Optimal Air Fuel Ratio's RUNNING LEAN VAG COM

[hodrosS42001]

Recently purchased a VAG-COM which yielded some interesting results about my (mystery 3- tune)

Here are some OVER simplified numbers:

ECU Requested ACTUAL

Boost 18.5psi 14.8psi

MAF Spike: 252 g/s (95 degrees outside)

but here is the one I am quiet confused about:

From 3500-6750 my A/F ratio recorded by the VAG-COM hovers around 19:1 (FULL THROTTLE) ....which is incredibly lean.

I mentioned in previous posts on this forum I thought I had a Full 3- tune but was confused with the 4bar FPR.. could this be causing this lean A/F ratio?

Would a simple change to a 5bar FPR correct this problem? I believe but am not sure.. that if this car had a full 3- tune using a correct 5bar FPR and it was replaced by a 4bar FPR at some point it would make the engine run lean.. like I am observing.. is this correct? I have a new one from Neuspeed and that I will install soon, unless this might not be the solution. Otherwise perhaps the Fuel Filter could be the culprit. Either way I know the car should not be running this lean. I have seen posts about 12:1 being ideal for a Stage 3 or 3- tune. The 19:1 is bad for the engine and is obviously robbing me of power and causing my turbo's to under boost.

Anyone have this RUNNING LEAN issue with Stage 3 or 3- tunes?

Any thoughts?

Thank You

[airjawed]

How are you measuring the A/F? What measuring block from Vag-Com?

[kyleb]

Post your WHOLE log. Again, how are you getting your afr numbers. Vag com displays in in voltage or lambda

[Don Supreme]

There is no way that car held 19:1 through an entire pull. It would run like shit(misfiring, knocking, etc etc) and or melt half way through.

@ 19:1 there is basically no fuel in the combustion chamber.

[julex]

VAG-COM afr is purely speculative and only true for stock and properly scaled aftermarket tunes. I bet yours doesn't have properly scaled MAF/injectors and as such is giving bogus readouts on calculated AFRs. Having said that, reading O2 voltage during a pull can give you a general idea where you are, to within 1.0 or so accuracy. To properly see the AFRs you will need aftermarket wideband o2 system though ,no way around that.

[hodrosS42001]

The numbers were taken using the lambda control. I took off my Fuel Filter.. it was completely clogged. Absolutely NO air flow.. so obviously no fuel flow. That is most likely the problem.. I was starving my engine. I will put a new one on tomorrow take more data and post the results.

[zadeluca]

what exactly are you trying to accomplisg here? you posted in the other thread that the car is running great, so why are you LOOKING for problems that probably aren't even there?

i have installed brand new fuel filters that out of the box i could not blow through. the fuel pump can, no problem. you were not "starving your engine."

if you were actually running that lean your car would be destroyed. listen to these guys when they tell you things, they have been around a long time and know a lot about this car. your A/F readings are wrong.

[hodrosS42001]

what exactly are you trying to accomplisg here? you posted in the other thread that the car is running great, so why are you LOOKING for problems that probably aren't even there?

i have installed brand new fuel filters that out of the box i could not blow through. the fuel pump can, no problem. you were not "starving your engine."

if you were actually running that lean your car would be destroyed. listen to these guys when they tell you things, they have been around a long time and know a lot about this car. your A/F readings are wrong.

Dude, I am 21 years old. This is the first car I have ever purchased on my own. I have never had a Audi never or had a car with a turbo or intercoolers or awd or had any modifications. I am trying to decode the uniqueness of my car as it is far from stock. With each attempt I discover new details in which I share for others. I come across good things and bad.

Since my purchase my father and I have:

replaced the dash. replaced both rear brake piston calipers. resurfaced the stock wheels. resurfaced and painted the stock calipers. rebuilt the secondary air pump. replaced fuel filter(newest). fixed driver side seat spring. replaced spark plugs. replaced ignition coils. resurfaced and repainted danged rust on driver side door... and other minor things.

We added a boost gauge and a borla catback exhaust.

We found through the use of an automotive scope my car has RSK04 turbo chargers.. and with my recent purchase of the VAG-COM a full 3- tune.

I have posted on this forum frequently during all this work and have recieved a lot of helpful criticism and suggestions. This has helped me a lot. And I believe that is the purpose of this forum, is it not? To learn? But in the end I am the one driving the car and the one who is observing subtle changes. I might get overwhelmed by emotion occasionally because of my admiration for this car, and maybe that is my immaturity but I don't think that is reason enough to be rude.

[jibberjive]

VAG-COM afr is purely speculative and only true for stock and properly scaled aftermarket tunes. I bet yours doesn't have properly scaled MAF/injectors and as such is giving bogus readouts on calculated AFRs. Having said that, reading O2 voltage during a pull can give you a general idea where you are, to within 1.0 or so accuracy. To properly see the AFRs you will need aftermarket wideband o2 system though ,no way around that.

Quoted for Truth (and emphasis for future people with similar threads).

[zadeluca]

Dude, I am 21 years old. This is the first car I have ever purchased on my own. I have never had a Audi never or had a car with a turbo or intercoolers or awd or had any modifications. I am trying to decode the uniqueness of my car as it is far from stock. With each attempt I discover new details in which I share for others. I come across good things and bad.

Since my purchase my father and I have:

replaced the dash. replaced both rear brake piston calipers. resurfaced the stock wheels. resurfaced and painted the stock calipers. rebuilt the secondary air pump. replaced fuel filter(newest). fixed driver side seat spring. replaced spark plugs. replaced ignition coils. resurfaced and repainted danged rust on driver side door... and other minor things.

We added a boost gauge and a borla catback exhaust.

We found through the use of an automotive scope my car has RSK04 turbo chargers.. and with my recent purchase of the VAG-COM a full 3- tune.

I have posted on this forum frequently during all this work and have recieved a lot of helpful criticism and suggestions. This has helped me a lot. And I believe that is the purpose of this forum, is it not? To learn? But in the end I am the one driving the car and the one who is observing subtle changes. I might get overwhelmed by emotion occasionally because of my admiration for this car, and maybe that is my immaturity but I don't think that is reason enough to be rude.

It seems like you have been making great progress in understanding and maintaining the car. My only point was, try not to jump to conclusions. The car is going to break from time to time, but if you can stay calm you will be able to fix it without throwing parts and money at it that it may not need (maintenance aside).

You have done all the same things I would have done, got Vag-Com, posted logs, etc. And as you said the car is unique, and that is where the expertise of these forum members (who are much more knowledgable than I) comes into play. They were able to confirm what I suggested in your other thread, that it is very likely that those readings are completely skewed because of the modifications done to your car.

We all get overwhelmed with these beasts. I have only had mine for 10 months and I already have experienced that they are usually broken more often than not. If you thought I was being rude, I apologize as that was not my intent.

[domantas]

yes, if tune is for 5 bar FPR then you will be running lean with 4 bar. I know you can convert them to 5 bar just dont know how, search around. Get yourself handheld A/F ratio wideband or take it to dyno. Dont rely on your vag com readings. These cars are not equipped with wideband sensors

[airjawed]

The numbers were taken using the lambda control. I took off my Fuel Filter.. it was completely clogged. Absolutely NO air flow.. so obviously no fuel flow. That is most likely the problem.. I was starving my engine. I will put a new one on tomorrow take more data and post the results.

I forget where I saw...but I don't think you can rely on blowing air through a fuel filter. If you have the new one try to blow through that one after it is 'wet' with fuel.

The pain about the fuel system is that you might have a crushed FPR...also there are injectors that look stock on the outside but are modified as well. Only way to really know how much fuel is being injected is by testing injectors and seeing fuel quantity sprayed out into containers. It is outlined in the Bentley manual.

[SynapticA4TQM]

The numbers were taken using the lambda control. I took off my Fuel Filter.. it was completely clogged. Absolutely NO air flow.. so obviously no fuel flow. That is most likely the problem.. I was starving my engine. I will put a new one on tomorrow take more data and post the results.

can you be more specific on this? when you say lambda control do you mean calculated from O2 voltages or from some reported AFR ratio? I'm not familiar with the S4 ecu, but the 1.8t ecu has some querks like the aver fuel injector on time (ie the reporting of it from the ECU) maxes at 16.42. That happens as early as 3k in some cases that I've seen. Comparitive tests have shown that they are clearly providing more fuel than what is being reported, at least by the Injector on time information. This is the crux of the comment in post #5. You know that you are well beyond where the engineer's intended performance for your engine. They designed the ECU to be able to properly handle and monitor the system in stock form. At that level you may need to get other equipment to monitor and keep track of what's actually happening.

If you truely believe that your AFR is anywhere near 19, the smartest thing you could do it cut your boost in half until you can know without a doubt what is going on. IF your AFR is anything near 19, you are shoving a bunch of air through your engine with very little fuel! If you haven't melted a piston, or destroyed a cylinder because of predetonation, then you've either been AMAZINGLY lucky, or your AFR is nowhere near 19:1.

I would recommend doing to self-study on Air/Fuel Ratios, typically at 17:1 cylinders will start to misfire which causes you to feel stumbling, bucking, and/or generally running like crap... I'm not sure an engine would even run at 19:1.

[hodrosS42001]

Yes the lambda was the 02 voltages. And it was only 19:1 at WOT it was less idling. Once changing it to the 5 bar fpr and new fuel filter it is around 13:1 and 12:1 at WOT.

Before I was having problems with cylinder misfiring and sputtering hopefully no long term damage was done.

[phila_dot]

There is no actual AFR and target AFR can never be leaner than stoich on these cars.

I'm not sure exactly what you are looking at, but you are definitely misunderstanding it.

[jibberjive]

Yes the lambda was the 02 voltages. And it was only 19:1 at WOT it was less idling. Once changing it to the 5 bar fpr and new fuel filter it is around 13:1 and 12:1 at WOT.

Before I was having problems with cylinder misfiring and sputtering hopefully no long term damage was done.

Just to make sure we're clear here, you're looking at the O2 voltage and directly relating that to AFR lamda (and getting your AFR #'s from that)? O2 sensors don't output AFR lambda, they output a voltage that is used on a non-linear scale to have a high resolution around 14.7AFR (and nowhere else). Look at the plot below for example: