Hi my friend has a 2010 RX8 GT had a reman engine replacement under warranty last year at 96k miles. Now the new engine has about 8k miles on it so mwe tried pushing the engine. At neutral the engine dont have problems revving to 9000 rpms but at load at 6th gear only stuck at 5500 rpms and 99mph limit...wont go past that, at one point the engine light started flashing then went away.

I know he has new spark plugs but not sure if he replaced the coils.

What could cause this?

 

Bad coils, bad cat. Do not drive it like this, unless you want to replace the engine again. Reviving to neutral is meaningless, there is no load, but if you get misfires and lack of acceleration in gear your cat is clogged and you are choking the engine.

That's probably what killed the old engine too.

 

Flashing CEL is always misfire, so yeah, ignition and cat will be the main suspect as Loki mentioned.

 

Ouch...I hope its just the coils. If its the cat he will probably just get a generic one.

 

A generic cat is a bit of a crapshoot. It may not last long. I had one for about 2 years, sold it, and heard it shelled out a few months later.

HJS ​or original Mazda can be counted on.​​​​​​ Everything else is at your own risk.

 

99 mph? You only need 88 to go back in time

 

as a little proof to the getting a quality cat argument, i had a weird rattle under my car, ended up my magnaflow oe style cat burst itself and the material was just rattling in the pipe. whats weird to me is ur saying it only happens in 6th gear? do u get the flashing CEL anytime? and does it go above 5500 when in 1rst through 5th?

 

He was just trying to get past 110MPH on the highway, this is the only reason why were in 6th gear...we haven't really tried any other gear...however shifting to 2nd, 3rd and 4th I know we were hitting around 6500rpm...but once were at full throttle at 6th gear it just want to stay at 5500rpms with 97-99MPH then flashing CEL for 5 seconds then goes away.

We were able to break 105 mph around 6500 rpm today...but it was a fluke, after that the car had the same issue again...weird.,

Could it be an SSV issue as well?

 

Not weird.
This behavior fits the model of a clogged cat very well.
If your friend doesn't want to pay for another motor, stop driving it until you've verified whether the cat isn't clogged.

 

It's not the SSV. Really gonna want to stop the speed record attempts until you figure this out, he's destroying his engine with each attempt.

 

yea if it was just 6th id point twords the trans, but if its not working in every gear and the cel flashing deffinatly sounds like the cat. remember the weak point of our engines is that exhaust port, if it cant breath it gets hot, if it gets too hot that side seal spring fails, when that fails, the engine goes pop. its not a hard thing to check, nor is it terribly expencive to replace, deffinatly cheaper than a new engine man