My 99 2.5 auto is having trouble on longer hills with A/C on. It runs good on the level and ok with the A/C off. It is not the normal lag with A/C, there is some loss of power from last summer. It has 180,000 miles recent fuel and air filters plugs and wires are also fairly new. no codes, no signs of misfiring. It has had the knock sensor replaced, but probably 50,000 miles ago, no signs of knocking, but there could be a timing cut and not able to notice it. I'm wondering if the cat converter could be getting blocked up, starts good and runs good otherwise.

My 99 2.5 auto is having trouble on longer hills with A/C on. It runs good on the level and ok with the A/C off. It is not the normal lag with A/C, there is some loss of power from last summer. It has 180,000 miles recent fuel and air filters plugs and wires are also fairly new. no codes, no signs of misfiring. It has had the knock sensor replaced, but probably 50,000 miles ago, no signs of knocking, but there could be a timing cut and not able to notice it. I'm wondering if the cat converter could be getting blocked up, starts good and runs good otherwise.

 

 

cat was exactly what i was thinking about....you may want to do a compression test for kicks....but any decrease here would usually be very gradual...

Have you heard any rattling noise coming from the cat?

No rattling, but I will jack it up and bang on the cats. The head gaskets were done last year and the cylinder bores looked fine, can try a compression test in the future.

No rattling, but I will jack it up and bang on the cats. The head gaskets were done last year and the cylinder bores looked fine, can try a compression test in the future.

 

I can't imagine that you have compression rings or intake/exhaust valve trouble, so I would be surprised if a compression test showed any trouble.

 

You might add a high quality can of injector cleaner to a full tank of gas. Get the good stuff like Chevron Techron that cost $6-7.00 per plastic bottle, not the cheap stuff that doesn't work well. Run that thru the tank down to about 1/8 tank. See if that helps.

I'll finish up this old thread I started. I spent some time and tried some of the recommended things and nothing obvious turned up. I ended up putting on a new front catalytic converter and that fixed it. I got a walker brand off amazon.com of all places, cheaper than rock auto for their standard brand. The old one looked fine and didn't rattle even when it was off the car, thanks for the replies up to this point.