(So i have a s10 blazer 4x4(note, this has 234k miles on it) that will start missing & backfiring when one of two things are met: The truck is in 2nd gear and starting to pass 30-35mph (i guess higher than average accel.), or the truck is at highway speed and the accelerator is pushed >1/4 of it's full travel.

The engine normally starts to miss a couple of times which then turns into tiny backfires through the TBI and sometimes the exhaust, if the accelerator is held in position the engine looses power, then begins to chug and stall out and severely lacks power. If accel placed fully to floor the engine can still be heard, with all the misses and backfires, but it feels as if the trans is in N and not engaged.

Truck status: TPS replaced, Recently cleaned the TBI, Replaced coil, new cap/rotor/wires/plugs, fuel filter is new, no vacuum leaks, new pcv.

I have a new O2 sensor for it and i'm considering the following to be the issue.
EGR valve?
Distributor (just replace the whole thing, there were rust flakes and crud in it when i replaced the cap)
Engine computer possibly?
Fuel pump?

 

Just drove it again this afternoon, i've been trying to get the truck to do the same thing again, i left the (-) terminal disconnected overnight and so far all it's done is pop'd a small backfire out of the TBI, it's now running smooth and actually feels like it has some power back. Idk, i'm going to reset the timing in a little while back to 0degBTDC, i's been at 6 to fix another issue it had.

 

Well, the timing was corrected, the trans filter replaced and still no positive result. So today I went and bought a computer, thermostat, and a temp. sending unit. I got the sending unit and thermostat because it had been running at like 210' during this so.... I thought maybe the computer was trying to compensate for the hotness of the motor by richening the air/fuel ratio to correct the "lean condition" the motor may have had. after doing so the truck runs perfectly well and i got to return the computer. Now i have a ride to go back home with while i'm on leave.

BTW, i'm in the navy stationed out of norfolk, my other home away from the sub is back in NC.

 

The blazer has now started it's same problem once again... It took me back to NC at least to be on leave and started all this about 5mi. from home. We've "Fixed" The catalytic converter, replaced MAP sensor, and new spark plug wires (due to the "new" ones glowing... ALOT)

I need this truck up and running before sunday cause i have to get back to norfolk. There's no way someone doesn't have any insight at all on this.

Problem, engine temperature doesn't matter... does it hot or cold. When going down the road quickly say 55+mph the engine will backfire or pop and the motor will loose power, it won't clear up until the truck has stopped and has sat for about a minute. Upon accelerating again the engine will choke up and backfire through the TBI. Does it at varying loads, and throttle positions.

IF PARKED and not moving you can press the accelerator slowly and steadily untill the engine stumbles. The engine will recover back to high idle then stumple again... it'll do so about 15 or so times untill it'll stumble so hard it will shut off...
*COMBINING CONSECUTIVEPOSTS*
I've now unseated the fuel cap, not all the way off, just not seated. It now only stalls when under alot of "power demand", accel. pedel further depressed and such. I'm thinking this is now a fuel pump issue or there is maybe a hole or crack somewhere in the pick-up tube that allows air in the line. My fuel tank level is low... like an 1/8th, it was higher when we were working on the truck, so now i'm going to baby it off and get some gas, reset the computer and drive it back...


Damn this truck.

 

I've now unseated the fuel cap, not all the way off, just not seated. It now only stalls when under alot of "power demand", accel. pedel further depressed and such. I'm thinking this is now a fuel pump issue or there is maybe a hole or crack somewhere in the pick-up tube that allows air in the line. My fuel tank level is low... like an 1/8th, it was higher when we were working on the truck, so now i'm going to baby it off and get some gas, reset the computer and drive it back...


Damn this truck.

 

I'm going to suggest four things:
Double-check your timing setting, have the ignition coil tested, test the fuel pressure, and clean the EGR valve. Let us know what happens then.

 

So here's the final word, not to be ignorant and not test all of the things suggested, but we went ahead and replaced the computer in it. Once installed i took it down the road for a test drive, everything operated fine, and after trying to re-establish the conditions when it caused it's problems it wouldn't backfire or stall at all. So we assumed it was ok.... untill i tested the cruise control (since the computer somewhat operates it) it maintained speed well untill i slid the accel. tab on the turn signal switch... then the truck **** itself for the last time. It backfired then lost power, i coasted it to the side of the highway and once stopped it backfired one last time and shut off. This time though it would not restart... at all. injectors were squirting but no spark was coming out of the coil (at this point i was kicking myself for not checking it per rriddle's suggestion) So my dad picked me up and we drove to advance auto and told our story about it. W/o telling him what we've replaced he said ignition module probably went out. So we pulled it off the truck and brought it back for testing... to which it failed 5 out of the 6 tests.. the only one the module passed was the "there's a chip in the black plastic thing" test. We pulled another one off the shelf... tested it for peace of mind..... and then installed it, the truck fired right up on only 1 cyl hitting off and now runs smoothly, accelerates as it should and is not giving me any more issues..... but the cruise doesn't work anymore.... and neither does my radio. Small price for a running truck right?

Thanks for the suggestions rridlle.

 

has it remain fixed since you replaced that module cause i have a 91 s10 that misses every once in a while and has backfired once dont know where from and was wonder if that fixed it for good

 

Hhmm, the thread is 1 1/2 years old and the OP hasn't posted since then, so I doubt that you will get an answer.