Intermittant problem.......

[kjc300]

Right, been through the mill with the cossie recently. Kinda since just before the rolling road day all sorts of probs have arisen.

Thought I had a TPS problem on the way back from pod, hasn't done it again since though



And now every so often with the ignition on before starting, the fuel pump will keep running and the car won't turn over (presumably because of the extra drain of the pump running)

Now there is an interesting symptom to this - when it happens, the ISCV is OPEN with just the ign on as when I unplug it I can hear it close. The fuel pump then stops!!!

Proper baffled!!!

[warrenpenalver]

hang on while i fire up the wiring diagrams.......

[warrenpenalver]

ok...... on P8 the power supply to the ISCV supplies power to a lot of sensors, eg injectors, cannister purge, ecu, boost control valve, and importantly the fuel pump relay trigger feed (its earthed by ECU). With the earths for the ISCV and fuel pump relay trigger controlled by the ECU.

Id get a multimeter on to find what may be an earth somewhere.

[kjc300]

ok...... on P8 the power supply to the ISCV supplies power to a lot of sensors, eg injectors, cannister purge, ecu, boost control valve, and importantly the fuel pump relay trigger feed (its earthed by ECU). With the earths for the ISCV and fuel pump relay trigger controlled by the ECU.

Id get a multimeter on to find what may be an earth somewhere.

Why can't things just snap, break or blow up


I have L8 warren, but it's probably just the same.

[warrenpenalver]

hang on i shall check...... L8 is slightly different in a few areas.

[warrenpenalver]

[kjc300]

Need to read the manual and see if there's a 'tech description' of the operation of the idle valve. Don't know if it's supposed to cycle on ign or not and then stay on? Removed mine and check for operation with 12v and it works fine - doesn't get stuck open or anything.

That earth is connected to far too many bits lol!!

[warrenpenalver]

I suspect theres a fault somewhere. The ISCV is controlled by the ECU earthing it.

plus the fact you cant turn it over is not good if it was just a faulty ISCV it would crank and start.

Do all the relays go skitz with clicking?? does it start with ISCV disconnected??

You have a multimeter?? check the ISCV wiring for an earth.

[Dave Henshall]

on a p8, when you turn the ignition on, the idle valve should click fullyopen/shut several times ( and you can hear it) this is to help keep the plunger clean, the L8 doesn't do this.

i had a couple of simialr problems.

1 was due to a low battery voltage, (just over 11v) and wierd stuff happened with the fuel pump NOT priming etc.
2 was a known problem when i got the car with a GGR pectel board fitted, occaisionally when you went to crank, the pump wouldn't prime, this was a known issue with the later generation pectel boards on P8 ecus. there was a timing problem on initialisation which couased a lockup - cycle the ignition off and back on and it would be ok.

[kjc300]

Now I think it's the ECU/chip, swapped it for an S8 that I still have - fuel pump primes as normal (unfortunately the S8 won't start either due to a sync problem but I knew that already ). L8 back in, pump continues to run. I can turn it over now, but it wont start and does an almighty backfire as soon as I turn the ignition on after trying to start it as the coil fires on ign.

[L8 ECU]

Kev,

I had this problem years ago, and am trying to recall how it was solved. Dammed if I can remember at the moment.

The schematic below might help, it shows clearly the main relays to pump and ISCV/injector feeds.

Title says "L8", but it's the same arrangement for P8 too:

[kjc300]

Cheers Doug, thats a good pic that

Going to try my ecu in somebodys car to see if it does the same.

[kjc300]

Right, this is now not an intermittant problem!!

Tried my ecu in Matt Baxters car - no worky!! Fuel pump primes (as normal though) turns over but won't start.

Going to try his in mine later when he finishes work!!