99 5.9L 4x2 (91K) Truck started lurching on the highway 55-60mph. It does it a bit at slower or faster speeds but not as bad as 55-60. No CEL. I replaced the cat in January and I think I replaced the 8mm wires/plugs at about 75K (can't find my manual right now).

I opened the hood and did the following: 1. Tightened a loose bolt on headers 2. cleaned the electrical connections to injectors 3. checked that all wires were on tight

Now the truck has a bad idle while still cold and backfires. It improves as the truck warms-up but still lurches at highway speeds. Also if I accelerate at 3K rpms it will initially have some backfire/lurch problems but then runs smoothly.

The only thing that I've done to it recently is put gas in it!

Any ideas?

 

The backfire is pre-detonation of fuel. That could be caused by improper timing causing the spark to happen before the piston fully compresses the mixture. It could also be the low octane in a fuel, an additive or higher octane could help that. Just a couple of things to check.

 

When is the last time you put a dizzy cap on it ?

 

Hmmm...even though I have the Mopar PCM I've been running 87 and staying off of the throttle. On Friday I put 91 in (full tank) and the next day started having problems. The water pump was replaced in January and the mechanics said that the timing chain was still tight.

Any thoughts besides just replacing the plugs and rechecking all of the wiring (MSD, spark plug, etc)?

 

put the distro cap on at about 75K as well.

 

Are the wires routed per the TSB to prevent crossfire? (do a search on here for"Plug Wire Routing"). 8mm or better wires? Plugs? Type? how old? TPS changed? Or at least tested? Does the truck have cruise control? Good plug wires are worthless without a good cap and rotor(read brass inserts).

 

OEM wire routing, 8mm wires, Autolite plugs. I haven't tested the TPS and I do have cruise control (but haven't been using it).

 

Yea I got a bad one 2 years ago and it missed and back fired after it warmed up and at low rpms.Put a duralast OEM cap n rotor on it,ran smooth as could be.

 

I re-routed the Taylor 8mm wires while checking them. Checked the connections on the MSD and disconnected the battery. I'm not expecting anything different but we'll see...

 

We'll that made no change. I did forget to mention that the truck shakes/jerks while shifting from 2-Overdrive, 2-3 or around 45mph. Then it smooths out until around 55-65mph. I think I'm going to put new Autolite 3923s in and run a scanner tool on it.

Any other quick and easy ideas?!