N75 - is it 078 906 283 B? anyone know how much $$?
02-10-2003, 02:38 PM
#11
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overboost...
<img src="http://pictureposter.audiworld.com/12010/audin75.jpg">
Based on my knowledge of how this thing works, I'm guessing one failure mode would be a leak from the green inlet to the purple, even when the valve is "closed" (if that's what you call it). And that would potentially cause crazy boost levels, as less pressure would be available to push the wastegates open.
So back to bench testing, if I apply say 10 psi to the green inlet, air should only flow from the right outlet in the diagram (control lines to the wastegate actuators). If I then apply 12V, the air should exit through the purple outlet on the left. Is that correct? Is there an input pressure at which the spring is overcome and air should begin to leak out the purple outlet?
Based on my knowledge of how this thing works, I'm guessing one failure mode would be a leak from the green inlet to the purple, even when the valve is "closed" (if that's what you call it). And that would potentially cause crazy boost levels, as less pressure would be available to push the wastegates open.
So back to bench testing, if I apply say 10 psi to the green inlet, air should only flow from the right outlet in the diagram (control lines to the wastegate actuators). If I then apply 12V, the air should exit through the purple outlet on the left. Is that correct? Is there an input pressure at which the spring is overcome and air should begin to leak out the purple outlet?
02-10-2003, 03:08 PM
#12
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everything you said is correct.
for when you apply pressure to the inlet and apply voltage to the coil, you'll get airflow out of both tubes (but the wastegates won't be getting that high pressure because of the parallel loss, as you know)
sorry, i don't know what sort of boost pressure causes the valve to start to open. it's a good test though. I'd cap off the wastegate side, then apply pressure until it leaks. It's pretty interesting. I'm going to a MBC this spring if I get new ic's and finish a few other things on my car. I hate this N75 stuff. I'll leave it plugged in though.
Have fun Phil!
Mike
sorry, i don't know what sort of boost pressure causes the valve to start to open. it's a good test though. I'd cap off the wastegate side, then apply pressure until it leaks. It's pretty interesting. I'm going to a MBC this spring if I get new ic's and finish a few other things on my car. I hate this N75 stuff. I'll leave it plugged in though.
Have fun Phil!
Mike
02-10-2003, 04:20 PM
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Re: that's the crappy part...the valve still clicks open under 12V, but, you
Hmm, maybe that is the problem I have right now. TBB and both BPVs are new (again...), both turbos are in fine working order, and mostly the car runs just like hell. But from time to time in the last three days it starts off furiously, and in excess of 3k rpm it completely goes off boost. No DTCs, all VAGged, everything is fine. Requested and delivered boost is fine all the time I log, and then I disconnect VAG COM, and guess what, the next time it does it to me again. Spuriously faulty N75? How do I check that??? Oh, and no heak soak in the ICs either.
02-10-2003, 04:24 PM
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i don't like the intermittent failures either. you can test out your car with a different n75.
if you want, i can let you borrow one that i know works without any issues.
log 003 and see if your throttle is cutting...maybe you can be real jerky on the throttle and make it spike and cut.
log 003 and see if your throttle is cutting...maybe you can be real jerky on the throttle and make it spike and cut.
02-11-2003, 12:24 PM
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Re: i don't like the intermittent failures either. you can test out your car with a different n75.
Thanks, I will log 003 and look what happens. I will have to go get a few more parts so I will just go to the dealer and get another N75. I start really to dislike the rubber contents in the S4. The last TBB held up for three entire days! I put it in 2/7/03, and yesterday I noticed it has a tear of about 3 cm.
02-12-2003, 11:16 PM
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Re: i don't like the intermittent failures either. you can test out your car with a different n75.
Ok, got it all sorted out. Spuriously faulty N75, N249 dead, and the three day old TBB had a 3 cm tear. Other than that, everything is fine. I will not use any rubberized or rubber-made objects for the next few days... They might ALL fail on me these days.
02-13-2003, 09:01 PM
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Re: wow! the triple wammie. lol. n249 too!? heheh..i just found a failed one in someone's car today.
yes. I was really ticked off. I start really to hate the rubber crap in there. Time for a BiPipe, but hey, this time I did NOT cut into any of my fingers, and I lost no tools/bits/clamps/washers. I was just cursing a whole lot more since the TBB has a slightly different shape now, bent downwards. You would not think a rubber piece bent slightly out of shape is such a bitch to put in, but it is. N75 and 249 are pretty easy to get in and out, but I intensely dislike the snap-on/crimp-together clamps. As for the N75 I tested it a long time until I could indeed reproduce its malfunction outside the car. And a shot N249 looks very entertaining. Can send pictures if so desired...