my car has confused the hell out of me so Im hoping someone here can help me fix it On my way to work yesterday morning, if I'd let off the gas and let the RPMS drop to 2000 and under when it got to 2000 it woulda backfire a few times, didnt think anything of it at the time figured i was just burning off excess fuel from my tune, but it was doin it in both competitive mode and stock. After work I was low on gas so I stopped to get gas, still backfiring at this time as well, and after I put gas in it I went to start it and it just sat there and cranked over, wouldnt start. Finally after giving in some throttle it started up and ran like **** for a few minutes. Since then my car will run 3.5-4.5 lbs of boost on stock tune and 9.0 on trifecta tune. Did this for awhile, I went to a friends house for a few hours, came out and it ran normal again. Stopped at the store on my way home, then head to the house and its doing the low boost problem again, until I get a few miles from home and it runs normal again 15.0 psi like nothings wrong (it switched from 3.0 psi to 15.0 while driving didnt shut it off or anything) as of the drive to work this morning it was boosting normal but didnt try my tune.

any ideas?

no boost leaks that I can find either

 

CELs?

 

nope none, thats what is making me mad because the car wont tell me whats wrong

 

Hmm...Limp mode can stem from tons of things. I would take it to your dealer while it's in that mode if possible. My limp mode came from the fuel pressure regulator solenoid or something going bad. Warranty fixed it and it still had my tune and mods on it at the time

 

yea im gonna take it to dealer its something fuel related i think, i just went to wendys on lunch and it ran fine to wendys then on the way back 3 psi until i got to the parking lot at work and i did a few passes in the lot and was hitting 22 psi...im so confused lol

 

Well if you're making boost then that's not Limp Mode. Limp mode (AKA Reduced Engine Power) will not allow ANY boost. Are you by chance running a BOV VTA?

 

nope my mods are hahn intake, injen ic piping (hot side, stock cold side) mpx 3 inch catless dp, 25 psi tune (raises rev limiter to 7 grand, deleted 2nd o2 sensor in dp)

 

Its not limp mode. Limp mode, you wouldn't be able to go over probably 3,000 RPMs and you wouldn't be able to go any significant MPH. You would also def have a check engine light. The computer goes into that mode when it senses something is severely wrong and it lets you drive the car slowly to the nearest dealership/shop to resolve your issue without causing more damage.

 

any idea what it is then if its not limp mode?

 

You have a turbo car so it could be a ton of things lol. First thing that always comes to mind is a vacuum line issue. Have you done anything recently to your car that involved your vacuum lines? There could be a slightly split line that is leaking air.

 

Subd to see what's wrond

 

This.

I had a similar issue you are having when attempting to run a Tial BOV VTA. Take it to the dealer. There's a bagillion vac lines on this damn thing so unless you've got time to go over them all, have your warranty do the work

 

yea im going too, im gonna put it back to stock this weekend and take it in...is 25 psi with the k04 pushing it? think it could be my turbo going out?

 

Eh...could be a slight leak in the diaphram thingy of your BPV?

 

Could be a TMAP sensor, too.

There are probably some codes being thrown, just not enough to trigger the CEL.

 

think I should start with that? think it needs cleaned or do I need to upgrade it?

 

Honestly, if it was a sensor acting up, it would throw a code. Thats how these modern cars work. Whether it was circuitry issue or the sensor sensing something wrong, it would throw a check engine light. You're having a pressure issue. Pressure issues on turbo cars for the most part don't throw any type of code but your engine will react to it, whether it be surging or bucking etc etc.

Focus on your vacuum lines, focus on a leak. You're having a pressure build and then pressure not build. It drives like crap then it drives fine. That tells me there is a primary line that may be or not be sealing properly. I don't feel its your bypass valve because you would still build boost pressure in your manifold (reflecting on your boost gauge) even if the valve never closed, you just wouldn't get the power feel because your air flow is lost before the throttle body.

 

You should start by dropping it off at the dealer

 

lol sandman, i will do that, but im a fix it urself type of guy i built my last car from the ground up so i was hoping it was something stupid I could fix on my own, NJHK - that makes sense...i wish i could build boost in neutral so i could listen to it and see whats goin on with my head under the hood

 

Good luck. If you need anymore help, let me know.

 

I had a similar issue but I never lost boost. i would backfire a lot and drivability sucked ass. i went to NLS and I threw P0300 and P0304 codes. I broke the clip on coil pack and I zip tied it to the harness and no more problems. I have noticed that if a coil pack is loose or malfunctioning that you don't get Cels right away.

 

I finally got a CEL its P0451 - EVAP System Pressure Sensor Performance, anyone ever gotten it or know where I should start with it?

 

Everything that I'm checking it could be anything related to your fuel system, from a loose gas cap, to a bad fuel pressure sensor, to bad hoses etc etc. Somehow though its sensing you're losing fuel pressure. Honestly, at this point, you may want to take your car to the dealership especially if you have a warranty (which I'm assuming you do).

 

yea i do, im going to once i put it back to stock tune and put my stock parts back on friday night, im gonna say its fuel pressure regulator like sandman said from the get go, dealership here I come.

 

Gotcha. Good luck to you.