Isssues are on a n 05 R53, only engine modifications are an ATI super damper, 15 percent SC pulley, and an alta CAI. Have kind of an odd one here. It's been 100 plus for weeks in my area and after a 150 mile trip last week the car was bogging down under load at lower rpms, similar to a failing crank pulley. I suspected overheating so I tested the rad fan to find that the low speed wasn't working. As a temp fix while I save up I hardwired high speed to a toggle and didn't have issues again until I had to make the same trip today. Trip down was fine, but hitting my exit near home I had the same symptoms, only this time in fifth at about 4k rpm. Parked at the gas station to check for overheating and all was well. Let it cool down for a while and managed to get around the block. Sat in some neighborhood with the fan running for about an hour and managed to baby her home. In neutral the car runs fine and I can rev to my hearts content. Double checked the belt, pulleys, and the ATI Damper and all was as it should be. I did notice that the panel over the fuel pump was very hot, so I'm suspicious of the fuel pump and filter, as it would make sense to me that a failing pump would be able to give enough fuel in neutral, but not under load. Also no codes whatsoever, no CEL, etc. I'm thinking it's either fuel/air related or one of the aging sensors that hasn't been replaced. I've ordered a new thermostat, housing, gaskets, and overflow tank just in case, along with a new pump, filter, map sensor, map sensor line (Since they break when they're old) pcv valve, and a couple other things that I haven't replaced since I bought the thing years ago. Any thoughts?

 

Try turning off the DSC and see if that helps.

 

I pretty much always run with DSC turned off. This isn't like a slight stumble, more like the engine forcibly being revved down to the point of dying. After sitting for a few hours it was normal again. Only seems to happen after a long trip on a half tank of fuel on a hot day.

 

Last month I had similar symptoms: at best the car was never at full power, at worst it would stop accelerating as if the the throttle were closed. It did stall out on me once on my neighborhood streets. For me, the symptoms were worst accelerating from a stop (traffic lights). I live in Phoenix, so all summer here is it's only hot, hotter and miserable so I can't say if heat was a factor but it did tend to be worst after driving several miles. No check engine light, no codes.

I ended up replacing the fuel pump and fuel pressure regulator without diagnosis because they were both original on my car. Last year I replaced the fuel filter housing thing (the assembly on the passenger side of the fuel tank) so I figured any fueling issues would mostly likely be the old parts in the fuel system.

That fixed it. My car has been fun to drive at full power again ever since.

PS. I have never driven with DSC off. I'll have to remember to try it.

 

That's awesome to hear! I'll add the regulator to my list of potential fixes as well. Thanks for joining the conversation!