'95 GMC 2 door Jimmy 6cylinder 4X4 automatic; it was running fine, noticed the fuel level was almost in the red, warm day, decided to go ahead on the highway, go to the DMV then get gas; got back in after 15 - 20 minutes turned over but would not start and run; just about to call AAA and it started and ran; put gas in left it running bad thing to do; and it has kept the same issue since; I have a new filter, oil pressure switch behind the distributor that was fun, new cap and rotor, great spark and new fuel pressure regulator and pump relay; fuel comes out when you disconnect the line from the filter and turn the key on; is it possible the pump is performing less than it should because of running it on low gas level? There is 170k on the motor, doubt the pump has been replaced, the fuel filter itself was rusty. It will start and run fine after many many tries, and then as soon as you shut it off, nothing. Pretty stumped. Up until the stop at the DMV it had run fine and the only difference was running real low on fuel. Thanks for any and all thoughts.

 

170 K... hot weather low gas.. enough to tip it over into unreliability. Many on here last much less in miles.

 

They need fuel to keep them cool & lubricated. then the mix of hot weather,not good.

 

The plug that goes into the pump inside the tank has a problem with failure when the pump has overheated from low fuel level.

It will function fine going down the road then when you shut it off it will not restart until you let it sit for a bit or keep cranking on it. Given time the amount of time needed will get longer and longer.

Been there done that on one S10 blazer and on a Jimmy

 

Yeah being low on gas forces the fuel pump to work harder to get gas up to the engine. The fuel also acts as a coolant and lubricant for the fuel pump.

 

NO, NO, NO! Running the tank low will not cause the pump to pre-maturely fail, nor does it make the pump work harder to get the fuel to the engine!

It is the fuel itself moving THROUGH the pump that keeps it cool and lubricated. Not the fuel around the outer casing. Regardless of the level in the tank, the pump must move the fuel under pressure from the same level every time.

Nor does running the tank low cause the pump to pick up any more debris in the tank than when full.

Just an old wive's tale that keeps being told as most believe what they have always been told rather than to look at the physics of how the system works.

 

Guys, let's put some reality into it.

First.. the pump isnt really working harder with a low tank. The Blazer fuel regulator runs at 59 lbs. That means if the fuel had the same Spec Gravity of water the pump would raise a column 135 feet high. 1 foot, then, is not all that much.
Online Conversion - Pressure Conversion

Second.. the vast majority of cooling and ALL the lubrication is by the fuel flowing through the pump. As long as the pump isnt pulling vapor the fuel is cooling and lubing it.

For 40 lb systems the old thing about wearing out the pump running low is BS and I know that for a fact. Wife an I have driven MPFI Fords over 500,000 miles without a FP failure and much of that at 1/4 tank or below. And my previous TBird ran 300,000 miles on the original; life of the car.

But at 59 lbs the pumps are operating at the edge of their limits. They work a lot harder. Any external cooling helps.. That's why there is a sump on these pumps. Fords {80's-90's} dont have sumps.
Some say that the fuel heats a lot if there's a low tank due to circulation through the engine compartment. I dont know, I'm sure there is some.

The bottom line is however that, on a blazer, 170K is a very good if not excellent lifetime for a pump. All you have to do is READ this site to know that. One incident at the end of it's life may or may not be significant.

Who's to know that a ninety year old catching a cold and his kicking the bucket a week later are really related.

 

I agree with AJBERT.

I have researched this also and you are correct.
It is an old wives tale.

Everything runs fine up until it doesnt run fine anymore!

 

thank y'all for the responses; about the only way to toast one is to run it without anything going through it.

 

agreed with that one. with nothing going through it, it will not be cooled.
Everything will eventually wear out. If your pump decides its time to die right after you put fuel in it, do you blame the fuel? Generally it is just a coincidence.