Missfire with a/c on

[Apex Predator]

Hi folks, new here. My car is an 02 GT and drives fine except when i have the a/c on and i try to accelerate in 5th 60-70. Sometimes the CEL will come on for a few seconds then turn off. Tried plugging my diagnostic computer but doesnt read any codes. Just replaced the fuel filter but didnt seem to help. Car loses power for an instant when accelerating in 5th at those speeds. With the a/c off the car drives fine. Coils?

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[Three50won]

I've never seen a CEL on the 99-04 GT come on and then go off...especially without throwing a code. From what I know, when the CEL comes on it stays on until the DTC is erased. At that point the ECU does not return to readiness mode until you've driven 500 miles. However if the problem is still present, then the CEL will return when you turn off the engine and re-start it. But again, I've never seen them come and go...at least not on the OBD-2 cars. So are you absolutely sure it's the CEL coming on? Maybe it's something else.

And are you sure it's misfiring, or is it just not accelerating? 5th gear is your OD gear so you're not gonna have a lot of acceleration at 60-70 mph. Try testing it in 4th. If there is still a problem then maybe it's the compressor. Maybe the pulley is seizing a bit when the clutch on the A/C compressor is engaged. Are you hearing any weird noises or smelling any rubber? Are there any pieces from the belt in the engine compartment? Is the A/C actually working when you turn it on? How old is the accessory belt?

 

[Apex Predator]

Thanks for the reply^^
Yes, I know I am in fifth and I try giving it half throttle for acceleration at those speeds and the cars just sputters. It missfires and the CEL will blink for about 30 secs then it will just stop. It's always in 5th with the a/c on and on those speeds. When i go WOT there is no problems. What i mean by WOT is if i downshift to 3rd at 60-70 . But in 5th if will missfire.

 

[Three50won]

Well I'm sorry but I can't help ya...this is interesting so I'll do some research and see if I can figure anything out. I'll keep an eye out for ya bro...