New observation The problem is gone with 1/2 - 1/1 gas on the tank.
Under 1/2 the problem is back. Tested this 3 times this week.
Let it run to under 1/2 = problem. Filled it back up, problem gone.

On the top of the fuel pump there is a square plastic part with a rubber membran that connects the pump and the fuel line, I think this is leaking and affects the fuel pressure when the fuel level drops under the this part.
This is the only part by this time that not is new.
On the ac delco pump kit I see that this part is changed out with a rubber tube.

 

Distributor cap and rotor.

 

Did you even read my last post?

 

Have you monitored your fuel pressure while driving down the road? If you have not, it may be time to do so. Get creative!

What you may be experiencing is a weak fuel pump. As the level of fuel in the tank decreases, the amount of work to supply fuel at pressure to the engine increases. Even a change of a couple inches in fuel level (static head = suction pressure on the pump) can uncover pump weakness. Not knowing more about the pump design (which is what I do btw), I won't get into more technical analysis. I believe these pumps to be designed properly for the application and that adverse conditions and/or wear/tear are what is affecting their operation.

Also, as the amount of work increases, the power demand at the pump increases. If the electrical power waivers at any time, it can cause the fuel pressure to fluctuate. This can be more pronounced at lower RPM when the alternator has a lower amp output. You may want to see if you can back probe the connection at the pump and try to monitor the voltage at the pump while the problem occurs.

More flies with honey...

 

Yes!

The pump pumps, thats its job. It sucks gas off the bottom of the tank. Full or half empty, it still pulls gas off the bottom of the tank. Not sure what a new pump costs for you, mine is $300. Better be damn sure thats the problem before I drop $300 and 8hrs work. Is it possible that the pump has a leak, sure, is it likely, no. There is nothing in the gas tank to bang into the pump and break it, unless you drove your truck into a brick wall or something like that.

Even if there is a leak in the fuel pump, once the gas level gets below that leak, it will no longer suck gas off the bottom of the tank and your engine will die due to a lack of fuel.

What Swart posted is a posibility as well. Weak fuel pump.

 

Mine was a broken (physically) egr valve. But I had a P0701 code.

 

I had the exact same problems with mine last year.

Bucked or jerked but only when cruising. throttle up, it goes away
If it was hot it would bog down or die after sitting at a red light or in traffic.
The lower the fuel level, the bigger the problem....

It ended up being a weak fuel pump.

$100-$300 depending on which model you have. Not really difficult to do, but kind of a pain if you haven't done it before.


It ended up being the fuel pump.

 

I got a 2000 model blazer and had the same problem and after changing MAF, TPS, plugs and wires and spider injector it turned up being the cap and rotor but the funny thing was i had put 3 yes 3 brand new caps and rotors on it before having to order a ac delco cap and rotor. It could also be time to change your timing chain too. But yes it could be the fuel pump, luckly mine was good for NOW. GOOD LUCK.

 

Hahahaha, I didn't mean no harm

I have monitored the fuel pressure when driving, still the same after the new pump was put in some weeks ago. 58 at key on, 52-54 at idle, 60 at WOT, fluctuating fast between 50-60 at cruise.

Someone told me it could be a leak pulsator at the top of the pump, this could cause problems at low fuel level.

But this 1/2-1/1 fuel ting only worked the 4-5 first times, now it won't go away with a full tank of fuel.

Did a vacuum test and it showed a retarded timing an restricted exhaust.

Ordered a new fuel pump, fuel filter, wires, cap, rotor and plugs. All ac delco. Also ordered a new wiring harness this time.
Fixed a exhaust leak and changed a some what clogged cat.

Waiting for a new MSD ignition coil.....and hoping for the best.
Not much more to fix at this time, as most is new

 

OK, I think I finally fixed my problem. Over the last days I changed my fuel pump and fuel filter one more time, this time to a acdelco set.
It fixed my low fuel pressure and the blazer ran much better!
But there was still some bucking and still a bit low on power.

I then took down the catalytic converter and checked it with a flashlight.
The inside was almost clogged up from parts that had broken off the cat core. Put in a new converter and guess what, the problem is now all gone!

Had a looooong drive today and it didn't buck, jerk og sputter at all.
And I got SO much more power to play with!

I'm so happy happy happy!