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Discussion Starter · #1 ·
2007 vw Jetta 2.0T fsi. The car sat for about 4 years, I got it for free from girlfriends moms boyfriend. I really need to get this car on the road because I don't have any other cars to drive.

Firstly I have a check engine light on for hpfp performance. I put in a new HPFP. Its not the pump, there is air is getting into the fuel system somehow. The air is slowly building up inside the HPFP and making the low pressure sensor malfunction because its measuring air pressure not fuel pressure. The engine starts to knock a little bit when it gets hot too, probably lean conditions. The problem seems to occur only when the engine gets hot and completely heat soaked.

There are no air bubbles in the system before the high pressure pump. The HPFP is new, and so is the sending pump and the fuel filter, and low pressure sensor.

If I clear the engine code and run the car it runs really good when its cold, and eventually when it gets heat soaked then air comes into the HPFP and check engine light comes on. It took 40 miles to turn on last time. I plugged in a fuel pressure gauge and the system holds pressure and has enough pressure. I can bleed the system at the check valve when its cold and only fuel comes out but when its hot It cant be bled because air keep coming out of it. So it holds pressure, which makes me think there is no leak in the lines, and its just the fuel vaporizing.

All I can think of is that the high pressure release valve is stuck closed and so when the car gets heat soaked the fuel boils because its not circulating. If its not circulating then some of the fuel in the fuel rail might get super hot and vaporize. It looks like the fuel that is released by the release valve mixes with incoming cold gas at the T fitting then goes back to the HPFP. This cools down the unused fuel. The injectors are in the cylinder so it seems like it needs to circulate in order to not get super hot from the very high temps in the cylinders. So I'm thinking the fuel is vaporizing and collecting in the pump. Which is only happening when the engine is heat soaked. I ordered the valve $125.

If I put in this valve and it still doesnt work then I have no idea what it could be. Maybe I need to do a better job checking the fuel lines before the hpfp

Any other ideas? Doesnt make sense that it holds pressure and still creates air bubbles or fuel vapor bubbles?
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