[V8] ECU grounding, etc. (abridged)

Jeremy Ward jward.v8 at gmail.com
Tue Oct 11 14:44:46 EDT 2005

Before you use the Holy Hand Grenade of Antioch, consult the book of
armaments - Chapter 24, Verse 470-1
"Throttle Position output signal checking"

-----Original Message-----
From: Coleman, David [mailto:David.Coleman at blackrock.com] 
Sent: Tuesday, October 11, 2005 11:25 AM
To: Jeremy Ward; v8 at audifans.com
Subject: RE: [V8] ECU grounding, etc. (abridged)


So ECU terminal 54 still has no good ground as stipulated in the manual,
and jumping it to ground makes no difference in the running condition.
As Jeremy pointed out, the wiring diagram does indeed indicate that 54
seems to jumper off 19:


And no, I don't have continuity between the two at the connector (good
ground at 19).  The thing is, when I trace the brown #54 wire from the
ecu harness connector, it runs up the loom and splits off among a small
cluster of other wires and leads to the first of five black plastic
harness connector boxes mounted to the firewall behind the ECU mounting

And the thing after that is, whatever these black boxes are (each about
the size of a thumb, mounted parallel to one another), all but the one
that the #54 brown wire cluster goes to have two halves, sandwiching an
in-cluster and out-cluster.  The first one has no other half, i.e. it's
a dead end.  WTF?

Could this connector box be for automatic transmission controls?  If so
that might render terminal 54 as not requiring a ground if the car's a
manual trans...(?)

Thanks for any thoughts!


> + Car starts only after a few 1-second cranking sessions.  Won't start
> w/ extended cranking.

> + Once warm, idle begins to fluctuate wildly (0-1500 rpm) until engine
> dies

> + Engine will immediately bog down trying to kill the motor if
> anything close to WOT, either revving or driving.

> + Car runs WAY too rich, in all running/driving circumstances
> I've replaced the FPR and spark plugs.  From there:

> + Code consistently shows 2324 (bad ECU ground, MAF wiring)

> + Running diagostic output tests indicate all injectors click, ISV
> actuates, but carbon canister solenoid no good

> + Replaced canister solenoid and associated vac hose clamps,
> now clicks away during output tests.

> Checked ECU:  
> + ECU voltage supply check asks to confirm ground at terminals 10, 14,
> 19, 24, and 54 of the harness connector ---  All were good except at 
> 54.

> + I also picked back up on the MAF sensor check procedure, which was
> asking to verify continuity between ECU harness connector pins 19 & 
> 37.

> No good.  Blames an apparent short between ecu pin 37 and terminal #5 
> of the MAF sensor connector.  So far no luck finding a short...
> So the upshot is: how does terminal #54 of the ecu harness connector 
> get its ground?  Any other thoughts?
> Delirious in Delaware,
> DaveC.
> '91 V8 5-speed

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