Check resistance between B3 (dist ref low/ground) and A12 (ECM ground?

I have a tach that reads high and gets progressively worse, EST chart shows B3 to be a ground, ECM pinout says it's "distributor ground refence low"...

I have about 50K ohms between B3 and A12

A quick check would be aprreciated.

Thanks

 

Strange question for the TBI board. . . However, one of the pins you cited is incorrect. Pin A12 is an ECM ground. Pin B3 is the MAT2 input.

The REF LOW input to the ECM is on pin D9. To gound that pin should measure about 50.3K ohm. The REF LOW pin on the ignition module is connected to ground within the distributor (mounting screw).

The DRP input to the ECM is a differential amp. It isn't grounded within the ECM.

RBob.

 

Could be year model differences...I'm using the Helms for my '89 Vin E section...B3 is listed (and measures the same as yours). D9 isn't used in my manual...regardless, looks like were on the same page here and my ECM seems okay...for grins I'll go measure D9 to A12...

I'll also need to measure on the module as well.

Thanks a bunch, what year schematic are you looking at?

 

I just realized something....maybe I posted the wrong ECM? I thought TBI ECMs were 746's?

 

I'm an idiot. I read the title as a '749. You are correct on the TBI being an '746, and pin B3 being REF Low.

Pin B3 is the REF LOW input. This is still connected to a differential amp, so the B3 to A12 will be about 50K.

(not such a strange request now, I'll go put my cone shaped hat on ).

RBob.

 

Well, no continuity at all from D9 to A12, ground is cool on the module though.

Also, no wire in my D9 on the connector, so my schematic must be okay for this part of the car anyway...('91 RS)

Thanks

 

I think we all have our moments. I seem to have them on a frequent basis

Anyway, moving to the ECM board

 

I'll be darned, first post I've ever had moved...thanks again for the help.