Power loss and misfire only between 5-7k RPM
 

I just bought an '04 MT a few weeks ago. It has 102xxx but the motor was replaced 35k ago. During the drive home after buying the car, I noticed it was very lacking in power and shuddered anywhere above 4k rpm. It pulled hard up to there then basically hit a brick wall and would barely rev any higher and started backfiring like crazy. So a few days later I found the misfire thread here and started in.

Currently I have: changed the oil, replaced the plugs with NGK Laser Iridiums, replaced the wires with NGK wires, replaced the coils, cleaned the MAF and IAT sensors, cleaned the ESS, cleaned the intake, checked the cat (fine...right now anyway), seafoamed it via the nipples and fuel tank (and it smoked like a locomotive), and did the brake stomp reset.

It ran progressively better with each repair, but after all this, it's still weak and shuddery (and backfires sometimes) between 5-6.5k rpm. Before, it would barely rev at all, now it does, it's just slower to increase. Before, it had no power after 4k, now it has power until about 5.3k rpm and after about 6.7k rpm. Once it gets to about 7k, it pulls hard again and stops backfiring all the way to redline.

I have searched my *** off (how I knew to do this stuff), but I don't know what else to do. I will have my fuel pump pressure tested, but is there ANYTHING ELSE IT COULD POSSIBLY BE??

Thanks guys, this is starting to seriously frustrate me :cussing:

How did you check the cat? Are you getting a CEL?

Soldier, when I first got the car I spoke to a friend who has an RX-7 and he pulled the codes and got several including a Random Multiple Misfire and an Insufficient Exhaust Flow. I took the cat off and even though it does rattle a bit, it wasn't blocked so I put it back on, at least for now. The CEL doesn't work for some reason, so i have to have the codes pulled to know if it should be on or not. I haven't pulled the codes since I fixed that stuff, so I don't know if it's still throwing a CEL or not, but I can check in a bit

Ok here goes:

P0301--Cylinder 1 Misfire Detected (I wonder if it's left over from before I replaced the coils/wires/plugs

P2004--Intake Manifold Runner Control stuck open, bank 1

P0420--Catalyst System Efficiency below threshold, bank 1

U0155--Lost Communication with Instrument Panel Cluster control module (now I know why the CEL isn't on, that $&@% that sold it to me must've disconnected it)

P0037--Heated Oxygen Sensor Heater control circuit low, bank 1 sensor 2

P0335--Crankshaft Position Sensor A Circuit Malfunction

Get the codes cleared, and see if any return. However, I was thinking that some of those would be the issue.

I did do a brake stomp reset yesterday and had the codes pulled today. Shouldn't the reset have cleared the codes yesterday, meaning these today are the returning ones? And there's obviously something wrong because of how it runs

For future use by future searchers. The problem was a faulty ESS, a faulty MAF, (both fixed, 80% better) and a stuck intake valve (yet to be fixed)

Wow, kudos to you for sticking with this car and working out the kinks, as you put it. Welcome to RX8 land. :)

"You will never get the real experience of fixing things until you own a rotary powered car."

thanks guys