[s-cars] Missing in action - still

[Robert Myers]

OK, I've been busy.

The miss in #4 ('95 urS6) is still with me - intermittently.  <grrrrrrr>

Yesterday I redid the wiring harness to the coil pack with solder joints 
and shrink wrap instead of crimps.  The reason is simply that I feel more 
sure of myself when soldering.  I put the coil pack back into the car and 
fired it up.  Miss still there.  Location #4 (as before).  Swapped PSO 
connectors.  Miss did not move.  Therefore (it sez here) the problem is the 
coil.  So, out comes the coil pack and in goes a new coil at position 
#4.  Put it back in the car and the miss is still at #4.  OK, I had to run 
an errand.  I took the truck instead of the S6.  Got back a half hour later 
and fired the S6 up.  NO MISS???  I took it for a 60 mile drive - no 
troubles whatsoever.  Came home parked the car in the garage and went to 
bed - exhausted.  This morning I fired it up and the miss is back.  Swapped 
PSO wires again.  Did not move (again).

Pulled out Bentley.  Checked the wiring diagrams and the component location 
diagrams and saw where what I though were the ground connection for the 
coil primaries are, in fact, the +12 volt supply for the coils.  Apparently 
the PSO grounds those lines to create a current change in the primary which 
then causes the secondary to pulse the spark plug.  That's opposite of how 
I thought it worked but...  I checked the voltage at each of those 
connections at the firewall with ignition both on and off.  All gave 12 
volts (nominal) with ignition on and zero with it off.  Did the same tests 
at the PSO connector end of the wiring harness with identical results.  OK, 
the wiring harness is at least continuous through the coil primaries and 
there are no shorts between any of the wires and ground.  I had already 
replaced coil #4 with a brand new one yesterday so the secondary for #4 
should still be OK.  Perhaps it's not impossible that the new one might 
also have been faulty but I kinda doubt it.

Since swapping connectors at the PSO did not move the miss the PSO and 
connections to the PSO from the ECU are OK.  If one of the PSO channels 
were not operating then the miss should have moved.  It didn't.  The 
ignition system appears to be OK.

That leaves injectors.  I checked resistances of injector wires from wire 
to ground.  One side showed high (infinite) resistance.  The other side 
gave a very quick reading which then shot up high before the el-cheapo 
meter could stabilize long enough to get a reading.  This behavior was 
consistent at all five connectors and with several repetitions at each 
injector connector.  I'm not sure exactly what this tells me but at least 
there appears to be no differences between position.  They all behaved the 
same.

I replaced injector #4 with one of the injectors I pulled out when doing 
the RS2 upgrade.  Miss still there.  The injector may be faulty - or 
not.  Can't tell from these results.  It's possible (unlikely but...) that 
the injector I swapped in might also have been faulty.  I doubt it.

The plugs are brand new.  The cigar for #4 was brand new with the coil 
yesterday.

If the problem is a fuel issue then about the only thing it could be is 
that injector #4 might not be getting the "fire one" signal.  How do I 
check this?  If the signal is missing then how do I solve the problem?

I suppose I could pull the fuel rail again leaving the injectors installed 
in the rail and see if #4 sprays when the starter is cranked.  Better have 
my fire extinguisher handy.  Any better suggestions?

Beuller?


Bob
Random Bushism: "The future will be better tomorrow." Governor George W. 
Bush, Jr.
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Robert Myers  304-574-2372
Fayetteville, WV
urS6 - Cashmere Grey
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