1993 Pontiac Firehawk (LT1)

I'm troubleshooting issues with my new 383. (recently installed, replaced old motor)
I found that my MAP, IAT and AC sensors all have voltage on their Ground wires.
I wanted to make sure I have all of my grounds done correctly.

I have
- One big flat ground from the chassis to the block. (driver's side)
- One group of small ground wires in the harness on the driver's side of the block.
(which appear to be the three from block 2 in the ECM)
- One big ground between the Starter and battery (passenger side of block)

Then I have two small black wires with white stripes, which I beleive to be O2 sensor grounds.
(I have a heated o2 conversion; but that shouldn't matter.
These come down in the insulated conduit from the ECM.)
They're near the starter, I had them bolted to the oil pan, but I was going to move them up to the block to match SHBox's photo.
http://shbox.com/1/g103.jpg

I just wanted to make sure I am not missing a ground somewhere.

 

That sounds like all of them on the engine.

 

The only other one I know of is the stud on the fender.

Is there anything else that would have been disconnected as part of an engine pull?
(I didn't remove the original, but I did put the new one in; which makes this that much tougher)

 

Nothing on the RH shock tower ground has to be taken off to remove the engine.

 

Do you see any reason I can't relocate the black/white O2 grounds up to the RH shock tower ground post?
That would sure make my wiring a lot easier.


So here's the real issue.
I'm finding 70mV on the ground side of my IAT/MAP/AC sensor harness.
Somewhere, something must be shorted and passing that voltage.
I'm worried that it may be inside the ECM since those three
circuits come together on B3.

When I check the harness ground on the block, I see a 0mV drop from there to the battery.
(Which is good ... except that it points at there being an issue in the ECM)

 

Diagram for reference.
Note that IAT, MAP and AC Press share a common LO reference circuit (blk).
What I am seeing, is an identical signal on the MAP's Ground (lt green)

 

Are you seeing this voltage with the key off or on? If with it off, I would not worry about it.

 

Key on, Engine Off.

The voltage is the same on both ground and low reference.
Which is really the problem since I don't see how the ECM can possibly get a
clean signal with additional voltage present. (Which probably explains the
low kPa readings and rich condition)