I'm talking about the ground that is impossible to get at with UIM still on the engine.

What EXACTLY does this point ground?
Is it a ganged ground of alot of stuff?
Just Emissions, (as one picture described)?
Does anyone know which components use this ground?
Do all the ground pins coming from the ECU use this point?

etc. etc.

Too many threads just argued about the info, then turned into whether or not the Ebay ultra ground whatever is worth it. Just looking for hardcore info that anyone knows off hand, or If i'll have to spend days disecting FSMs some more.

 

The many harness grounds are all tied together.
They serve multiple functions.
Besides carrying current they stabilize the bias in many sensitive sensors and help to supress electrical noise from disturbing the ECU.

 

If you do some searching you'll see that the more grounding you have the better off you are. The stock wires are known to be corroded/brittle and old.

BTW NEVER buy one of those shitty grounding kits.

Your spending an extra $30+ on some big gage wire and good terminals.

I found some extra speaker amp wire lying around and just used it for my grounds.

 

The one under the UIM grounds the ecu and injectors basically.

 

Yea, as for grounding, I've cleaned up every connection I can reach. But the most important one, or the one that solves most driveablility problems it seems is the one under the UIM. I want to know specifically where those wires are coming from so i can redo them somewhere, where I can reach.

 

Then download the factory service manual from the net. The WIRING schematics. Look at the EGU and EMISSIONS CONTROL SYSTEM.

They are the grounds for the ECU electrical circuit. That is where the ECU gets its grounds. Period. I'd tell you the wire/pin numbers on the ECU but then you wouldn't look at the wiring schematic. DOWNLOAD THE FSM. WIRING SCHEMATICS. PERIOD.

And so help me God, if someone says/tells you to ground the ECU chassis I'll kill that sob.

 

Speaking of the ecu ground. I never did that one. What exactly was the theory behind that one?

Should the ground pin outs be grounded?

I ended up adding grounding into the already existing ones like the boost sensor(OMG the stock wires were so bad!)

 

Pins 2R(spliced to 3A near the ECU), 3A and 3G all go to the ground point 24 on a 86-87 series four car. Ground point 24 being the ring terminal with two wires on the top of the rear rotor housing.

Most every sensor on the engine has a Brown/Black wire going to it and the other end going into pin 2C on the ECU. Useless sensors like the AFM, boost sensor, tps, stuff like that.

I've one 87car that the only way it won't hesitate at 3500, is to add an additional ground wire to pin 2R (and by default to the other ground wires). I can make the hesitation come and go just by disconnecting/reconnecting that extra ground I made. My problem isn't the grounds at ground point 24. I KNOW all about that ground and KNOW it's bonded good to the rotor housing. I'm pleased as punch with my additional ground and I'm not going to pursue why I have to have that extra ground spliced to the ECU ground wires.

My other two cars have the stock factory grounds and nothing more and have no problems. Both the other 87 and 86. Other than that I have no additonal grounds and don't need them/want them. The above is just my opinion. There's other opinions out there.

So all those sensors get their ground one way or the other thru pins 2R, 3A and 3G. Plus the electronic circuit for the ECU's other circuits are tied to those two wires.

There was a TSB that can be found on ALLDATA.COM on early 86-87 that had another ground spliced to the brown/black wire on the pressure sensor. That was to help the AFM's ground. That's what the TSB says.

All the brown/black are mechanically spliced together at some point in the EMISSIONS harness before they go to pin 2C.

 

Hmm Maybe when I upgrade to the Rtek 1.7 I'll add that 2R ground in.

I had huge hesitation problems in my car and have a dyno chart to prove it(chart would jump back and forth). I added in a ground at the boost sensor and it instantly went away.

 

It grounds a lot more than the just ECU, and it does not directly ground the injectors! There are no injector grounds! Like Hailers said, grab the FSM wiring diagrams, read and learn.

 

************************************************** ************************************************** ****************************
It sounds like the TSB put out by MAZDA worked on your car. It was for 86 (and I think 87 cars) and they explain that what your doing is adding a ground for a afm problem. It makes sense since all those brown/black wires on the Emissions harness are spliced together inside that emissions harness.

The following are words off another site concerning the TSB I talked about:

If you encounter a 1986-87 RX-7 vehicle with a surge or stumble during acceleration at more than 2500 rpm, this may be due to an improper ground between the emission control unit and the air flow meter. Test for the symptom according to the procedure shown in this Service Bulletin. (Refer to Service Bulletin Category 4, No. 036/87.)8888888888888888888888888888888888888888888888 888888888888888888

It also says this: The ground circuit of the emission control unit has been improved since November 1, 1986.