S701 on the harness

[zaq123]

does Anyone know where S701 is located on the harness? I would like to wire Coolant temp sensor and TPS (using factory wiring via AIT/AirMass ECU ground , motronic pin 26) directly to ECU ground and need to find that S701. Looks like S701 also terminates Oil level sensor which grounds everything to the motor

[ForcedFirebird]

What year harness?

From memory, that's the strut tower in late model and back of valve cover in eta?

[zaq123]

What year harness?

From memory, that's the strut tower in late model and back of valve cover in eta?

1990. Shock tower is G103. That S701 is probably a splice somewhere. Thought its near 55pin connector and will be easy to separate but no...only S700 is there for all shielded cables (O2, crank sensor etc). Should have done all that planning when rebuilding the harness..Oh well, it would be probably easier just to make new lead from 55 to TPS. Just want to make sure TPS isn't using chassis ground (oem arrangement) before too much stuff are put together restricting the access under there

[ForcedFirebird]

Back at work. Just looked at the ETM. Not sure what you are trying to achieve, but all those splices at s701 end up at g103. Typically you want the sensors to ground at the same point the ECU does, which all those sensors are tied together and grouped at the strut tower.

The m20 harness has several splices under the tubing, might have to split the loom farther down from the 55 pin. Will look around, think there's a harness here that's already had plugs pirated from it, I can sacrifice it to see - just gotta remember which crate it's in. :/

[ForcedFirebird]

Here you go, right at the firewall grommet, s701 (black cap), s703 and s111:

[zaq123]

Back at work. Just looked at the ETM. Not sure what you are trying to achieve, but all those splices at s701 end up at g103. Typically you want the sensors to ground at the same point the ECU does, which all those sensors are tied together and grouped at the strut tower.

The m20 harness has several splices under the tubing, might have to split the same loom farther down from the 55 pin. Will look around, think there's a harness here that's already had plugs pirated from it, I can sacrifice it to see - just gotta remember which crate it's in. :/

thank you for looking into it.

I'm trying to find that S701, separate TPS and coolant temp sensor and connect them to old Air meter ground in the loom (my IAT sensor ground) so they all can be grounded only at ECU. (Air meter/IAT ground is not grounded to anything but in ECU).

TPS, Coolant temp and oil level are all spliced together at S701 (diagram).

That splice sends only one BR/OR wire to G103 (strut tower). Oil level sensor is also grounded to the motor through its housing....unfortunately.
Otherwise I could disconnect that one wire at G103 and send it to ECU....I want to keep the oil level sensor thought..

Diagram is not exactly accurate as S700 (shield ground) is near 55 pin connector and not before G103 as diagram shows (makes sense as one wanted to run shielded cable as close to ECU as possible. Those don't even go through G103) and go through Rubber grommet very close to 55 pin connector

Hard to tell from the picture wire colors. Are they brown orange under those splice caps?

[ForcedFirebird]

I use these to find splices and grounds:
Here's where I followed the s701:

[ForcedFirebird]

I have always just used the two wires coming to the AFM for IAT, never had any issues. It's OK for sensors to be grounded inside the ECU, you are closest tot he PCB in that case.

Every ground on the car makes it's way to chassis, sensors are just more accurate when they are all grounded with the ECU, not just any nearby to the sensor itself (unless it's designed as a single wire, like the brown gauge sensor).

See here: https://www.r3vlimited.com/board/for...o-e30-afm-plug

[zaq123]

I have always just used the two wires coming to the AFM for IAT, never had any issues. It's OK for sensors to be grounded inside the ECU, you are closest tot he PCB in that case.

Every ground on the car makes it's way to chassis, sensors are just more accurate when they are all grounded with the ECU, not just any nearby to the sensor itself (unless it's designed as a single wire, like the brown gauge sensor).

See here: https://www.r3vlimited.com/board/for...o-e30-afm-plug

That's what I'm trying to do. IAT uses two wires (from Air meter wire loom) with one being grounded only at ECU. I want to connect grounds for TPS and coolant temp sensor to that IAT ground. This will prevent noisy sensor signals , especially TPS one which is essential for ITB mode. Obviously ECU ground is not isolated from chassis but OEM arrangement is not the way to send the signal for TPS unless it’s just OEM throttle switch


Thank you for those diagrams, especially the first one. Good visual

Sent from my iPhone using Tapatalk

[ForcedFirebird]

That's the same ETM you are using. If you go to the bottom, you have splice/connector/ground numbers, followed by what page the diagram is on. I'm at home and on the phone now, but if memory serves me correct, it's page 8001-3 or so

[ForcedFirebird]

The stock wiring has a stable enough signal for ITB mode with a MS PnP, just have to swap two wires.

[zaq123]

The stock wiring has a stable enough signal for ITB mode with a MS PnP, just have to swap two wires.

ok. just following up on this. Stock wiring maybe works ok but it is defentely far from ideal. Sensor grounds are all going back to DME through a chases ground which makes these signal conductors to share the actual power (no good regardless of what ECU one is going with).
Rama of RHD makes nifty adapter harness for PNP EcuMaster into M20. It features separate leads to TPS, IAT to isolate signal grounds for the obvious reason.
ECU, Haltech, Megasquirt....or whatever, it's highly desirable to have sensors be grounded only at ECU. While I have the access (no glovebox installed yet), it would be a shame not to take care of this now.

Luckily, FF helped me to find that S701 connector (thank you sir) which is Yellow cap with 4 BR/OR wires (3 thin BR/OR from sensors and one thick BR/OR that goes to the strut tower for the chassis ground).

2 splices later, all my important sensors (Coolant temp, TPS and IAT) are on the dedicated sensor ground. In OEM Montronic 1.3, there are two dedicated signal grounds that go back to 55 pin, pin 10 (stock narrowband) and pin 26 (OEM AFM common wire or IAT ground). I used pin 26 (grey blue in the same loom area where the yellow cap is) to splice BR/OR of TPS and Coolant temp sensor for a clean signal back to ECU. The only BR/OR that remains grounded at the same yellow cap splice was the oil level sensor which is also grounded through its housing at the oil pan. Which is actually another reason why OEM arrangement is no good as sensor grounds where bonded to chassis at two different locations (oil level sensor housing and the strut tower) creating undesirable (for signal wiring) ground loop.

701 splice is easily accessible from the glovebox area. Just in case someone is also looking to do the same while using stock harness/55pin for your standalone ECU. If one ever goes back to OEM Motronic, this arrangement should work as well IF pin 26 is grounded in stock DME (something I haven't checked yet).....or it can be easily reversible with the same 2 splices