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vwnewton, VW Owner,ASE Master and L1 Advanced
Category: VW
Satisfied Customers: 307
Experience:  25 years of VW obsession turned into a job, last 15 years as a VW Tech.
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My friend has just changed the head gasket on s 1997 T4 VR6.

Customer Question

Hi. My friend has just changed the head gasket on his 1997 T4 VR6. Whilst the head was off he turned on the ignition to wind up the drivers window and heard a continueous clicking sound coming from the fuse box. Now the engine is built up again there is no spark. I checked the cam sensor for him which had not output signal. Cam sensor changed - still no spark. Tried a fuel pump relay (position 12 in relay plate) borrowed from a MK3 Golf TDI as it was the same relay. Still no spark. Tried a known good coil pack. No good. Can't hear the fuel pump working either. I'm really struggling to find any info with it being a VR6 model. Van was running fine before (apart from the leaking head gasket). Any help or ideas would be apprecieted.
Submitted: 1 year ago.
Category: VW
Expert:  Ross replied 1 year ago.

Hi I'm Ross, thanks for trusting me to help you today. I am a diagnostic and repair technician and I look forward to working with you.

This sounds like a problem with the ECU, Have you carried out a diagnostic scan yet to see if there is anything obvious stored in the memory?

Customer: replied 1 year ago.
Not yet. Should be getting hold of a diagnostic scanner tomorrow. I was thinking the problem could be linked to the ' clicking noise' when the ignition was turned on. My friend says it didn't stop when he turned the ignition off, only when he disconnected the battery. Are there any other relays that could affect the engine management? Am I correct in thinking the ECU takes its power from the fuel pump relay? I am ensured all the engine earth connections are connected but would it be worthwhile running a extra cable from the engine to the battery negative to make sure the engines earthed?
Expert:  Ross replied 1 year ago.

Ok great. The ECU is fed from the fuel pump relay but it also has its own power supply.
An earth problem is perfectly possible so I would advise checking the ECU Earths, and coil pack.

I have seen ECU Failure occur from powering the ECU with certain connectors disconnected, certain earth feeds can cause the power to back feed through the ECU Components and cause them to burn out. The fuel pump will not run without a feed from the ECU, so keep that in mind, the coil pack amplifier can also burn out with its earth disconnected which is a possibility.

Its going to be difficult for me to give you specific advice as to what it might be and other than ECU failure caused by powering it with various circuits disconnected, there is a good chance this is something very simple such as a bad ground etc... I think you will need to have a good probe about with a mutimeter at the relays, switching and switched sides, also check the ECU power supply from the relay at the ECU connector if not already done. Do an EOBD scan ASAP And let me know what if anything is found as this may offer a clue.

I'm attaching some diagrams of the ECU wiring which is not great but will give you a rough idea of how the circuits and relays work.

Expert:  Ross replied 1 year ago.

file attached

Customer: replied 1 year ago.
Thanks Ross. This diagram sheds a bit more light on things for me. I'll let you know about the diagnostics ASAP.
Expert:  Ross replied 1 year ago.

No problem, just reply when you are ready and I will get back to you ASAP. Feel free to ask if you need any assistance in the mean time, thanks, Ross.

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