ECU and IGN wiring questions

[ravege]

Background, car has TT chip, SM reading direct off Powerlogger, no A/C and the non-lock trans has no 3rd/4th switch outputs.

ECU harness questions:
Can A8 and A9 (ALDL serial data and diagnostic test) be omitted from the harness?

Can D12 be omitted if TPS, IAT and Coolant Temp Sensor are grounded individually? (say to a ground block that the ECU has ground connections to)

Is the purpose of B10 to prevent the car from starting if not in P/N? Can this be omitted if left open, or would it have to be grounded to allow the car to start?

Can the grounds into A12, D1 and D10 be mapped to specific functionality (i.e., is D10 just a ground re-route to D12?)

How does D6 work? The ECM is presumably grounded to the motor, the O2 sensor is grounded to the motor, so why a separate ground to the motor from the ECM for the O2 sensor?

Can A2 and B8 (A/C Clutch control and A/C request) be omitted from the harness?

Is there a limit to how many sensors C14 (+5V) can support?

Ignition Module question:
Are the power outputs to the cam and crank sensors 10V? Using a 12V source will throw off their signal inputs?

Can the cam and crank sensors also use a ground block the Ignition module is grounded to and not use the Ignition module ground lines?

Thanks!

 

[GNVenom]

Background, car has TT chip, SM reading direct off Powerlogger, no A/C and the non-lock trans has no 3rd/4th switch outputs.

ECU harness questions:
Can A8 and A9 (ALDL serial data and diagnostic test) be omitted from the harness?

Can D12 be omitted if TPS, IAT and Coolant Temp Sensor are grounded individually? (say to a ground block that the ECU has ground connections to)
D12 must return to the ECM. It's the sensor return, potentially different than the engine ground.

Is the purpose of B10 to prevent the car from starting if not in P/N? Can this be omitted if left open, or would it have to be grounded to allow the car to start?
The PN switch has no effect on starting the engine. It's a housekeeping input to tell the chip when to apply highway fueling and timing, among other things.

Can the grounds into A12, D1 and D10 be mapped to specific functionality (i.e., is D10 just a ground re-route to D12?)
All electronic grounds must be terminated at the same point. If you daisy-chain the grounds, it may place an overload on the end of the chain being as the ECM outputs are mostly grounded signals.

How does D6 work? The ECM is presumably grounded to the motor, the O2 sensor is grounded to the motor, so why a separate ground to the motor from the ECM for the O2 sensor?
D6 is the O2 signal return, and must be attached to the electronics ground for the ECM to interpret the O2 signal properly.

Can A2 and B8 (A/C Clutch control and A/C request) be omitted from the harness?
Yes.

Is there a limit to how many sensors C14 (+5V) can support?
Yes, the 5 volt source is shared with the ECM logic chips and can be overloaded easily.

Ignition Module question:
Are the power outputs to the cam and crank sensors 10V? Using a 12V source will throw off their signal inputs?
The power source for the Cam and Crank sensors are taken from the module and are both filtered so they're slightly lower than the Vcc input. Don't use a 12 volt source.

Can the cam and crank sensors also use a ground block the Ignition module is grounded to and not use the Ignition module ground lines?
There is only one ignition ground, black/red, and again, it's the Ignition Reference ground. Must be attached to the ECM for proper ignition operation. The module case is grounded via bracketry holding the module to the engine block, which is necessary because the coils have outputs only, and need that return.

Thanks!

 

[ravege]

Thank you for taking time to answer my questions John!

"D12 must return to the ECM. It's the sensor return, potentially different than the engine ground."
And on stock nearly 30 year old harness, *probably* different than engine ground! But if starting from scratch, if I can literally trace new copper from each sensor to battery negative and new copper from ecm to battery negative, there should be no change in readings as far as the ecm is concerned, is what I'm trying to get at.

"All electronic grounds must be terminated at the same point. If you daisy-chain the grounds, it may place an overload on the end of the chain being as the ECM outputs are mostly grounded signals."
My line of thinking here was, for example, if one of those grounds was devoted to entirely say transmission or aldl lines which I planned on eliminating, than that ground would not be required.

"D6 is the O2 signal return, and must be attached to the electronics ground for the ECM to interpret the O2 signal properly."
Understood, but why not use a 2 wire sensor like the Coolant sensor or IAT? Just not available at the time? It's this pin in and the TPS/CTS/ATS ground pin that makes me ask what A12, D1, and D10 are for since D6 and D12 are explicitly spelled out.

"Yes, the 5 volt source is shared with the ECM logic chips and can be overloaded easily."
Yikes, what I was afraid of. Do you have an estimate of how many sensors can be spliced into this? I currently have MAP and Fuel Pressure senders tapped into this at the moment. As an alternative, what would you recommend if one wanted a +5V source for sensors that doesn't come from the ECM?

Ignition module ground: again, if the ignition module case, ECM and cam+crank sensors can all trace back via new copper to battery negative, are the interconnects needed? I'm looking at putting the ignition module inside the cabin near the ECM and having an amphenol connector to route everything through firewall. I want to minimize the number of wires that have to go through.