Putting a 99 5.3 into an old car. I’d like to keep the TH350 in the car, but am wondering how much of the 5.3’s A4 electronic transmission stuff I need to route to the PCM (and wire to “something” on the car) for the engine to start and run. I’d like to remove wires that I don’t need. I’ve read the LT1swap site and see what he shows can be removed for a non-elect trans, but wanted to ask those with experience.

For example, I know pin 34 gets a ground when in park/neutral, but I’m not sure that is required. The car already has a safety switch to inhibit the starter. Does pin 34 need a signal at all? I understand that’s how the computer knows it’s in gear or not, and thus may affect idle, but will the PCM allow starting if this isn’t grounded?

Is there anything in the programming I need to adjust so the engine/computer work well with the TH350 as obviously it won’t be getting all the signals back from the transmission that it expects. Will the computer get confused if all the settings in the PCM are for a elect A4 and it’s not getting anything back? Are there check engine things I must turn off too?

 

You can remove everything transmission related from the harness.
The park/neutral wire is the neutral safety. It can either be wired to a shifter, or disabled in the PCM.

 

It works fine without a pin 34 earth signal, as you said the PCM simply doesnt know if its in gear or not. The PCM doesnt control cranking (your already present safety switch does that) and without an earth to pin 34 ive found they start just fine.

That said, its not a bad idea for the PCM to know its in P/N or a gear, it does help with tuning (especially with cams and tight converters), so if you already have a working safety switch it wouldnt be too difficult to give pin 34 an earth should you need to, and can do this later on. With large cams the airflow requirements are quite different in P/N vs gear at idle, so when you pull it into gear it helps when the PCM knows whats going on and can apply the different settings, which can be tuned.

If you have access to a tuner like HP tuners you can set it to 'manual automatic' in the tune. But before this existed they ran fine with non elec. trans swaps even with the A4 wires/connectors just taped up and not being used... and it will also run with or without a speed signal input to the PCM. Removing them is fine but id leave the wire on pin 34 should you decide to use it later on.