Megasquirter grounding questions

[beast02er]

I know I know, that's what the MS EFI forums are for, but I can't quite get my answer there and it seems posting something similar there gradually earns you the do not help card.

So I know you 02ers are always helpful, and have done something in the same car as me.

I'm a little confused on sensor grounding with the relay board in the equation. What I don't get, is do you run a wire between the MS unit and the relay board to each DB37 connector, and then run the sensor ground on each sensor to its spot on the relay board, or do you ground the wires going from the MS unit to a ground, and then ground the sensor grounds to this same spot? I'm just a tad confused if you can't tell, and all the info I seem to find doesn't show it all as a full wired up assembly (there are nice wiring pics, but they don't include the relay board).

-The main point of this is i'm having trouble getting my TPS wired up to respond correctly, so I gotta get it set right. Hope you can help.

Bryan

red73

(the never ending project!)

[cowlum]

I am slightly confused as to what you are asking. but if I understand you correctly here is what I think the answer is.

The TPS has three wires comnig out of it. Two of which go back to inputs 22 (signal) and 26 (5Vref) on the relay board. The third goes to a common ground in your engine bay.

I painted a picture.

You can find info here (how to determine which wire is which on the TPS)

http://www.megamanual.com/v22manual/mwire.htm#tps

and the pins of the relay here

http://www.megamanual.com/v22manual/mwire.htm#rb

hope this helps (and that im correct its been a while

[Pinepig]

Ground everything to the same damn spot on the body somewhere, it helps avoid an ohms issue for sensors.

[cowlum]

Actually studying the relay board web page it seems that pin 14 (on the relay board) may be the ground for the TPS sensr. but im not sure. Ill have to check what I did when I get home.

any one else?

[Grover]

I've been looking at this too as I'm a few days/weeks behind you in the process. From what I can see, assuming you are using the standard DB37 connector cable from the relay board to the MSII unit, the TPS return (ground, I believe) gets wired to screw number 14 on the 20-terminal screw block. From the wiring diagram of the DB37 connector cable, this indicates that it grounds to pin 19 on the MSII DB37. I see no reference that it gets grounded anywhere other than the relay board. I'll say again though, that I am in the construction phase of my installation, so those who have it up and running may be able to provide better guidance. Hope this helps and by all means, send me an email when you get it 100% confirmed.

[JohnN]

board, you want to terminate the TPS on the relay board. The sensors for IAT and CLT should also be grounded at the relay board.

Check out the link at: http://www.megamanual.com/v22manual/mwire.htm#rb

The board software doesn't allow me to format the table. You'll have to add the formating yourself ;-)

The table about 1/4 down the page:

Relay Board JP1 Terminal Block Pin-Out

Pin Function Pin Function

1 Injector 2 (ground by MS) 11 S5 (used for MS-II ignition output signal)

2 Injector 2 (ground by MS) 12 Vref (+5 Volts)

3 Injector 1 (ground by MS) 13 TPS Signal

4 Injector 1 (ground by MS) 14 TPS Return (Ground)

& VR sensor negative lead, if used

5 Fuel Pump 15 Tach/Ignition

& VR sensor positive lead, if used

6 Fast Idle 16 Air Temperature Sensor Signal

7 S1 (used for MS-II IAC 1A) 17 Air Temperature Sensor Return (Ground)

8 S2 (used for MS-II IAC 1B) 18 Coolant Temperature Sensor Signal

9 S3 (used for MS-II IAC 2A) 19 Coolant Temperature Sensor Return (Ground)

10 S4 (used for MS-II IAC 2B) 20 O2 Sensor Signal

[cowlum]

I have checked and I grounded everything to the body (all is working well after 1000ks). Im about to do another push and install EDIS so I may change the grounds at the time.

Can anyone explain why one method of grounding is any better tan another?

[JohnN]

directly on the MS) is that it reduces the chance you'll get a ground loop (there is a voltage potential between the two ground points). Because both the temp sensors and the TPS are sensitive to relatively small changes in resistance, putting your grounds in different places increases the likelihood of that happening.

As long as all the sensor grounds are at the same potential as the MS (grounding to the relay board or to the MS) you're OK.

Regards,

John N

[beast02er]

So then for the DB37 grounds on the MS side and the relay side, do you take wires from each end of the DB37 and run them to the same ground point?

Currently I have them running from the MS to the Relay board, but then there is no actual grounding going on...

[JohnN]

one goes to constant 12V, one to switched 12V and the other to ground.

That is then the common ground for the entire MS and relay board.

Regards,

John N

[Grover]

Not to hijack the thread, but does anybody have a photo of how they did two things: 1. The integration of additional diodes to get a tach reading (this is completely confusing me) and 2. Shielding the four wires coming from the EDIS module which need to be shielded to pin #7.

[cowlum]

I am still not sure what you mean by ground at each end of the DB37. As far as I can tell, the relay board has the main ground for everything. The megasquirt grounds through the db37 cable to the ground from the relay board. as in the picture, there is only one ground.

I will be changing my setup to gronud through the relay board soon.