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Old 01-17-2012, 03:32 PM   #1
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A brain twister for some, help me diagnose this 986

Ok, im having no luck diagnosing this boxter without throwing some more parts at it.

The car is a 1999 Boxter 986, 2.5l, 150,000 miles. The car has never thrown any codes relavant to its characteristics in the history ive worked on it.

Live data feeds all active, fuel pressure is at 50psi, no codes, ever


Car came in for a miss, was driven with an inactive cylinder for 3 weeks, a few hundred miles. Ignition coil was cause for miss. Test drive the car, it lacks the full performance for sure, runs ok but just doesnt have full power. Heres the kicker, every once in a while i will try to accelerate and the car will cough, then cough, and lose all ability to accelerate, it will idle usually but sometimes will die out.

I replaced the throttle body because we were out of ideas, no dice, anybody have any ideas. Thanks, Joshua
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Old 01-17-2012, 03:40 PM   #2
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Start with the cheapest and easiest fix - disconnect the battery for 5 mins to reset the ECU. Then re-connect the battery and drive 20-40 miles in varying conditions to allow the ECU to re-learn the optimum tune for the engine now that the coil pack is fixed.
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Old 01-17-2012, 04:08 PM   #3
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Inactive Cyl and no CEL error codes? Serious DME problem. A missing cyl should cause a flashing CEL requiring a flatbed ride the the Porsche Dr. Clearing the DME and fresh fuel might be a good start. I want to know A/F ratios, compression and spark advance also.
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Old 01-17-2012, 04:36 PM   #4
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melted cats on dead cyl. side?
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Old 01-17-2012, 05:41 PM   #5
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Quote:
Originally Posted by Topless View Post
Inactive Cyl and no CEL error codes? Serious DME problem. A missing cyl should cause a flashing CEL requiring a flatbed ride the the Porsche Dr. Clearing the DME and fresh fuel might be a good start. I want to know A/F ratios, compression and spark advance also.
+1, but I would get it properly scanned before resetting the DME to see what it says first..............
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Old 01-19-2012, 05:14 AM   #6
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the ignition coil was the problem for the inactive cylinder, the car doesn't miss. the car of course had the cel on for the miss.

This is an entirely different problem, intermittent complete loss of power, and lacks full power all the time. Runs fine otherwise just not full performance
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Old 01-19-2012, 05:15 AM   #7
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we have had a the $60,000, autotel scanner on it, and 2 other $ 10,000 to reveal NO CODES
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Old 01-22-2012, 09:35 AM   #8
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Sounds like poor fuel pressure or bad pump. put a gauge in to confirm.
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Old 01-23-2012, 05:36 AM   #9
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Poor power is usually a good indicator the mass air sensor is failing, and sometimes, you wont even have a fault code. It just wont measure enough air, and the fuel system wont enrich the mixture under a load. It may be bad enough to cause a misfire, sometimes it wont.

You may see lean tendencies on long term adaptation ( part load )...
Try swapping one in, they sell the inserts fairly cheap
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