My very own update thread - AZ edition (picture heavy)

[BaseDrifter]

Still on the hunt. Put everything back together yesterday with a "C" N75 and got 14psi on the first pull and 12psi on the second pull.

My searching adventure yielded another gem from Walky. I'll reply to it like he posted it himself!

Do you have vag-com? That would be very helpful here.

3psi sounds like wastegate spring pressure. So either the N75's atmospheric input is blocked (unlikely), or it simply isn't getting a signal. Usually "limp mode" will give you about 5 psi, but we shouldn't rule that out either. So first thing to do is check for codes with vag-com (generic scan tool may not reveal everything here).

No codes stored and I was able to get WG spring pressure and limp mode pressure correctly. I'm using a genuine VAGCOM cable.

If no codes, the next thing I would do is an output test on the N75 to make sure it is working. That will test the power supply, the wiring, the valve itself, and the ECU ground signal all at once, so it cuts out a lot of messing around. It should click back and forth about once per second during the output test. During that time you can check it for flow by blowing in the pressure port. It should alternate between flow and no flow if it is working correctly.

Everything checks out when doing the output test as well as manually checking the wires. I've done an output test using a test light as well as two different N75s (a C version and H version) with what should be correct results. I blew into the valve and the air flow was correct, no leaking.

That is pretty much all there is to checking the boost control system. You've already checked the turbo/exhaust/boost leak avenues by using an MBC and making sure the car can actually make boost. You could use vag-com to log the n75 duty cycle, but if it isn't giving a signal it should show a fault code for "why" in any case (ie: too lean, no maf signal, etc). Not a bad idea, though. I guess that would my 3rd step if the first 2 didn't find anything. In summary:

1 - check for codes
2 - check n75 valve and circuit using output test mode
3 - check ecu for boost request (n75 duty)

After following all of the above steps I'm no closer to finding my lost boost. I can hit 20psi with the WG shut, so I must still be having an electrical problem. Since the output test comes back good, the only thing I can think is that I have three bad N75s. I just find that rather unlikely since they all spec out when checking their resistance, none of them leak air, they all worked properly during the output test, and the H valve I purchased brand new. I don't see what else I could try, so I'll be going to the junkyard to pull at least two more N75s out and try them.

I'd really appreciate some input on this from our local gurus. I'm still learning as I go.

[kraylon]

Sounds like your car has a mysterious gremlin just like mine does.

[RENOxDECEPTION]

Maybe diverter valve isn't sealing?

edit.
Meh, but i read you get 20psi with n75 out.

[redline380]

The hardware seems to check out based on getting 20psi with the WG vac disconnected.

let me get this straight. With no vacuum line hooked up to the wastegate nipple, you make 20psi before it starts bleeding off? Seems low to me. With the wastegate shut all the time I'd think it should reach 30psi or more. My personal opinion is to look at the wastegate diaphragm and or spring, and of course boost leaks.

[BaseDrifter]

Yeah, thought about that. I had my 007 out of the car recently, checked it for leaking, and re-lubed it.

Turbo has been replaced, I put a high flow cat in, all the vacuum lines have been checked or replaced, boost leak test doesn't come up with anything, N75 output test is good, DV has been serviced, N75 has been swapped. What's left? That's basically the whole turbo system.

I might get to the PnP tomorrow, hopefully I can snag a couple more N75s.

[RENOxDECEPTION]

When did the problem start happening? wasn't it before that 034 meet?

[BaseDrifter]

let me get this straight. With no vacuum line hooked up to the wastegate nipple, you make 20psi before it starts bleeding off? Seems low to me. With the wastegate shut all the time I'd think it should reach 30psi or more. My personal opinion is to look at the wastegate diaphragm and or spring, and of course boost leaks.

That 20psi was at 3500rpm or so. I didn't bring the car anywhere close to redline. Once I saw the boost climb past 18 I let off. I recently replaced the turbo and made sure to check the waste gate for any looseness and it felt fine. I tested operation of the WG on the bench with compressed air and it would open and close fine, no rattling. I did not measure at what PSI it's cracking open though.

When did the problem start happening? wasn't it before that 034 meet?

I've had this problem for going on 2 years now. I can barely remember the last time I saw more than 15psi, except for when I had the WG vac line disconnected.

[RENOxDECEPTION]

Does AEB ECU allow checking for requested vs actual boost?

[BaseDrifter]

Does AEB ECU allow checking for requested vs actual boost?

Nope, no MAP on AEBs unfortunately.

[RENOxDECEPTION]

So how does the ECU tell what the air pressure is at? Maybe that's reading high.

[redline380]

Yeah, no MAP kinda sucks. If you happen to have a spare ecu around, or want to try a junkyard one and return it, it could rule out an issue with the tune.

[redline380]

So how does the ECU tell what the air pressure is at? Maybe that's reading high.

It doesn't. It just reads mass air coming in, and AFR (narrowband, mind you) of the air going out. Its why going BT on AEB sucks

[RENOxDECEPTION]

It doesn't. It just reads mass air coming in, and AFR (narrowband, mind you) of the air going out. Its why going BT on AEB sucks

ha.

[redline380]

ha.

I've been on this kick where my avatar is a political figure and my sig is a good quote. I'll keep them coming.

End of thread derail.

[BaseDrifter]

Yeah, no MAP kinda sucks. If you happen to have a spare ecu around, or want to try a junkyard one and return it, it could rule out an issue with the tune.

Wish there was a way to get a MAP wired in easily, but it doesn't appear so. Hell I've got the MAP port ready on my intercooler now since I swapped it with an AWM unit!

When this problem started a couple years ago I had an APR tuned ECU. It would spike to 20, hold 18, and taper to 15psi by 5,500. It ran that way from when I bought the car in 2010 until 2012 when the boost dropped to 15psi. Despite the lost few PSI, the car still ran great.

In 2012 I ran into a problem where the engine would just shut off. No flashing CEL, no codes stored at all. What would happen is that I would start the car, and within 5 minutes I would hear a rapid clicking from the relay panel, the RPMs would stutter and the car would shut off. The problem was completely resolved by running a stock ECU, so something went wrong with my chipped ECU. I sent the chipped ECU to a member (or former member) here on AZ who swapped the APR chip to a new ECU. That ECU didn't work when I got it back and it was determined that the APR chip itself had gone bad. I ended up getting a custom tune instead.

While running a stock ECU, I wouldn't see more than 5-6psi. 3psi less than the 7-8 an AEB should be seeing stock. When I put the custom tuned ECU in, I was still getting at least 3psi less than the tune called for (16-17psi.)

I can pull the ECU out of my dad's A4 and run that tomorrow and report back.

[RENOxDECEPTION]

Possibility lukas, Barometric sensor, F96, perhaps it's reading you're at a high/low altitude instead of sea level, therefore thinks you are attaining a higher boost level than you actually are.

http://www.ecstuning.com/Search/853_919_562/ES423436/

Located in the ECU plastic box, and can be monitored with vcds.


Sealevel vs. 6000ft fucked with my boost gauge by about 4-5psi, read higher at sea level.

[kraylon]

This may sound totally dumb but check your battery voltage and grounds, sometimes electronics will start acting weird when they either aren't getting proper voltage or ground.
It's a long shot but maybe worth the 10 mins it takes to check these

[BaseDrifter]

Possibility lukas, Barometric sensor, F96, perhaps it's reading you're at a high/low altitude instead of sea level, therefore thinks you are attaining a higher boost level than you actually are.

http://www.ecstuning.com/Search/853_919_562/ES423436/

Located in the ECU plastic box, and can be monitored with vcds.


Sealevel vs. 6000ft fucked with my boost gauge by about 4-5psi, read higher at sea level.

That's a thought. I'll check it out with VAGCOM and see what it's reading. I live 43ft above sea level lol. If I go to the yard tomorrow I'll see about getting a barometric sensor as well.

This may sound totally dumb but check your battery voltage and grounds, sometimes electronics will start acting weird when they either aren't getting proper voltage or ground.
It's a long shot but maybe worth the 10 mins it takes to check these

Nothing is too dumb to check! I haven't noticed a change in voltage over the years though. My battery is a year old and I see ~14v when the car is running. No corrosion on the terminals or ground under the coolant tank.

Thanks for the input guys.

[kraylon]

a few years ago on my birthday of all days I had the oil sensor on the bottom of the oil pan start acting stupid by giving me random oil low warnings, long story short what was causing it was the ground cable on the battery terminal had gotten loose some how where it bolts to the body, I tightened it up and sensor start functioning correctly.

[BaseDrifter]

I just went and checked the ambient air pressure and it was reading 558.8mbar which is ~8.1psi. The altitude correction was at 1.6%.

Doesn't sound correct to me. Shouldn't I be seeing 14.7psi at sea level? (Note I had the engine off if that makes a difference, I don't see why it would though.)

Reno, can you check your ambient air pressure reading for reference?

[RENOxDECEPTION]

I will if you tell me what field it is in vcds :P

[BaseDrifter]

Block 113 for ambient air pressure and 006 for altitude correction.

[RENOxDECEPTION]

I'm at 12.4 PSI up here.

[kraylon]

Read those same blocks with the car running and see how that effects it

[RENOxDECEPTION]

Read those same blocks with the car running and see how that effects it

-_-

I think since I have ATW that it will display MAP readings instead of Ambient if I start the car... Lukas does your VCDS say Absolute Pres. under field 116?

I can go again if lukas needs me to, for right now, I just brought my laptop back inside and hooked it up to my screen again.

[BaseDrifter]

Damnit, so much for that theory. Started the car up and it was reading 1029.6mbar or 14.9psi.

[RENOxDECEPTION]

Why would it change when you started the car? Not trying to diagnose, just weird that it would change as it's supposed to be a reading of external pressure.

[kraylon]

It's moving more air, but the car also isn't going to make boost without running,
This has got to be getting to the point of pulling your hair out.

[BaseDrifter]

Why would it change when you started the car?

I can only assume that when the car is off the sensor reads at its "at rest pressure", 558.8mbar. Just a guess.

Did you take your reading with the car on or off?

It's moving more air

This is the ambient air pressure sensor though, located in the ECU box.

[RENOxDECEPTION]

It's moving more air

AEB does not have a MAP sensor, and the Barometric sensor is in the same box as the ECU.

I can only assume that when the car is off the sensor reads at it's "at rest pressure", 558.8mbar.

Did you take your reading with the car on or off?

0RPM, off. I can read it again if it needs be.

[BaseDrifter]

0RPM, off. I can read it again if it needs be.

No need to rush out and do it now. It appears that my sensor is reading the correct ambient air pressure. I'd be curious to see what yours reads with the car on at some point though.

The difference between our engine off readings could be due to a design change in the sensor from AEB to ATW.

[RENOxDECEPTION]

IDK if my car even has a barometric sensor :o

I was under the assumption that was a difference between aeb and atw.

I'll research it more tomorrow. I need some rest.

[BaseDrifter]

Looks like your block 006-4 is different than mine. You might find altitude correction % in block 112.

Block 113-4 reads ambient air pressure for me, not absolute.

[MetalMan]

What about logging the barometric sensor and altitude correction?
Also your IAT sensor is reading correctly, right?

Though both of these shouldn't matter if the requested boost (which AEB does display) is appropriate, as I think you said it was a couple pages back. Requested boost will be affected by ambient conditions and IAT.

[RENOxDECEPTION]

118-4 seems to monitor MAP pressure which stays at 870mbar at idle, and jumps up to 900ish when I gas it in neutral, block 113-4 stays at 850mbar no matter what I do, it must be something external since it doesn't change with engine RPM

[BaseDrifter]

What about logging the barometric sensor and altitude correction?
Also your IAT sensor is reading correctly, right?

Though both of these shouldn't matter if the requested boost (which AEB does display) is appropriate, as I think you said it was a couple pages back. Requested boost will be affected by ambient conditions and IAT.

Should be, I'll do some more logging tomorrow or Sunday.

I ordered a Glowshift Elite 10 150psi oil pressure gauge which showed up today. Everything is smaller than I imagined, especially the sender, which is not a bad thing. I'm waiting on the M10x1 tee fitting and M10x1 to 1/8 NPT adapter so I can hook it up.









The next batch of parts for my dad's A4 also showed up. SS front brake lines, a new OEM reservoir, suction pump, 1L of fluid, and two front caliper bushing kits.

[RENOxDECEPTION]

That is the exact same sender mine had! And mine was Prosport halo.

[BaseDrifter]

Haven't got a chance to do more logging for my boost problem, but I attacked the oil pressure gauge install today after my adapters showed up.

http://www.42draftdesigns.com/VDO-M1...ptor_p_94.html

http://store.42draftdesigns.com/M10x...ptor_p_57.html

$28 and a nice big box for these two dinky things. Oh well!



Stock oil pressure sender.



I neglected to get a second crush washer to use between the T adapter and oil filter housing. I attempted to use this washer which I believe is for the turbo somewhere, it's a bit too large and is leaking a drop or two at idle. I'll have to pick up the correct crush washer and take it all apart tomorrow. Yay.



Mocked up before install.



Due to the tight clearances, I installed the T adapter first and was barely able to get it clocked correctly. Having the side port point up is the only way I could see to make it work. I really had to hog it down to get it pointed this direction.



For the constant 12v source I decided to use this handy-dandy fuse I pulled from the junkyard. It clips onto the top of the relay panel. All about that OEM fitment!





Gauge sitting in place. I haven't fit it to a vent pod yet. Some of you may be familiar with my polar bear fleece pajamas, you can see my other pair of pajamas in this photo. Gotta be comfortable while you work!





At a "luke-warm" idle.

[Believer]

What about logging the barometric sensor and altitude correction?
Also your IAT sensor is reading correctly, right?

Though both of these shouldn't matter if the requested boost (which AEB does display) is appropriate, as I think you said it was a couple pages back. Requested boost will be affected by ambient conditions and IAT.

I have very similiar issues to Lukas. How can we verify that the IAT sensor is reading properly? I assume the temperature of the intake air will always be higher than ambient, but how can we know how much higher it's supposed to be and/or if it's malfunctioning?

[MetalMan]

One easy test: if your car is parked in the shade or it's night-time, and the engine has been off for at least a few hours, the IAT should read ambient temperature. (this would be checked with engine off)
Otherwise while the engine is running it should be reading above ambient. Can't really say by how much as there are many factors.