Hey guys Im new to this site but I've been reading your threads for a few months because I've bought the blazer from hell but you guys all seem to know what your doin so here goes it. I have a 96 blazer that starts fine will sit at idle fine, ive left it sit there and warm up to operating temp and it still idles and reves up to 3000rpm fine and no codes. as soon as I start driving (maybe 1/2 a block 15 mph) it will hesitate and the rpm's will drop only 100 or so. if you continue to drive it only gets worse especially if you get on it and come to a stop, it fights to stay running.(and still no codes). If you turn it off for 2 min it will act just like it did when you first started it untill you get on it or drive for a bit. now I've replaced the egr 2 times, mass air flow, map, tps, coil, ignition module all from the junk yard. I've replaced the plugs cap and rotor with brand new parts trying to fix the hesitation and fuel pump a few months ago due to a complete failure from my old pump.

I know this is alot of info but I'm just trying to explain the best I can please help if you can!

 

sounds like another fuel issue do a pressure test and post results.. heres the link on the test procedures..https://blazerforum.com/forum/showth...ht=fuel+system

 

You could also try removing the O2 sensor directly ahead of the catalytic converter and driving it. You will have a massive exhaust leak, but if it gets better, then your catalytic converter is restricted.

 

thanks guys I will try both but I have to get my hands on a pressure gauge for the fuel pressure test though.

 

x2 on the catalytic converter

 

Checked my fuel pressure and heres what I found.
ign on not running 58 psi
after 2 seconds 50 psi
after 2 minutes 43 psi and it keeps droping
running the pressure jumps anywhere between 45-52 psi
give it gas and hold the throttle it jumps to 54 psi but settles at 48 psi
driving 50-54
turn the ign off 42 psi and drops a psi every 30 seconds.

seems a little low according to the test procedures but not sure if this would cause it to run bad? Havent got to pull the o2 sensor waiting for it to cool down but I will post my results.

 

x3 on cat..only because it happened to mine and its done the same thing yours is doing..

 

I took the o2 sensor out right before the cat and it still ran like poop. same exact issues no change. I'm lost.

 

ok still sounds like a fuel deliver problem..pull the upper plenum off, turn the key to the on position only and check for leaks..if there isnt any its possible the fuel pump is going bad

 

It does seem low. The next thing I would do would be to pop out the fuel filter and test there. If the pressure is still low and still drops, then the check valve in the tank is bad and the pump has become a little weak. If it holds steady there and is in excess of 60psi, then the problem lies under the plenum.