My 1992 K3500 454 has a terrible misfire. It is worst on cold start up, but it is still there when warm. All spark components have been replaced at least once. The misfire seems electrical and not air/fuel related. I am no expert, I make that assumption because the problem is intermittent, and the misfire is hard, like an ignition cut.
I have been searching various threads on the internet for months, and no one has exactly the symptoms I have had, and the ones that were similar were all fixed by things I have already replaced.
The misfire is worst at low throttle, 2000ish rpm. The truck will buck, backfire, misfire, stumble, surge etc.
Sometimes, the truck will run perfectly fine, although rarely.
Two separate shops have told me theres nothing wrong with my truck and they don't want to work on it anymore. One being what used to be the best independent shop in town, the other being a dealer.
The misfire used to be accompanied by a jumping tachometer but the last shop replaced the cap, rotor, plugs, and wires (for the 3rd time) and the jump in the techometer went away, but the misfire is still present.
New Parts (related to how the truck runs at least):
Vortec fuel pump
Fuel filter
Distributor
Cap and rotor 3x
ICM 3x
Plugs and wires 3x
Coil
All temp sensors
All grounds cleaned/replaced and added extra just to be sure.
High flow cat
5&7 plug wires not crossed
I'm sure there's more that I'm forgetting
I am sure the intake gaskets need replacing, but I am not at all convinced that is causing the problem. That explains a high idle but not a hard, intermittent misfire.
The only things I can think of that might cause this issue are:
TPS
EGR
FPR
I managed to drive the truck without misfiring one day and got almost 12mpg. But most of the time it gets 5.5 mpg just to give you an idea of how bad it is.
Anyone else have this issue?
I have been searching various threads on the internet for months, and no one has exactly the symptoms I have had, and the ones that were similar were all fixed by things I have already replaced.
The misfire is worst at low throttle, 2000ish rpm. The truck will buck, backfire, misfire, stumble, surge etc.
Sometimes, the truck will run perfectly fine, although rarely.
Two separate shops have told me theres nothing wrong with my truck and they don't want to work on it anymore. One being what used to be the best independent shop in town, the other being a dealer.
The misfire used to be accompanied by a jumping tachometer but the last shop replaced the cap, rotor, plugs, and wires (for the 3rd time) and the jump in the techometer went away, but the misfire is still present.
New Parts (related to how the truck runs at least):
Vortec fuel pump
Fuel filter
Distributor
Cap and rotor 3x
ICM 3x
Plugs and wires 3x
Coil
All temp sensors
All grounds cleaned/replaced and added extra just to be sure.
High flow cat
5&7 plug wires not crossed
I'm sure there's more that I'm forgetting
I am sure the intake gaskets need replacing, but I am not at all convinced that is causing the problem. That explains a high idle but not a hard, intermittent misfire.
The only things I can think of that might cause this issue are:
TPS
EGR
FPR
I managed to drive the truck without misfiring one day and got almost 12mpg. But most of the time it gets 5.5 mpg just to give you an idea of how bad it is.
Anyone else have this issue?