xr4tic

Well, I went to the strip (before they closed for the winter) to see what it would run.

Car was full of 94 octane gas, 16psi of boost, running full street weight (nothing removed)

1st run was a 14.3 @ 103mph with a bogged launch.
2nd run was a 13.9 @ 104mph with clutch slippage.

My EGT's were hitting 1700+F after the first run, so I did some datalogging for the second.

After looking at the logs, I didn't make any more runs.

RPM....g/s...timing...O2 voltages
3960 142.71 -18.8 0.86
5680 188.40 -24.0 0.83
7080 187.22 -22.5 0.71

2nd
3600 091.94 -15.0 0.575
4560 168.33 -24.8 0.87
5120 187.36 -24.8 0.835
5680 187.29 -24.0 0.815
6240 187.36 -20.3 0.78
6640 187.43 -22.5 0.745
6760 120.14 -28.5 0.66

3rd
4880 171.59 -22.5 0.85
5040 179.86 -21.8 0.825
5320 186.53 -22.5 0.82
5520 187.29 -18.0 0.81
5720 187.29 -18.0 0.785
5880 187.08 -16.5 0.785
6080 187.22 -21.0 0.77
6240 187.01 -16.5 0.705
6400 187.22 -18.8 0.73
6520 187.08 -17.3 0.685
6680 187.01 -17.3 0.74
6800 187.08 -19.5 0.695
7000 109.79 -24.0 0.735

The O2 voltages are dropping to 0.69V, and the MAF is maxing out at 187 g/s at @ 5000RPM. The boost does not drop off at higher RPMs (manual boost controller) so that's not why it's leveling off.
I'm guessing because the ECU doesn't think it's getting more air (which it is) it leans the fuel out, causing bad things to happen.

My car is also setting a CEL for long-term fuel trim too Rich - 25%

So what are the indications of a bad MAF? My car is a 97 with 91K miles on it, so it's possible it's a bad MAF, but I want to be sure before I shell out the money for a new one.

Audi2ptzero

anything below .85 is going lean.

You might want to turn the boost down so that you just reach 187 g/s and still hold .85-.86 at the 02's. The maf is not reading any higher so your injectors never stay open long enough to give you the fuel you need.

The long term rich DTC is caused by getting too much fuel during Part Throttle where the 02 sensor has to tell the ecu to adjust. So the problem is that your chip is not tuned well to the injector size your using.

SMOKINA4TURBO

just wont go to 188:-). Your MAF appears healthy and your turbo is sucking good.

I think theres not much way around it then to go bigger MAF and then you gotta get new chip...not sure what your doing or using for management right now.

Also dont be fooled either by part throttle and WOT. My car untuned ran pretty rich at part throttle and WOT in full boost would be lean.

I'm pretty surprised your car through that code as my car never has had that problem.

xr4tic

I know that part and full throttle are two different things, but it shouldn't be trying to lean the mixture 25% while cruising.

I can't believe I'm maxing a 3" MAF out at only 1 bar.

Audi2ptzero

Maybe your turbo is sucking in too much air flow for the giac/maf combo since it is tuned for a T28 on a stock 1.8 motor. But lucas is running the PES maf with 440's and is making just under 400 hp on a custom GIAC chip.

Yippers®

The PES/GIAC solution must not alter the std meter 'table' for the air coming thru the OEM sensor (knowing how much is entering but not metered)and runs an adjusted fuel supply based on the metered+known unmetered.
Here's the Air Mass Flow of a log I ran a while back. I've seen mass up in the 220+ range before.
Air
Mass Flow
g/s
35.83
53.61
113.75
156.94
182.08
198.06
210.97

I think John either needs stand alone management or help from GIAC with adjusting the PES tables for his boost and displacement.

Audi2ptzero

and then cutting fuel back for that set ratio. But that still does not mean your stock MAF reads higher then 187 g/s, it just means the ecu just reads 187 g/s as 220 g/s. The point of the reply as to tell john that the readings from the maf will never be higher then 187.

But if you were to flow more air would you want to do it thru a stock maf housing or thru a larger maf housing? Seems everyone is so worried about TB size they dont really look at the stock maf as a problem.

Yippers®

I wasn't slamming GIAC/PES for their approach.

The 'limit' on the mass of air that can pass thru the OEM MAF housing is obviously above the amount necessary to supply the GT-25 on our 1.8's.

The MAF sensor set up deals with voltages. If the table said 4.8volts= 480 g/s then that would be the reading on the vag com. The 187 "limit" strikes me as being the limit of the OEM voltage to mass table.

I've no idea how APR 'beat' the 5 volt limit but I don't think it was by chopping the voltage a set amount (like divide by two). In discussions with Juan (when he was working on the KO4 kit) he shared some of his data as I did w/ him) and that data showed the voltage for mass of air is not nearly linear.

My point to John was that the chip he is running was adjusted based on the PES MAF housing with the OEM sensor (taking into account the known mass of air not metered thru the sensor)and that with his setup he was exceeding the airflow the chip was 'tabled'to deal with.

xr4tic

by my calculations, 16psi on my 2.0 is the same as 20psi on a 1.8, so I'm definately not flowing more than a T28 kit on a 1.8T right now.

xr4tic

it's like the transfer function (voltage vs. flow) hasn't been changed.

But even if it hasn't, then the larger MAF would throw the values off by 30%, meaning 187g/s is actually 243g/s, and there's no way I'm flowing that much (at least not yet anyways