Golf 7 GTI hard starting issue with fault P21F9

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dtauwel
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Golf 7 GTI hard starting issue with fault P21F9

Post by dtauwel »

Hi guys.Firstly, I used to be a technician with VW but opened my own independent workshop specializing in Audi & VW vehicles only. So this Mk7 GTI popped a Big End bearing in September 2020. The vehicle was with the dealership that recommended an engine (Head, block & sump only) replacement at a cost of around R135000 So i had the vehicle collected from the dealership by a towing company. So there is the 1st hick-up, I never drove the vehicle before repairs were done. I use mainly ODIS software for diagnostics but also VCDS. On the diagnostic logs done before we removed the engine, various faults including this P21F9 was already logged. We did not make much of it as we had already identified the mechanical fault and thus did the repair accordingly for around R70000. So about a week after he collected the vehicles my troubles started. Blaming the hard starting problem on us and claiming it was not doing it before. Long story short, the fault only occurred when he had the vehicle, but with us it never happened, eventually managed to re-produce the fault only after leaving the vehicle at idle for a prolonged period and the wanting to restart the engine thereafter. There is a Turbo Replacement recommendation from VW AG as per TPI 2037633/4 released n 24/09/2015. So if any one has viable proof to contradict the TPI, please share before I remove the Turbo for no reason. Thanks

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THANAS
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Re: Golf 7 GTI hard starting issue with fault P21F9

Post by THANAS »

Doubtful that the turbo would affect starting. More likely culprits would be a failing injector(s) or leaking HPFP seals.
dtauwel
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Re: Golf 7 GTI hard starting issue with fault P21F9

Post by dtauwel »

THANAS wrote:Doubtful that the turbo would affect starting. More likely culprits would be a failing injector(s) or leaking HPFP seals.
Valid speculation yes. Took off the downpipe and turbo inlet this morning and to my surprise there is play on the turbine shaft. It does make sense that at idle it can run at a richer fueling rate due to lack of air supply caused by Turbo failure. But it's a 50/50 scenario though

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dcmk4
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Re: Golf 7 GTI hard starting issue with fault P21F9

Post by dcmk4 »

dtauwel wrote: Wed May 12, 2021 9:30 am at idle it can run at a richer fueling rate due to lack of air supply caused by Turbo failure.
At idle, the motor is in vacuum so regardless whether the turbo has play or not, it is not providing any positive pressure.. therefore wouldn't affect fueling.
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THANAS
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Re: Golf 7 GTI hard starting issue with fault P21F9

Post by THANAS »

dcmk4 wrote: Wed May 12, 2021 9:43 am
dtauwel wrote: Wed May 12, 2021 9:30 am at idle it can run at a richer fueling rate due to lack of air supply caused by Turbo failure.
At idle, the motor is in vacuum so regardless whether the turbo has play or not, it is not providing any positive pressure.. therefore wouldn't affect fueling.
Agreed. And even if it was causing additional restriction the manifold pressure sensor would just read a lower value and correct the injected fuel quantity.
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Re: Golf 7 GTI hard starting issue with fault P21F9

Post by s3 freak »

Bump.. Did you come right?
dtauwel
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Re: Golf 7 GTI hard starting issue with fault P21F9

Post by dtauwel »

We're still busy with that vehicle, I sent the turbo in for strip and assessment, only found a crack on exhaust housing at the wastegate. I had the injectors bench tested as well. All injectors passed.
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