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RedRotors
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Jeff, indeed that's my next step. Thanks!
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Ahsai, it is definitely running rich. If you check the excel log I posted (link below the durametric screen shot pic) youll see the maf kg/h and voltage. Both are substantially higher then they should be reading. This was taken after a dme reset with stock maf housing.
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All good questions. Fuel is a couple months old, but good. I did all the basics as preventive maintenance. New plugs, updated coil packs, and checked fuel pressure. The car is a 2002, so it runs a returnless fuel system and E-gas. The throttle is opening and the proper adaptation is done every time I disconnect the battery. I've verified the TPS with Durametric. I've also replaced the pre cat O2s. I also replaced the chain tensioners, properly locking the cams and crank, nothing moved or slipped. Verified deviation on durametric. I even replaced the AOS for good measure. All maintenance work was done before attempting to start it for the first time. I've retraced my steps many times to check my work. I'm at a loss. When it runs from cold start for those first 15 sec it does sound great. From cold, it starts in open loop, its seem that when it goes to closed loop it falls apart. Another interesting fact, if I spray MAF clean at the intake filter, just one tiny spray, the car smooths out and runs fine for another 10-15 sec. It definitly runs smooth way longer that it would take to burn off the MAF cleaner. I've done some stand-alone tuning in my past, mostly on speed density systems, but it seems that the MAF needs to be scaled. Just weird...
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Schnell, I've ran the car with the MAF unplugged and it runs in a similar fashion, maybe slightly worse. With the MAF unplugged the DME falls back on known good MAF values. I do not think those values are manipulated with the custom tune, so with larger injectors and larger MAF housing, the car no longer has a known good value to fall back on. This is why I had it flashed back to stock, and used the stock housing, granted it still had larger in injectors, but still behaved the same way with the MAF unplugged. Crude I know, but the injectors are a PIA to replace. DBJoe996, I stopped in and saw the tuner Tuesday to drop off the DME. He has more work that he can handle at the moment. He offered to take it, but pointed the the other cars that have been sitting... Testing the MAF IAT, I have 3 of them now, the all test 1.8K ohms at 26 deg C. Waiting on the DME to test voltages. I've also smoke tested the engine for vacuum leaks, only 1 small one from the brake booster O ring, it was replaced. I'll keep you posted. Thank you for the advice.
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I understand your comments above, and almost expected it. This has been an on going issue and I am doing my best to eliminate possibilities. The car was dyno tuned by Frank Smith and ran perfectly for years, I know because it was previously a good friends car. I have nothing but respect for his tuning abilities. Since then, they car was sold to another local that was not knowledgeable. The supercharger needed the bearings replaced, the car sat, and I purchased it. Put it all back together and it has this issue. This is my first Porsche, but far from my first tuned, modified, or supercharged car. I posted here after a couple months of pulling my hair out, with the car on the lift, in hopes someone has come across this in their past. Thank you for the helpful advice, 12V, 5V reference, and ohming the maf are the next on my list. 2 bad mafs are unlikely, but not unheard of I suppose.
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Gentlemen, thank you. Yes, the maf was replaced with the same Bosch 986 part number that I removed. Yes, it's install in the correct orientation. I will check the 12V supply and the 5V reference voltage and reset the dme. The tuner has my dme currently. I had I flashed back to stock to see if anything would change. Right now he is reflashing the proper tune back. I didn't want to over complicate my original post, but the car has a VF charger kit on it. Most recent diagnostic work was done with the charger disconnected, stock flash, and the stock maf housing. The dme was verified good and ran another car. Now it's being flash back to the custom tune that matches the injectors and the larger maf housing. Any idea why its pulling so much timing?
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Thanks for the quick reply. I was thinking the 11 kg/h maybe a default for open loop cold start. I attached an excel spreadsheet of the log while it was running. IIRC it's around 30 kg/h while trying to idle. Ive replaced the maf and I get the same readings. I can certainly log fuel trims and post back.
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I also should've mentioned that the car will not rev. The throttle body is opening and adaptation was done. It runs severely retarded timing -9 deg or so while it's trying to idle. I figure the retarded timing is why it won't rev, and the timing is retarded because of the high maf voltage at low rpm. The maf voltage and high kg/h is the root of the problem, would you agree?
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I picked up a 996 a few months back, not running. It will start and runs for 10-15 seconds and sounds perfect, after that the idle drops and it stumbles around 500-600 RPM until it eventually stalls. It runs pig rich. With the Durametic, in a keyed on state, not running, I am seeing high maf voltage and high mass air flow HFM numbers. Even with the MAF unplugged the 11 kg/h never drops or goes away. I've tried another MAF with the same results. Any clue why the MAF voltage is so high? I've included a Durametric log. Other data seems to be in line, cam deviation is 1-2 deg. Any insight would be very helpful! 2017_07_23_16_26_30.xls
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oh, the VF supercharger instructions for the 996 and 997 explain the wiring of the sensor. Here's the link https://www.vividracing.com/catalog/productdocs/vfporscheinstall.pdf
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Mother, Bringing this back from the dead. I cant find info anywhere online about this topic. What was the sensor sourced from? By the pic it looks like possible VW VR6? The largest importance is ensuring the temperature curve is the same as the IAT in the MAF.
