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Discussion Starter · #1 ·
Morning All,
A couple of weeks ago I swapped the tired old Allard intercooler on my 1.8t for a new Airtec kit (not overly impressed) and have had a couple of electrical issues since then.

Pulling on to a motorway from a service station, accelerating hard I had a handbrake light, oil pressure light come on and other gauges go off. A quick restart failed to clear it and a longer later stop led to the the immobiliser kicking in. Pulling the earth wire cleared the problem, although the fuel tank was stuck on full.

A couple of days later another spirited take off led to similar warnings and flashes on the dash which also cleared when the battery was disconnected.

Neither time was the engine affected and it ran 100+ miles on both occasions without issues.

I've checked all the earths, etc on the engine that may have been disturbed with the intercooler swap and they all seem fine, but wondering if there is anything else worth checking?

As far as I can tell the only permanent issue is the fuel gauge.

Any thoughts?
 

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Did you disturb the outside temp sensor that clips into the bumper?

They're all sender related (handbrake light for brake fluid), so you might've disturbed a shared sender ground.

Check for coolant in the fuel sender unit plug under the back seats.
 

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Discussion Starter · #3 ·
Did you disturb the outside temp sensor that clips into the bumper?

They're all sender related (handbrake light for brake fluid), so you might've disturbed a shared sender ground.

Check for coolant in the fuel sender unit plug under the back seats.
I have had issues with the outside temp sensor in the past and actually just fitted a new one having sorted some earlier wiring issues down to it but that all seems fine now.

Everything is working fine now bar the fuel sender, but will dig out the seats to check the sender.
 

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Immo can only be blocked by a cluster not handshaking with the ECU - which is achieved with a dedicated k-line to the ECU. Shy of that being interrupted or the cluster not powering up, there's nothing else.

So if you have an immo fault, combined with all of the other cluster faults, I'd say the cluster is shitting the bed.
 

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Good shout that, the cluster acts as a bridge for the ground for several sensors too, so that would make sense.
 

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Discussion Starter · #6 ·
Immo can only be blocked by a cluster not handshaking with the ECU - which is achieved with a dedicated k-line to the ECU. Shy of that being interrupted or the cluster not powering up, there's nothing else.

So if you have an immo fault, combined with all of the other cluster faults, I'd say the cluster is shitting the bed.
Everything generally works fine.

The immobiliser occasionally kicks in if I quickly put key in ignition to start the car, doing it normal speed never causes an issue. I am not sure if that if that is considered a fault, I have seen similar in other cars, they just take a little time to wake up and recognise the key.

The two recent and only dash crashes that i have had seem to have been down to very hard acceleration with a fully loaded car. I have tried to recreate without any success.

The only problem currently is that the fuel gauge goes from empty to full when the ignition goes on and then stays up there even though there is only half a tank.


I'm going to check the tank wiring and trace back to the cluster.

Where's the best place to go to find wiring diagrams?

Thanks
 

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Cluster wiring might be easier to check, two screws and the unit pulls out. Two plugs, see below for diagrams for each plug. Pin 7 ground goes to pin 9 (I think) in the T14a plug. A short to this ground made my fuel level gauge inaccurate (among other things).

Haven't got a fuel pump pin out to hand, but IIRC pin 1 is switched live, and the opposite end of the plug is the sender ground from pin 7 on the cluster. Not sure about the two in between.

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Discussion Starter · #8 ·
Cluster wiring might be easier to check, two screws and the unit pulls out. Two plugs, see below for diagrams for each plug. Pin 7 ground goes to pin 9 (I think) in the T14a plug. A short to this ground made my fuel level gauge inaccurate (among other things).

Haven't got a fuel pump pin out to hand, but IIRC pin 1 is switched live, and the opposite end of the plug is the sender ground from pin 7 on the cluster. Not sure about the two in between.

View attachment 52034 View attachment 52035
Perfect, thank you.

What's the best manual to get for the car?
 

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Perfect, thank you.

What's the best manual to get for the car?
Bentley manual is good, and there's a few links floating around on other forums to download a copy.

Never used the Haynes manual for the mk4, but they're available for under a tenner on eBay and that could be a good choice if you wanted a hard copy manual.
 

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Discussion Starter · #10 ·
Bentley manual is good, and there's a few links floating around on other forums to download a copy.

Never used the Haynes manual for the mk4, but they're available for under a tenner on eBay and that could be a good choice if you wanted a hard copy manual.
Perfect, thanks.
 
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