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1998 S8 misfire when warm, CAT and ESP lights


bigchris1981
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Morning all,

Wondered if I could pick your minds...

After 6 months of on/off misfires when warm, and a dead fuel pump, this weekend I replaced both the cats, both lambdas, both ignition amplifiers...took the car for a drive....and the warning lights cam back on.

VCDS says there is intermittent voltage fault to cyl 2 and intermittent misfires on random cylinders.

I tried swapping over coilpacks and the fault doesn't move.

Not sure where to go next:

1 - Do I replace all the coilpacks and pencils on the off chance?

2 - Wondered about engine speed sensor? These seem to die across the VAG range and might explain the ESP light coming on?

3 - When MAF sensors die on MK4/5 golfs, they have a habit of putting the ESP light on...maybe the MAF?

4 - Intake manifold gaskets?

5 - other random air leaks?

Any other suggestions? It's only when it's got warm (10-15 minutes of driving from cold), and the fault then stays until it's properly cooled down again.

The logical bits of my brain that are still hanging on in there make me thing it must be a rubber/rubber covered component expanding or cracking open when it's warm...but the ESP thing...air leak?!

ARGH.

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  • 2 weeks later...
  • 2 weeks later...

So, Beru who make the OE coils sell them through Euro Car parts with the spark plug connect...which is too short.

ECP have now advised Beru that the spark plug connector they spec for the S8 is wrong.

Now waiting on TPS (VAG) to supply the spark plug connectors to me tomorrow.

New coils alone have not got rid of the misfire, fingers crossed that the old spark plug connectors are borked...otherwise, where do I look? :/

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Finally fixed yesterday. Number 4 injector was shorting under load when hot...but the code didn't show until the spark plug connecters had been replaced!

Total now running at: Fuel pump, cats, lambdas, ignition amplifiers, coil packs, spark plug connectors and 1 x injector!

Appears to be up and running better than at any time I've driven it...good times. :)

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