Hi - I've been reading through a lot and plan on replacing the fuel pressure sensor this afternoon, just want to talk through a couple things

Car info - 2007 S40 T5 AWD 6spd manual, 115k miles, mostly highway. I'm the sole owner and while I don't do enhancement work on it, I pay particular attention to how it runs. I haven't had any real concerns until this year, starting around 95k miles.

My gas mileage has slowly decreased from around 27-29 to around 24-25, mainly in the last year. I use regular gasoline, and drive aggressively most of the time, but no racing, excessive speeds (80ish on highway).

I lived in a temperate area for the first 4 years, and recently moved to NY. The first trouble I had was a 'reduced engine performance' light one or two times last winter. It happened on a couple of pretty cold days, and then nothing until recently.

About 3 months ago, 110k miles, it started shuddering on acceleration at 2200-2500 rpm, and then a noticeable absence of boost after that. Coupled with that, I started having the CEL blink, then go out, and eventually it stayed in. I hooked up a reader and got codes consistent with a misfire, so I replaced the plugs (yesterday). One well, furthest towards driver side (US), had obvious signs of water and rust, so I am pretty sure the misfire came from there. I'm still waiting for the CEL to clear. Does it clear upon repair plus time/mileage, or do I have to reset it myself?

So now I still have the stuttering and loss of power. Like I said, I'm going to replace the fuel pressure sensor today if the part I ordered is the right one.

But what confuses me is the loss of turbo boost over 2500 rpm when the stuttering clears. Is that an indication of something else, or is it a symptom of the sensor malfunction?

Thanks for reading, if you need/want more info let me know. I didn't buy this car to drive like a pansy, so I'm getting pretty anxious to get my power back.

 

The CEL will eventually clear with enough starts without trouble. But why wait? Just buy a code reader from the local auto parts store (little more $)or Harbor Freight (little less $). Get the CAN BUS compliant model. About $60 at Harbor Freight. This works for all modern cars so it will last a long time.

I'm thinking you have the problem resolved with a new fuel pressure sensor. A new one fixed up my 2005 T5.

Watch the fuel you use though. Different areas use different fuel blends. I'd try premium fuel once the sensor gets replaced then work my way down to regular to see if there is any change.