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Fuel pump going, questions:

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Blazer >> Mechanical & Maintenance >> General Tech Help >> 2nd Gen (1995-2005) Tech >> Fuel pump going, questions:

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Fuel pump going, questions: - 3/17/2008 11:30:10 AM

Smoked

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Hi there.
I just recently purchased a 99 Blazer Zr2 which I love. I've detected a whining sound coming from the rear of the truck, sounds kinda like a train off in the distance on it's horn..anyways, when i shut the truck off it continues for a second or two before dying. I get normal response to partial throttle driving but when i get 'on it', the truck does not respond.

I have surmised it's a fuel pump on it's way out but i have a few questions.

1. Would this affect my fuel mileage as well as the performance hit i've observed?
2. Is the pump hard to replace? Is it in the gas tank or exterior?
3. Any thoughts on how long it might last before dying completely? Should I avoid driving anywhere until i've replaced it?

thankjs

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99 Blazer Zr2 4x4 automatic.
94 Camaro z28 6spd. 332rwhp/332rwtq

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RE: Fuel pump going, questions: - 3/17/2008 11:40:03 AM

rriddle3

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1. Yes, it could affect the the mileage and performance.
2. I would consider the replacement difficult. You have to drop the gas tank to get to the pump assembly inside.
3. No way to make this estimate.

First, test the pump by connecting a fuel pressure gauge to the schraeder valve on the fuel inlet line at the top rear of the engine. With the key in the 'on' position, the pressure should read ~55-62psi. Turn the key off and watch for pressure drop. It should not be more nthan ~2-3psi. Let us know what you find.

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RE: Fuel pump going, questions: - 3/17/2008 11:59:34 AM

Smoked

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I will do that tonight..thanks for the suggestions.

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RE: Fuel pump going, questions: - 3/17/2008 1:44:27 PM

swartlkk

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While you have a fuel gauge on it, try to drive around with the gauge so you can see it. Remove the hood if you need to. You will want to watch the fuel pressure as you drive around to see if it ever drops below 50psi. If it does, but remains higher during low power usage, then it is quite possible that hte fuel filter is plugged up, restricting the flow, thereby limiting the pressure the pump is capable of delivering to the fuel injection system.

Other things that could cause the problems you describe would be fouled spark plugs, bad wires, worn distributor cap/rotor, dirty MAF sensor, and/or a failing TPS sensor, plus a few others, but those are the higher frequency items. Some of these may result in a check engine light, but not all of the time. Most can exhibit drivability concerns without triggering a CEL.

Hope this helps!

< Message edited by swartlkk -- 3/17/2008 1:51:45 PM >

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RE: Fuel pump going, questions: - 3/17/2008 6:20:55 PM

Smoked

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Thanks for the extra suggestions swartlkk. With the help of my friend and resident motor genious we took the blazer out and did some diagnosing with a fuel pressure guage and autotap for some ecm logging.

When we hooked up the guage and turned the key to ON, the pressure went up to about 65psi...turned the key off and it dropped WAY down.

Began driving... fuel trims showed a lean condition but even...so o2 sensors are good. Pressure when driving normally steady just around 65psi but when i get on it, it drops quite a bit. Turn the car off and it holds for a few minutes then drops a few psi.

So that's the results... my buddy will join up in an hour or two and post more specifics and ask questions about the motor but he's thinking regulator from what we saw. Does the blazer fuel pump have it's own regulator? The pump still makes the harmonic kind of whine...so whether or not its' pumping enough fuel something has to be wrong with it no?

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RE: Fuel pump going, questions: - 3/17/2008 9:01:09 PM

Pur_SSyn

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Hello, I'm Craig's buddy (genious?

)

I'm fairly new to this motor, however the symptoms are pointing to a weak/faulty fuel regulator. Upon prime, the fuel pressure will
reach ~ 50 PSI and drop quickly when the pump is shut down (approx. 5 PSI per second bleed down).

While driving under moderate load in town, the pressure is steady, but the short and long term trims are maxed out.

If the throttle goes wide open, the pressure drops about 5 PSI and wont recover until the throttle angle is reduced to below
70% (or thereabouts).

I'll study the scans more in depth tomorrow, and do some reading on the 4.3L Vortec. The only questions I have at the moment
are:

- Where is the regulator located?

- Where is the vacuum signal for the regulator taken from?

Thanks!

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RE: Fuel pump going, questions: - 3/17/2008 10:22:40 PM

swartlkk

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From: Waterloo, NY
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The regulator is located under the upper intake plenum. The vacuum source is direct from inside the plenum.

I doubt that your regulator is weak. The regulators in these trucks typically fail, flooding the engine with fuel. To rule out the regulator & injection spider, you should remove the filter, and adapt the fuel gauge fitting to the fuel line that runs into the tank. If you do not get 60psi or greater, the pump is at fault.

As I said above, I would replace the filter first as it seems that there is a restriction in the flow...

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RE: Fuel pump going, questions: - 3/18/2008 5:33:30 AM

Smoked

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quote:

As I said above, I would replace the filter first as it seems that there is a restriction in the flow...

So the sound i'm hearing from the pump(noticeable in the cabin) is potentially normal you think?

thanks for the suggestions!

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RE: Fuel pump going, questions: - 3/18/2008 5:43:26 AM

swartlkk

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The noise level may be an indication of problems with the pump, but a filter is a few dollars... The pump is $$$ I would hate to replace a pump, then come to find that the filter was the cause!

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RE: Fuel pump going, questions: - 3/18/2008 5:48:51 AM

Smoked

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quote:

ORIGINAL: swartlkk

The noise level may be an indication of problems with the pump, but a filter is a few dollars... The pump is $$$ I would hate to replace a pump, then come to find that the filter was the cause!

I completely agree it makes sense to start with small, easy and cheap. I'm just nervous about the pump.. that has to be what's making the noise. I guess there really isn't a way to determine how much life is left in it either is there? I just don't want the car to die on a long trip that's all :)

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RE: Fuel pump going, questions: - 3/18/2008 5:51:35 AM

Pur_SSyn

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I agree with replacing the filter first. The pump may be laboring due to the restriction.

The only thing that isn't clear is the quick bleed down of rail pressure when shutting down the
pump.

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RE: Fuel pump going, questions: - 3/18/2008 5:59:46 AM

swartlkk

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Ah Pur, I missed the 5PSI per second bleed down. Does it bleed all the way down to zero pressure? This would be indicative of a failed FPR... But again, if you were to isolate the pump, you could check to make sure that it wasn't a failed check valve or seal in the pump itself. It is easy enough with the proper adapters when you have the filter out.

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RE: Fuel pump going, questions: - 3/18/2008 6:06:47 AM

Pur_SSyn

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I can't say how low the pressure will drop as I didn't allow it to settle long enough.
That's an easy test that can be performed again.

We may be dealing with multiple issues, so it's smart to get the filter changed and
redo the tests.

Thanks,
Tino

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RE: Fuel pump going, questions: - 3/18/2008 6:14:45 AM

Smoked

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Okay..i'm not hearing that it's not okay to keep driving... but that the pump has the potential to go at any point still exists(i know that's true of any car but more likely in my case).

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RE: Fuel pump going, questions: - 3/18/2008 6:26:54 AM

swartlkk

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The fuel pump in any vehicle can just decide not to run at any point in time. That is the nature of the beast. It sucks I know, but hopefully it won't leave you stranded.

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RE: Fuel pump going, questions: - 3/18/2008 6:28:15 AM

Smoked

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quote:

ORIGINAL: swartlkk

The fuel pump in any vehicle can just decide not to run at any point in time. That is the nature of the beast. It sucks I know, but hopefully it won't leave you stranded.

Yeah that's true.
What does the stock pump sound like...can you hear it in the cabin when you're not moving(i.e. no road noise)?

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99 Blazer Zr2 4x4 automatic.
94 Camaro z28 6spd. 332rwhp/332rwtq

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RE: Fuel pump going, questions: - 3/18/2008 6:39:18 AM

swartlkk

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From: Waterloo, NY
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Some are loud, some are quiet. It really does vary. Sorry I cannot be more specific for you. The noise should be more of a high pitched whine than a growl though.

My old '01 Bonneville was quiet as a mouse until I had the fuel level sending unit replaced and from then on, I could hear the pump whenever I was sitting at idle.

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RE: Fuel pump going, questions: - 3/18/2008 6:39:59 AM

Pur_SSyn

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Craig, it's fine to drive as long as you're not into hard acceleration.

The fuel pressure is sufficient for low load, in city and highway cruising. There is about 4-5%
of trim headroom to adjust so there is no extreme danger of running lean.

I sent you an e-mail about the filter. Let me know and we'll get that replaced ASAP.

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RE: Fuel pump going, questions: - 3/18/2008 6:42:13 AM

Smoked

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quote:

ORIGINAL: swartlkk

Some are loud, some are quiet. It really does vary. Sorry I cannot be more specific for you. The noise should be more of a high pitched whine than a growl though.

My old '01 Bonneville was quiet as a mouse until I had the fuel level sending unit replaced and from then on, I could hear the pump whenever I was sitting at idle.

No growl, it's a whine :) First time i heard it i thought i was hearing a train in the far distance on its' horn :)

Tino, i replied to you pm :) Let's get that fuel filter changed before the weekend.

Thanks guys!

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99 Blazer Zr2 4x4 automatic.
94 Camaro z28 6spd. 332rwhp/332rwtq

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RE: Fuel pump going, questions: - 3/18/2008 8:10:14 AM

Pur_SSyn

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I've been reading and searching the forum, as well as Google to learn more about the fuel
delivery, and engine itself.

From what I gather, this is a two piece manifold with a throttle body and air delivery on the
upper portion, and a common fuel distribution point, with injectors spraying into each runner
(on the lower intake portion).

I see there are two distinct fuel systems depending on the model year, so I 'd like to learn more
about the 1999 version.

Are there any photos available that show the injectors/spider assembly on the motor with the
top half of the manifold removed?

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Post #: 20