jrmotorsports55

iTrader: (9)

Searched and have not found the answer for sure. I'm re-installing my lc1 (both grounds currently wired to ground stud on engine), as I have read that it is best to run the sensor ground at the ecu. From what I can tell, on a 96 it is the black wire with blue stripe (connector 3, pin O). Can someone please confirm this?

Thanks,

Jason

Joe Perez

iTrader: (8)

This is correct. Black / Blue at 3O is the analog sensor ground for a '96-'97.

jrmotorsports55

iTrader: (9)

Cool, thanks. I'll get it rewired.

Jason

jnshk

A few related questions:

I'm preparing to improve my wiring some before I install the ms3pro in my '97 and I'm trying to double-check all of my connections. One thing that was confusing me is the sensor return on the factory schematic. The schematic shows all of the sensor grounds joined at a "junction connector (right side of I/P)". This "junction connector" is just a cable lug that is bolted the the intake plenum (at the back of the intake, below the injector sub-harness connector), right?

Is it better to run the grounds for my ms3pro and LC-1 on dedicated wires to that point, or to tie into the wiring harness at 3-O?

My understanding was that in order to avoid potential ground offset/noise issues, the ground wires should all be run individually to a single lug at that location, except for the "sensor return" on the ms3pro which could be tied into the factory harness. Does this sound correct?

Joe Perez

iTrader: (8)

Ideally, all sensors' ground connections should be made directly to the ECU itself, and not directly to a ground lug on the engine.

If you're using the factory wiring harness, you'll be fine for most sensors. For sensors which you add (MAT, WBO2, etc), just run their ground wire back to the ECU and splice it into the blk/blu wire as near to the ECU connector as practical.

Remember that wire is NOT CONNECTED TO GROUND WITHIN THE HARNESS.

You need to connect that wire to one of the MS3P's analog ground wires, and then those two must ALSO be connected to a wire that actually goes to ground (eg: the blk / light green wire at 1O)

jnshk

OK, so the wire at 3-O has a junction somewhere in the engine bay that brings the various sensor grounds together before terminating at the ECU connector, but it is NOT the lug which bolts to the intake manifold? They remain isolated from ground until they pass through the factory ECU? If so, that is good news to me.

Based on my understanding of the above passage, I was planning on running 5 individual wires (gray pins 3,5,7,9 & white pin 16) directly from the MS3P to the lug on the back of the intake manifold, and connecting gray pin 18 (sensor return) to 3-O on the factory harness. Does this sound like the correct strategy? Do I need to make a jumper from gray pin 18 to one of the other ground wires? (And if so, why wouldn't they just build the harness that way?)

My understanding was that it is designed so that the sensor return (gray pin 18) is not to be connected directly to any ground, but rather it passes into the MS3P and makes a connection to ground inside the MS3P unit. But I have some confusion because the schematic on page 15 shows pin 18 junctioned to ground with all the other wires, and the schematic on page 16 shows it as the return point for all the sensors but does not show them connected to the engine ground (which makes sense with the above passage, as it says to avoid grounding them to the engine or chassis).

I know this is probably a really simple thing that I am overthinking and subsequently misunderstanding, but it's driving me bonkers. Thanks for your patience!

Joe Perez

iTrader: (8)

I believe you mean white pin 18. Grey pin 18 is one of the many high-current grounds.

That aside, what you have written is correct.

On my car, I did not connect white pin 18 to ground externally. I use it as the ground return for my MAP sensor and my Wideband O2 sensor. If I had a 96-97 car, I would also connect the black/blue wire to white pin 18 of the MS3P, as that is functionally equivalent to the original terminal 3O on the factory ECU.

Sorry I was a bit vague earlier, I missed where you said you had an MS3P as opposed to a regular MS3. The rules differ slightly in this regard between the two.

jnshk

Yes, white connector not gray connector. I've been looking at these diagrams so many times that I apparently started mixing things up!

That cleared it up, thanks!