Mysterious Missing Boost

[ActiveMonkey]

Let me please start with saying that I am not new to Audis. With that said, there's no more only so many things that could cause this much missing boost. Let's start at the beginning. After searching for a couple years I finally found another B5 A4 to buy.

2001 Audi A4 1.8TQM (AWM)

After purchasing the car, I want to my local muffler shop and had a 2 1/2 inch exhaust put on from the turbo back and a magnaflow muffler. Once I had my exhaust I went to 034 Motorsports (local shop to me) and I had them install their 91 octane tune with the cat delete. woot. Here's where I start scratching my head.

My previous Audi was a 1998.5 Audi A4 1.8TQM and I had a bunch of mods on there but at heart it ran an APR stage 1 tune and later on I changed to the GIAC stage 1 tune. Both tunes were a significant improvement to stock. Back to my current Audi which just received its new tune. When I get in the car to leave 034 motorsport i'm like a kid on Christmas about to open his big gift which is that first wide-open throttle pull and have my butt dyno bring a big smile to my face. But when I finally have a chance to mash on the gas in 2nd and 3rd I don't really notice a difference over stock. Shouldn't i notice some improvement? I thought to myself, "they did flash the ECU, right?" Being in a hurry I didn't have time to go back so I went on my day. As I continued my short drive home I kept thinking what the hell could be causing this. Do I have the world's largest boost leak? Is my N75 valve bad? Is my diverter valve bad... I have tremendous faith in 034 motorsport and I do not doubt their work. So before bothering them, I decided to see what I could find.

So I started with the basics, I searched the whole engine and cannot find any boost leaks. I traced down every single vacuum line, checked every hose and clamp but nothing. I then said screw it and purchase a new diverter valve, no improvement. I did start to doubt myself into thinking that this is a 2001, maybe you just won't notice an improvement. Then I thoroughly backhanded that thought out of my head and hooked up my Bluetooth OBDII scanner. It was reading only 10 psi of boost. I personally hate trusting electronic gauges so I went and purchased a boost gauge to help diagnose. The mechanical boost gauge only shows 8 psi. I never did purchase a new N75 valve, but could that really cause this big of a problem?

Operating under the assumption that 034 motorsports did in fact flash my ECU with a 91 octane stage 1 tune, what the hell could cause such a large loss in boost?

[a4kamila6]

Interesting story and truthfully I am curious what the issue is. Looks like you might find it before someone posts

[tar]

Call 034... Plain and simple a stage 1 should At least be 16psi if not more. You will notice a tune stock the car is anemic. Stage 1 its decent still not fast but noticeable better

[RENOxDECEPTION]

vcds, log and monitor requested vs actual boost....block 115
also monitor wastegate duty cycle 114
post logs

likely a wastegate problem.

[ActiveMonkey]

Tomorrow I will disconnect the waste gate and see what it will boost.

[RENOxDECEPTION]

Careful.

[ActiveMonkey]

I just take my gas my foot off the gas pedal when I hear the hissing get really loud, right?

[RENOxDECEPTION]

Take your foot off the gas if your boost goes over 19ish. But with wastegate hose off you can spool it until hard limp mode...or death of something...probably turbo.

[ActiveMonkey]

I was joking, sorry.

I will be very careful

[RENOxDECEPTION]

Invest in vcds if you plan on owning the car very long. Worth it's weight in gold.

[ActiveMonkey]

Definitely on my to do list

[ActiveMonkey]

I'll be disconnecting the wastegate tomorrow, but I was looking through the engine today and I did notice a slight wear in the vacuum line going to the Combi valve in the rear of the engine. I replaced it with new line, but no improvement.

Video of boost gauge. Only 8psi...
https://youtu.be/iAc-prJxY_s

[RENOxDECEPTION]

That valve only gets vacuum at idle on cold starts.

Your problem resides in either wastegate, wastegate lines, dv, or major boost leak.

edit: or n75

[ActiveMonkey]

Pressure test tomorrow AM, hopefully that will uncover something.

[RENOxDECEPTION]

Pressure test tomorrow AM, hopefully that will uncover something.

Tomorrow I will disconnect the waste gate and see what it will boost.

what happened to this?

[ActiveMonkey]

I didn't have time to disconnect it. This will be on the to do list for tomorrow

[ActiveMonkey]

So I disconnected vacuum/boost line to the wastegate and capped the bung on the N75 valve. Since the wastegate was disconnected, shouldn't the boost have basically spiked?


Video is of me doing WOT pulls with the wastegate disconnected
https://youtu.be/D12ZBYk-qBM

[RENOxDECEPTION]

Since it got slightly better with wastegate disconnected you can conclude it is either a giant boost leak or a wastegate not closing. More than likely the latter.

[RENOxDECEPTION]

Boost leak testing is easier though. When engine is cool try to wiggle the wastegate around if you can reach your hand in that far, if any play, remove turbo and preload wastegate nuts.

[ActiveMonkey]

I'm guessing the wastegate flap is toast. Luckily I have a 2003 A4 as a donor parts car.

[RENOxDECEPTION]

Yeah turbo should be making >20 with the wastegate closed and disconnected. Boost leak test, then check wastegate, then pull turbo and adjust.

[ActiveMonkey]

Already pulled the turbo from the doner, unfortunately two of the studs came out and one of the turbo to manifold bolts snapped. i'll drop this off at the machine shop in the morning and hopefully I can swap it for mine Wednesday.

[RENOxDECEPTION]

c̶a̶n̶ ̶s̶w̶a̶p̶ ̶o̶v̶e̶r̶ ̶t̶h̶e̶ ̶e̶x̶h̶a̶u̶s̶t̶ ̶h̶o̶u̶s̶i̶n̶g̶.̶

[ActiveMonkey]

I wouldn't even know where to begin on how to take that wastegate flap out of the exhaust housing.

[RENOxDECEPTION]

adjust first, no need to replace if it's just loose.

[ActiveMonkey]

You're talking about these nuts having worked loose causing an exhaust leak through the wastegate flap which would limit the amount of boost I could produce. correct?

[RENOxDECEPTION]

You're talking about these nuts having worked loose causing an exhaust leak through the wastegate flap which would limit the amount of boost I could produce. correct?

[ActiveMonkey]

Hmm... really seems like either way I'm pulling the damn turbo and putting one of them back in. It seems rather far-fetched to me that the nuts would've simply come loose. Don't get me wrong I hope this is the case so I can sell this extra k03, but nevertheless I will wait until it comes back from the machine shop before I remove my turbo so that no matter what a healthy turbos getting reinstalled.

[RENOxDECEPTION]

Good plan, boost leak test first though.

[ActiveMonkey]

After testing the wastegate I hook everything back up but I swap out the N75 valve for the from my donor car. Now it does this. In fourth gear it virtually holds 14 psi.

https://youtu.be/hq5OFdfBPmM

[RENOxDECEPTION]

Vcds would be nice because you could log the duty cycle of the n75

Also see requested vs actual boost