I'd look at the used fuel pump first. It is the "pressure" pump.
My son's 16 valve jetta died on the highway, it got towed home. He is tired of messing with it so I am buying it. Can't pass up a half decent Mark II.
The issue: I was able to get it to run, but I pretty much had to double the VE maps. and megalog viewer still says some areas are running lean. He said he replaced the in tank fuel pump before, with a new one. He replaced the outside fuel pump, what I refer to as the "boost pump" with a used pump off of one of my cars. Pressure gauge on the fuel pressure regulator says 30 PSI.
I haven't had a chance to look at it yet, I have a VR6 all taken apart in my garage.
Question: if the in tank fuel pump fails, does the boost pump have enough suction to pull the fuel up from the tank, or will it just cavitate? I always thought the in tank pump was a low pressure, high volume pump that just needs to push it up to the high pressure pump. I see potential problems as pumps, the fuel filter, the sock or whatever filter is on the in tank pump, blocked or kinked fuel lines, and probably a messed up pressure regulator.
Flow is restricted in some way, and the system is trying to open the injectors up twice as long to get enough fuel. Is there anything I am missing here?
What if I decide to just replace the old antique fuel pump stuff with a Walbro or something like that? I did a search and saw some people had done that, but no specifics on how they set it up.
Does a Walbro 255 output bypass the boost pump, accumulator, and all that stuff and go straight to the pressure regulator up front (with a filter in there somewhere)? Use the existing plastic fuel line, or run a hard line or something from front to back? If prices were not so steep I would replace with VW components but sticker shock is pretty harsh on these parts.