Guys... what am I missing?!?!?! It’s driving me crazy. I bought a 97 s-10 LS with a 4.3 . 93,xxx on in it that sat for a year or 2. Obviously it needed a fuel pump. I put one in, started up just fine. Ran some injector cleaner through it. Ran fine for maybe 3 months. I dropped the tranny pan one day changed the filter and fluid for general maintenance. Drove it to the parts store to get something for another vehicle. Truck drove fine there. On the way back I stopped at a light, hot day, mid 90s, light turns green and push the pedal about half way and it bucks like a horse from missing. (I’m sure it’s a mis and not the tranny ) I get home let it sit, start it up run fine. 5 miles down the road it will start to buck again. I can turn it off for 30 seconds and start it back up and floor it and it will do fine, try it again and it bucks. When the struck is started on a cold start it runs like a bat out of hell, after it warms up is when I have the bad mis under any type of load. Here is what I have done so far:
fuel pressure at 58 idle swings a little past 60 when I hit the gas, does not drop at all when I shut the motor off
timing is right on the money, distributor points directly at 6 when car is at tdc
new plugs, plug wires, distributor, distributor cap, distributor rotor, coil, ignition control module, crankshaft sensor, even tried to shim crank sensor with the shim gm provides as there was a bulletin about this from gm, camshaft sensor, thermostat (because mine didn’t seem to open enough when I boiled it), pulled egr and tested the reading with a multimeter while pushing needle in and out, new fuel filter, cleaned maf sensor and verified it’s not dropping off when warm with scan tool charts and I’m sure I’m forget to mention something in addition to what I just listed

my long term fuel trims were in the single digit negative ms before I changed the plug wires is the only obvious thing I saw in my readings, didn’t have a change to check them after and they plug wires were definitely bad because I i misted then with a spray bottle in the dark near the exhaust and it saw them arcing

it it only does it when it’s warmed up. Everything I replaced needed to be replaced and the mis has gotten better but not fixed. It seems to idle slightly rougher when it’s starts to act up but I can floor it in neutral and not hear a mis but in gear it bucks back and forth back and forth, and it does it consistent, like in a pattern almost. It seems it’s worst the longer I sit at a light with the motor running. I feel like if I floor it while it is acting up the motor will die. Well today I was red to test the coil, I waiting for it to act up, turned it off, swapped the coil, turned it back on, put it in gear touched the gas and it immediately shut off and now it won’t start from no spark on either coil. I pushed it back to the house and tried and tried. I put the original crank sensor on it and I got some spark but not start then no spark and at that point I said the hell with it for the day lol. Before it got to this point it always started right up no matter what and never sputters when shutting it off that’s why I don’t think it’s a mechanical issue. And it ideals great since I replaced all the worn out parts. The only code I have ever gotten from it was a p0300 or 301 I think, what ever one was random multiple misfire and I got that code from day one which I expected since it sat with bad gas and old plugs and wires and a worn distributor gear. At this point I’m starting to think a bad ground im over looking or the pcm. I don’t have and flickering lights or any weird electrical problem other than my radio clock will be wrong the next day wafted I set it (it doesn’t go to 12:00 either like it’s losing power, it’s like the clock is either too fast or slow if that makes sense) Anyone got any ideas or delt with this? Thanks!

 

Might be the fuel injectors spiders need cleaning (I don't these can be cleaned, as they really are not meant to be reused) or replacement,would be my guess.

 

I was thinking that but the fact it runs perfectly from a cold start makes me lean away from that. I made a video of what it does when I floor it. I floor it and hold it down in this video, then I let off and floor it again and hold it down.

 

Look for something in the fuel tank possibly obstructing the fuel from the pump

 

You got debris somewhere when you let it sit it settles when you're running you circulating fuel stirring everything up needs a cleaning

 

I think you may be correct. Some gas stations don't replace the fuel dispenser/pump filters very often.

 

Well, I gutted the cat, still does same thing. When I put the fuel pump in it a few months back I did see some debris in the gas tank but I didn’t think it was that much. Like I said it ran great for 3 months. Maybe what ever accumulated on the walls of the gas tank over time from me driving it got knocked down. Idk. I’m going to jack the bed up some time this week and drain the gas and clean the tank with a rag and make sure I get everything and make the the sock on the pump is clean. Someone else said that it could be a ect sensor telling the ecu the motor is the wrong temp. But my scan tool says it’s working and I assume it reads from that temp sensor and not the one for the gauges on the dash. I was worried that maybe it’s a stretched timing chain because some meantioned that but if it were a stretched chain wouldn’t it do it all the time and have a hard time starting sometimes? I had a car with a jumped chain and it ran kinda normal other than having a hard time starting sometimes and Dieseling when it was shut. My truck does none of that. Starts right up every time and doesn’t chug at all, other than under aceleration when warm.

 

Y’all nailed it. Pulled the bed off and the pump out. Lots or rust from it sitting. Cleaned it out and instant results. Thanks guys