I need some help with a 1998 Blazer S-10 LS, 4.3L V6, auto, 4wd, thottle body fuel injection, 146,000 miles. On the highway, about 65 mph, 2000-2200 rpm, and climbing a hill. Pressing the accelerator (with or without cruise control) to maintain 65mpgcauses it to downshift, rpm goes up to 2800 to 3000 rpm and the service engine soon light comes on. Looking at the codes, it's always a random engine misfire. I've had to a chevy dealer and an independent diagnostician who can't find the problem. The distributor cap, rotor, wires, and plugs are all new, I've replaced the O2 sensors and the manifold temperature sensor, and the readings from all the other sensors appear to all be within normal limits. I was told that the fuel pressure was correct. The transmission was just rebuilt, and was told that the car is shifting correctly and within normal lmits. Other that that, the car starts and runs flawlessly. I have an obdII readerthat gives me both freeze frame and real time data,but nothing on the freeze frame data seems to jump out. I have noticed that the ignition timing advance seems extreme at times andlags when calling for more power, but I can't get anyone to confirm that this may be a contributing factor. I opened a case with GM, but was told that they can't help me, and I have to work with a dealer. I'm now wondering where I have to look next, e.g. fuel, distributor, crankshaft position sensor, computer? Hoping that someone out there may have run into this or something similar, or may have some suggestions on likely culprits or things to look at more closely. Any thoughts or suggestions welcome!

 

If youknow the cylinder its misfiring in, you need to take the spark plug out and clean or replace it.