Hey guys, I'm new to this forum! I had a question that I'm hoping you can help me with. My Rx8 has 113,000 miles on it, with a brand new motor from Pettit Racing that has only 3,500 miles on it. Just recently (last 500 miles), the car hasn't been able to rev past 7k rpms when WOT. Then when it gets up to 7k, if I let out on the gas and try and rev it past 7k gingerly, it will go all the way to 9k. So I took it to 8k with about half-throttle, then gave it WOT at 8k, and it bogs down and the rpms go back down to 7k. It has a stage 2 fuel pump, new coils, plugs, wires, etc. I gutted the catalytic converter thinking this was the problem and it had no effect. I have no idea what could cause it to do this (maybe clogged fuel filter or something). I'm just trying to get some ideas of what to check that im not thinking of. Its not throwing any codes, idles perfect, has all of its power until I hit around 6k rpm, then slowly makes its way to 7k rpm. Gas mileage is not so good anymore either.

 

Please don't take this link as an insult.
A) it is a good method of searching the forum.
B) You'll be able to get your own diagnosis by searching SPECIFIC threads.

When did you replace your ignition? Before or after the engine replacement?

 

I have searched around, just trying to see if anyone has any certain ideas based on these specific symptoms.The ignition was replaced after motor swap.

 

Something is clogging up your system. Being able to get to 9k with light load points to this. What are your AFRs throughout the rev range? Can you data log it occurring?

I'd point to your cat, but if you gutted it, that won't be the problem.

Edit:
By clogging up your system, I generally mean AFRs. Something is restricting fuel flow, air inflow, or exhaust outflow. If you drop the demand low enough that each is under the threshhold you are experiencing, you can rev fine. You should be able to get a direction to start looking with some OBD2 data.

 

I dont have anything to data log it. Is there anything decently cheap out there I can buy that can read my AFR, MAF, etc?

 

With the coin dropped on the rest of the stuff you mentioned, I assumed you would have something.

You can spend as little as $20, as much as $150 for a bluetooth OBD2 adapter, pair it with your smartphone and your choice of OBD2 app. If you have an Android, Torque is by far the best. Pony up the $5 for the paid version, it's TOTALLY worth it and only increases your total cost by a fraction. The OBD2 adapters largely get faster and/or more durable the more you pay, though there are exceptions.

 

Additional: While I have it pinned WOT, the revs bounce around from 6.8k - 7.5k, it doesn't sit at one particular RPM, and the exhaust stutters and backfires while this is happening.

 

Oh, ok, that seems different, and sounds like a severe misfire. Possibly a problem with your intake valving. If the valve that opens around that RPM is fluttering, it could be completely messing up the air/fuel mixture pretty randomly, and could produce that effect.

Just one option. Anything else that starts interrupting the spark, drenching the spark, etc... could do it too.

 

Is there a specific set of intake valving (or whatever you want to call it) that operates in the 6k-7k rpm range?

 

Yes, I believe so. Check the technical document attached to the bottom of this post: https://www.rx8club.com/new-member-f...4/#post3663975 (Post #5 if that link doesn't bring you to it)

 

It looks to be the Auxillary Port Valve or the Variable Intake Valve. The CEL is throwing 3 different codes: P0420, P0455, and P0620.