OK, so Monday I replaced my spark plug wires. Ever since, the 99 Blazer feels like it's in passing gear on the highway. At 65mph, the RPM stays around 2900, unless I'm coasting on a downhill grade, which my overdrive comes back on.

Is it possible I knocked or bumped anything loose while changing my wires? I can't seem to find anything that would be in the way. I replaced my distributor cap and rotor today, but that didn't help anything. Also made double sure all the wires were seated well on the plugs.

Is there anything I can do about this soon? I have to drive someone a few hours out of town tomorrow, so several hours of running 2900-3500 rpm is going to be hell for both me and the truck, which already has 150,000 miles. I plan on visiting a transmission shop on Monday, since they're closed today.

 

Is your SES light on? Maybe a sensor got unpluged by accident.

 

Yeah, it's been on since February. Something about catalyst bank 2, which I thought we fixed a few months ago for the same code.

Anyways, I drove it on the highway for a while today with my cruise set to 65. Going crosswind or against the wind, it seems to be shifting into 3rd. I goes back into overdrive when I turn the cruise off, but it takes forever to get back up to speed, even when I push the pedal farther than I usually would. It tends to wanna jump between 3rd and 4th and gets all jerky sometimes like it doesn't know which gear it wants to be in.

The problem seems to start above 55, but I don't travel on the 55mph roads because they're out of my way. The truck overall just feels wimpy now. I keep thinking one of my cylinders isn't firing with my new wires, but my dad doesn't think he feels anything like that when I had him take it for a second opinion.

I'm thinking of buying a new set of wires from another store and trying that, just in case. Is there an easier way to test wires for defects than changing them out? Unless it's a nasty coincidence, this problem started the day after I changed wires. The plugs were changed out last year, hopefully that has nothing to do with it.

 

So I just got back from Autozone. My code is p0420, something with bank 1 efficiency. That's the same code I got a few months ago and replaced the o2 sensor from recommendation. That light went away after it was replaced, and showed up again last month. Is it just bad timing that I need to replace my exhaust again, or what else would be causing my truck to suddenly struggle to keep up with people on the highway?

 

Check that you didnt disconnect one of the tranny vacuum lines when you changed the wires.

 

I was looking for them, but I must not know where to find any. I'm gonna try again in the morning I think. I've gotta locate some schematics or charts or something to help me locate things. The only things I came noticed thus far I might have nudged was some kind of sensor plugged in to the exhaust near the driver side plugs. Thank y'all!

 

If it is located between 3 & 5 then that might be your knock sensor, the computer uses that to change the timing and air/fuel ratio depending on knock noises it "hears" in the block. If the sensor is damaged this might tell the computer to run in "default/limp home mode"...