Secondary Air Injection
06-10-2008, 11:04 AM
#1
Rennlist Member
Thread Starter
Secondary Air Injection
Porsche 993's "Achilles heel" The S.A.I. System
and how it relates to the "CHECK ENGINE" light
Mike Bavaro
Bodymotion Inc.
JSR Member
FIRST SOME HARD FACTS:
S.A.I. is an acronym for " secondary air injection." This air injection system is part of the vehicle’s
emission control compliance. It does not negatively effect the vehicles performance when correctly
operating. This system does significantly lower harmful tail pipe emissions. Any vehicle manufactured
with such a system, driven in the U.S., must have the system fully operational within designed limits or
it will cause the vehicle to exceed maximum allowable emissions. When certain situations arise to cause
an actual failure, or, conditions exist that the vehicle’s on-board computer diagnostics predict such an
occurrence is likely to cause elevated levels of emissions, it will set a fault code in the ECU (electronic
control unit) and turn on the "check engine" light. Any vehicle with a check engine light on will not pass
state mandated annual inspections.
MOST FREQUENTLY ASKED QUESTIONS:
How do I know what is the cause of my "check engine light?" Excellent question: the answer is,
you don't. In fact no one will know which one of, or combination of, the 144 possible fault codes that
can cause the dreaded "check engine" light to illuminate on your dash, until a scanner and qualified tech
pulls the code or codes and analyzes the data. Codes PO410 and PO411 indicate air injection problems
on one or both cylinder banks. Other fault codes for mixture trim out of range and a myriad of oxygen
sensor codes may accompany the SAI codes if the system is not repaired and the car is continually
driven with the check engine light on.
My check engine light is not on, what preventative maintenance can I do? The system has no
maintenance intervals; cleaning the lower ports is not advisable or recommended unless or until the
problem occurs.
Is it inevitable that all 96-98 normally aspirated 993's will experience this failure? Eventually,
probably yes.
Do 1995 models have this system? Yes they do, however you will not get a "check engine" light
when it malfunctions. OBD 2 (on-board diagnostic 2) was not mandated by the government until 1996.
95 models with malfunctioning S.A.I. systems may not pass the oxides of nitrogen test. That's why pre-
96 cars have to go on the dyno to test emissions.
Is the likelihood of failure higher with age and mileage? We found patterns and driving habits that
seem to affect this situation. Among them are track driven cars seem to rarely have this problem, or it
happens at very high miles. 993's driven around town, short trips, a/c on high all the time, seem to be
more frequent. We have done an alarming amount of cars from Florida and Texas. We recently have
done 4 cars with less than 50,000 miles on the odometer; two of them used a quart of oil every 1,000
miles. This oil consumption was thru the valve guides and our simple external cleaning would not work.
The passages had to be drilled out because the carbon was so dense.
What are my chances of solving my problem with Bodymotion’s "engine in car" port cleaning?
Actually very good. We have repaired roughly 100 of these SAI problem cars. Some have been
driven for five or six years without a return problem. We test the car and can give you and idea because
we flow test the system before and after and can predict by the results how long the artery cleaning may
last. The permanent solution is to replace worn valve guides and or rings if necessary and ream all the
ports with the engine apart.
How much does it cost? The external, leave the engine in, cleanup testing and reset is $1,295.
And if it is too far gone? Engine removal, reinstallation, disassembly of upper cam housings,
gaskets and reaming is around $4,000; add $1,500 if the valve guides need replacement.
What if I ignore the light? It’s been on for a while and the car runs great. See above comments
regarding repair chances of success. The longer the car is driven with the check light on, the worse the
compaction of carbon becomes, eventually requiring total overhaul vs. less expensive in- car option.
How long will Bodymotions' clean up cure last? Depends on all the variables above, but we have,
to our credit, gotten many cars not only through inspection, but extended by years, the need for engine
teardown.
Tech Babble and History of Secondary Air Injection
The above situation is accurate for all cars produced from 1996 and newer. The manufacturers have,
over the years, devised different ways to achieve lower emissions. There are many systems that interact
to achieve that common goal. That goal , of course is less carbon monoxide, carbon dioxide,
hydrocarbons, and oxides of nitrogen. These oxides are the real green house killers and complete
burning of the spent exhaust gases and filtering thru the catalytic converter are key to today's drastically
lower emissions.
Back to the S.A.I. system in Porsche. This air injection system has been in use since the 1970's. The
early belt driven air compressors took horsepower from the engine to drive them; most were removed in
the interest of performance. Today the pumps are 12 volt D.C. driven. Very powerful, they deliver, on
command from the ECU, pressurized atmospheric air to the exhaust system, upstream of the catalytic
converter(s). The air, atmospheric, same as we breath with 21+% oxygen content, mixes with the red
hot exhaust gases and causes an additional burning. This additional combustion, in conjunction with the
three way catalytic converter completes the job and air is almost breathable at the tailpipe. Kind of like a
sewerage treatment plant that boasts drinkable water on the outlet pipe. Maybe its true, but I'll pass
on being the test dummy.
In years past the delivery system included a one way valve, also called a diverter or gulp valve. This
one way valve did just that; allow fresh air to flow in, but kept hot exhaust gases from back flowing and
damaging the pump and hoses. Also used in the past was external piping. This plumbing system,
usually made of stainless steel tubing, delivered the air to the external exhaust manifolds. Due to the
harsh environment these plumbing systems quickly corroded, collapsed and caused under hood exhaust
leaks.
Most manufacturers, including Porsche, now integrate the plumbing system into the engine block, or
cylinder head casting. This eliminates the external plumbing and associated problems, but creates other
glitches. This is the area of concern in the 1996-1998 Porsche 993 3.6 liter non-turbo engines. 1999 and
newer liquid cooled cars have the same system, but, the delivery is thru tunnels and portals cast into the
one piece cylinder heads. These ports are huge and are not subject to the clogging in the earlier air
cooled models. The air cooled 993 has small passages (5 and 6 mm diameter) in the camshaft housings.
These are the capillaries that connect the fresh air source to the cylinder heads. These passages are not
accessible with the engine assembled. The connecting passages into the cylinder heads are accessible
from the exhaust ports once the entire exhaust system is removed. Once the clogged passages backup
into the cam housings the clean up is very difficult or plain impossible.
THE SOLUTIONS:
If you have followed along so far, or if you skipped the above explanation, we have arrived at the
problem; the clogging of the arteries. Porsche did not use one piece cylinder heads until the liquid
cooled engines arrived in 1999. Therefore the job of plumbing injected air utilized various drilled
passages thru the camshaft housings first, then through portals in each cylinder head that lead to the
exhaust port behind each exhaust valve. It is because these passages go thru both the cylinder head and
the cam housing they follow routes that have angles causing carbon to lodge and built up. This build up
of carbon eventually restricts airflow to each cylinder. When one or both banks are restricted enough to
a point that causes the exhaust gasses to emit, or potentially emit harmful emissions, as monitored by the
secondary oxygen sensors, it triggers the check light. Once this fault circuit is energized the car will not
pass emissions certification, and will be rejected at state inspection. Since Bodymotion has been both
an N.J. State Inspection Facility and, licensed Emissions repair facility and we have been repairing and
servicing Porsche's for 25 years, we see these problems frequently. In fact Bodymotion Inc has
calculated that over the past 10 years we have now repaired around 100 of these S.A.I. problem cars.
Our technicians have developed both mechanical and chemical remedies for all but the worst cases.
These worst cases are usually those cars that have been driven while the check light has been on and
ignored. Also those driven locally, extended curb idle time, and always those with high oil consumption
and heavily worn valve guides. Once cleaned, the ports are flow tested and compared to known flow
rates, it is at this time we can predict the success of our repair in terms of immediate results and long
term health of the system.
993 cylinder head with the cam tower removed. The
passage that the pointer is indicating is 6 mm diameter
and goes directly to the exhaust port behind the valve.
The underside of camshaft housing. This teardrop port is
what mates to the cylinder head below it.
Camshaft tower. At top is the hole that feeds the fresh air to the top of each tower. A large passage runs inside
fore and aft is of sufficient diameter and does not clog. The small 6 mm channels that lead down to the head are
the areas of heavy and inaccessible carbon blockage.
and how it relates to the "CHECK ENGINE" light
Mike Bavaro
Bodymotion Inc.
JSR Member
FIRST SOME HARD FACTS:
S.A.I. is an acronym for " secondary air injection." This air injection system is part of the vehicle’s
emission control compliance. It does not negatively effect the vehicles performance when correctly
operating. This system does significantly lower harmful tail pipe emissions. Any vehicle manufactured
with such a system, driven in the U.S., must have the system fully operational within designed limits or
it will cause the vehicle to exceed maximum allowable emissions. When certain situations arise to cause
an actual failure, or, conditions exist that the vehicle’s on-board computer diagnostics predict such an
occurrence is likely to cause elevated levels of emissions, it will set a fault code in the ECU (electronic
control unit) and turn on the "check engine" light. Any vehicle with a check engine light on will not pass
state mandated annual inspections.
MOST FREQUENTLY ASKED QUESTIONS:
How do I know what is the cause of my "check engine light?" Excellent question: the answer is,
you don't. In fact no one will know which one of, or combination of, the 144 possible fault codes that
can cause the dreaded "check engine" light to illuminate on your dash, until a scanner and qualified tech
pulls the code or codes and analyzes the data. Codes PO410 and PO411 indicate air injection problems
on one or both cylinder banks. Other fault codes for mixture trim out of range and a myriad of oxygen
sensor codes may accompany the SAI codes if the system is not repaired and the car is continually
driven with the check engine light on.
My check engine light is not on, what preventative maintenance can I do? The system has no
maintenance intervals; cleaning the lower ports is not advisable or recommended unless or until the
problem occurs.
Is it inevitable that all 96-98 normally aspirated 993's will experience this failure? Eventually,
probably yes.
Do 1995 models have this system? Yes they do, however you will not get a "check engine" light
when it malfunctions. OBD 2 (on-board diagnostic 2) was not mandated by the government until 1996.
95 models with malfunctioning S.A.I. systems may not pass the oxides of nitrogen test. That's why pre-
96 cars have to go on the dyno to test emissions.
Is the likelihood of failure higher with age and mileage? We found patterns and driving habits that
seem to affect this situation. Among them are track driven cars seem to rarely have this problem, or it
happens at very high miles. 993's driven around town, short trips, a/c on high all the time, seem to be
more frequent. We have done an alarming amount of cars from Florida and Texas. We recently have
done 4 cars with less than 50,000 miles on the odometer; two of them used a quart of oil every 1,000
miles. This oil consumption was thru the valve guides and our simple external cleaning would not work.
The passages had to be drilled out because the carbon was so dense.
What are my chances of solving my problem with Bodymotion’s "engine in car" port cleaning?
Actually very good. We have repaired roughly 100 of these SAI problem cars. Some have been
driven for five or six years without a return problem. We test the car and can give you and idea because
we flow test the system before and after and can predict by the results how long the artery cleaning may
last. The permanent solution is to replace worn valve guides and or rings if necessary and ream all the
ports with the engine apart.
How much does it cost? The external, leave the engine in, cleanup testing and reset is $1,295.
And if it is too far gone? Engine removal, reinstallation, disassembly of upper cam housings,
gaskets and reaming is around $4,000; add $1,500 if the valve guides need replacement.
What if I ignore the light? It’s been on for a while and the car runs great. See above comments
regarding repair chances of success. The longer the car is driven with the check light on, the worse the
compaction of carbon becomes, eventually requiring total overhaul vs. less expensive in- car option.
How long will Bodymotions' clean up cure last? Depends on all the variables above, but we have,
to our credit, gotten many cars not only through inspection, but extended by years, the need for engine
teardown.
Tech Babble and History of Secondary Air Injection
The above situation is accurate for all cars produced from 1996 and newer. The manufacturers have,
over the years, devised different ways to achieve lower emissions. There are many systems that interact
to achieve that common goal. That goal , of course is less carbon monoxide, carbon dioxide,
hydrocarbons, and oxides of nitrogen. These oxides are the real green house killers and complete
burning of the spent exhaust gases and filtering thru the catalytic converter are key to today's drastically
lower emissions.
Back to the S.A.I. system in Porsche. This air injection system has been in use since the 1970's. The
early belt driven air compressors took horsepower from the engine to drive them; most were removed in
the interest of performance. Today the pumps are 12 volt D.C. driven. Very powerful, they deliver, on
command from the ECU, pressurized atmospheric air to the exhaust system, upstream of the catalytic
converter(s). The air, atmospheric, same as we breath with 21+% oxygen content, mixes with the red
hot exhaust gases and causes an additional burning. This additional combustion, in conjunction with the
three way catalytic converter completes the job and air is almost breathable at the tailpipe. Kind of like a
sewerage treatment plant that boasts drinkable water on the outlet pipe. Maybe its true, but I'll pass
on being the test dummy.
In years past the delivery system included a one way valve, also called a diverter or gulp valve. This
one way valve did just that; allow fresh air to flow in, but kept hot exhaust gases from back flowing and
damaging the pump and hoses. Also used in the past was external piping. This plumbing system,
usually made of stainless steel tubing, delivered the air to the external exhaust manifolds. Due to the
harsh environment these plumbing systems quickly corroded, collapsed and caused under hood exhaust
leaks.
Most manufacturers, including Porsche, now integrate the plumbing system into the engine block, or
cylinder head casting. This eliminates the external plumbing and associated problems, but creates other
glitches. This is the area of concern in the 1996-1998 Porsche 993 3.6 liter non-turbo engines. 1999 and
newer liquid cooled cars have the same system, but, the delivery is thru tunnels and portals cast into the
one piece cylinder heads. These ports are huge and are not subject to the clogging in the earlier air
cooled models. The air cooled 993 has small passages (5 and 6 mm diameter) in the camshaft housings.
These are the capillaries that connect the fresh air source to the cylinder heads. These passages are not
accessible with the engine assembled. The connecting passages into the cylinder heads are accessible
from the exhaust ports once the entire exhaust system is removed. Once the clogged passages backup
into the cam housings the clean up is very difficult or plain impossible.
THE SOLUTIONS:
If you have followed along so far, or if you skipped the above explanation, we have arrived at the
problem; the clogging of the arteries. Porsche did not use one piece cylinder heads until the liquid
cooled engines arrived in 1999. Therefore the job of plumbing injected air utilized various drilled
passages thru the camshaft housings first, then through portals in each cylinder head that lead to the
exhaust port behind each exhaust valve. It is because these passages go thru both the cylinder head and
the cam housing they follow routes that have angles causing carbon to lodge and built up. This build up
of carbon eventually restricts airflow to each cylinder. When one or both banks are restricted enough to
a point that causes the exhaust gasses to emit, or potentially emit harmful emissions, as monitored by the
secondary oxygen sensors, it triggers the check light. Once this fault circuit is energized the car will not
pass emissions certification, and will be rejected at state inspection. Since Bodymotion has been both
an N.J. State Inspection Facility and, licensed Emissions repair facility and we have been repairing and
servicing Porsche's for 25 years, we see these problems frequently. In fact Bodymotion Inc has
calculated that over the past 10 years we have now repaired around 100 of these S.A.I. problem cars.
Our technicians have developed both mechanical and chemical remedies for all but the worst cases.
These worst cases are usually those cars that have been driven while the check light has been on and
ignored. Also those driven locally, extended curb idle time, and always those with high oil consumption
and heavily worn valve guides. Once cleaned, the ports are flow tested and compared to known flow
rates, it is at this time we can predict the success of our repair in terms of immediate results and long
term health of the system.
993 cylinder head with the cam tower removed. The
passage that the pointer is indicating is 6 mm diameter
and goes directly to the exhaust port behind the valve.
The underside of camshaft housing. This teardrop port is
what mates to the cylinder head below it.
Camshaft tower. At top is the hole that feeds the fresh air to the top of each tower. A large passage runs inside
fore and aft is of sufficient diameter and does not clog. The small 6 mm channels that lead down to the head are
the areas of heavy and inaccessible carbon blockage.
06-10-2008, 11:11 AM
#2
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Why do you feel its not advisable?
My check engine light is not on, what preventative maintenance can I do? The system has no
maintenance intervals; cleaning the lower ports is not advisable or recommended unless or until the
problem occurs.
My check engine light is not on, what preventative maintenance can I do? The system has no
maintenance intervals; cleaning the lower ports is not advisable or recommended unless or until the
problem occurs.
06-10-2008, 03:43 PM
#3
Rennlist Member
Thread Starter
Unless a flow test is done there is no way to determine if any blockage of any kind exists. Since customers depend on us for accurate info, it would be a guess, a $1300 guess. It would be like a healthy person going to the doctor and asking for stint or angio-whatever just to be sure he doesn't get a blockage. If your car uses a quart of oil in less than 1,000 miles, you may try,but since you probably need valve guides anyway, why waste the $$. remember , as mentioned in the article, we have some 993's with 100K on them and have not yet had a check engine light. I guess if someone asked us to do it as a maintenance, after all consideration, we would oblige them.
06-10-2008, 05:26 PM
#4
Nordschleife Master
Mike, thanks for the great write up on the SAI issue. 
- Is there any downside to clogged ports on a 95 with OBD I?
- Is there any advantage to removing the SAI system on a 95?
Last edited by FlatSix911; 06-10-2008 at 06:25 PM.
06-10-2008, 06:16 PM
#5
Instructor
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Mike,
Your write up and answers seem to imply that premature valve guide wear is the main culprit of SAI issues. I was under the impression that while premature valve guide wear will clog the SAI, the SAI may clog despite a healthy top end.
What percentage of cars are you seeing with clogged SAI and healthy valve guides?
Eric
Your write up and answers seem to imply that premature valve guide wear is the main culprit of SAI issues. I was under the impression that while premature valve guide wear will clog the SAI, the SAI may clog despite a healthy top end.
What percentage of cars are you seeing with clogged SAI and healthy valve guides?
Eric
06-12-2008, 10:45 AM
#6
Rennlist Member
Thread Starter
Ted,
No performance down side, but as mentioned in the article, if your state has a required dyno test for pre-OBD-2 cars (N.J. uses ASM 50/15 standard) it may fail in cold weather or if the car is not fully warmed up pre-test. However most likely, if it other wise is in a good state of tune and is not consuming too much oil through ring and guides, it should pass ok
Also as mentioned, since the air pump is not crankshaft driven, they do not take away engine power or performance, so other than make your car 50 state federally illegal I see no advantage
No performance down side, but as mentioned in the article, if your state has a required dyno test for pre-OBD-2 cars (N.J. uses ASM 50/15 standard) it may fail in cold weather or if the car is not fully warmed up pre-test. However most likely, if it other wise is in a good state of tune and is not consuming too much oil through ring and guides, it should pass ok
Also as mentioned, since the air pump is not crankshaft driven, they do not take away engine power or performance, so other than make your car 50 state federally illegal I see no advantage
06-12-2008, 10:46 AM
#7
Rennlist Member
Thread Starter
Eric,
I'm not sure thats what I implied, but rather, the design and excecution of air delivery by the manufacturer is the root of evil. Therefore in my opinion, most will see this failure sooner or later because carbon production is a by-product of all combustion, harder driven cars build up less, around town cars revved slower build up more. All cars including 911's use oil, this adds to carbon, and of course the more you use (oil) the faster the accumulation. I'm not sure what you consider "healthy' valve guides. Guides wear from day one and the flexible stem seals do a good job of keeping oil from, freely flowing down them. Remember guides need oil to survive, the engine has to use some oil. If you use a quart of oil between changes (5,000-7500 miles) synthetic oil, i would say thats probably normal and "healthy" and drive the car like it should, you may go 100K before the passages clog. But if like a large percentage of cars we see with 40-60K on the clock, use a quart of oil in 1500 or less miles, no matter how hard you drive, we might be seeing you soon.
I'm not sure thats what I implied, but rather, the design and excecution of air delivery by the manufacturer is the root of evil. Therefore in my opinion, most will see this failure sooner or later because carbon production is a by-product of all combustion, harder driven cars build up less, around town cars revved slower build up more. All cars including 911's use oil, this adds to carbon, and of course the more you use (oil) the faster the accumulation. I'm not sure what you consider "healthy' valve guides. Guides wear from day one and the flexible stem seals do a good job of keeping oil from, freely flowing down them. Remember guides need oil to survive, the engine has to use some oil. If you use a quart of oil between changes (5,000-7500 miles) synthetic oil, i would say thats probably normal and "healthy" and drive the car like it should, you may go 100K before the passages clog. But if like a large percentage of cars we see with 40-60K on the clock, use a quart of oil in 1500 or less miles, no matter how hard you drive, we might be seeing you soon.
Trending Topics
06-12-2008, 12:54 PM
#8
"Unless a flow test is done there is no way to determine if any blockage of any kind exists."
Actually, the PST2 (and later) Porsche tester can "force" a SAI test and
then one can evaluate how the O2 sensors respond to determine the
effectiveness of the SAI system, e.g. the air passages.
More info here"
www.systemsc.com/pictures.htm
Actually, the PST2 (and later) Porsche tester can "force" a SAI test and
then one can evaluate how the O2 sensors respond to determine the
effectiveness of the SAI system, e.g. the air passages.
More info here"
www.systemsc.com/pictures.htm
06-13-2008, 09:35 AM
#9
Rennlist Member
Thread Starter
Loren,
The test does not report the condition of air passages or the amount of blockage, one has to assume the effectivness based on the readings from bank one and bank two. We prefer the manual flow test, it not only tests side to side flow, but individual cylinder port flow, this the PST2 tester cannot do
The test does not report the condition of air passages or the amount of blockage, one has to assume the effectivness based on the readings from bank one and bank two. We prefer the manual flow test, it not only tests side to side flow, but individual cylinder port flow, this the PST2 tester cannot do
06-13-2008, 01:00 PM
#10
"The test does not report the condition of air passages or the amount of blockage"
The key for most/all late 993 owners is whether a CEL will occur because
of a SAI test failure or a failure to set the SAI readiness code (and the
subsequent ones that are dependent), which the Porsche tester SAI
Short Test will determine. For most Porsche shops that have a Porsche
tester, this only takes about a 15 minute effort.
The key for most/all late 993 owners is whether a CEL will occur because
of a SAI test failure or a failure to set the SAI readiness code (and the
subsequent ones that are dependent), which the Porsche tester SAI
Short Test will determine. For most Porsche shops that have a Porsche
tester, this only takes about a 15 minute effort.
07-30-2008, 04:57 PM
#11
Rennlist Member
Mike,
Thanks for the great writeup. Very informative. You talk about normally aspirated OBD2 993 cars. What about us turbo owners? Don't we have the same SAI issues?
Thanks
Hal
Thanks for the great writeup. Very informative. You talk about normally aspirated OBD2 993 cars. What about us turbo owners? Don't we have the same SAI issues?
Thanks
Hal
07-30-2008, 05:43 PM
#12
Race Director
Unless a flow test is done there is no way to determine if any blockage of any kind exists. Since customers depend on us for accurate info, it would be a guess, a $1300 guess. It would be like a healthy person going to the doctor and asking for stint or angio-whatever just to be sure he doesn't get a blockage. If your car uses a quart of oil in less than 1,000 miles, you may try,but since you probably need valve guides anyway, why waste the $$. remember , as mentioned in the article, we have some 993's with 100K on them and have not yet had a check engine light. I guess if someone asked us to do it as a maintenance, after all consideration, we would oblige them.
My car burns no oil between 2,000 mi. oil changes, I start it at 1/2 between low and full and it pretty much stays there until I change it.
I'll post the link to my SAI port cleaning adventure thread if you wish.
Last edited by Slow Guy; 07-30-2008 at 07:31 PM.
