Engine wont rev above 2500 RPM's

Hello Ken!
Before replacing everything I replaced I disconnected the exhaust manifold from the cylinder head. The engine kept acting the same.

I think there's something wrong with the injection time. I compared these datas with datas from a known good engine and the injection time was very different.

Hello Ken !
I've already replaced the MAF sensor even though there was no dtcs related to MAF. The MAF I removed from my vehicle? Works very well in another vehicle. I replaced every sensor on the engine. I also replaced the ECM. I wasn't a brand new ECM. I got it from eBay.

Hello Ken
I'm very sorry. You first told me to remove the exhaust and you were right. Th me cat converter was clogged. I told you I had checked it before but I inspected it using an endoscope through the hole of the heated oxygen sensor. I completely removed the exhaust manifold as you said and the engine revolutions can reach the red area. Thank you very much.

Mazda RX8 inside fuse panel on left side door frame has a 20 amp fuse that if blown during battery hookup or install or disconnection will blow. This 20 amp fuse is tied to the fuel throttle system and will not allow motor to rev up past the 2500-2800 rpm. Change that yellow 20 amp fuse and it should give you full throttle response.
That’s what happened on my 2005 Mazda RX8. Replaced and issue corrected low cost.

Someone else replied that a mass airflow sensor issue is known to cause this problem. This is true.

Due to a vacuum leak the mass airflow sensor can also act up and cause this problem.

Unfortunately differentiating between the two is not something the computer usually can do.

Try spraying highly flammable accelerant from an aerosol can such as starting fluid near the vacuum lines. Or just replace all of them. If you do the first test and the engine revs up while you're spraying that stuff. There's a vacuum leak there.

I think that'll fix what you have going on. I have had this problem on multiple vehicles. It was a vacuum leak every time for me.

I do realize sometimes it could be the mass airflow sensor. I'm not saying that's not the cause. You said you already covered replacing that mass air flow sensor though.

Another cause of this is a bad ground to the mass airflow sensor. The wire that goes directly from the mass airflow sensor to the next connection may have a bad ground to it. You may have to replace it. I have never had this problem but I know it's one of them.

My first experience with the same issue I had taken the vehicle to a Ford dealership. All the master mechanics at that dealership could not figure it out. Some of them were 30 years into the job. It took me quite a long time to figure out what the problem was. I hope this helps for you and anyone else who reads it.