I have a 2000 ZR2 blazer with serious issues. Heres the history i bought the truck with a knockin motor found a donor blazer with 58,000 miles and swapped the engine transmission and transfer case. After swapping all that out it ran fine on a few short drives and drove home fine. Went out later for a drive and it lacked power it got so bad the truck wouldn't go more then 10mph. Had it towed changed fuel filter ran great for test drive then again no power did some checking and found the MAF sensor had oil in fhe screen, now the engine that was put in came from a blazer that had been rolled over. Cleaned it out changed air filter and truck ran great next couple of days.

Now the truck runs and drives however if u floor the gas either from a stop or any speed the rpms stop between 2300-3500 and the truck decelerates if you give it 75% throttle or less it drives fine. But u can sit and put the peddle to floor like driving 60mph and the dam thing slows down like if you put the brakes on. The worst part is its intermitant one time it drives fine and can floor if and truck rpms will go 5000 no problem next drive it acts up. Vehicle temp and outside temp or weather don't seem to be a contributing factor.

I then had 4 different mechanics look at it and no one ever seen anything like it. It is not setting my check engine light which does work, scanner doesnt show anything out of specs, had fuel pressuee check if was in the lower end of the spec so replaced it and spec is fine but did not fix the issue and yes I used a delco pump. Also I have swapped out PCM, TP sensor, intake and spider injectors, fuel pressure regulator, full tune up, removed cat, pulled distributor to check no issues but swapped with one that was used but good. Each time somthing was done the truck would run fine for a few days then back to acting up again. This all has been going on since last October. Now just the last two days it has got worse both times I drove somewhere and ran fine then went to drive soon after and I couldn't speed up more then 30mph. If I floor the gas rpms stop at 1000 and if keep pedal down it makes a pop noise which I can feel in the pedal itself. Anyone experiance this its been goin on long enough!!!!
Please please help!!!!!

 

plugged cat?

 

x2

remove the pre cat o2 senors then drive it if its better. If so pull the y-pipe with the cats and replace.

I knocked mine out but had to cut the pipe so i could get to it. Then I had it welded back together. I live in iowa so no emission testing for me . Add that with a super 44 muffler and it sounds nice after it gets warmed up.

 

Cat isn't the issue that I cut that off and straight piped it right from the start.

 

Two things come to mind.

1. Plugged muffler. Bits from the cat could have clogged the muffler substantially.
2. Vacuum leak.

Other than those two things, I'm just as stumped as you are.