OBD 1 to OBD 2 comp and drivetrain swap

95SleeperAcheiva · 11-13-2008, 02:15 PM

OK! I'm down to 2 wires. This is probably a stupid question, but i thought i'd ask anyway. I think I've 2nd geussed myself 50 dozen times through this whole thing.

Oil Pressure and Coolant temp gauge sending wires.

On OBD 1 they go from sending unit to gauge, directly. They read via Ohms.

On OBD 2 they go from sending unit to body control module, then to gauge. They also read by ohms, appeears to be same sending units.

Gauges are OBD 1 chassis original.

Question:
Can I just wire the gauge to sending unit wire back into the new harness and sending unit? This won't hurt the info going back to the new OBD2 comp right?

IsaacHayes · 11-13-2008, 05:49 PM

If your gauges are obd1, just wire the sensor to them like it was before. The ECM might throw a code looking for that info however. Depends if the ECM has a 2nd input for CTS like the 3 wire ones or not. I dont know much about BCMs and how they interface with the ECM. But it wont hurt anything not having the inputs going to it and right to the cluster like before. It just may cause check engine lights or somethign but wont fry anything.

95SleeperAcheiva · 11-14-2008, 12:34 PM

thanks isaac, I'm just going to splice into the wire so it will still be communicating with the ecu, I'll go try that now, might still be a few days before i have an answer, I got to still run fuel lines, heater hoses, put the axles in, radiator, fans, fluids, and mount the new ecu, obd2 fuse/relay box, and make heat shield for it, cause the harness wouldn't reach for me to extend into the cabin, and i didn't feel like extending it, so they getting mounted on the firewall, plus, hope the battery still fits and get the air filter box mounted in there somewhere.

IsaacHayes · 11-14-2008, 08:33 PM

Splicing into it will result in incorrect readings. The CTS for sure, probably the OPSU as well. They need dedicated sensors, or it will read wrong from the resistance it measures. Probably read half as much resistance or something.

Get the 3 wire CTS. One runs to the gauges, and one runs to the ECM and ground. Run the OPSU to the gauges and see how the ECM reacts. It may not start or something without an OPSU signal. You'd have to open up the ECM in tuning software and see wha ttrouble codes/etc it has.

The_Raven · 11-14-2008, 08:49 PM

Quote:

Originally Posted by IsaacHayes

Splicing into it will result in incorrect readings. The CTS for sure, probably the OPSU as well. They need dedicated sensors, or it will read wrong from the resistance it measures. Probably read half as much resistance or something.

Doubtful.

The imput impedance on both the ECM and the gauges is high enough that there shouldn't be any change is readings. If there is it would be very slight.

I've read of a few people using a 2 wire CTS and splicing both the ECM and gauge to the same output connector of the CTS.

It's not a perfect way, but I can see it working.

IsaacHayes · 11-14-2008, 11:01 PM

Then how come MS can't share the CTS with a stock ECM? I wonder if it makes a slight enough difference in the reading to cause a bigger problem.

The_Raven · 11-15-2008, 03:16 PM

Quote:

Originally Posted by IsaacHayes

Then how come MS can't share the CTS with a stock ECM? I wonder if it makes a slight enough difference in the reading to cause a bigger problem.

The input impedance on the MS might be too low, and causes problems with the OEM ECM, when used in a piggy back scheme.

Personally I've not found the MS to be a very highly thought out unit, and has plenty of shortcomings, this being one of them, isolation of the inputs.