99 4.3 misfire at cruise

[craig82]

Any help would be greatly appreciated. I have currently had the truck in 2 different shops, one dealership, and one mechanic I know. My problem is that when the truck is at or above 2krpm its starts to buck and jerk. It does not happen when in neutral and revving the engine at or above 2k. It mainly does this while cruising. The ses light is on and is the P0420 cat sensor bank 1. Would this cause the truck to miss at certain rpm? The truck has a new cap, rotor, wires, and ac delco platinum plugs. I have been reading about a possible distributor gear problem with 4.3 vortec engines. The truck has plenty of power at WOT and the cat does not appear to be affecting power. Again, any help would be greatly appreciated.

[j cAT]

Originally Posted by craig82

Any help would be greatly appreciated. I have currently had the truck in 2 different shops, one dealership, and one mechanic I know. My problem is that when the truck is at or above 2krpm its starts to buck and jerk. It does not happen when in neutral and revving the engine at or above 2k. It mainly does this while cruising. The ses light is on and is the P0420 cat sensor bank 1. Would this cause the truck to miss at certain rpm? The truck has a new cap, rotor, wires, and ac delco platinum plugs. I have been reading about a possible distributor gear problem with 4.3 vortec engines. The truck has plenty of power at WOT and the cat does not appear to be affecting power. Again, any help would be greatly appreciated.

your problem may be the distributor....rather than replacing first check for proper fuel pressure of 60-66psi key on engine off ...then see if the pressure does not drop more than 5 psi in 10min....when I say 60 - 66 psi that does not mean it squirts pretty good ! need a pressure guage....you may also need a new pressure regulator this is under the uper intake , many have had issues with this....part ...

next the dtc 420 is saying the driver side cat converter is not good .....possibly ???? so you swap the driverside downstream with the passenger down stream O2 sensor...if the same 420 returns then the cat converter is bad....question is why ....this is where it gets complicated ???? intake leaks , coolant in the exhaust etc....

if the problem becomes dtc 430 then the O2 sensor is bad..

have fun !

[craig82]

That sounds better than pulling the distributor. The help is greatly appreciated.

[craig82]

If I pull the distributor, do I have to get someone with a scan tool to get the timing perfect? With all the posts I have read, the symptoms seem very close to the ones I am experiencing. I will be checking the fuel pressure tomorrow, but I dont think that is the problem because it runs great at full throttle.