Hesitation, staggering on acceleration and poor gas mileage.

[MT-2500]

Originally Posted by 534BC

sounds like it is not a regulator at all and simply a simple relief valve , in either case if it's plumbed in between the pump and the next component then it can indeed cause the problem (of low pressure) I supose this is when to pinch that return line off and keep testing at the test port , right?

Pinching off the return line is one of the first steps in testing.
Pinching off return lines shuts off all pressure from being returned back from tank.
Then if the fuel pump is putting out good pressure and is not leaking back into the fuel tank. And a supply fuel line is not leaking off.
The injector unit/injector and or the fuel pressure regulator is leaking the pressure off.
On this one the injector body and injectors and fuel pressure regulator are all inside the upper intake.
To check them for leakage you need to pull the upper intake and prime up fuel pressure and watch for leakage.
Bright spots and raw gas in the intake is the thing to watch for.
MT

[MT-2500]

If it is working right it regulates/holds the fuel pressure from 60 to 66 lbs according to engine vacume.
Full load/no vacume it should go to 66 lbs.
No load /full vacume it drops pressure back to 60 lbs.
It does regulate from 60/66 lbs pressure.
And it dumps all extra pressure back into the fuel tank.
But you could say it works as a relief valve to.
It relievs all extra pressure.
MT

[JoshBarber]

Originally Posted by MT-2500

If it is working right it regulates/holds the fuel pressure from 60 to 66 lbs according to engine vacume.
Full load/no vacume it should go to 66 lbs.
No load /full vacume it drops pressure back to 60 lbs.
It does regulate from 60/66 lbs pressure.
And it dumps all extra pressure back into the fuel tank.
But you could say it works as a relief valve to.
It relievs all extra pressure.
MT

After enitial teardown, fuel pressure regulator showed no signs of leak off nor while running. Pressure continued to only be 54psi while running....0psi off. Appears to be the fuel pump, or the checkvalve there-in.

This is what I'd told the mechanic ahead of time. I gave him a paper that I printed up giving him all the pressure readings and information I'd already concluded after pinching the return line..as well as making it clear on the phone that I believed it to be the pump or pump valve, although I needed to pull a pressure test at the filter (thanks to MT-500's suggestion). He said he would do so "not to worry about it", that he'd take care of it, and that he wouldnt be charging me to diagnose it.

After diagnosing it originally:

He told me he was sure it was the regulator. I didnt question if he pulled pressure at the filter, as I'd already been adement about it...and felt I was telling him how to do his job when he was doing me a favor to begin with. I told him thats fine, to remember that I told him otherwise.....
sure enough......NOT THE REGULATOR.
So he appologized for the delay/inconvience, and didnt charge me for the tear down.

Current status:
He's now told me he's sure its the fuel pump, and that he checked pressure at the filter with the same result.

Instead, he ordered a new GM pump assembly for 18gallon tank (pump/level sending unit etc) from the dealer normally $500 (received @ his cost) for $420(part) + $90(labor) to drop the tank and install it. $510 total.

I could've got an AutoZone Bosch pump for $346 and had it installed = $436 approx.

But I've been told by many people that the aftermarket pumps die out quick. I figured for an additional $75 it was worth getting a part that is made specifically for my vehicle, and has a better reputation. I'm tired of purchasing cheaper parts from AutoZone and having them not mate up to my vehicle correctly because they're made to fit 20+ various different vehicles.

I'm hoping the fuel pump is the cause of the horrible MPG and surging as well as the hard start. Hey...if nothing else, Im looking forward to a quietter pump, and a accurate fuel guage for the first time since I've owned it!

I will report back.

[MT-2500]

Originally Posted by JoshBarber

After enitial teardown, fuel pressure regulator showed no signs of leak off nor while running. Pressure continued to only be 54psi while running....0psi off. Appears to be the fuel pump, or the checkvalve there-in.

This is what I'd told the mechanic ahead of time. I gave him a paper that I printed up giving him all the pressure readings and information I'd already concluded after pinching the return line..as well as making it clear on the phone that I believed it to be the pump or pump valve, although I needed to pull a pressure test at the filter. He said he would do so "not to worry about it" that he wouldnt be charging me to diagnose it.

He told me he was sure it was the regulator, although he hadnt checked pressure at the filter. I told him thats fine, to remember that I told him otherwise.....sure enough......not the regulator.
So he appologized for the delay/inconvience, and didnt charge me for the tear down.

Instead, he ordered a new GM pump assembly (pump/level sending unit etc) from the dealer normally $500 (received @ his cost) for $420(part) + $90(labor) to drop the tank and install it. $510 total.

I could've got an AutoZone Bosch pump for $346 and had it installed = $436 approx. But I've been told by many people that the aftermarket pumps die out quick. I figured for an additional $75 it was worth getting a part that is made specifically for my vehicle, and has a better reputation. I'm tired of purchasing cheaper parts from AutoZone and having them not mate up to my vehicle correctly because they're made to fit 20+ various different vehicles.

Will report back after its installed.

Thanks for letting us know how it is going.
And 10-4 on cheaper parts.
Always better to go dealer OEM or if you do go aftermarket make sure it is OEM quality.
A lot of aftermarket parts co. have parts made up to there own specs.
They may even carry a major brand but are not full OEM quality or specs.
After you get the fuel pump replaced I would recheck the fuel pressure and check for leakdown.
Before you can rule out a bad regulator it needs to be tested under normal fuel pump pressure.
The 55 lbs of pressure may not be enough to make it leak or show up bad or good. The normal fuel pressure of 60-66 lbs will test it.
If no leak down down and 60-66 lbs of fuel pressure after fuel pump replacement it will be in good shape. It should run a lot better.
And gas mileage should go back to normal
Good luck and let us know how it goes.
MT

[JoshBarber]

Originally Posted by MT-2500

Thanks for letting us know how it is going.
And 10-4 on cheaper parts.
Always better to go dealer OEM or if you do go aftermarket make sure it is OEM quality.
A lot of aftermarket parts co. have parts made up to there own specs.
They may even carry a major brand but are not full OEM quality or specs.
After you get the fuel pump replaced I would recheck the fuel pressure and check for leakdown.
Before you can rule out a bad regulator it needs to be tested under normal fuel pump pressure.
The 55 lbs of pressure may not be enough to make it leak or show up bad or good. The normal fuel pressure of 60-66 lbs will test it.
If no leak down down and 60-66 lbs of fuel pressure after fuel pump replacement it will be in good shape. It should run a lot better.
And gas mileage should go back to normal
Good luck and let us know how it goes.
MT

I assume if it proves to be the pump alone, that the computer must overcompensate for the lack of pressure, and burn more fuel somehow?

[MT-2500]

Originally Posted by JoshBarber

I assume if it proves to be the pump alone, that the computer must overcompensate for the lack of pressure, and burn more fuel somehow?

Yes it will do things like that. The computer does not actually know what the fuel pressure is but low fuel pressure will cause less fuel to go threw the injector and the system to burn lean and when the computer sees it has a lean mixture or engine running lean it will try to rich up the fuel mix with more injector pulse and in turn burn more fuel or lower gas mileage.
On that 4.3 engine the injectors are very sensitive to fuel pressure.
Low fuel pressure can cause a no start cold. A lot of times the injector will not squirt fuel without the 65 lbs of pressure cold.
After you get it started cold it will run and start all day on lower fuel pressure but may not run quite right and may actually burn more gas.
MT

[JoshBarber]

Originally Posted by MT-2500

Yes it will do things like that. The computer does not actually know what the fuel pressure is but low fuel pressure will cause less fuel to go threw the injector and the system to burn lean and when the computer sees it has a lean mixture or engine running lean it will try to rich up the fuel mix with more injector pulse and in turn burn more fuel or lower gas mileage.
On that 4.3 engine the injectors are very sensitive to fuel pressure.
Low fuel pressure can cause a no start cold. A lot of times the injector will not squirt fuel without the 65 lbs of pressure cold.
After you get it started cold it will run and start all day on lower fuel pressure but may not run quite right and may actually burn more gas.
MT

I figured that was the case. I'm surprised it always has started on the second try with only the jump to the 60lbs psi when the pump primed, then back to zero as soon as it shut off.

I'm going to pick it up now. He said pressure reads and holds perfect.
As I said...$510....(ugh....but at least it fixes a bunch of issues....poor fuel level readings, noisey pump, shitty mileage, hard cold starts, and the surging/hesitating).

You gotta admit...$90 to drain/drop the tank and install the new one is pretty cheap. I've done it without a lift with my father on his truck, and its a PITA. Just wish the Dealer pump wasnt such a ripoff. Oh well...a least I got it for $420~!

Should I assume my plugs are all gunked up from running rich now? Or no?

I'll give another report back after driving.

[JoshBarber]

GODDAMNIT!

Job was completed, unfortunately I couldnt get home to get my fuel pressure gauge to bring with me when I picked it up. So I just had to take his word.

The car started immediately on the first click. Good

Pump was quiet as a mouse...no loud buzzing. Good

No surging at all on the drive home. Good

Get home, replace the fuel filter, and recheck pressure at the fuel rail.

OK explain this:
Key off = 60psi
Key on = 64psi then drop to 60psi when pump stops priming (and holds)
Engine running = 54psi !!!!!!!!! (it moves up a bit with acceleration, but 54psi @ Idle)

WTF!?!?!?!?!?!?!

Where am I leaking NOW!?!?!?!?!?!? Is the regulator leaking when running? Or is it the fact that I have a lower intake manifold gasket leak? I know I have this gasket leak. Would it have anything to do with it? Its supposed to HOLD 60-64 while running right? Im so pissed. I plan on calling him first thing tomorrow and telling him something is still not right.

HELP!

[MT-2500]

Originally Posted by JoshBarber

GODDAMNIT!

Job was completed, unfortunately I couldnt get home to get my fuel pressure gauge to bring with me when I picked it up. So I just had to take his word.

The car started immediately on the first click. Good

Pump was quiet as a mouse...no loud buzzing. Good

No surging at all on the drive home. Good

Get home, replace the fuel filter, and recheck pressure at the fuel rail.

OK explain this:
Key off = 60psi
Key on = 64psi then drop to 60psi when pump stops priming (and holds)
Engine running = 54psi !!!!!!!!! (it moves up a bit with acceleration, but 54psi @ Idle)

WTF!?!?!?!?!?!?!

Where am I leaking NOW!?!?!?!?!?!? Is the regulator leaking when running? Or is it the fact that I have a lower intake manifold gasket leak? I know I have this gasket leak. Would it have anything to do with it? Its supposed to HOLD 60-64 while running right? Im so pissed. I plan on calling him first thing tomorrow and telling him something is still not right.

HELP!

Ouch.
Unless you fuel pressure gauge is off/sticking some.
If you have another blazer handy to try it on it .
It looks like the fuel pressure regulator is not regulating right or bypassing the fuel pressure to much.
It would take a large external leak to drop the pressure while running.
Engine running at idle should be 60-62 range full load or engine cranking should be 65-66 lbs range.
Full engine vacume should be 60 lbs and no vacume /engine under full load or engine cranking should be 65-66 lbs.
If the regulator was leaking external you would see a fast leak down on fuel pressure with engine off.
When you take it back to the shop take your fuel pressure gauge with it and check it with his pressure gauge.
It is very easy for a fuel pressure gauge to be off or out of calberation.
The lower intake/coolant leak should not affect the fuel pressure.
Let us know how it goes.
MT

[JoshBarber]

Originally Posted by MT-2500

Ouch.
Unless you fuel pressure gauge is off/sticking some.
If you have another blazer handy to try it on it .
It looks like the fuel pressure regulator is not regulating right or bypassing the fuel pressure to much.
It would take a large external leak to drop the pressure while running.
Engine running at idle should be 60-62 range full load or engine cranking should be 65-66 lbs range.
Full engine vacume should be 60 lbs and no vacume /engine under full load or engine cranking should be 65-66 lbs.
If the regulator was leaking external you would see a fast leak down on fuel pressure with engine off.
When you take it back to the shop take your fuel pressure gauge with it and check it with his pressure gauge.
It is very easy for a fuel pressure gauge to be off or out of calberation.
The lower intake/coolant leak should not affect the fuel pressure.
Let us know how it goes.
MT

Compare the Before and After (Im thinking maybe he only checked the regulator with the key on...which meant it only had a bit of pressure when the pump primed, and then dropped to 0psi as soon as it stopped...which might have not shown a leak) Does this sound like the regulator.

BEFORE-------------------------------------AFTER

KEY OFF : 0psi--------------------------------------55-60psi

KEY ON: 60psi prime - immed. drop to 0psi------------60psi prime - immed drop/hole @ 54psi

ENGINE @ IDLE : 54psi-------------------------------54psi


Sound like the regulator is opening to quickly?
The new pump basically just solved the problem with the line not holding ANY pressure. With the old pump it ran at 54psi but didnt hold when engine was off. Now it runs at 54psi, and holds in the line when shutoff.

[MT-2500]

Originally Posted by JoshBarber

Compare the Before and After (Im thinking maybe he only checked the regulator with the key on...which meant it only had a bit of pressure when the pump primed, and then dropped to 0psi as soon as it stopped...which might have not shown a leak) Does this sound like the regulator.

BEFORE-------------------------------------AFTER

KEY OFF : 0psi--------------------------------------55-60psi

KEY ON: 60psi prime - immed. drop to 0psi------------60psi prime - immed drop/hole @ 54psi

ENGINE @ IDLE : 54psi-------------------------------54psi


Sound like the regulator is opening to quickly?
The new pump basically just solved the problem with the line not holding ANY pressure. With the old pump it ran at 54psi but didnt hold when engine was off. Now it runs at 54psi, and holds in the line when shutoff.

That is what the pressure reading indicate.
But to be sure that the fuel pump is good even if it is new pinch off the return line and see if the fuel pressure jumps up to around 75-85 lbs of pressure or more.
But do not hold/run it at full pressure on it for over 30 seconds.
If the fuel pump is not putting out good full pressure check things like voltage to it and grounds.
If it is good and capable of putting out the full pressure of 75-85 lbs then it points to the fuel pressure regulator not holding the correct pressure.
Let us know how it goes.
MT

[JoshBarber]

Originally Posted by MT-2500

That is what the pressure reading indicate.
But to be sure that the fuel pump is good even if it is new pinch off the return line and see if the fuel pressure jumps up to around 75-85 lbs of pressure or more.
But do not hold/run it at full pressure on it for over 30 seconds.
If the fuel pump is not putting out good full pressure check things like voltage to it and grounds.
If it is good and capable of putting out the full pressure of 75-85 lbs then it points to the fuel pressure regulator not holding the correct pressure.
Let us know how it goes.
MT

I just spoke to him and asked him a few questions. He said you cant run the vehicle with the cover off to watch the regulator for leaks...not sure if thats true or not. But that means he only took the cover off to view the regulator for clean spots, and to look for a leak with the key on.

As I said before, when he looked at it, it only held pressure when the fuel pump primed, then dropped IMMEDIATELY when the pump stopped. So perhaps there wasnt any sign of obvious leakage when there was so little pressure from the pump leak, like you'd mentioned....although, I asked if there were any clean spots and he pretty much said it didnt look like it, there was consistant buildup of carbon throughout.

He's saying maybe my fuel pressure tester is shit...(from AutoZone) but I doubt it. I'm thinking he didnt bother to locate the source of the 54psi after he saw that the pressure was now staying in the line.

I'm going to check the return line again tonight when I get home around 430pm. I'll post my results.

The trucks new fuel gauge doesnt seem to be completely accurate either. Kind of a let down. Maybe all the pumps for our vehicles have a little play in the sender unit? I dont know. Still no sign of surging.

[MT-2500]

10-4 On you can not run it with the cover off.
But you can jumper the fuel pump and watch for external leakage and with fuel pump jumped the pressure reg should hold and regulate 65-66 lbs of fuel pressure at the fuel rail with the fuel pump running.
And while it is running you can pinch off return fuel line and the pressure should jump to 75-85 lbs of pressue. Just do not let the fuel pump run over 30 seconds at that full pressure.
When the pressure jumps to 75-85 lbs unplug fuel pump jumper. And then recheck regulator for external leaks.
But in your case if the new fuel pump is putting out good pressure and the fuel pressure on fuel rail is not up to par and it will jump up if you pinch return line off the regulator is not holding the right pressure.
You might as well get a new one for it.
MT

[solarflareq]

I dont know if yours hads went this far gone. but my regulator leaked to the point where it ended up dumping 1ltr of gas into my oil when it finaly pop'd ..

easyest way to tell is take the plenum off and get someone to turn the key on and watch it presure up.. we knew what had happend right away when it"gas" spit out the side of the regulator.

Ive seen sites where you can buy the regulator replacement but most places will want you to buy the whole "spider" setup. you can get them like 300 rebuilt/refurbished.

I know the "vacume leak" sound you speak of. sounds verry similar to me my truck. used to start good in the mornings but if i drove it down town shut it off it, I would have to wine over to start. its worth a look. 10$ gasket and just tighten it back to spec if you see nothing wrong.

[JoshBarber]

what vac leak are you referring to