I am a newbee here. I searched and read a lot of stuff on this site, but I still need to ask for help. My poor college son bought a nice a4 Quatro. It needed a radiator and timing belt was due. he got price reduced to cover it. The Mass Air floe sensor was poor but he drove it until he could afford one. by the time he did the car was really slow. We put the new one in and the turbo doesn't seem to power up. We do not know why there has not been any noise. Did this get put in low boost. What would you tell a mechanic to check 1,2,3,.... . 103,000 miles,auto,passenger side. We did not have the computer reset thinking it would set its trims on its own. He put about 500 miles on since.

 

Any cel? If so what's are the codes? Prob in limp mode, get it scanned and reset it. They can reset it or you can disconnect the battery for a few and reconnect.

 

No check engine light. I did pull the negative batt cable and re-attached. Did not help. I pulled the pan off and checked out the hoses I could see. I wanted to see if there is something I can check before paying my mechanic to rummage around. He said he wants to pull the inlet hose and see if he can tell if the blades turn. But by reading these forums maybe I should have him hook up to see if any codes are on and reset trims from the bad MAF first. Is it hard for him to check what the boost pressure is now, then stick his finger in to it wiggle things.

 

Can try a boost leak check too, pretty simple to do and only requires the use of an air compressor. But if you dont have a cel then it might be hard to figure out what is going on here. The computer can read boost pressure and compare it to what is requested and if there's too large of a difference then it will throw a cel. You can always take it to an automotive store and they can read codes for free just incases theres a hidden code without a cel. By reseting the computer when you pulled the battery terminal method, all the trims are reset as well. Next step I would do it take it to get scanned, or better yet get vag-com (ebay cable and freeware from ross-tech), boost gauge ($30 on ebay for a glow shift one and very easy install), and boost leak check (always good and easy to make by using a 2" pvp end cap or the famous tennis ball method). But honestly, im guessing theres just a big leak somewhere and needs to be found, or a bad N75 valve. The N75 valve connects to the wastgate to tell how much air to pass by and build boost. A boost gauge is good anyways and will be nice for the for boost leak check since you want a gauge somewhere to measure the pressure. If the turbo wasn't allowed to spin you would know by some pretty nasty noises. Good luck on the fixen, keep posting, specially if you find a fix!

*and to for him to test the boost pressure will take one cut of a hose and then plug in a gauge of his choice and test drive; 1 min of work and 10 seconds of drive time. And to feel the blades for shaft play prob will take around 15-20 from the intake side, and 15 min from the back side. Also, Ive seen cased that the wastgate flapper will break off and get stuck in the cat, if he undo the cat and move it to the side you can check this, but I would do this later for now.

*Link for an aftermarket N75 valve, http://www.ecstuning.com/Audi-B5_A4-...ctrical/ES122/
Ive seen stock ones go for $30 too. GL again!

 

Thank you for the advise. I copied it and will maybe share with my technician. He is used to people trying to tell him stuff they think they know. I would try to do this stuff but it is about 30 degrees in my garage. I replaced the steering rack and front control arms on this car. When I was younger I would have loved to tinker with this Audi instead of the well used Mopars I had to drive. I thank you for your input and we all appreciate you helping with advice. I'll let you know sometime next week what I find out.

Elroy

 

Im pretty sure disconnecting the battery does not reset the ecu on these cars. i think the only way to clear the codes it to reset it with an obdII connector or with vagcom.

 

It does, I've always disconnected for a few min and turned the key on to drain the caps... Works like a charm and did it multiple times before getting vag-com.

 

By "turn the key on" do you mean not to start or turn the key on and let it sit?

 

Disconnect the battery and try to start the car or put it on the on posisition. Its just a quicker way to make sure the computer is reset by draining the capacitors.

 

I took it to the shop that changed the timing belt, because the tranny lines to the radiator leaked. He fixed that free but did not put the scanner on. He said the turbo was not working and thought it would cost me to much to do just that and not get any concise info. So I pulled the intake side off and turned the finns, did not notice any shaft play. From what you said the n75 valve may be the problem. If I pulled the small hose off the (actuator) ? would that tell me any thing? I could push the rod toward the turbo and heard a sucking sound in the vacuum chamber. Is the N75 valve controlled electronically, what goes wrong with it? Do I have to pull the turbo the check the waste gate?