High RPM Power Loss
 

Hey,

Im kind of stumped as to what could cause my high rpm power loss, but i know for sure its there.

In 1st gear it feels very good untill 5k rpm, then it feels like i hit a wall from 5-9k rpm, if im in second gear at 4k rpm then push the gas pedal down a little bit it picks up speed, but then when I press the gas pedal down even further while its accelerating there is no change in acceleration at all, like if my car only had 50% pedal movement it wouldn't make a difference at all in my acceleration, so the second 50% of gas pedal movement does next to nothing for me.

Most will probably say I got a clogged cat and that might be true, but the weird thing is the car was e-tested before i purchased it less then two months ago and it passed with good numbers, but the fact I got a p0037 rear o2 sensor heater citcuit error it makes me thing there might be something wrong with the cat and it killed the o2 sensor from heat maybe. Im on the look out for a used BHR midpipe

I don't know much about the intake system yet, but could the SSV, VDI, or APV have something to do with this?

I remember seeing some dyno results where the graphs showed steady power untill 6k rpm then the power would even out, somebody said something about VDI I think, ill look more into that and I will try to test all the solenoids when I get the chance

Info on my car:

Car starts good hot or cold, 2004 RX8 6-speed 137,000km, p0037 for rear o2 sensor

New air filter, new coils, new wires, new plugs, cleaned ESS, cleaned MAF/IAT

After changing and cleaning all the above for sure the car felt a lot better, but only down low, up high there is power loss for sure still

And trust me, its not all in my head the car is slow up high, I will try and make a video of a 0-60 run with it when I get the chance.

Any idea's are appreciated, thanks

APV and SSV

Rear O2 sensor does not effect performance

your engine might be low on compression, cuz 2004 (fym for NA market) is the most problematic model.

High LOAD power loss is usually related to one or more of the following:
- A restriction in air flow in
- A restriction in exhaust flow out
- Heat soaking parts that are strained at high RPM (like coils)
- Fueling problems, where to little or too much fuel is being added
- drivetrain drag problems

What you describe sounds to me like it's a clogging cat, the restriction is open enough to allow 'normal' power below a certain threshhold, throttling anything above like a restrictor plate. If you recently had ignition failure, that could have certainly killed your cat.

You can't rely on the ECU to tell you if had failed, as it will only pick up if the honeycombs blow out completely, and even then it won't always pick it up. A clog typically still detects as just fine to the ECU, as it is still filtering the exhaust, just not nearly as much of it.

The ideal solution to detect a clogged cat would be a pre-cat and post-cat exhaust pressure sensor set, where the ECU looks for too high of a pressure differential. Or too low seeing that the cat has failed. By I don't know of any manufacturer taking this approach yet.



As NYCGPS notes, it could also be a valve problem with the valves not letting the correct amount of air in. But I'd point at the cat first.

Thanks for the tips!

Im on the lookout for a BHR midpipe, I would have just hollowed my cat but my god are these cats ever expensive, so ill just do the smart thing and get the midpipe, if it doesn't help at all i would just go back to the cat and sell the bhr midpipe which seems to hold value good.

Since my rear o2 sensor is fried and im getting a midpipe, would it be smart to just not buy a new rear o2 sensor and just install the broken one on the midpipe and leave it unplugged? The only thing making me want to buy a new o2 sensor is to get rid of the check engine light but since I will be running a midpipe I imagine a new code p0420 will show up, and since the sensor has no effect on mpg and power at all I dont see a point in getting a new one, the only thing that bugs me is i read one person post that it does have effect on mpg but everybody else says it doesn't, he was probably talking out his ass

In the meantime while trying to find the midpipe im going to use Jon316G writeup for testing the ssv and apv

whoever said the rear O2 sensor effects MPG can be ignored (while we're at it, might as well kick his ass)

stock CAT is ALWAYS expensive. especially a Rotary. it shouldn't cost 1800 that's some stealership prices (READ: MSRP), u can get it much cheaper at places like Mazmart but it will cost more than a 1000. There are aftermarket cats which works just as well (at least within the CAT's own warranty period) that cost around 3-400 bux. you can look into that if u really need a cat.

It was proven NYCGPS. It's not a drastic difference, but it IS used in closed loop when your engine load stops changing after some time. The lean burn with negative split timing thread.

Here: https://www.rx8club.com/engine-tunin...4/#post4209124


The discussion about this is scattered through the thread though.

never saw that one before, time to read.

Yes this is some good info!

I think I will buy a new rear o2 when i get my midpipe and see my highway mpg, then i will try disconnecting it and see if it makes any difference.

oltmann was saying that a few subaru guys claim the rear o2 sensor gives them gains without a cat, im going to have to do some testing in the near future.

but for now i got to take my car in to the body shop to get some minor rust on the rockers and rear wheel well taken care of before it gets out of hand. two days without my 8 and hes lending me a civic ughhh! this will be boring, good mpg though lol

Any update on the power loss issue? Was it your SSV or APV? Or did it end up being your cat?

well I hollowed my cat and switched to bhr ignition one day apart so its hard for me to tell which one made a bigger difference but its definitely smoother and faster then it was before, night and day difference during the winter.

But now that winter is over and the warm weather is coming i'm noticing quite a lot of power loss. I purchased a 6 meter endoscope from ebay with led on it and I plan on running it to the vdi and ssv to see if they function properly while im driving, im pretty sure they are ok cause i got no CEL but the power loss makes me wonder so I need to eliminate the them from the equation. Most likely its my slightly above minimum spec compression numbers causing the power loss in the warm weather or maybe I need to switch from 87 octane to 94 and see if that makes any difference.

Also I just put a new rear o2 sensor a few days ago with a hollow cat and believe it or not im getting 1-2 mpg more while cruising so it looks like the rear o2 sensor has a little bit of an effect on mpg, i get 21-22 mpg pure city driving compaired to 19-20 mpg before

^^^why would you run anything less than 92 octane gas? thats part of your problem right there, shity gas = shity power

2nd that. I used low octane once on an old engine and my MPG was definitely better but power will suffer. Your issue does sound like typical cat failure though.

Have you done the whole "check if it's glowing" test at night after driving hard? That's not always a direct tell-tale that the cat itself is bad but is also a visual indicator that your car is running too rich. I had a brand new cat replaced by Mazda glowing on the 2nd day after replacement because I had a deeper problem with the car.