Fuel is not returning to the tank and there is too much pressure on the feeding line. Got a 99 VW Polo which uses the MP9 fuel injection system, the car won't start it only start when I kick start it even though the starter swing well. Check the fuel lines, the fuel is pumped up to the intake but nothing is coming out of the return line to the tank, I replaced the fuel pressure regulator and it worked for a couple of hours and went back to the issue again. I'm thinking that the fuel is not getting into the injectors, would like to know what would cause the fuel not to return to the tank when it goes to the engine. I also have a new fuel pump and battery.
The only things that are likely to cause fuel not to return are either a failed fuel pressure regulator, or an obstruction in the fuel rail. Even though you recently replaced the fuel pressure regulator, my guess is that it’s the cause. It’s not impossible for new parts to fail, especially if they were not of original equipment (OE) quality. I would suggest getting a new fuel pressure regulator from the dealership, and put that part in to see if it makes a difference. If it doesn’t, then you will need to have a qualified professional, such as one from YourMechanic, inspect the fuel system and diagnose the cause of the no start condition.
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