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Corrado VR6 intermittently cuts out dead... help!


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Hoping that someone can help me, as this has got me completely baffled...

 

1994 Corrado VR6 intermittently cuts out for no apparent reason: No misfire, stutter or change in engine character before it cuts out - just an instant stall, dead.

 

Fault can happen when car is sat idling or when it's being driven, more likely to occur when car has been running for more than minutes and warmed up.

 

Car runs perfectly outside of this fault, it's just sailed through it's MOT, emissions readings are spot on - car behaved perfectly through it's test, but stalled on it's way there and on way back after. 

 

When it cuts out there are no dash lights illuminated: oil pressure, coolant, brake, ABS warning and ignition lights all stay off.

 

Mileage and clock stay constantly on when fault happening and don't flash off or disappear/flicker as fault happens.

 

Car can stays 'dead' for a few minutes, re-trying to start it does nothing - no dash lights illuminate and no sounds from any relays. Other times it re-starts straight away.

 

Car has a Scorpion 1218T alarm, which still works perfectly throughout the fault - car will arm and un-arm as normal, locking all doors and illuminating the separate dash alarm LED.

 

Arming and un-arming the alarm does not reset or clear the fault - car stays in dead state even after this proceedure... until car decides it's time to start again.

 

There are NO faults on VCDS when scanned (apart from the normal crank sensor G28 fault code '00513 03-00 no signal' when any VR6 engine is off, which clears and stays off once started).

 

I've recently changed the ignition switch 6N0905865 twice (Meyle) & both the ecu relay 109 and fuel pump relay 167. Also been through all the fuses. No change.

 

I removed and checked the cars ECU yesterday, to look for any damage or burns on the main PCB - all looks perfect.

 

In the 19 years I've owned this Corrado (and 32 years of VW ownership) I've never had a fault I can't rectify... until now.

 

Any help or advice would be most appreciated.

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The dealer-fit scorpion alarm cuts three circuits - the starter, the coil and fuel pump.

 

Intermittent problems are difficult to fix as you don't know if you are measuring the real value or the intermittent...

You need to determine if the coil or fuel is the problem (or both!).

 

The fuel pump could be immobilised through the signal from the ECU (to stop the relay energising) OR the wire from the output of the relay to the fuel pump.

You could put a 12v LED across the fuel pump - so you can see if there is 12V across it.

Beware that the fuel pump is controlled by the ECU: only when you crank the engine is 12V across the pump. When the ignition is turned on, the fuel pump is primed with a short pulse.

 

You could also put a 12V LED across the connector to the coil pack - Is there 12V across pins 1 & 5 (guessing your car is a coil pack).

Then put the LED across each other pin and ground - when you crank the engine, each pin should flicker the LED as the ECU fires the spark plugs.

 

Once we know which circuit is faulty, we can delve in a little deeper to find the real underlying problem.

 

 

Good luck! Report back with your findings...

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Sorry for the delay... think I've sorted it!

Had a good going through the wiring under the drivers side of dash, all okay.

Checking behind the fusebox I found a plug not quite seated correctly, think it was plug G1 or G2 (tricky to see behind in there).

Since clicking it back in correctly (& making sure the rest are seated tight) it's been as good as gold... even feels better to drive.

Thank you to everyone that contributed for your time and knowledge on this issue... 

Cheers guys.

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