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Discussion Starter · #1 ·
I have a friend who has a MK6 tdi. After sitting over night it'll crank but not start. If you spray just a little starting fluid in it, it will fire right up and idle as long as you let it. It revs fine in neutral. When you drive it it won't rev past 2,000-3,000 RPM. Up until that RPM range it doesn't feel like it's lost any power. Feels like limp mode to be, but the glow plug lights don't flash. Any ideas? Any and all help is appreciated.
 

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I have a friend who has a MK6 tdi. After sitting over night it'll crank but not start. If you spray just a little starting fluid in it, it will fire right up and idle as long as you let it. It revs fine in neutral. When you drive it it won't rev past 2,000-3,000 RPM. Up until that RPM range it doesn't feel like it's lost any power. Feels like limp mode to be, but the glow plug lights don't flash. Any ideas? Any and all help is appreciated.
Maybe you have a small air leak on the fuel line/filter? I had an issue once where the fuel filter was not quite right (aftermarket) and was missing and o-ring on top. So I was not getting a fuel leak, but air would enter the fuel line if it sat for a long time. Took a long time to crank but once fired up would run fine. Might try to see if you can prime the system with the fuel pump a couple times after sitting overnight and would allow to start without starting fluid?
 

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Discussion Starter · #3 ·
Maybe you have a small air leak on the fuel line/filter? I had an issue once where the fuel filter was not quite right (aftermarket) and was missing and o-ring on top. So I was not getting a fuel leak, but air would enter the fuel line if it sat for a long time. Took a long time to crank but once fired up would run fine. Might try to see if you can prime the system with the fuel pump a couple times after sitting overnight and would allow to start without starting fluid?
We tried priming the fuel system with VCDS already to see if it made a difference. Nothing changed. We looked for fuel, and air leaks everywhere and I can't find anything. We put a new mass air flow, and a new map sensor on it and still the same issue. Right now we're currently cleaning the intake manifold to see if maybe the swirl flaps were stuck shut. We also used VCDS to test the actuator, and the N75 valve there fine, and the fuel pressure reads fine. Maybe the veins are stuck inside the turbo?
 

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Hmmm... do you have any error codes at all with the Vagcom scan? I would be surprised that there are none. So, if you run it for a while, then shutdown, it would restart okay, and only has issues with restarting after sitting overnight?
Since you have a Vagcom, then you should be able to plot requested boost vs. actual boost to see if there are any issues with the turbo. Maybe there are two things wrong, but I don't think (not an expert here, just own several TDIs) that a stuck turbo vanes would cause a non-start. I still think fuel as first option. Fuel pressure may be okay, but volume delivery could be an issue. Have you changed fuel filter recently? It is definitely fuel at least on the cold start since spraying starting fluid fixes that. The other thing that comes to mind, most vehicles have a check of things that need to be okay before a start is allowed, and otherwise it won't allow the fuel pump (not HPFP, the in tank one) to run - part of the start relay sequence. Would have to do some research to find out what all needs to be okay on this vehicle. Definitely do a full scan with Vagcom, otherwise I'm out of ideas.
 

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Discussion Starter · #5 ·
Hmmm... do you have any error codes at all with the Vagcom scan? I would be surprised that there are none. So, if you run it for a while, then shutdown, it would restart okay, and only has issues with restarting after sitting overnight?
Since you have a Vagcom, then you should be able to plot requested boost vs. actual boost to see if there are any issues with the turbo. Maybe there are two things wrong, but I don't think (not an expert here, just own several TDIs) that a stuck turbo vanes would cause a non-start. I still think fuel as first option. Fuel pressure may be okay, but volume delivery could be an issue. Have you changed fuel filter recently? It is definitely fuel at least on the cold start since spraying starting fluid fixes that. The other thing that comes to mind, most vehicles have a check of things that need to be okay before a start is allowed, and otherwise it won't allow the fuel pump (not HPFP, the in tank one) to run - part of the start relay sequence. Would have to do some research to find out what all needs to be okay on this vehicle. Definitely do a full scan with Vagcom, otherwise I'm out of ideas.
Looked at Actual and Specific boost. Seems to be fine, full scan on vagcom only shows where an airbag has been deployed before. No engine codes at all. I'm starting to run out of ideas myself. Lol Someone had mentioned that an injector could possible have a very high return causing it to not be able to build enough fuel pressure for an initial start. However, I thought if that was the issue we would be able to scan a check engine light.
 

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You can check fuel injection qty for each injector with Vagcom. It gives it in strange units as I recall, but perhaps that might give clues as to an injector or fuel qty problem.
 

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Discussion Starter · #7 ·
My friend has a picture, we hooked my car and his car up to VagCom and driven both of them. Small difference with the injection quanity, I figured possible where we have diffrent tuners.
 
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