View Full Version : inconsistent boost ...not boost leak

05-17-2007, 07:14 PM
Hey, I got the APR programming in my car and it has run like a dream, until my mass air flow sensor crapped out, i replaced the MAF sensor and the check engine light went out but i still am experiencing the same problem before i put the MAF sensor in just not to as much of an extreme. This is mostly noticeable in 2nd and 3rd gears when punching the gas the turbo will spool up spike at about 18 pounds and it will usually hold steady at about 16, instead it spikes then drops down to like 12 or 13 then spools up to 16 then drops down to 12 or 13 again and back up to 16, it continues to do this as long as you are punching it. So I put my car back in the stock mode running about the normal 8 pounds of boost and it runs flawlessly, for this reason i dont think its a boost leak, any input?? let me know if you need any other info from me that might help you out.

05-17-2007, 07:50 PM
it may be a boost leak only leaking out at higher boost.... Im in the same boat as you... it will be fixed in a week or two, i just need some time, in the mean time ill just not boost at all

05-17-2007, 08:06 PM
I had the same problem with the GIAC-X chip. It is from your boost spikeing too high. The computer tells the N75 to reduce boost. I ran a MBC to control the spike and it fixed the problem. Then I even bypassed the N75 completley and made even more power.

05-17-2007, 09:24 PM
You should find someone to VAG your car and see if any fault codes were thrown. Did you hearing any popping like sounds by any chance? Did you have a flashing CEL when the stutter in boost occured?

05-18-2007, 12:05 PM
vast mbc. done deal.

05-18-2007, 03:00 PM
nah no popping or anything like that it doesnt really make the car shutter or anything even you can jus feel the car not accelerating smooth and i can watch the boost gauge jump around im waiting to hear back from apr to see if i might need to get them to reprogram it for some reason cause of the new MAF what do you mean by "vast MBC" i dont know all the abbreviations

S4 in_lowplaces
05-18-2007, 04:24 PM
How long has the new software been on the car, remember the car needs time to adapt to new settings, usually 200 miles untill your good to go.

Vast is a mortor sport company that dose instals and fine tunning, MBC = Manual Boost controller, you attach it next to the N75 valve and you can control how much boost your turbos produce, if your ECU is producing to much Boost the N75 valve will cut your throttle. So if you set yoru boost to say 17 PSi that is what you will boost, and it wont taper as much. When they say you need a TCD that is a throttle cut defender that VAST sells, it tricks your N75 valve into thinking there is no exxessive boost so it doesnt cut yoru throttle. DId i miss anything?

05-18-2007, 04:57 PM
haha nah you didnt miss anything, i got the software back around christmas time and it was runnin perfect til i replaced my maf sensor until about 2 months ago

S4 in_lowplaces
05-18-2007, 05:27 PM
hmm wierd, sorry man i gotnothing for you, these cars area PITA for sure!!

05-18-2007, 06:59 PM
i'm having the same problem now 2. Car will boost to 18 or 19 then taper down to like 12 psi around 5200 rpm. when boost comes on ,it hits hard but doesn't stay long. i also have installed mbc/tcd and i still have this problem. haven't really chcked for boost leaks yet. also i'm thinking maybe the fact that i'm still running the stock f-hose and throttle body boot, not sure though. my car has been a PITA since i bought 2 yrs ago, but i love her like a son

05-18-2007, 07:28 PM
Well, first of all, 18psi spikes on the APR chip is fine and normal. You shouldn't need an MBC or TCD to limit the boost ... And before I get hazed for saying that, what I mean is that your stock N75 can handle 18psi (unless your N75 is leaking -- at which point you can replace that). Becuause the APR chip is known to spike to 18psi with no adverse effects on most cars, I would venture to say that the 18psi spikes are NOT your problem ... I would go straight to what you changed that made your car acting weird ... The MAF ... Any chance you installed the wrong maf? Didn't hook it up correctly? Got the wrong one and didn't wire it correctly? I would start there before you go start to install an MBC and TCD ... With that being said, however, those two things can help you -- but I don't think it will in your case.

05-18-2007, 07:33 PM
disconnect the ecu for like an hour.

05-18-2007, 07:37 PM
disconnect the ecu for like an hour.

Do you mean the battery? If not, why disconnect the ecu for an hour? Wouldn't having it disconnected for 5 minutes have the same effect? Not tyring to be ignorant, i'm really curious?

05-21-2007, 06:23 PM
the MAF is the correct one it was a direct replacement from audi too so there shouldnt be anything wrong with it, after talking to apr today they said like another person had posted it might be a boost leak that only leaks at higher pressure he said pressurize the system to about 20-25 psi and listen for leaks for starters, i am also runnin the stock f hose and throttle body boot so that could be a lil bit of it but i dont think that is the major problem, the other thing i had considered which someone else said if maybe the n75 valve is takin a crap, i will post back if i figure it out.

05-21-2007, 06:27 PM
sounds like N75 valve to me

05-21-2007, 06:28 PM
sorry for the confusion i just realized today that i posted this in the s4 category i actually have an a4 however regardless of the car the troubleshooting help is gonna help me either way, im gonna try to do the pressure test tommorrow if possible

05-22-2007, 10:41 AM
Movin to B5 A4 ... (You do have a B5 A4, correct?) ... Either way, the answers should be the same, but now you have some more eyes on your problem. Good luck.