loss of power after 4000rpms?

[RidinDirty]

buddy of mine had a OBDII scanner and everything givin to him and so we plugged it up last night and went out to a few diffrent areas to do some quarter mile runs cuz its has a thing on there to do your quarter mile times and it has a dyno.dyno i know wont be accurate but it will give me a relative idea of what ive got...anywho. when i hit about 4000 rpms u feel a dramatic drop in power. ive heard this is cuz the computer cuts the amount of fuel getting to the motor at that point anybody know what it is or why it does this?

[SSpdDmon]

At 4,000rpms, the PCM switches over to using just the MAF to calculate fueling. Up until 4,000rpms, it uses the MAF and some internal equations in the PCM. 1st, I'd say go to your local autoparts store and pick up a can of Quick-Dry Electronics Cleaner and a new paper filter. Then, clean the inside of the MAF, install the paper filter, and see if it's any better. If you have bolt-ons that free up power (headers, catback, lid, etc.), you could be running lean and need a tune. Try cleaning the MAF first though...

[Sarge]

That and worn or weak valve springs do that> If he has a cam and stock valve springs you can bet the farm the vavle springs are not stout enough to close all the way and you get a loss of power just as you described. Worn valve springs do the same thing. Easy as hell to replace.

[9t8z28]

I have the same problem with a bone stock 20,000 mile motor. Only thing I have is a K&N and a lid. It looses power at 4,000RPM's sometimes, not all the time. When it doesn't do it, it F-in SCREAMS.

[2manycis]

both of you clean your mafs and remember not to charge your k&n

also did that guy just say he used an obdII scanner for dyno #s and 1/4 mile times?

[RidinDirty]

ill have to clean the maf i guess cause im stock except for flowmaster cat back and k@n air intake. yeah my buddy had lil OBDII scanner and it has a thing on there that will read ur quarter mile time and a dyno...the quarter mile is acurate...as for the dyno it just gives relative numbers nothing accurate but when it was plugged in my buddy had it hooked to the laptop and i did a run starting in 3rd from just below 1500 rpms to just above 5000 rpms and on that graph it showed a significant decrease in power at the 4000 rpm mark but then seemed to go back up after that

[9t8z28]

Cleaned MAF with MAF cleaner and still has the same problem! Then I put the stock airfilter in and it still does it.