[Ravalli Surfer]

Firstly --- don't use your car for a bank-job getaway!
Secondly --- there's no such thing as "vapor lock" in a fuel injected vehicle .... it's kinda technical - but there's no sucking if the pump's in the tank -- just push - push push --- kinda gasoline Lamaze.

IIRC --- SPECTRA is Chinesium junk --- correct me if I'm wrong.

Did you get the manufacturer's name of the THIRD pump?

Was it:我是垃 ?​

Your choice in mechanics is sadly misplaced as they aren't doing you a favor selling you poorly performing parts.

Get a real Delphi pump in there and it should be a lot better .... and NO --- you cannot install an add-on check valve.

 

[Ravalli Surfer]

Even with cheap Chinesium parts, that three pumps could all fail exactly the same way kinda stretches the imagination......

Not impossible, mind you .... just a big Saran Wrap stretch ... that's all.

Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose Diagnose ................. and when that's done ......... change the offending part .........

I made a mistake in thinking this problem was logically diagnosed --- I can see now that there was no logic nor diagnosis at all.

 

[Ravalli Surfer]

I cannot speak for all the years of TBs - but there is usually a Schrader tap into the fuel rail --- someplace.

 

[Ravalli Surfer]

1. Replace pump
2. There is no #2 at this point

 

[Ravalli Surfer]

Thanks Ravalli, I was afraid of that. Am I correct in thinking that the only place for the pressure to leak would be through a bad pump? I don't see or smell a leak (all the lines are new from tank to engine). If the pressure leak was into the engine, can I assume that there would be performance issues or fault codes?
Thanks again for your assistance

On your vehicle, the PRV is in the pump.

That it leaks is now a given with your pressure test --- and think that ... if the pump was frame mounted outside the tank ... what kinda mess you'd have with gasoline squirting all over the place...!

 

[Ravalli Surfer]

The PRV is not monitored by the computers --- just the running pressure (but indirectly so) --- or some can detect extended crank-time which would lead you back to the pump ... or the pump's internal filter ... or the frame rail filter .... or insufficient voltage to run the pump eg: defective-but-not-yet-failed relay, high resistance in the electrical-side of the pump, etc.

 

[Ravalli Surfer]

PS ... the running pressure itself, it not so much being monitored --- but the results of it is.

You'll get Short Term- and Long Term- Oxygen Sensor readings that are offbase values for your vehicle.

 

[Ravalli Surfer]

Where does the '05 hide the fuel pressure regulator?

Dropping pressure could be because of back-flow through the check-valve, or forward-flow through the regulator.

There is no externally accessible FPR on the '05s

 

[Ravalli Surfer]

The pulsation dampeners were long ago done away with as problematic and leak-prone.

Yup -- there are no serviceable parts in the fuel pump assembly --- and there's no option for just-a-pump module replacement either.

I THINK the '03s were the last production run for an accessible FPR --- and it had a return circuit elimination at about the same time --- IIRC.

Eliminating the return line saved a few bux on every car that didn't have it ... talk to the corporate bean counters.​

I have no experience with a non-return PRV system on our vehicles --- but my Isuzu 2.6 has an inlet-type of PRV that controls the pressure TO the injectors without any return line at all..

 

[Ravalli Surfer]

Not sure if you figured it out but i have the same issues.

One thing i noticed is that if i do key on -key off -key on, you can hear the pump do a high pitched priming sound. Do the key on key off until you hear the sound drop the pitch mid prime and then it will start. This gets it going everytime. It almost feels like the pump takes too long to prime the main line (since it drains back to the tank). I have time off coming up and i will be dropping the tank and putting the entire fuel sending unit into a bucket of gaz. Ill connect it to a clear section of tubing as i am curious to see if it is a priming failure, or a priming duration issue since the priming on these is only 3 seconds (duration of the priming sound).

I replaced my pump with a delphi pump and the problem persisted. I was told that the 03+ have a back flow check valve on the main fuel line, although i haven't verified this fact yet.

Imma gonna call you on that post-pump check valve --- I have not seen one in many years --- and for super sure my '05 TB/EXT 4.2 doesn't have a check valve that's not IN the fuel pump.

 

[Ravalli Surfer]

Like i said, i haven't verified the information yet. I do find it strange that in certain cases like the OP, not one, not 2 but 3 fuel sending units were bad.

The only other thing i can think of is the 2 cheap pieces of hose between the pump and the upper connector. This material prone to "flex fatigue" View attachment 64109

"Flex fatigue"? Never seen it there.

The corrugated lines are necessary so when the pump is installed, the lines can conform to the depth of the fuel tank.

The pump rests on the bottom of the tank and I don't think there's any reason to find problems where there are none.

There are ways to destroy the sending unit if care isn't taken to ensure that the arm is not bent or forced into positions of which it is not designed.

Times, when several parts exhibit the same failure, are not always the fault of the part --- but the size of the hammer used to install it.