[V8] ECU grounding, etc. (abridged)

Tue Oct 11 18:44:48 EDT 2005

... while I've found the wiring diagram to be pretty much literally
correct in its description of the connections and how they are made you
may well want to be a bit skeptical.  The wiring diagram may show a
direct wire connecting two points, when the connection may be a bit more
indirect.  

We've had the discussion here in the past ... proper grounding can be a
very tricky thing ... it is better to keep the grounds for sensors
separate for grounds for things that the ECU drives ... but then ground
needs to be connected together somewhere.  The example I always come
back to is the two grounding lugs that attach to the back of the engine
below the left cylinder bank ... I've never had the need nor time to
investigate, but I fully expect that one of the ground lugs provides the
reference for the sensors and the other for the driven components ...
but through the Kostal connectors multiple signals called "ground" pass
through different pins.  There may also be splices within the confines
of the wiring looms ... if you've got a more involved grounding problem
you're going to have to dig in and understand this sort of thing more
completely ... 

Steve B
San Jose, CA (USA)
> 
> So THOSE are the Kostal Connectors... I see, said the blind carpenter,
> as he picked up his hammer and saw.
> 
> The Kostal that the ECU's #54 brown wire leads to is #11 ("Motronic to
> Automatic Transmission").  So I can see why I would have a dead end
> there (though I gotta wonder why it's not a similar situation w/ #s 12
> and 14 (Instrument panel to auto trans, engine compartment to auto
> trans).
> 
> Crap.  Or good.  Either way, the lack of ground at the ecu harness #54
> is expainable.
> 
> I guess it's on to figuring out why the MAF test requirement for 19-37
> continuity ain't there, and from there to the TPS, and then to the
> crusher.  Just kidding -- I won't check the TPS.
> 
> -dave-
> 
> 
> 
> 
> 
> 
> > 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:
> >
> > http://www.sjmautotechnik.com/trouble_shooting/v8_pinout.html
> >
> > 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
area.
> >
> > 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!
> >
> > DaveC.
> >
> > > + 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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