Second topic is the hole in the firewall. The computer (ECU) is installed in the passenger cabin, and there is a wiring harness that must go through the firewall to the engine compartment.
J20TBIharness.jpg
This is the harness laid out on the bench. The computer end is next to the gray box and blue connectors in the foreground. The engine end has three groups of branches - one group goes to the top of the engine and controls the injectors and reads the engine sensors for temperature, throttle position and manifold pressure, amongst others. The second group is much longer and goes to the vehicle speed sensor, starter trigger and 02 sensor. The last group manages power with some fuse holders and the fuel pump relay.
You want the middle part where everything is in the same bundle to go through the firewall. Howell gives you a grommet for the firewall and says to make a 1.5" diameter hole in the firewall. I did some tests to mock up what this firewall hole needs to be. MysticRob at IFSJA
https://forums.ifsja.org/forum/tire-kic ... -o-d-452-2 tells how he took the harness apart and carved away some of the fuel pump relay socket to make it all fit through the prescribed 1.5" hole.
My first test (on my mock-up) was to file a couple of notches in the 1.5" hole to clear the corners of the socket. This still did not give enough room for the "octopus" of the harness to pass through - I would need to take all the tape and split loom off of the harness, as did Rob, to make this work.
Instead, I went to a larger hole. McMaster-Carr offers a larger grommet for a 1.625" hole that has a 2" diameter and a 0.875" center hole for about $5
https://www.mcmaster.com/9600K222/ I found this will fit in a 1.75" hole, and everything will go through without a lot of dismantling of the harness.
Here's my mock-up in a panel I scrounged from a discarded dishwasher:
J20TBIharnessMockup.jpg
You need to pay attention to the order that you pass the various items through the hole: fuel pump relay socket first, then the fuse holders, the injector sockets, and so forth. The octopus will fit through the hole if you squish the split loom some and walk it through. I used my huge step drill, but a hole saw would work and is cheaper than the big bit. I split the grommet to fit over the harness.
J20TBIsmallerGrommet.jpg
This is the larger hole with the grommet that Howell supplies.
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