The car:
305 TBI from an 88 firebird (on an L69 engine). Walboro 255 fuel pump about 5 years old. Made stock FPR adjustable per Ultimate TBI mods. Setup has worked for that same 5 years.

Problem:
No fuel pressure.

Facts:
When the pump is dead-headed, it will hit 25 psi on the first prime, 50 psi on the next prime (I only need 15 to run the system).
When I disconnect the return line and put it in a can, priming the pump causes it to shoot out like a garden hose, but shows no pressure on the gauge.
When I try to start it, no pressure shows and it'll stumble around idle for 5 seconds or so and die.
If I pinch off the return line sufficiently (used vice-grips), I get pressure and car runs like nothing is wrong.

What I've done so far:
Completely disassembled the fuel portion of the TBI unit. Cleaned it, new gaskets and a brand new membrane and spring for the regulator. Assembling the regulator is still practically a two-man job thanks to the spring pressure, but it refuses to resist any more than 1-2 psi when installed. It's acting like there is no spring pressure at all, but it's as difficult as ever to assemble the regulator due to the spring pressure.

Physics tells me that this should work. It worked for 5 years, and now all of a sudden this reliable method of controlling fuel pressure seems to just...not work?!?

Has anybody else seen this phenomenon?

I'm thinking of just moving on by installing another regulator in the return line of the system to build up the pressure. If I do this, are there any suggestions on how to disable or bypass the stock unit, in case it suddenly decides it wants to work while I'm driving somewhere?

Thanks

 

Take some pictures of the regulator torn apart. I want to see how you are reassembling it before it goes togather. Almost sounds as if your regulator diaphram is defective or is being installed backwards.

 

I doubt you could have placed the cup that cradles the spring upside down?

It has been 10 years since I had a stock GM FPR but I dont recall it having that much resistance to require an xtra set of hands. After all with it adjustible you should be able to take almost all press off spring. My recollection is that I had too much of a shim so press too high on first attempt.

sounds like fuel is bypassing FPR seat and or injectors.

 

I've attached pics of the parts and how I assemble them. I've installed the original spring for now, seeing as how the new one didn't make any change to the situation. Keep in mind this problem occurred without any dis-assembly or assembly of these parts (or any fuel system parts). It just started happening out of nowhere.

The diaphram appears to be in great shape. Both the old one and the new one behave the same.

I concur with Ronny's observation that the fuel is bypassing the FPR seat. The injectors do not leak (verified with paper towel under and priming the pump). I just can't explain why.

When I said a 'two-person job', I was trying to convey that the spring is still plenty stiff and should hold plenty of pressure. It hasn't gone limp or broken.

I'm totally lost. I just looked at prices for new, in-line regulators. I could probably buy an entire replacement throttle body at that price!!! I really don't like the thought of that, considering this fuel system is on the chopping block already.

 

Either the fuel pump is bad or the hose between the pump and the sender outlet tube has split. Being a 5-yr old pump puts it right in the middle of the era of bad '0169 Walbro pumps...

With the return line pinched off should have had 70+ psi of fuel pressure on the first prime.

RBob.

 

I was a little disconcerted when I saw the dead-head pressure test myself, but I chalked it up to air in the test line when this was done. I've had this thing apart half a dozen times now.

The pressure held steady for well over a minute after turning the pump off. If the hose between the pump and the sender outlet tube had split, would the pressure remain after the pump is off?

If the pump itself was bad (which i'm not saying it's not), how can we explain why the car runs when the return line is pinched down (not completely closed...just enough to build up about 20 psi)? The regulator should be doing the same 'pinching' that I was doing to the return line. I didn't test it on the street under load due to safety reasons, but just in the garage it seemed to be working just like it did when it was running.

...didn't know there was an era of bad pumps, though. I've heard nothing but great things about the Walboro 255.