I have a 98 blazer 4.3L 4dr 4WD. It'll will run O.K. when cold, but it seems after about 15 minutes or so of driving, especially at highway speeds, all of the sudden it looses power, and the more I give it more gas, the more it will fall flat on it's face and sputter, back fire, pop, and generally run horrible. If I let off the throttle, it idles perfect. If I just barely touch the gas it still runs good, but if I give it just a touch over just touching the gas peddle, it just wants to die. I can pull off the road, get out raise the hood and move the throttle lever by hand and anything past just touching it and it pops, sputters, and backfires. The more I try to give it more gas, the worse it goes. Now here's the funny part. If I turn off the engine and count to three, start it up again, it runs perfect, for about a couple minutes or so, then does it again. I've changed the fuel filter, Dist cap & rotor and plugs. Happened two days ago during the end of a 2 hour drive. Had about 1/4 fuel still left in the tank. Have since filled it and ran that down to 1/4 again, using fuel injector cleaner and a new fuel filter. no help. No codes. (Took four hours to get home!) Any help would be GREATLY appreciated. (Don't have a fuel pressure tester right now.) Thanks guys!

 

Have you checked the Mass Air Flow sensor? Sometimes when the MAF gets dirty it can't properly read the amount of air coming into the engine. Does the exhaust smell gassy when the engine is at operating temp? Could be a plugged cat.

 

I actually swapped the MAF with another good one I had - no help. I'm leaning toward the fuel pump low fuel press, I'm guessing. I'm gonna try to rent a Fuel P guage from autozone or somewhere and take reading before I start, at idle, and after it begins to run poorly. That's about all I know to do. Wouldn't a bad Throttle position senser show a fault code? If not, it could be that going bad when it get warm, Like the windings opening up. One thing though is that it's hard to start. I mean I gotta keep cranking for about 5~10 seconds before it fires up. Especially after it sits for awhile.

 

I have a 95 Blazer that is doing the same thing. Someone told me that the catalytic converter may be bad and once it heats up the fiberglass swells and restricts the flow thus causing the engine to bog down. I replaced it. Best customer of the day for the shop, I just went in and said, “please do not test anything, just change the catalytic converter.” He said yes sir and did it. Guess what, as soon as it warmed to running speed it bogged again. I am where you are, having the Auto-zone test. Think I may change the fuel pump anyway, any suggestions on a good one? Amazingly, other than this small issue, the car runs great and looks great. I know it very frustrating for my son though as he drives back and forth to college in it.

 

IMHO fuel pump replacement on a Blazer over 75k miles should be done as a preventative measure. The fuel pump will fail, and if it fails at in inopportune time, it can cost up to 2k to get fixed, as the case was with my Daughter, when her 97 Bravada fuel pump failed (she was out of state at college), had it towed to dealer, and the bill came to 2k.

The DELPHI fuel pump has the new harness, which is often identified as why the pumps fail prematurely. I would only install a DELPHI pump, excellent product AND excellent DIY instructions. RockAuto is a great place to purchase them, but Ebay often has them for $60 less than RockAuto. Just make sure if you purchase one on Ebay it is in fact the DELPHI, not just a DELPHI part number on a copycat fuel pump.

I sleep well at night knowing our S10 and Bravada both have DELPHI fuel pumps with the updated wiring harness installed.

 

Alternator maybe ,easy to check

 

Going for a fuel pump, but gonna try to get a pressure gauge on it in a couple days, just to make sure before I go through dropping the tank.

 

Hey are there any updates to these posts? I'm having the EXACT same problems on my 97, minus the backfiring, I'm trying to figure out if I should change the MAP or MAF, If the CAT didn't fix the problem I have no idea what else this could be... I can only take mine up to 1.8 rpms or so before it bogs down to nothing, never stalls. just bogs down.. can only get it to about 40 mph and its my only way to work!

 

Check your Ignition coil, a bad one can act weird when it's hot, happened to me once, bad coil

 

I've done some more research and had someone look at it, it appears the CAT got clogged up, possibly broke.. and it lodged in the tail pipe great for me..