looks like you gained several degrees of advance in the 4k+ rpm range. Rusty can you give me the part number off of the BARO sensor?

 

Does the barometric pressure get fed into the ECU's boost control mapping? If it does, you might be tricking the ECU into giving you more boost than measured. Try dialling your MBC down the same amount as you dialled the barometric pressure up and see if you end up back at your original hp/torque curve.

The ECU measures pressures in absolute (i.e. barometric pressure + boost pressure), but I'm guessing the wastegate is likely controlled based on gauge pressure (just boost pressure).

 

It definately gets up quicker and then gains a bit more gradually. After you get kicked in the pants, do you find that it spools alot smoother?

 

looks like you gained several degrees of advance in the 4k+ rpm range. Rusty can you give me the part number off of the BARO sensor?

I think gaining the advance was an effect, not a cause, because I was already getting knock retard. Simply increasing the advance would have triggered more knock retard, and it didn't. If it is a cause, then it must be in conjunction with something else.

Part number from ETKA is 853 919 562.

 

I think gaining the advance was an effect, not a cause, because I was already getting knock retard. Simply increasing the advance would have triggered more knock retard, and it didn't. If it is a cause, then it must be in conjunction with something else.

Part number from ETKA is 853 919 562.

maybe if fueling increased that is helping control knock ie less correction needed = more net advance.

any chance you can get a manufacturer part number (ie motorola) I'll see if I can find the data sheet.

 

Does the barometric pressure get fed into the ECU's boost control mapping? If it does, you might be tricking the ECU into giving you more boost than measured. Try dialling your MBC down the same amount as you dialled the barometric pressure up and see if you end up back at your original hp/torque curve.

The ECU measures pressures in absolute (i.e. barometric pressure + boost pressure), but I'm guessing the wastegate is likely controlled based on gauge pressure (just boost pressure).

I have no clue what the ECU does with the barometric pressure. I'd love to find out. I've heard several logical explanations, but they were all guesses, no actual knowledge.

The ECU is not giving me boost - the Dawes' MBC is. I was running 15 lbs before the mod, after the mod it was running about 17 lbs, so I dialed the MBC back down to 15 lbs. So the boost is the same before and after.

The AEB does not have a charge-pressure sensor, so the ECU never knows the actual boost. I have a boost gauge.

 

maybe if fueling increased that is helping control knock ie less correction needed = more net advance.

That's what I had concluded.

any chance you can get a manufacturer part number (ie motorola) I'll see if I can find the data sheet.

No chance at all. I did open up the sensor box once, way back at the beginning of this hair-brained project, but I'm not going to do it again...

 

A thought crossed my mind this morning - any idea how the MAF works? If it is velocity based (hot wire anemometer springs to mind from my University days as a cheap flow measurement device), then you need air temperature and pressure to convert to mass flow.

So, using this theory, the raw signal from the MAF is adjusted using the ambient temperature probe signal and the barometer signal in the ECU to get mass flow. If you jack the barometric pressure up (from actual), the ECU thinks the mass flow is higher than actual (higher pressure = higher density = higher flow for the same measured MAF flow velocity) and therefore adds more fuel (your rich condition). The O2 sensor then needs to trim the fuel down.

Feel free to poke holes in my theory as I'm making this stuff up as it comes to me (i.e. no direct experience).

fascinating...

Good God, am I a car geek or what?!?!?!?!? :crazy:

doh, I was thinking this stuff is fascinating too

 

Yes the mass air sensor is the hot wire type. It holds a specified temperature at all times, more voltage to maintain temperature means more mass flow.

Incidentally the mass air sensor also cleans itself on every start by heating up to remove contaminants. Apparently it doesn't clean off K&N oil very well.

 

A thought crossed my mind this morning - any idea how the MAF works? If it is velocity based (hot wire anemometer springs to mind from my University days as a cheap flow measurement device), then you need air temperature and pressure to convert to mass flow.

So, using this theory, the raw signal from the MAF is adjusted using the ambient temperature probe signal and the barometer signal in the ECU to get mass flow. If you jack the barometric pressure up (from actual), the ECU thinks the mass flow is higher than actual (higher pressure = higher density = higher flow for the same measured MAF flow velocity) and therefore adds more fuel (your rich condition). The O2 sensor then needs to trim the fuel down...

This is exactly what an engineer at work told me. However, like you said, if it was just adjusting MAF, then the trims would simply lean it back out for no net effect. However, my trims not only didn't lean out, they richened +1%.

 

What if the barometric pressure data is used for no purpose other than setting ignition timing/retard (along with the intake temperature and coolant temperature data) and is never correlated with the MAF data? Just a thought...

 

A simple timing retard may result in a richer mixture - but it would have been trimmed out. Also a simple timing retard would have resulted in less boost, not more.

I got:

1) A richer mixture - richer in a good way because it increased efficiency as evidenced by increasing boost.
2) The richer mixture did not get trimmed out. This is stunning. I have finally defeated the trim mechanism! :icon_eek:
3) If you look at the timing curves (purple line) on the dyno charts, you'll see that I actually have a net advance for timing, although that could be due to slightly lower IAT's (orange line).

In my original "baro -> timing" post, I stated that the lower-altitude settings appeared to retard timing. I was wrong - I based that statement on less observed knock retard - but like I said above, I wasn't logging O2, and I wasn't logging timing (just knock retard). If I had only logged the right things the first time, I would have discovered that my original hypothesis was correct - which was that setting it for a lower altitude would allow it to run richer. The richer mixture allows the ECU to give it more timing.

And this is why I think that it must have something to do with lambda reg. Think about it - in closed-loop, the ECU reads O2 voltages and adjusts the trim to make it 14.7:1. If you add fuel, no matter how you "add" it (via timing retard, changing the load tables, accessing a different area of the fuel map, increasing fuel pressure, larger injectors, etc., etc.), the car is going to run richer, the average O2 voltage will be higher, so the ECU will trim fuel to get the O2 volts back down to lamba. It seems to me that the only way to get richer w/o affecting trims is to alter lambda regulation. And how that relates to altitude is beyond me... :crazy: :hmmm: :Yikes: :bowdown: :thumbup:

 

Somebody's eventually going to snap to the fact that I only have 110 g/sec MAF (sky-blue line, for air, get it?), and say "You can't get that much HP with only 110 g/sec MAF!?!?!"

And they'd be right.

Except I have a Holey MAF...

 

And to be thoroughly scientific here, I should remove the Baro Mod and see if the HP drops back down. But I'm lazy and don't want to re-adjust the Cartech, and every time I drive the car it proves that those dyno charts aren't lying. This car's always been a bit "raw" in its power delivery compared to a chipped car. No longer - it's silky smooth, a delight to drive, a real kick-in-the-pants. This is the most satisified I have ever been with this car. I am just incredibly delighted with its performance.

It will be interesting to see if a chipped car gets the same benefit. Can't wait to see someone else try it... Jess? Chas?

 

Wow Rusty! This is very cool and something I wouldn't mind trying. I'll look over your fist post that you did a while back. If you have any hints on where to find the goodies to do this mod, that would be helpful.

 

I got this via PM and thought I'd share the answer(s) with everyone:

I just read your thread on the Barometric Pressure Mod. I like cars and have some knowledge, but to be honest I am a mechanical NOOB. I have a 2004 stock 1.8t/tip. I think its incredible what you did to your car, especially considering your performance numbers without chipping your engine. Now as for the Barometric Pressure Mod is that something that could be done to my stock 1.8t motor? Would there be pros/cons to me trying that? (read: me having that done by someone that knows what they are doing). I live out in Cali, so would the elevation difference between CA an CO matter? and lastly, in your opinion after doing your mod, can i still get chipped?

I honestly don't know the answers to any of your questions. I think it would be a hoot for someone with a stock motor to try this. If you look at the original writeup, I did it in a non-invasive way, so this mod is totally reversible if it doesn't work out. If I were in your shoes I'd jump on it in a heartbeat. Just DON'T buy a $90 pot. Use a $10 one from Radio Shack or something.

But PLEASE get a VAG-COM and proceed cautiously, logging data as you go. In addition to keeping your engine healthy, it may provide "us" with some more insight into exactly why this mod works.

 

10% for $10 sounds fair. I just gotta get the nads to start splicing :nervous:

 

Bump for move from Garage to GD.

 

Hello,

More information about de BARO sensor.

http://1.8t.org/~quattroman/Audi B5...injection and ignition/AEB/MFI/24-123 Turbocharger boost control & checking.pdf

Regards,

Paul

 

Barometric Pressure Mod yields 10% HP/TQ gain

Remember this?: Adjust Timing using Barometric Pressure Circuit

I did some more experimenting, and went from 200WTQ/170WHP to 220WTQ/190WHP by setting the barometric pressure signal equivalent to near sea-level. Here's the before and after dynos:

The "before" dyno is one that I've been :banghead: against for a long time - I thought I was going to be stuck there until I got some fuel management. I ran four dynos "after" and they all agreed. Seat-of-the-pants it's been a tremendous punch, even better at lower altitude. After doing this mod I drove to Tennessee and back for Christmas. The car ran flawlessly at all altitudes in-between, and pulled like a mule at 1500 ft. with five people in the car. And torque-converter de-locking in 5th gear at peak torque was worse than it's ever been.

I do not know why the mod does what it does. I have suspicions, but that's all - I suspect it primarily modifies lamda regulation, making it run richer closed-loop. Secondarily, maybe alters load tables, and may or may not affect timing directly. The reason I suspect lamba regulation is that, as I adjusted the device "downward" elevation-wise, the car started gaining boost while running richer (O2 sensor voltages increasing during open-loop). I compensated this behavior by turning down the peak fuel pressure on my Cartech, from 90 to 75 psi. And my fuel trims actually went richer, from -6% to -5% or so. If the ECU knew it was running richer, it would have trimmed out more fuel, i.e. gone more negative. So I got almost 20 extra HP with 15 lbs less peak fuel pressure than when I started.

Note that the boost for both graphs is the same. The mod gave me more boost (from 15 to 17) but I turned it back down to 15.

I missed this O2 behavior the last time I tried the lower altitude (parallel-resistance) settings, because I wasn't logging O2 voltage. I only logged O2 for the higher altitude, series-resistance settings.

The other reason I think lambda reg (or maybe load table adjustment) is that it pulls so much stronger during closed-loop. Around town, I have so much power now, it takes very little boost to keep abreast of traffic; as a result, around-town mileage has gone up from 15 to 20mpg. Highway mileage is about the same, 28-32 depending on how fast I go. It'll be interesting to see my next emissions inpection report.

I used the "retard timing" a.k.a. "lower the altitude" setup, where the added resistance is in parallel with the signal, thus lowering the effective resistance, corresponding with lower altitude. The final value was 2-1/2 turns on my 50K Ohm 10-turn pot, which is 12.5K Ohms. The total effective resistance calculates to be 2.58K, which is 72 feet based on the altitude data I logged (see first baro pressure post).

The funny thing is that the VAG-COM data block for barometric pressure compensation doesn't agree with this. At my altitude of 5300 ft, the value is typically -17%. I would expect it to go to zero or near zero, but it's currently reading -21%. Whatever - it works!

I'd like to see someone else try this... at your own risk, of course. Log a bunch of data and pay attention to it. I can't guarantee anything other than it works in my car. It would be interesting to see the effects on other engines, especially other engine codes - mine's a cable-throttle AEB. Maybe this interacts in a fortuitous way with one of my other mods, like the Holey MAF? With that in mind, here's the mod list:

'98 AEB cable-throttle engine
Stock ECU (Motronic 5.9.2 IIRC)
Stock K03 turbo
Stock 2.25" exhaust (with resonator removed)
COAM (Colorado Outlaw Airbox Mod)
Dawes MBC 15lbs boost
440cc injectors
2 bar base fuel pressure
5 bar fuel pressure at max boost via Cartech FMU
'Holey' MAF
Port-matched intake
Port-matched exhaust
FMIC
Baro Mod

Rusty i adjust mine thru my APR Vtune software and it works i'm pushing some VERY good numbers thru time advance and such

 

Rusty I know very little about this at all but I have done a lot of environmental testing and the first thing that pops to my mind is that the atmospheric conditions ( barometric / temp / humidity ) on the before date and the after date might have been radically different thus skewing the comparrison. It would have been nice to have the before and after done on the same day for a truer spread.

Needless to say the end result DOES speak for itself. Good job.

 

BACK from the DEAD with an UPDATE:

Apparently, engine codes that use a MAP sensor have the barometric pressure sensing built-in to the MAP sensor (Passat TDI and barometric pressure sensor). So this mod only works on AEB's, and as of this date, I can only say for sure that it works on unchipped AEB's. I suspect that this mod does something equivalent to what the chip tuners do to the load tables, lamda tables, or whatever. Jeff Moss agrees (please forgive the shameless namedropping).

However, it DOES indeed WORK:

Rusty I know very little about this at all but I have done a lot of environmental testing and the first thing that pops to my mind is that the atmospheric conditions ( barometric / temp / humidity ) on the before date and the after date might have been radically different thus skewing the comparrison. It would have been nice to have the before and after done on the same day for a truer spread...

The comparison was not skewed. I can go out there right now, turn the knob down (i.e. turn the mod off) and the car will feel dog-slow. Turn the knob back up and all is well. This thing works.

Also, as of this date, only one other person has tried it. He used a 5K pot instead of a 50K pot, so it didn't work. If you try this, please follow the partlists exactly:
You need a 5K resistor.
You need a 50K (preferably 100K) potentiometer.
And a 10-turn pot is highly desired. Enables you to really fine-tune the adjustment.

 

Hello,

The signal from Barometric Pressure -F96- sensor influences
- Boost pressure limit
- Mixture composition at engine startup.

 

I've got a VAG. I'll by the parts, and do the logging on my GIAC chipped AEB...but what should I log?

 

Basic logging to make sure you aren't blowing up your engine is 002,031,020.

002 = RPM plus basic fuel and MAF values
031 = O2 sensor volts
020 = knock retard

Log them all together in a WOT 3rd gear run from 2000-redline. 031 and 020 don't have an RPM field, so you must log some other field (that has RPM) in conjunction, else it doesn't make sense.

To get the dyno charts like I have, you'd have to do an E-mail Dyno

Or, a simpler thing to do would be a CAPS run (sorry, don't have a link handy). Anyone want to supply a link?

If you don't feel an immediate butt-dyno improvement, then I'd say it doesn't work.

Oh, since my webhosting is down I'll have to send you the diagram...

 

very interesting, i wish i could try this on my chipped aeb. but dont have a vag com yet.

 

Sounds like a fun project for the weekend. Guess I'll hit radio shack on the way home.:lol:

 

I bet you're not gonna find a "10-turn" pot at Radio Shack. OTOH a good 10-turn is expensive...