]

You are not going to fit all of the wiring through the factory pass through. It is not large enough.

I’m using that for some auxiliary circuits, but the main harness will something twice the size of that at a minimum.

Are you keeping the factory HVAC operational?

 

[paradigm]

You are not going to fit all of the wiring through the factory pass through. It is not large enough.

I’m using that for some auxiliary circuits, but the main harness will something twice the size of that at a minimum.

Are you keeping the factory HVAC operational?

There is a factory heater box that I am hoping to keep operational. I was eventually looking to reinstall the factory A/C (Car was originally an AC car).

 

[64nailhead]

It’s difficult to get the wiring into the cab with all of the HVAC system in tact.

The best option is on the driver side below the master cylinder and toward the tunnel. Pretty much to the right of the throttle pedal looking at it from inside the car.

 

[ElkySS89]

I mounted the PCM where the battery is from the factory and moved the battery to the driver side. F-bodies had the PCM under the hood from the factory and rarely have issues so I don't see a problem with it.

 

[Rt Jam]

Not sure if all G bodies have this hole. This is a 2" hole where the ECU wires used to pass through on an 87 Grand National. On passenger side behind glove box.

With a Haltech 2" grommet I was able to fit all the wiring for a Holley Terminator X max plugs 4 power wires and 2 fuel pump wires.

At first I was convinced they all would not fit. Some connectors are huge. I passed the big stuff through first and stayed persistent and it all went through.