Bucking at around 45 mph??

[frito-bandito]

My 1994 w/ 4.3L & 4L60E throttle body does the same exact problem and has been for about 18 months, but it gradually gets worse and throws out a Code 13 (O2 sensor not getting voltage)

 

[dcZ71]

Just to update...I was going to put my stock packard plug wires back on in place of my jegs ones but one of them wouldnt stay on the cap because the inner part was damaged ...so i said screw it and put back on a couple wires i took off. And then today I had not one skip when idling in gear and no jerks in overdrive so I dont know what happened. maybe a wire wasnt tight before or something. i did wipe off a little dielectric grease off the two spark plug ends that i took wires off. dont know if they could affect or not. anyways its good, for now at least.

 

[Hogg]

These are teh same symptoms my truck had when it need a distriuter gear.

peace
Hog

 

[Mike]

Could be any number of driveline vibrations or incorrectly running engine.

 

[KennyB01]

if it is the converter or the switch their is a way to unplug the lock up and that will tell you. the trans. shop unplugged mine and i have not had no trouble. its been working good for a couple of years now, i figure when i get my trans. rebuilt i'll have it fixed, but the guy said it could either be the switch that runs it or the converter itself. but it will tell you which direction to look.

 

[GWKP]

well im back finally with bad news , when i did the trans pull and replaced the torque converter (my TC had a hairline crack in it) that did seem to fix it i guess band aid wise
but just recently my truck is not doing a buck anymore but a full blown surge and is giving me horrible MPGs. So i thought ok maybe im having an electrical problem? scanned for DTCs and found 2 codes P1121 and P1122 i believe anyways it said low tps voltage and intermittent low tps voltage. Checked the actual tps and it was good as could be, so i unplugged the tps and went down the road the surge was completely gone! but im not just going to leave it as if i really want to fix it. searched and it seems to be common problem with these trucks. so i dug deeper and watched all outputs of interlinked sensors when it acted up. results were that my map sensor was pulling way too much voltage and starving my tps, egr, and ftp sensor. maybe i will figure it out and post back ; im almost positive it is a ground issue anyone feel free to chime in with good tips or info

 

[LPG PWRD]

7 times out of 10 this is caused by a worn distributor gear. What's worse is they typically wear on one side so you don't always feel it. I'm not saying that's the case here but definitely worth a check, especially if you're on the original distributor.

These are teh same symptoms my truck had when it need a distriuter gear.

peace
Hog

Damn, i thought i would bring something to the plate but these guys beat me. Remove your dist. cap and try and turn the rotor back and forth, there should be no movement, if you have movement, replace your dist or dist gear. The cam timing will be off and you will most likely have to do a relearn.

 

[frito-bandito]

Would a bad distributor cap cause this?

 

[daddy_dandy]

Would a bad distributor cap cause this?

Possibly. The Gen 2 GMT400s have incredibly sensitive ignition systems and they chew through caps like crazy. I ALWAYS carry an extra one with me. Anytime I have spark problems I check in this order, cap; rotor; wires; plugs then coil. If you're experiencing a slight miss under load (usually 45-52 MPH in OD) pull the distributor and look at the gear. They have a tendency to become "knife edged" on one side.

Could be experiencing symptoms of timing chain stretch. You can pull the cap and rotate the engine by hand. There should be less than 1/4" of slack/slop between the rotation of the engine and rotation of the rotor. Hope that makes sense...Maybe someone else can word that better.