Hello, 04 Blazer, 80k miles. It's been doing this for a while, but is becoming more frequent. What happens, is that while in 4th/torque converter lockup, it feels like 4th is shuddering, like locking/unlocking. It only does this going up hills, either at 45 or 70. If it is a long uphill, the check engine light will start flashing, signaling a multiple misfire. I'm not sure if this is a torque converter lockup shudder, or a misfire. I have done plugs, wires, cap, rotor, and fuel pump last spring. If it is a misfire, why is it only under load/going up hills? Looking for insight, help is appreciated, thanks!!

 

Does it log a misfire code as well as the light ...do you have access to a real time scanner to see if there is misfires ?

 

Sounds like an arcing spark plug wire

 

The light stops flashing shortly after getting over the hill and stays off. I don't have a real time scanner to check.

If it's an arcing plug wire, why is it only doing it up hills?

 

more load gong up the hill.

 

Sign of bad spark wires, check to see if they are on fully. Cheap wires will also do this. Is there any skip when idling?. Open hood at night, take out Underwood light. Look for arcing from wire to metal.

 

Alright, I'll have to check that. Yes, it has a slight misfire while idling now, that just started. Scanned for codes and it has p0301 stored but the CEL isn't on. I'll check out cyl 1 plug and wire and at the cap.

 

Thanks for the help guys, it was the wires, was arcing onto the exhaust manifold. Much better now!!

 

Good news, thanks for telling us