2003 auto model, 130k, new plugs, no codes. Hard acceleration passing 6000rpm, random misfiring begins, all the way to 7200 cutoff. Does not happen in neutral no load situation. Happens every time under load, but strangely, annoyingly, NO CODES come up. Any ideas? Techjunkie.

 

What ECU or ECU flash tune do you have? I would not drive hard under load past 6K again, as you are increasing the odds of walking.

Sounds like the tune on it is not stock and the timing map for 80%+ loads is not correct above 6k. Stock would limit at 6600 for 2003 model. Generally you get 7200 when someone changes the tune.

Not good to go past power band top of ~6200rpm on stock non revup engine anyway.

Assuming it has an aftermarket tune, the knock reduction in the tune or lack thereof is what is responding/adjusting. Having the tune software will allow you to see when and how much knocking occurred, plus action to pull timing to avoid detonation.

Or, I could be completely off base.

Good luck and Happy Independence Day.

 

The other question to ask is, what brand and type of spark plugs were installed? Did the misfire start right after this change?

 

Thanks guys, some more info. My son and I bought the car two months ago. On a long delivery trip, about a thousand k's, I noticed when overtaking at around 60 mph that the gear changed down from 5th to 4th I think, but acceleration was very sluggish and revs hung up at about 5200. Potentially embarrassing if not dangerous! It would not change back up until you backed off the accelerator. I took it to a dealer who confirmed the problem but offered no solution. No codes were showing. I decided to change the plugs as a first elimination step. I used dealer supplied NGK-PLFR5A-11. No change to symptoms. In my previous post I neglected to to say that the rev band and misfiring [or knock] occurred while using manual first gear only as my local street has a 35 mph limit.
The car has an aftermarket crossflow exhaust fitted, so there is a good chance the ECU has been fiddled with. Next step is to get the dealer to do an ECU reset.
Thanks again for your input, I will keep you posted!
PS, problems notwithstanding, a really fun car to drive! My other wheels are a Lexus RX450H, a 72 MGB series 2 and a 66 series 1 E type Jaguar [XKE for you guys!]

 

I spent a bit of money, received advice from experts, some pretty far out there, who drove the car. At the end, was not convinced, so went back to basics and did a workshop manual reset of the ECU. Fixed!! I still don't know why the dealer/workshop/service people didn't do or suggest that in the first place. Lesson learned again!
Anyway, got to like driving the go kart so much, I bought another one. 2003, manual,105K, twin turbo etc and the list goes on. For me! Son a bit miffed 'cos he can't drive it for a couple of years. See you on the road.