Help with Air/fuel ratio potential problem

[Vman]

I have a 1999 996, in the process of doing some dyno work on both Dynojet and Dyno Dynamics Dynos (load bearing), we discovered that the car was producing a max of 258 hp, but that the air/fuel ratio started at 16 and went down to 13 betwen 3,500 and 4,500 rpm, the problem is after 4,500 rpm the air/fuel ratio kept rising up to around 14.5 and no lower than 13.6. The car is running a U.S OBD 2 program with a K&N aircharger, Scargo headers, high flow cats and stock mufflers. The airfuel/ratio problem was the same with the stock airbox. We have about 300 miles driving the car since loading the US OBD 3 program.

Is this a dangerously lean situation? How would you go about improving identifying the problem, as I am told your fuel air ratio should be around 13 to 13.5 to generate maximum power or this okay?

If it is a problem, how should we go about fixing it?

Fuel filter - has been changed

Bad fuel pump relay - how do you test?

Bad fuel pump - how do you test?

Bad fuel sytem relay - how do you test?

Bad injectors - anyway to test? Does the Swepco injector cleaner work?

Note - before I purchased the car it was running on a mix of 110 leaded race gas and pump gas and had no cats, it was running the ROW DME program and producing about 275 HP on a dynojet dyno and averaging about a 13.2 air fuel ratio above 4,500 rpm...Note - the last dyno test on the car before me buying it and changing to the US DME program and adding back cats is less than 3 months old

Thanks,

VMAN

[viper501]

Stoichiometric is about 14.5. So your A/F is 'safe' even if it isn't the best power output.

[1999Porsche911]

Yes, runinng that lean at WOT will increase the risk of frying your engine. How was the afr measured? Left, right or both tailpipes? I find it hard to believe that you would run that lean. Maybe a problem with dyno's sensor. Take a look at your after cat O2 sensor readings at wot above 4500 rpm using a scanner. What are their values?

Edited February 11, 2007 by 1999Porsche911

[Vman]

Both runs were measured on separate dynos using the right tailpipe.

Yes, runinng that lean at WOT will increase the risk of frying your engine. How was the afr measured? Left, right or both tailpipes? I find it hard to believe that you would run that lean. Maybe a problem with dyno's sensor. Take a look at your after cat O2 sensor readings at wot above 4500 rpm using a scanner. What are their values?

[1999Porsche911]

Both runs were measured on separate dynos using the right tailpipe.

Well, the first thing I would do it check the other tailpipe to see if it also shows bank 2 is also showing lean at WOT. If bank 2 shows proper AFR, then the problem is with bank 1, (injectors, o2 sensors or exhaust componants). If it shows the same (and it is an accurate reading), then the problem would include a componant that controls both banks, such as MAF, fuel regulator, tuning, fuel pump, vacuum leak, etc. Check what the after cat sensors show...both banks.

Edited February 11, 2007 by 1999Porsche911

[Vman]

Thanks

Both runs were measured on separate dynos using the right tailpipe.

Well, the first thing I would do it check the other tailpipe to see if it also shows bank 2 is also showing lean at WOT. If bank 2 shows proper AFR, then the problem is with bank 1, (injectors, o2 sensors or exhaust componants). If it shows the same (and it is an accurate reading), then the problem would include a componant that controls both banks, such as MAF, fuel regulator, tuning, fuel pump, vacuum leak, etc. Check what the after cat sensors show...both banks.

[Vman]

We tested the fuel rail pressure and fuel pump volume flow according to the factory manual. Also, the maf and 02 sensors read no fault on the porsche system 2 tester. Note - O2 readings for both before and after cat banks were over 850 mv above 4,500 rpms. Any ideas would be helpful, we are left to conclude that either we have a bad MAF that is not showing up on the tester, or the porsche ecu just can't handle the extra requirements of the K&N aircharger, racing headers, and high flow cats, in which case we will have to be looking for a piggy back system like a unichip to try and remap the fuel curve. Let me know if you guys think we are missing something, as a custom programmed unichip to pull down my airflow ratio to a safer level will set me a back about $3K.

Thanks,

VMAN

Thanks

Both runs were measured on separate dynos using the right tailpipe.

Well, the first thing I would do it check the other tailpipe to see if it also shows bank 2 is also showing lean at WOT. If bank 2 shows proper AFR, then the problem is with bank 1, (injectors, o2 sensors or exhaust componants). If it shows the same (and it is an accurate reading), then the problem would include a componant that controls both banks, such as MAF, fuel regulator, tuning, fuel pump, vacuum leak, etc. Check what the after cat sensors show...both banks.

[1999Porsche911]

What was the MAF reading at idle? Test to see if the program shut off all the error reporting of the DME. Remove the MAF cable from the MAF and see if you get a CEL. Some programs shut off the system so they can push the limits of the engine. Also check to see if whoever did the tuning put a resister inline on the MAF cable to reduce voltage output. This is sometimes done to reduce current to the DME when an intake mod is done a which increases airflow and therefore voltage to the MAF.

[Vman]

The following was taken while running stock Porsche OBD2 program, no inline tuning has been done.

MAF readings at idle (between 695 to 800 rpms) with zero throttle ranges from (.59 to .84 lb./min) or (4.5 to 6.5 g/s). Porsche system tester 2 shows the MAF with no errors.

Other points of reference at 98% throttle position

RPM 3944, Timing -14.5, vehicle speed 125 mph, MAF (lb/min 12)

RPM 4321, Timing, -21, vehicle speed 65 mph, MAF (lb/min) 8.9)

RPM 5169, Timing, -34, vehicle speed 79 mph, MAF (lb/min 22.89)

RPM 7020, Timing, -22.5, vehicle speed 110 mph MAF (lb/min 19.6)

Any help would be great. Any idea if their is a more advanced way in the Porsche system 2 to determine if the MAF is having issues, but not showing a fault.

Thanks,

VMAN

What was the MAF reading at idle? Test to see if the program shut off all the error reporting of the DME. Remove the MAF cable from the MAF and see if you get a CEL. Some programs shut off the system so they can push the limits of the engine. Also check to see if whoever did the tuning put a resister inline on the MAF cable to reduce voltage output. This is sometimes done to reduce current to the DME when an intake mod is done a which increases airflow and therefore voltage to the MAF.

Edited February 15, 2007 by Vman

[Vman]

What was the MAF reading at idle? Test to see if the program shut off all the error reporting of the DME. Remove the MAF cable from the MAF and see if you get a CEL. Some programs shut off the system so they can push the limits of the engine. Also check to see if whoever did the tuning put a resister inline on the MAF cable to reduce voltage output. This is sometimes done to reduce current to the DME when an intake mod is done a which increases airflow and therefore voltage to the MAF.

Edited February 15, 2007 by Vman

[1999Porsche911]

Your MAF reading at idle is fine, but at speed, it is not registering high enough. This means that the computer thinks there is less air than is actually getting to the engine and the computer is adding too little fuel, causing your lean condition.

Why just 98% throttle. Is this a 99 C2. Your cable may have stretched a little and you need to remove it from the throttlebody and twist it once or twice (effectively shortening it) until you get 100%. This can be tested without driving the car.

Edited February 15, 2007 by 1999Porsche911

[Vman]

New MAF in car, old stock airbox with clean filter back in, going to dyno tommorow with fingers crossed. Will deal with the throttle cable after we fix the air fuel ratio problem, thanks for the tip though

Thanks,

VMAN

Your MAF reading at idle is fine, but at speed, it is not registering high enough. This means that the computer thinks there is less air than is actually getting to the engine and the computer is adding too little fuel, causing your lean condition.

Why just 98% throttle. Is this a 99 C2. Your cable may have stretched a little and you need to remove it from the throttlebody and twist it once or twice (effectively shortening it) until you get 100%. This can be tested without driving the car.

[Vman]

Chasing a ghost.....

Today I went back to the two wheeled dyno and the car spiked to over 14.5 airfuel ratio above 5,600 rpm, I was just about ready to spring for a motec or tec 3 ecu and rewire the whole car, then the dyno guy suggested we pull the abs fuse as sometimes even with traction control off the abs/abd system can do weird things on the dyno. With abs fuse pulled, the car averaged 12.5 air/fuel ratio above 5,600 rpm's, so it may have never had a problem in the first place. I am out about a grand in new maf's and fuel delivery, vac testing, and dyno time, but have peace of mind again.

Also, it seems the K&N aircharger that I took off that is now in the trash added 7 hp and tq accross the board, but given the oil I found in it (even after letting it dry out over night before installatoin) I am glad it is gone. We added 5 gallons of 100 unleaded race gas to the remaining 3 or 4 gallons of 91 pump gas and found about 5 more hp and tq. I think race gas will not be part of the equation going forward given the fun in storing it in one's garage and dispensing with the cans. All the tests were run on a dyno dynamics dyno - eddy current type (supposedly much more accurate than a dynojet).

The numbers....

The car put down 263 hp and 230 tq at the wheels (the gains came from scargo racing headers, high flow 100 cell cats, and switching from OBD2 to ROW DME program (richens up the car to take advantage of more freely breathing headers and cats). Note - the car with the same modifications and the US OBD2 program put down 240 hp on the the dyno. While these numbers may not sound great for those that have seen inflated dynoject dyno numbers ( my car has shown up to 278 hp at the wheels on a dynojet) we are confidant that we have increased real horsepower and torque accross the curve by 20-25, so now our little 3.4 Lis about where the 3.6 L starts out and the car is totally driveable. Note - we tried a custom ECU program from one of the common vendors and gave back 25 hp...so I have little faith in those chip guys, as they seem to be outdone by ROW software which is in your mechanics porsche system tester 2 and should cost you about an hour in labor to get to. Finally, testing has shown us that ROW software adds no measurable horsepower and TQ unless you change the restrictive stock headers and cats.

New MAF in car, old stock airbox with clean filter back in, going to dyno tommorow with fingers crossed. Will deal with the throttle cable after we fix the air fuel ratio problem, thanks for the tip though.

Thanks,

VMAN

Your MAF reading at idle is fine, but at speed, it is not registering high enough. This means that the computer thinks there is less air than is actually getting to the engine and the computer is adding too little fuel, causing your lean condition.

Why just 98% throttle. Is this a 99 C2. Your cable may have stretched a little and you need to remove it from the throttlebody and twist it once or twice (effectively shortening it) until you get 100%. This can be tested without driving the car.