Any other ideas?
 

Car runs fine when its cool out side and motor is cool. I drove around fine all day until it got up to the warmest part of the day. It didnt used to happen unless it was a day up in the 90's. Today it only got up to about 73, so it is getting worse. As the day heats up, it starts having trouble. Mostly in second gear under moderate acceleration. It is basicly like you have let off the gas pedal. even though you are holding it down. Shift into third and slowly accelerate until the RPM's get to around 4000 then its acts like you are letting off the pedal when you are not. Replaced fuel pump with BHR, new coils and plugs.
If I shut the car off and then back on, it will run fine for another 15-20 mins then starts happening again.

Any help GREATLY appreciated.

No CEL's I should add. Also, someone the other day mentioned the cat. Could it act like that? or would it start acting up after a few mins like its doing?

Yes, that sounds like classic cat clogging. Restricted exhaust flow is choking the engine. More power = more air = more exhaust. Capping the air flow in or out will cap the power able to be made.

Continuing to drive on a clogged cat can lead to additional damage such as roasted O2 sensors, melted wiring, damaged engine seals, warped engine housings, or even a fire under the car.

Well, no CAT now,and I thought it was fixed. seemed to run better than ever for 2 days. Today after warming up and idling for a long time waiting for my daughter to get out of school, problem came back. I cant get the RPM above 3500-4000 rpm when hot. Runs fine cold ( when I say cold, I dont mean cold, I dont take it to redline until the temp gauge is in the middle) When its really hot, you cant rev past 4000. it feels like you have let off the gas pedal no matter if you put it to the floor.

Clogged catback?

When I took the cat off, it didnt look bad at all, now I'm running a straight pipe.

catback, not the cat....all the honeycomb went straight in there...?

Honeycomb was intact on both sides.. cat looked to be in pretty good shape. 62K miles.

coils? plugs? How old?

Just replaced coils and plugs 2 weeks ago, along with the fuel pump.... This totally has me stumped.

I guess I am done... I owe on the loan equal to what the car is worth in trade in. The Car has been very reliable until the last month. I have to drive all day long for work. I still love the car, but I must have reliability.

Anyone solved this problem. My car has done this a couple of times, once last summer and last night. Only on long trips, after a few hours of driving, summer but not real hot. No codes either time. Engine was running a little rough and then progressively rougher and would miss on acceleration, got progressively worse till I pulled over. No codes.

First time, last year, I had it towed long distance, changed wires, coils and plugs, checked 02 Sensors, cleaned MAF sensor, replaced air filter, reset NVRAM, dealer said the fuel pump tested fine, but I'm thinking of replacing it next and inspecting fuel filter. Also need to check wiring harness--noticed a smell of burning plastic a while back. 2nd engine with about 40k miles. Will also clean the ESS. Will check the Cat again and the SSV.

Compression numbers were marginal. Mazda replacing under warranty. Third engine. 9 days before the warranty expired.

New engine, but problem not resolved. Drove on the highway, till it was losing power again at the high end, and took it back to the dealer to show them that the problem is not resolved. Finally, there was a code for random misfires. They saw the problem on the new engine, tech listened to the idea that it might be a clogged cat or catback, tested it without any cat or catback, no problem, with cat but no catback, no problem, but as soon as they put the catback back on, problem reappeared. Before they did not believe the catback could be clogged, especially the service advisor, but now they believe. 02 test of cat seems to show that it is fine. Am putting on a new Borla catback next week. Hopefully that will solve it. Will keep you all posted.

The other idea, that the fuel pump might be failing or the fuel filter might be clogged is still not considered a possibility because they say that would trigger a lean code.

New catback. Seems much improved, but problem still not resolved. Back to basics this weekend.