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P0306 and misfire; need opinions.

Wrongwayislost77

New member
Sorry for the long read, just being descriptive.

Cliffs:
Low RPM misfires under increasing/high load
Comes and goes
No visible physical cause

Tried:
Swapping a spare TPS sensor: no change
Swapping injectors 4 and 6: no change
Swapping in a spare 3/6 ignition coil: no change
Tested for a vacuum leak: no change
Harsh language: no change

In-Depth:
So my 2000 GT is experiencing random misfires in the 1500-2200 RPM range when under high load. For instance, I'll be cruising in fourth gear and converter locked, doing 48 mph, and as I come to a slight hill, I tip into the throttle and it immediately begins to misfire, getting progressively worse, until I let off and tip in enough to downshift. It will misfire in this situation in second or third gear as well.
However, if I floor it at 35 mph, it'll grab first, pull with a stutter here and there, shift great, then pull through that gear with more hesitation as well. But if I'm on the highway doing 63 mph or ~2250 RPM it will only sometimes buck. It comes and goes without any notable pattern...

As this does not set a code unless I really abuse it, I'm thinking a component failure somewhere upstream of the plugs, as I've checked them all and they were immaculate. Once it finally threw a code and it gave me a cylinder 6 random misfire, but after inspecting the plug wire, plug, coil, and cps wiring, I could find nothing wrong. Start her up and voila, she's fine for a month and then it comes back...

Any ideas?
 


I'd try harsher words.

Kidding aside though...it could be a wire on it's way out...as nice as it looks...if it is only making a connection part of the time...how old are the wires?

Also, you could try seafoaming it...could be a sticky valve if it has higher mileage on that cylinder...

Or, since it is free...take your ICM off and have it tested at your local auto parts store.
 
Plug wires arent more than 20k old. I'm going to swap the 2 & 6 plugs and the 4 & 6 plug wires, to see if/where it moves. Then I'll have tested what I can, and after that, I guess I'll seafoam it and see how it feels. Thanks, blue.
 
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