Ok here's the deal, 2 months ago I was planning a trip to Mississippi to drop off a trailer load of stuff for the Hurricane victims. So before the trip I thought I should do a little preventive main. (If it ain't broke don't fix it??) New Plugs, wires, cap and rotor, new Breather, PCV Valve and change all fluids. The Truck was running fine before the changes BUT now she Idles fine and when you give it gas it's fine, but when your just cruising and using a little throttle she kicks and bucks like an ol' Mule. What in the heck did I do??? Has anyone had this issue before?? I rechecked the plug gap and also put the old plugs back in no change. I also replaced the EGR Valve thinking that maybe the issue. Still no Change.

 

Could be a few things. Your cat might be starting to take a dump on you. You can take it to the dealer and they can do a flow test on it, nd if its bad they will replce it as long as your under the specified millage. But if its not bad youi have to pay for the test [&:]

Could also be a fuel pump issue, and your pump is taking a dump and not supplying enough presure.

And last it could be the tranny [&:] Does your RPM fluctuate while when it happens? How many miles are on it? Auto or Manual? Last time you changed the fluid and filter?

 

because you said the truck ran right before you did this preventative maintenance, theoretically it has to be one of these things that is causing your truck to "buck". it sounds to me like it's something electrical. did you try putting the old wires, cap, and rotor back on. if not, i would do this one at a time as to pinpoint the problem. -justin-

 

My truck is a 5spd Manual, I had the Cat replaced last year and the fuel pump is also newer about 8,000 miles old. as for plug wires I went up to 8mm duralast wires. I put on the old plugs no change so then I did the old wires still no change I dont want to have to pull the cap and rotor again it was such a pain the first time but I can't see what they could be doing and why it would only happen at Cruise Control type driving ( just maintaing speed not actually accelerating and also has a smooth 800 RMP Idle). I do appreciate the help though keep it coming Thanks

 

Welcome to DF... Check for a vacuum leak and verify your wiring from the cap. you might also want to have a look at the egr stuff at the back of the intake. I dont have one so I dont know if there is any wiring that goes to it or not or if there is any vacuum lines... also, there is some check valves in-line with some of the vacuum lines so you'd want to verify vacuum on both sides of them.

 

oh yeah, now it hit me... check your o2's and the heater circuit. I had a blown fuse on mine and it was causing a similar problem. turned out that the o2 circuits are now fused and that fuse had blown. swapped out the fuse and it has never had that problem again.

 

Thanks Steve I'm glad I found this site Its Great. And thanks for the Idea I'll check the O2 sensors and fuses I never thought of those.

 

I dont think your truck is going to have the o2 sensor fuses... I think it was added to the fuse box in '99 or so... anyway, if your o2's old, might just want to swap it out anyway.

 

No problem with O2 sensors a little dirty but not bad at all. after looking a the slip when I had the cats replaced they were replaced also last year. I guess I'm gonna have to pull the cap and rotor. is there any way to test those parts off the truck ??