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

 

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.

 

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

 

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!

 

Thanks for the extra suggestions swartlkk. With the help ofmy 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?

 

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!

 

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...

 

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

thanks for the suggestions!

 

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