Blocked Fuel Return Line?

[rparker888]

Good day all,
Finally signed up after years of lurking as I have a very puzzling problem. Car is a 1990 UCF10RGKW with a possible plugged fuel return line. My question is if there is some sort of safety valve that shuts the fuel return line (in case of accidents etc.). Currently my fuel pressure is pegged at 48psi with or without vacuum applied to the Fuel Pressure Regulator (FPR).

Disconnecting the Return Line and returning it to a separate fuel can, I get 42psi w/o vacuum applied and 35psi w vacuum applied which is to spec.

Applying compressed air (via duster) into the banjo fitting reveals that initially there is some gurgling at the fuel tank for maybe 2 seconds then it become completely blocked and a huge rain of fuel back through the return line on me. Yes, I opened the fuel cap. Nice. This is what leads me to believe there is some check valve that might have been triggered. Even now, it can't receive anything into the return line.

Any thoughts from those who have touched the fuel lines before?

For reference, what prompted me to do this search is a slightly rough idle and a miss on sweeping the rev range. I haven't been able to solve this for years. I've since decided that I'm going to have to do it myself since the local mechanics can't even feel the problem or tell me that its an old car and shouldn't be expected to perform flawlessly. I can't accept this.

Thank you for your help and time.

Regards,
Ryan E. Parker

 

[Zuffen]

As far as I know there are no check valves in the fuel return line.

I've done 3 engine swaps with 1UZs and all have had open return lines to the tank.

I would suggest disconnecting the fuel return line at the tank and ty purging it with air. if that is clear I'd connect it to the FPR and run it into a can and see what happens. At least that way you will know where the problem is.

Another option is rather than running it into a can why not use a long piece of hose and shove it down the fuel filler and go for a drive?

 

[rparker888]

Ok, that's confirmation enough that I've probably got to get my armpits wet with fuel. I'll try the fuel line into the filler test first.

Thanks for your help.

Ryan

 

[Zuffen]

If you're a smoker, take a break!

 

[rparker888]

If you're a smoker, take a break!

HAHAHAHA. In this instance, I don't look forward to a bombastic experience.

 

[dweinhart]

I might check the hard line on the driver side engine bay where the hose connects to it. There are some bends before it goes below the firewall. When I was installing FMU, I had to move those lines and the hard line wanted to kink. If there was previous work done (engine pulled) the hard lines for the return may have gotten crushed or kinked (hard right angle) thus restricting the flow. I saw no check valves between the bay and the tank..