Hi Amarin,

It's good to hear from you.
Have you been watching Laser headlights?
They're 4X brighter in new Audi's and maybe VW's now.
Lasers sound dangerous if aimed wrong, but they must have overcome that to go into production. Good for another post.

I'm in the speculation mode here, and glad to discover another temporary
fix for this intermittent fault that's documented by the service records
and notes from the refreshingly honest previous owner.

I don't see a ground loop problem at all, but that's likely why Volvo didn't
ground the RPM sensor harness at the bell housing.

I'll be interested to see if ECU reboot gets the car running after the next
surprise shutdown.

Elecrolytic caps aren't the only caps that fail / go out of limits.
I've seen other types fail causing oscillator circuits to quit and
kill some machines. This is why replacing caps in the old ECUs is a good idea.
Using the highest quality long life caps, and NOT old radio shack and flea
market parts as some people think.

One engineer at the UK site designed a LH mod for the fuel pump control based
on a 555 IC Have you seen it, and heard any reports pro or con?
It's buried in the UK FAQ, maybe our 700/900 FAQ?

****Connector faults*****
Look at this recent AWD post where it looks like a problem with a throttle
control module connector.
Start with the May 7th post This was a new fault after BZ resolved his vaccum leak.

https://www.brickboard.com/AWD/volvo/1688720/V70-XC70/2002_v70t24_engine_rpm_surges_idle_cold.html

*What's wrong with his connector?

Unfortunately BZ has a track record of asking questions and disappearing for
months until he has another question. He doesn't bother to report back
what he and/or his dealer did to finally solve his problem.

*Zinc Paste ACZP
ACZP was first suggested to me by wiring guru Dave Barton.
Look at this very interesting article by Brickboarder Ron Kwas.
http://sw-em.com/anti_corrosive_paste.htm

(His article highlights other problems with volvo connectors, for instance
toasted relay sockets for fuel relays where people were blowing 30 amp fuses
in a 25 amp circuit, and the normal current draw is around 11 amps
loose pins draw current when arccing and make a toaster it seems.)

*What's the best way to service connectors?
Clean (Beware strong solvents that can wreck bullet connectors)
I've used 90% isoprpyl alcohol and scrub with a toothbrush, blow off
with compressed air
Deoxit- when and where?
Repair or replace loose/bad pins
What lube?
Penetrox A is not compatable with rubber or polyethelene insulating materials
(Beware of destroying bullet connectors with the wrong chemicals)
Penetrox A-13 is OK with the above and very pricey
Dielectric silicone
Spray silicone
Copper based anti seez applied carefully so as not to short out any pins?
other?

Also see a section of the 700/900 FAQ Oxidized connectors. (pg 66)

I looked at LH and EZK interconnections and found several series connectors:
C2, C3, C50, C51, C54
Some of these are by the driver side firewall tie-wrapped underneath a bracket
to the strut post. I'm afraid to take them apart after having the OBD port
connector insulation fall apart. (photos on request)

Shielded cables for LH and EZK.
I found no shielded cables for LH.
EZK has three:
7/24 Knock Sensor connector C132 pin 7, pin 6 gnd to EZK 12,13
7/25 RPM (CPS) C156 pins 1 & 2 coil, pin 3 gnd to EZK 10,23,11
4/15 Power stage pin 5 to EZK pin 16 (output control line)
pin 3 gnd

I have a snap ferrite to put on the CPS harness, that wont hurt and
can help reduce any RFI pickup that can upset the RPM signal.
Maybe the fault is with CPS connectors?

I can only speculate why the ECUs locked up.
Old ECU caps, RFI, faulty connectors? Does the LH ECU need a mod?
I wont be surprised if the ECU will behave normally for 3 months before another
surprise shutdown. So this is the nastiest of faults to correct.


Here's the plan for the next time it quits:

First grab any OBD codes from ports 2 and 6.
Instead of reading current on fuse 1 and 11, just check for +12V at fuse 11
with the probe on either leg up top of the ATC fuse F-11.
If there's no 12 volts then FUEL is shut down via either of two fuel relay
coils & points or the LH switching ports 21 and 20.

The ECU controls switched grounds to enable both fuel relay coils,
both lines through C3 connector somewhere in back of the glovebox.
How hard is that to find?

In the off chance I get ambitious:
Test LEDs or 14v grain of wheat lamps on pin 1 and 5 of the fuel relay socket
to check 12V at both fuel relay coils.

Jumpers to fuel relay socket pins 2 & 4 to ground could bypass a failed LH ECU
to operate the relay and determing if ECU swiching failed.
It would quickly enable the fuel circuit including both pumps if LH crapped out.

****** WARNING ***** (For anyone reading this)
Jumpers to be used ONLY ON A TEMPORARY BASIS! Jumping those FI relay points would defeat program safeguards and keep the fuel pumps running ALL the time, including after you shut down the car and remove the key.

Best regards, Bill