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Discussion Starter · #1 ·
Hi Folks; My 2005 Envoy 4.2 had a rusty fuel pump / sender that leaked and had to be replaced. I had my trusted shop replace it as I was not looking forward to dropping the tank. The car was hard to start with the new (Spectra, I believe) unit. It turned out that the internal check valve was bad. The pump was replaced with another unit of the same make. Still hard starting. I was told to let the fuel pump run for several seconds before cranking. Not happy with this, I requested the pump be changed with a different brand. This THIRD pump was OK for approximately 10 months but now the car is hard starting again, particularly bad if the car is hot and an hour our two have passed since shutoff (vapour lock?)
Rather than change the fuel pump yet again, would it be possible to install an external check valve in the fuel line?
Thanks, Peter in Canada, otherwise loving my Envoy!
 

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'05 Chevy TB EXT
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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.
 

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How do you know the hard starting ten months later is the same problem as hard starting previously?

Connect a fuel pressure gauge, diagnose pump problem instead of assuming pump problem. If it's the pump, I'd think the shop owes you some warranty work.
 

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Discussion Starter · #4 ·
Yes, it is only an assumption that it is the fuel pump check valve. I made the assumption because, as before, performance was completely normal once the car starts. Also starting is better if I leave the ignition in the run position for a few seconds before cranking. I can't smell any gas leaking, so (assumption only) I figure gas must be leaking back into the tank. I have a fuel pressure tester but will have to locate the connection point on the Envoy. I have read on another thread the one should stick with an ACDelco pump.
 

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'05 Chevy TB EXT
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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.
 

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Discussion Starter · #8 ·
Found the Shrader valve, top front of engine just slightly to the drivers side on the incoming fuel line. The pressure drops almost to zero, almost immediately aftershutting of ignition.
 

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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.
 

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Discussion Starter · #11 ·
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
 

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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...!
 

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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.
 

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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.
 

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There is no externally accessible FPR on the '05s
Yeah, but is it integrated into the pump assembly, or is it serviced separately?

The OP is blaming the check-valve, but this pressure loss could just as easily be the regulator. If the regulator is part of a "Pump Module", it doesn't matter--the whole works gets replaced; and perhaps under warranty. But if the regulator is separate, that might explain repeat fuel pump replacements--the pumps could have been fine, the regulator was bad.

I've never had an '05 "pump module" apart. The only fuel pump I've ever dicked with on a GMT360/370 is my '03--and the regulator is up by the engine.

For that matter, there could be a leak in the fuel plumbing inside the tank. Years ago, there was either a rubber hose or a damper assembly that connected the pump to the steel tubing. That hose, or the damper could rupture and leak inside the tank. I expect the same could happen with the integrated "Pump Modules".
 

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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..
 
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