any advice---low boost

[peiserg]

I've got the APR chip in, otherwise stock rs6. On the dyno, in the "stock" setting, the car is only putting out 8 psi (12-1300 mb). I'm told by my tech that the ECU is requesting 1800 (and 2200 for the high boost 91 octane setting), but only getting 8 psi, and 12 psi respectively. He's convinced there is no boost or vacuum leaks. What sensors or valves could be the culprit. I just installed brand new DV's, which solved a previous problem (lower power on the high boost settnig vs. stock setting).

thanks. this is phoenix area if that matters. for what it's worth, i took it to audi dealership, and they told me all is well. this was with my car putting 318 HP at the wheels...

[Hy Octane]

What kind of air temps you have out there?

[Ultslpr]

I tried APR and had teriible results; started at 328 WHp and gained 5 WHP; chip kept putting car in limp mode due to sudden boost amounts. Go with GIAC chip; huge results with awsome amounts of torque.

[skiwi]

at what point is the boost shortfall noticed? low rpms, you will expect a shorfall as the turbine is not fully spooled - however at over 2,800 rpm you would expect little difference between requested, and actual, boost.

have you thrown any codes?

have you checked your maf's for any differences in flow @idle (indicative of vacuum leaks), and at high rpm (boost)?

as you'd no doubt expect, you can't diagnose these sorts of issues over the internet without having to do a bit of work...

[peiserg]

The "stock" setting, which nets me 8 psi, runs 8psi almost across the RPM range (3000-redline). same with the "hi boost 91 octane" setting. 12 psi, flat as a pancake (almost) across the rpm range. this is measured on an awd dyno.

I upgraded teh DV's. That did address the issue of my high boost setting actually losing me power, but overall pwer is only up 20 hp from 5000 rpm upward. APR and my tech have been discussing this over the phone to troubleshoot. Apparantly per the vag com, the apr ecu is requesting more boost, but for some reason it is not being delivered. I guess (i hope) there's a relatively limited number of potential reasons for this, assuming the chip is doing what it's meant to...which is reqeusting more boost.

For what it's worth, i did ask about the MAF sensor, and was told they were checked and each of them readout very close to one another. I just picked up a thrustsensor, which i'm told is a likely potential culprit.


regarding the earlier post about apr only netting you 5 hp and throwing codes... no codes thrown here. SO you returned your ECU to apr, they restored it to stock, you had it reflashed with GIAC and that was it? no other mechainical issues to be dealt with?

[O.CT USA]

2200mbar = 1.2 bar which is more than 14.75psi. If your comp is request x amount of boost and you are not getting then its a leak or a faulty N75

[peiserg]

ok, as a latest update, the thrust sensor was replaced, without much change. while the engine area is apart, I am having hem change the N75 valve as per OCT's suggestion. After this point, my tech suggests sending ECU back to have them either reprogram or return to stock form.

OCT, what is the importance of 2200 mbars benig more than 14.75 psi? my knowledge of cars is restricted to old school, non turbo vehicles. I thought my tech said 2200 as the high boost setting, tho I'm not sure.

[O.CT USA]

ok, as a latest update, the thrust sensor was replaced, without much change. while the engine area is apart, I am having hem change the N75 valve as per OCT's suggestion. After this point, my tech suggests sending ECU back to have them either reprogram or return to stock form.

OCT, what is the importance of 2200 mbars benig more than 14.75 psi? my knowledge of cars is restricted to old school, non turbo vehicles. I thought my tech said 2200 as the high boost setting, tho I'm not sure.

1.2 bar = 17.40456psi. I was lazy to convert. Also 0.8 bar = 11.6 psi

Basically if you have a vagcom(www.ross-tech.com) tool handy you can diagnose leaks or other problems. You can log the car by using 3rd gear pull from low rpm till it shifts to 4th gear. If you see a difference between the request and recieved of more than 100mbar through out the entire range, then there is a leak.

How does your car feel after all those parts have been replaced? It could be a hose. My suggestion would do a log/smoke test/ or pressure test.

[peiserg]

the n75 part is going to be here monday. I didn't drive the car after the thrust sensor, but my tech said there was not much difference. for what it's worth, car has only 8000 miles.

he did say he pressure tested the system. I'm assuming that is sufficient to detect a boost leak? I would think that with all this technology, there would be some way to detect location of a boost leak aside from flowing smoke over everything? Is there some part I can buy that "plugs in" to the system to pressureize it so I can check at home for a leak?

At any rate, assuming the n75 doesn't change anything (and i don't have high hopes right now) I will take the car back and ship out the ecu and tcu. But before I do that, is there a magic formula for smoke testing? you guys use cigarettes or soapy water over the hoses or what? I assume just having somone rev it in neutral builds enough boost to get the desired results??

he did say that while the engine was open for the thrust sensor, he went over all the hoses, and didn't notice anything suggestive of a leak...and his entire garage (literally) is full of turbo vehicles that he works on...100% audi and VW.