If you have a dent in your fuel tank, it might have damaged the protective liner inside.
I realize your machine only has 90k on it, but I have had two different vehicles over the years that had similar symptoms, but were not fuel injected engines.

The problem was rust clogging the fuel lines, at the tank.

On one of them, I was able to give a little blast of compressed air from the engine compartment through the fuel line, and that dislodged all the debris, then it ran great for a bit, then it completely clogged the fuel system. Both times I ended up replacing the fuel tank.

 

Sirlion,
The 01 as a plastic tank. Thanks for the info. I am looking at all possibilities at this time.


Istalled the new MFI, no help.

At redline my fuel pressure drops to ZERO, with the old spider it dropped to 40-44 psi. I assume that was becauce that is the pressure the poppets closed at. When it drops to zero, remove foot from gas pedal, the pressure will slowly increase back to 48-49 psi, start to accel again, the pressure drops back to zero. Maintain WOT, engine dies, pressure increases back to 58-61 psi erratic--not steady, (engine not running) step outside listen to the pump it is whinning with a high pitch squeal. It sounds like the pump has a bad bearing, that kind of squeal, the squeal is in unison with the fluxing of the pressure 58-61. Turn the pump off and back on, squeal goes away pump maintains 62 psi, truck runs again. By the way this is done with the pump wired direct to the battery with an inline fuse and switch to turn the pump on and off. Another thing, when the pump is whinning/squealing the switch gets hot, like the pump is pulling too many amps. But it did not blow ths 15 amp fuse. The switch is rated at 20 amps. After turning the pump off and back on 62 psi constant, the switch cools down.

When faulting, as I said, foot off the accel, 48-49 psi, on my pressure gage pushed the relief button, the truck dies immediately.

It happens at times other than redline, it does exactly the same thing. I use redline because it is the quickest way to induce the problem. Under normal conditions it may not happen for 50 miles, alot of gas and alot of time.

There are no external leaks.

Which side of the FPR is the fuel pressure test port located, supply from the tank or return to the tank?

How many amps should the pump pull?

I have read alot i n the forum about the pulsator, I cannot find any information about where it is located or what ot looks like. So, where is it and what does it look like?

I understand the pulsator can be replaced with a piece of standard fuel line. Correct?


Thanks
A/M/G

 

Not enough fuel supply at pressure. The MFI spider has electronic injectors that will open whenever commanded to regardless of the pressure so your comparison between the old SCFI and new MFI pressures when the problem occurs makes perfect sense.

All signs point to a fuel supply problem whether that be a clogged filter, weak pump, or a restricted line...

 

I have looked the lines over several times, they look ok. Replaced the filter, it had very tiny bits of black particles in it--going to replace it again. I suspect the pump is bad because of the squealing. I am replacing the pump again and doing a thorough inspection of the tank when removed.

I am going to try to do this today. I will report back.

Thanks
A/M/G


Replaced the pump and filter. The problem is solved at this time. The pump is still wired direct to the battery. Today I am going to wire it back to original condition. So at this point in time 3 pumps have been changed. It is said the third time is the charm.

The filter had some debris in it, I am going to start buying my gas at another place and all of my other vehicles are going to get new fuel filters. The filter in the Blazer had been in less than 6 months, it should have been little to no debris in it.

After I wire it back to original and drive it a few days I will report back.


Thanks
A/M/G

 

Done, Fixed, Corrected, Complete. Three pumps!!!!! Hope the pump last a LONG time.

Thanks,
A/M/G

 

What kind of pumps were they?

 

First one, Airtec?, last two Delphi.

 

I recall reading an article that said
"Do not re-fuel at a station that had the tanker filling the in ground tanks at the same time as you are re-fueling", because it is stirring up any debris in the bottom of the in ground tank.
This could have been the source for the black bits in your fuel system.

again ... Good job !!

 

Maybe, I don't know. Thanks, it has been a bear.

 

If anyone figures out this problem please let me know, I'm fighting the same issue with my 2000 Blazer with a 4.3. No codes, just a slight hesitation and sometimes it will die out if you get into the throttle to hard. If you feather the engine up it will rev. as far as you want it to go. If you stomp on it, it'll die out stalling if you hold it down.