Low power/boost in heavy rain

[prizrak]

I posted this on all the Audi forums already but figured maybe someone here knows.
Basically this happened to me the other day while driving in very heavy rain. I don't have a boost gauge (car still under warranty can't install gauge w/o voiding it) so all results are from the ass dyno.

So I was driving in pretty heavy rain and I noticed that whenever I would put my foot down to overtake or downshift the car wasn't running as fast as it normally did but more importantly I barely heard my turbo spool while normally I can hear it pretty well. The rain was also getting progressively less over the past couple of days and the car has been running better. Today it's been pretty dry all day and the car is running like I'm used to.

Not seeing CEL or any other irregularities in the way the car runs just the boost/performance.

I know that weather conditions affect the amount of power the engine can make but it's a bit strange to me that I am not making the same amount of boost.

Car is set up with APR Stage 1 (done through OBD II port) which raises boost from 11psi to 15psi and improves throttle response from the drive by wire. Other than that no work has been done on it beyond normal maintenance.

[Spectre]

Water is not compressible.

[Dogbert]

Originally Posted by Spectre

Water is not compressible.

Damn, beat me to it.

[LeVeL]

Originally Posted by Spectre

Water is not compressible.

This. Dry air = more power than humid air.

[MrChips]

Originally Posted by Spectre

Water is not compressible.

Originally Posted by LeVeL

This. Dry air = more power than humid air.

Liquid water is incompressible, water vapour (which I hope is the only physical state of water getting past your air filter) is compressible, just like air.

So why does moist air result in less power production as compared to dry air? It's less dense, but not by much. Water molecules are lighter than an "average" air molecule (the molar mass of water is 18.02 g/mol, whereas the mean molar mass of air is 28.97 g/mol).

Let's take a sample of 1,000 air molecules. Assuming it is of standard composition and completely dry (no water whatsoever), there will be 780 nitrogen molecules, 209 oxygen molecules, 10 argon molecules and one other molecule of one of several other gases. Now, let's introduce as much water vapour into this air sample as we can. In standard conditions, we can add as many as 10 water molecules to this sample - which means 10 other molecules must be displaced to fit all this water in. Since water is lighter than the other components of air, it will reduce the air density - but not by much. In real-world conditions, the density difference between totally dry air and saturated air is close to one half of one percent.

With the difference being such a small number, I dare say you likely wouldn't notice the difference in power between saturated air and dry air. If we're going to blame the weather for horsepower loss, variations in barometric pressure will cause the biggest changes, especially near sea level. I am assuming since the OP is reporting heavy rain that he would have been in the midst of a low-pressure system - even then, unless you're driving in the middle of a hurricane or a powerful nor'easter, the air density won't change more than two or three percent. Again, probably not a noticeable power loss without a timed accelerations or a dynamometer.

[Spectre]

Hate to tell you this, but liquid water does get past your air filter in a heavy rain.

You have also failed to explain why the OP's turbo wouldn't spool in heavy rain, since you have just 'proven' that it should have. However, since it evidently *didn't*, something is wrong.

[_HighVoltage_]

Originally Posted by prizrak

I don't have a boost gauge (car still under warranty can't install gauge w/o voiding it) so all results are from the ass dyno.

Car is set up with APR Stage 1 (done through OBD II port) which raises boost from 11psi to 15psi and improves throttle response from the drive by wire. Other than that no work has been done on it beyond normal maintenance.

So, hang on a second. If you install a boost gauge you will void the warranty, but adjusting the boost itself won't?

[the Interceptor]

I have noticed that a lot of Turbodiesels (at least the ones I drove) are quite meterosensitive, having less power when it's wet and more at a cold, clear morning. Thus, I think that expecially Turbos with some grunt are meterosensitive.

[LeVeL]

Originally Posted by _HighVoltage_

So, hang on a second. If you install a boost gauge you will void the warranty, but adjusting the boost itself won't?

I'm guessing that he can just switch to the stock map if he goes to the dealer or something.

Originally Posted by the Interceptor

I have noticed that a lot of Turbodiesels (at least the ones I drove) are quite meterosensitive, having less power when it's wet and more at a cold, clear morning. Thus, I think that expecially Turbos with some grunt are meterosensitive.

Well cold air makes perfect sense - its basically additional cooling and you can make more boost

[otispunkmeyer]

^ cooler charge = higher volumetric efficiency, can = higher torque/power, you dont necessarily need more boost. just the denser air. you can keep the boost fairly constant and just drop the temperature.

[ja404]

Are you getting any CEL? I know the 1.8T ignition despises rain. I've gone through two coil packs, both went during heavy rain.

[p0w3r]

Originally Posted by _HighVoltage_

So, hang on a second. If you install a boost gauge you will void the warranty, but adjusting the boost itself won't?

APR chips are undetectable by most dealer software

...but if they do enough digging and send stuff to Audi USA they might be able to as i heard a few cases.


I was gonna say to check the coilpacks too...but its strange that it gets better when its dry. My car acts the same in rain and dry days and it has an APR chip aswell...

[MrChips]

Originally Posted by Spectre

Hate to tell you this, but liquid water does get past your air filter in a heavy rain.

You have also failed to explain why the OP's turbo wouldn't spool in heavy rain, since you have just 'proven' that it should have. However, since it evidently *didn't*, something is wrong.

Unless you're driving through huge puddles, you shouldn't get any amount of water into your intake that won't change phase or atomise before it makes it's way deeper into your engine. I will concede that atomised water is still liquid water, but it shouldn't really be in any kind of quantity to cause any problems.

As for the OP's problem, pretty much what needs to be said has been said already - check your coil packs. Alternatively, it could be that your air filter got waterlogged somehow - a wet air filter, especially a paper one, won't flow as well as a dry one. Try and figure out if your filter did get wet (the lowest part of the filter should be very dirty if it did), and try to figure out a way that will prevent it from getting wet again, if that is the case. Also, if you've got a stock airbox in this car, check it to make sure you didn't collect any crap that could obstruct any air inlets into the airbox - I've noticed that many VWs and Audis of several models will occasionally suck a bunch of leaves and other light stuff into their airboxes.

[prizrak]

So, hang on a second. If you install a boost gauge you will void the warranty, but adjusting the boost itself won't?

APR distributes their software through Audi dealers here. There are bunch of mod friendly Audi dealerships here, if you do mods through them they will honor factory warranty. Installing a boost gauge through a dealer is way too expensive for my taste.

Are you getting any CEL? I know the 1.8T ignition despises rain. I've gone through two coil packs, both went during heavy rain.

No CEL, no evidence of coilpack failure, I've been through 3 already

Alternatively, it could be that your air filter got waterlogged somehow - a wet air filter, especially a paper one, won't flow as well as a dry one. Try and figure out if your filter did get wet (the lowest part of the filter should be very dirty if it did), and try to figure out a way that will prevent it from getting wet again, if that is the case. Also, if you've got a stock airbox in this car, check it to make sure you didn't collect any crap that could obstruct any air inlets into the airbox - I've noticed that many VWs and Audis of several models will occasionally suck a bunch of leaves and other light stuff into their airboxes.

Thanks thats whats gonna happen today (finally nice weather and I have some time) I do clean leaves and shit out of the air box once in a while.

I wouldn't be surprised that my filger was waterlogged it was VERY heavy rain, think Chinese GP F1 rain

So finally got around to checking the air box. Was not very successful, Audi sux at air box design. I can't see the bottom of the filter without taking it apart and taking it apart involves unscrewing a bunch of shit and taking hoses off. I might as well order a high flow filter from AWE or ECS Tuning and just replace the crappy old one.