OBDII CEL: carbon buildup - just the facts, please.
10-04-2003, 12:25 PM
#31
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DAN,I HAVE RECENTLY HAD A 993 IN WITH JUST THIS PROBLEM.THE CAR HAD A CHECK ENGINE LIGHT ON AND WE CHECK IT.I SHOWED THE AIR INJ.ISSUE.WE RESET THE LIGHT AND THE COSTOMER WENT AWAY. A WHILE LATER THE LIGHT RETURNED AND WE RECHECKED THE FAULT.THE SAME ISSUE WAS DETERMINED TO HAVE FLAGGED THE LIGHT.WE DIASSEMBLE THE ENGINE AND FOUND MOST OF THE PORTS AS WELL AS THE AIR INJ. TUBES WERE COMPLETLY PLUGGED.WE ALSO CHECK THE VALVE GUIDES AND THEY WERE WELL WORN.USING CHEMICAL AND MECHANICAL MEANS WE WERE ABLE TO CLEAN OUT THE OFFENING PARTS.A NEW SET OF NON OE GUIDES WERE INSTALLED AND THE ENGINE WAS REASSEMBLED.THE PROBLEM IN MY OPINION IS NOT THE PUMP/PASSAGE DESIGN,I BELIEVE IT LIES IN THE VALVE GUIDE WEAR RATE.
10-04-2003, 01:38 PM
#32
You guys are having a very common problem which I see often
here in SoCal working with independent shops and Porsche
dealers. As has been described, the secondary air passage
becomes restricted and thereby prevents cold start air injection
into the exhaust. The OBDII system detects this by monitoring
the front and rear (to the cat) O2 sensors.
On some cars the problem is not really the secondary air, but
just bad O2 sensors. This is rare, though. The only long term
solution, that my shops have found, is to do a valve job to
eliminate oil burning and thus carbon buildup in the air passage.
Cleaning the carbon from the passage is only a short term fix.
Mercedes Benz has a similiar problem on their engines of the
same years. The solution for those is again a valve job.
The Mercedes Benz problem occurs at about the same
mileage as with Porsche.
I've seen in some cases that Porsche will warranty the
problem based on the 50K/5yrs given that it's emissions
related. After this mileage or age, I doubt that Porsche will
do much from a warranty basis. It's like any other long term
failure, if it's not a safety or a MAJOR design problem then it's
the owner's problem. This is typical for most auto manufacturers.
Check out the website systemsc.com under Diagnostics
and Technical for info about OBDII and its problems.
Good Luck
Loren
'88 3.2
here in SoCal working with independent shops and Porsche
dealers. As has been described, the secondary air passage
becomes restricted and thereby prevents cold start air injection
into the exhaust. The OBDII system detects this by monitoring
the front and rear (to the cat) O2 sensors.
On some cars the problem is not really the secondary air, but
just bad O2 sensors. This is rare, though. The only long term
solution, that my shops have found, is to do a valve job to
eliminate oil burning and thus carbon buildup in the air passage.
Cleaning the carbon from the passage is only a short term fix.
Mercedes Benz has a similiar problem on their engines of the
same years. The solution for those is again a valve job.
The Mercedes Benz problem occurs at about the same
mileage as with Porsche.
I've seen in some cases that Porsche will warranty the
problem based on the 50K/5yrs given that it's emissions
related. After this mileage or age, I doubt that Porsche will
do much from a warranty basis. It's like any other long term
failure, if it's not a safety or a MAJOR design problem then it's
the owner's problem. This is typical for most auto manufacturers.
Check out the website systemsc.com under Diagnostics
and Technical for info about OBDII and its problems.
Good Luck
Loren
'88 3.2
10-04-2003, 04:50 PM
#33
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J. PELLEGRINO
1)I'd like to clarify what you are saying is that the worn valve guide is ultimately causing SAI to clog up?
2)What happens if these ports and the air inj. tubes are plugged and NO repair is done to the engine, what happens besides the CEL will come on periodically?
My question is for those who have had the engine work done or going to, did you ask your repair shop whether you have to do this all over again after the next 30-50K miles? And why not? What are they doing to your engine different that would prevent the same problem occuring again?
1)I'd like to clarify what you are saying is that the worn valve guide is ultimately causing SAI to clog up?
2)What happens if these ports and the air inj. tubes are plugged and NO repair is done to the engine, what happens besides the CEL will come on periodically?
My question is for those who have had the engine work done or going to, did you ask your repair shop whether you have to do this all over again after the next 30-50K miles? And why not? What are they doing to your engine different that would prevent the same problem occuring again?
10-04-2003, 05:14 PM
#34
Having the secondary air injection restricted or plugged will
not damage or effect the running of your engine. It will only
cause the check engine light to be "on", and you will NOT
be able to have the car emissions tested.
The secondary air injection only occurs for a short duration
during the cold mode, before the catalytic converter "fires",
to reduce the emissions level. The air pump which supplies
air for the air injection is turned off after the engine begins
to warmup and the secondary air injection ends.
Good Luck
Loren
'88 3.2
not damage or effect the running of your engine. It will only
cause the check engine light to be "on", and you will NOT
be able to have the car emissions tested.
The secondary air injection only occurs for a short duration
during the cold mode, before the catalytic converter "fires",
to reduce the emissions level. The air pump which supplies
air for the air injection is turned off after the engine begins
to warmup and the secondary air injection ends.
Good Luck
Loren
'88 3.2
10-04-2003, 07:10 PM
#35
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Does anybody have a sense or experience that TwinTurbos are more or less prone to the ODBII CEL: Carbon Buildup?
Or does it come down to the babied, lugged in traffic or run hard profiles?
Many thanks,
Grant
96tt
Or does it come down to the babied, lugged in traffic or run hard profiles?
Many thanks,
Grant
96tt
10-04-2003, 09:50 PM
#36
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"Having the secondary air injection restricted or plugged will
not damage or effect the running of your engine. It will only
cause the check engine light to be "on", and you will NOT
be able to have the car emissions tested. "
Knock on wood, I have not had this problem. However, makes me glad I'm in a state that doesn't inspect cars.
not damage or effect the running of your engine. It will only
cause the check engine light to be "on", and you will NOT
be able to have the car emissions tested. "
Knock on wood, I have not had this problem. However, makes me glad I'm in a state that doesn't inspect cars.
10-05-2003, 06:14 PM
#38
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We have the best looking Porsche with the most problems.
i'd rather take a 7 year old 993 than a 99 MY 996 any day of the week.
i think 993s are holding up really well as they age. the Carbon Buildup issue is the most high profile 'flaw' that i'm aware of.
i liked dan's original post - lets get a true count of the # of people who've had this problem. otherwise the emotions associated with doing an expensive fix tend to obfuscate the issues.
