Hey,

I've been trying to figure out why my 1.7 D-jet only idles for 30-40s and then dies. It will start really well after 20-30 minutes of rest and then do the same thing. I've been through my FI, tested everything (CHT included) and everything checks out.

I took a look at the fuel lines--thought I had a kinked supply line and found that I can start the car, it will idle, and when it dies, large bubbles (like two or three big ones) of air back-feed into the clearish supply hose that runs from the fuel tank to the filter.

Air isn't supposed to be in the lines, eh?

I guess what I should mention is that this just started happening. I was previously able to idle just fine. The fuel pump is old and I was surprised it worked (29PSI or so when I hooked a guage to it this summer after installing the d-jet). I'm pretty sure the fuel lines are hooked up correctly...

Would a faulty proportioning valve cause fuel (and subsequently the air bubbles that I see) to drain back into the tank?

Could be a pump dying.
Could also be temp related...its cold now.

test the cold start injector
test the AAR valve.

Rich

Some observations:
1. First of all, why do you have clear fuel lines? Apparently, it's convenient for watching bubbles, but you should have proper 30R9 fuel-rated lines.
2. You shouldn't have bubbles. Particularly coming OUT of the inlet to the pump. I'd suspect the pump.
3. You can verify the pump by checking the fuel pressure after the car dies.

Thanks guys,

Dave--the plastic lines are the amber ones that come through the tunnel, which (ideally) should be replaced with the stainless ones. I had my LED headlamp on it and I could wiggle the hose from the filter to the pump and noticed some large bubbles backfeeding.

I will check the fuel pressure and go from there. The pump itself does run. I believe the pump has been hacked into once before to repair of possibly the check-valve. (according to the PO who sold me in the injection system). I have a new pump on the shelf!

You state that the DAPO opened up the old pump.
You have a new one.

What part of this seems complicated.
Swap the pump...see if you found your problem...

Rich

There's no check valve in the stock pump. You might be thinking of the over-pressure relief valve. The relief valve is located inside the little crimped-on metallic cap, about the size of the tip of your little finger.

That valve isn't designed to be serviced. If your previous owner opened it up, he probably wasn't able to crimp it back together properly and it's likely bleeding off pressurized fuel back to the return fitting on the tank.

Even if the PO didn't mess with it, I would blame the pressure relief valve if the pump is still turning smoothly. I had a pump which pumped fine gradually stop working because the spring was losing stiffness. (I ended up replacing the spring with one from a pump with a dead motor, but I would not recommend that route for the reason stated above.)