Re: Stubborn Vehicle

["Steve Abbott" <abbotts@xxxx>]

I'm probably waaay off beam here, but from experience with this setup 
in V6 (and other) Volvos, I've found that all sorts of weird running 
problems can sometimes be traced back to rotted wiring insulation 
causing partial or total shorting of one wire to an adjacent one, 
even inside the wiring loom. Could this be a possibility? Only proper 
fix I've found is to pull the entire loom apart and replace or re-
cover all the wiring. Pig of a job. 

Cheers
Steve Abbott

--- In dmcnews@xxxxxxxxxxxxxxx, "cruznmd" <racuti1@xxxx> wrote:
> Yessir.
> 
> #5335 is the most stubborn car I have ever owned. It's enough to 
make
> grown man cry. After all that care over the weekend with the guys, I
> have yet another show-stopper (sort of).
> 
> Problem: The frequency valve is no longer working.
> 
> Please read carefully. There's a lot of info here. :)
> 
> Tests: 
> 1. Fuses 1 & 7 are good.
> 2. RPM relay is working. (pulled cover off and observed both 
contacts
> closed when engine runs)
> 3. Lambda relay is working. Provides power to ECU correctly as noted
> by voltage on green/yellow wire to ECU. ECU is grounded (cleaned &
> checked)
> 4. Jumpered 87b to 30 on RPM relay to power lambda system. Valve 
does
> not buzz.
> 5. 12Vdc is present on red/purp wire to freq valve. (grounded to 
block)
> 6. 12Vdc is NOT present across valve wires (red/purp & red/brn) The
> ECU provides ground on red/brn. No ground appears present at any
> time.(problem here?)
> 7. CO screw adjusted to encourage different behavior from ECU/freq
> valve. No effect.
> 8. Valve does not buzz when WOT switch is closed (fixed ratio)
> 9. Valve does not buzz when engine is cold before O2 sensor kicks in
> (fixed ratio)
> 10. Valve does not buzz when AA battery is applied to sensor lead.
> 11. I CAN open and close valve manually by providing ground from 
valve
> (-) terminal to block since ground is missing from the ECU. Valve
> operates. (I pretend to be the ECU this way by applying ground)
> 12. Dwell meter indicates no signal from ECU, reads zero. Tested IAW
> the manual.
> 13. Lastly, cleaned and checked the lambda ground on the intake, 
and 
> performed a continuity check on freq valve ground wire (red/brown)
> from the ECU plug, to the freq valve. Wire is unbroken.
> 
> I'm always told the ECU's never fail. I have done everything I can 
to
> avoid blaming the ECU. I have tried to eliminated the ECU as the
> cause. I know I'm going to get flamed for this, but that's where 
this
> seems to be leading. I believe the ECU switches ground on and off 
very
> rapidly to make the valve buzz. The ground wire (red/brown) is 
intact
> but the power circuit for the valve reads as an open when the system
> is powered up. Again, the RED/PURPLE to the freq valve reads 12vdc, 
so
> there is power. The ECU doesn't seem to be applying ground.
> 
> Am I crazy? Has ANYONE here ever had the ECU fail?
> 
> Thanks,
> 
> Rich A. &
> The Stainless Steel Mule (#5335)