Misfire in 996 Turbo
11-13-2011, 11:19 PM
#1
Track Day
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Misfire in 996 Turbo
I am anxious to hear the collective ideas from all of you regarding my 2003TT X-50. The car currently has 40K miles (approx 65K Km) on the odometer and the following engine modifications completed at around 15K miles (24+Km):
• Billet diverter valves
• B&B 100 cell cat exhaust
• GIAC Software
• EVOMS Air intake
At 32K miles the car began to have a slight “miss” most noticeable from first to second gear at 1800 RPM and occasionally at 4800 RPM at 1 Bar. At 34K miles, the MAF sensor went out while at the track. I was hopeful that replacing this would cure the slow speed miss and occasional high-speed one that was now very evident between 4200-4800 RPM; this was not the case. I had the dealer do a smoke test to determine if there was a vacuum leak and there was none. My extended warranty was about to end so I had a complete inspection of the car including leak-down and the engine passed with excellence. New plugs were placed at that time. I am still experiencing the above misses that feel somewhat like a Rev limiter nibbling away at the fuel or spark. Today I replaced the fuel filter with certainty that the problem would be solved: no such luck. To be sure, it is not the GIAC tune; I re-mapped the software back to stock with no fix. The car is very strong and in second gear under boost, will fly past the hic up with just a small fart, but in third and fourth gears, where more time is spent, it becomes quite noticeable. A local Porsche mechanic is suggesting I replace the coil packs, as this has been a problem for the 996 turbos'. When I checked with the dealer, there is a coil pack ID number of 997 602 104 00 which seems to indicate a newer version. I have no “check engine lights” nor is this car driven in the winter elements. My son thinks a diverter valve may be stuck.
Summarizing what I have done to find a cure:
• Replaced plugs
• Replaced MAF sensor
• Replaced fuel filter
• Ruled out vacuum leaks as a source
• Switched software back to stock
Who agrees with the mechanic and who with my son? Are there any other possibilities that I have not considered? Thank you!
• Billet diverter valves
• B&B 100 cell cat exhaust
• GIAC Software
• EVOMS Air intake
At 32K miles the car began to have a slight “miss” most noticeable from first to second gear at 1800 RPM and occasionally at 4800 RPM at 1 Bar. At 34K miles, the MAF sensor went out while at the track. I was hopeful that replacing this would cure the slow speed miss and occasional high-speed one that was now very evident between 4200-4800 RPM; this was not the case. I had the dealer do a smoke test to determine if there was a vacuum leak and there was none. My extended warranty was about to end so I had a complete inspection of the car including leak-down and the engine passed with excellence. New plugs were placed at that time. I am still experiencing the above misses that feel somewhat like a Rev limiter nibbling away at the fuel or spark. Today I replaced the fuel filter with certainty that the problem would be solved: no such luck. To be sure, it is not the GIAC tune; I re-mapped the software back to stock with no fix. The car is very strong and in second gear under boost, will fly past the hic up with just a small fart, but in third and fourth gears, where more time is spent, it becomes quite noticeable. A local Porsche mechanic is suggesting I replace the coil packs, as this has been a problem for the 996 turbos'. When I checked with the dealer, there is a coil pack ID number of 997 602 104 00 which seems to indicate a newer version. I have no “check engine lights” nor is this car driven in the winter elements. My son thinks a diverter valve may be stuck.
Summarizing what I have done to find a cure:
• Replaced plugs
• Replaced MAF sensor
• Replaced fuel filter
• Ruled out vacuum leaks as a source
• Switched software back to stock
Who agrees with the mechanic and who with my son? Are there any other possibilities that I have not considered? Thank you!
11-13-2011, 11:30 PM
#3
What plugs were used in replacement, hopefully not the Beru? I'd be inclined to do the coil packs. Billet diverter valves need cleaning and lube every 1 - 2 yrs, check the F hose they are attached to while your at it. Where did the "stock" file come from, is it in fact your original file?
11-14-2011, 01:38 AM
#5
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I would start with the coil packs. And while your hands are in the engine compartment, rebuild your DV's. If your DV's are sticking they will usually bleed boost.
If these do not cure your "miss" then you might need to look at your variocam modules.
If these do not cure your "miss" then you might need to look at your variocam modules.
11-14-2011, 01:54 PM
#7
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I am working a similar issue. I just changed the plugs, visually the coilpacks looked fine but when I put it all back together there was no improvement. I understand there is a procedure to check the resistance of each individual coil pack- does anyone have details of that procedure (which pins and how many ohms resistance?)
Other question is that if we upgrade to the 997 coilpack, is the wiring harness compatible?
Thx
Other question is that if we upgrade to the 997 coilpack, is the wiring harness compatible?
Thx
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12-13-2012, 12:41 PM
#10
Racer
Sorry to bump an old thread, but I have a similar sparatic issue on mine. Every so often, under acceleration only, it will stumble or shudder. Not really bad but enough to bother me.
The car has been sitting for years, its an 02 with 9800 miles. Im assuming the plugs might be fouled or corroded.
Its kinda feels like it may be a boost leak. Funny thing about it, I paid for a PPI at a Porsche dealership that said the car was PERFECT.
The car has been sitting for years, its an 02 with 9800 miles. Im assuming the plugs might be fouled or corroded.
Its kinda feels like it may be a boost leak. Funny thing about it, I paid for a PPI at a Porsche dealership that said the car was PERFECT.
12-13-2012, 12:45 PM
#11
Rennlist Member
NSX - Sounds like its time for a tune-up. Give Kevin a call or email.
12-13-2012, 12:50 PM
#13
Racer
I need it serviced, where should I go? Im 2 few blocks from Schneider Nelson half the year, and 10 minutes from Catena for the rest. I like to use one place and stick with them.
Im open to suggestions.
Im open to suggestions.
12-13-2012, 01:09 PM
#14
Rennlist Member
I have mine serviced at New Vernon Motor Coachworks. (http://www.newvernoncoach.com/about.html) Its about 30 mins north of New Bruns. They did a UMW tune-up this past summer (plugs, coilpacks, MAF, etc.) Well done, timely, reasonable charge. Website focuses on Ferraris, but they service plenty of 911s.
I had dealer (Jack Daniels) do warranty work only.
I'm sure Catena or Schneider would do a fine job...but, $$$. (One north jersey dealer reportedly charges $500/oil change).
