I have a 2009
987.2 Cayman
Base with 82,000 miles and the following mods: 1) de-snorkle; 2)
FabSpeed
exhaust
; 3)
FabSpeed
ECU
tune; 4) short shift kit. It has been throwing the P0491 and P0492 codes for a while. I have replace the secondary air pump and check valve, but the codes came back. So this is the solution that finally worked. This not my day job and others may be able to do this faster and/or better with less removal, but hopefully this will give you some guidance on things to do and things to avoid.
All U.S. gasoline cars are required to have a Secondary Air Injection (SAI) system for reduction of
exhaust
emissions on cold starts. To operate effectively, catalytic converters need to reach at least 750oF. Even though the oxidizing reaction is exothermic, it takes an amount of time for the catalyst to reach that temperature. Until that “light off” temperature is reached, the engine exhausts undesired pollutants including CO, NOx, and unburned HC. The SAI reduces the inefficiency of the cold catalyst by increasing the amount of O2 in the
catalytic converter
until the catalyst reaches its “light off” temperature. This is usually only about 60-90 seconds on cold starts. This is a decent YouTube video:
. The first part discusses the purpose of SAI.
Other than affecting emissions, properly functioning SAIs do not increase performance, and improperly functioning or non-functioning SAIs do not adversely affect performance. The latter just throws a CEL that prevents successful emissions inspection (in those locales that require them).
The SAI system for the 987.2 Cayman and Boxster is shown below and consists of an air pump 1, a check valve 6, a distribution manifold (or “console”) 5 and two distribution pipes 12 and 13. The distal end of the distribution pipes 12, 13 attach to ports in the cylinder heads (front of the engine) and channels within the heads distribute the pressurized air into the exhaust valve pockets downstream of the valves so that pressurized air (excess oxygen) from the air pump reaches the catalyst during cold starts. This system is located on the top of the engine under the plenum (“distributor tube”)
To my understanding, the 987.2 SAI system is very basic in that it does not use a vacuum-controlled check valve or a pressure sensor. Rather, air pressure generated by the pump 1 overcomes the check valve spring and opens the port to the SAI piping. I believe the O2 sensors are used to detect an excess of O2, during cold starts rather than using a pressure switch in the SAI piping. When the system fails, the errors codes P0491 and/or P0492 are thrown, and the check engine light comes on.
To my understanding, the 986 Boxster (1996-2004) and the 987.1 (2005-2008) SAI systems are different (e.g., vacuum controlled check valve) and are not addressed here.
Common failure modes of the 987.2 SAI are: 1) the pump relay; 2) the pump (motor or impeller); 3) the check valve; and 4) clogged cylinder head channels. Any of these failure modes may cause a P0491and/or P0492 OBDII code.
The pump relay 5 is shown in the figure below and is located in the trunk well on the left (U.S. Driver) side and can be easily tested.
Assuming the relay is okay, the pump can be tested in at least 3 ways. First, on cold start up you should be able to hear the pump in operation. If you don’t hear it on cold start, the pump is not pumping. Second, I believe you can use a Durametric device to energize the pump without starting the engine. The pump will be easily heard with the engine off and air pressure should be felt at the exhaust tips (unless the channels are fully blocked). Third, if you can get to the air pump electrical plug (under the plenum) you can power the pump with a 12-volt battery. Unfortunately, getting access to the electrical plug almost always requires removal of the plenum (“distributor tube”) as the plug is located inches away from the pump. Never spin the pump motor for more than 90 seconds at a time – it is not designed to run continuously.
Assuming the air pump spins the impeller, the problem may be the check valve. Several articles indicate the check valve is the most common failure mode. Not sure if that is model specific; the air-cooled 911 engines certainly had problems with the check valves. Replacing the check valve on the 987.2 requires removing at least the plenum.
If the relay, pump, and check valve are functioning, then all that’s left on the 987.2 SAI system are plugged channels in the heads. I don’t believe (but don’t know if) a bad O2 sensor would cause a P0491/P0492 CEL code, and I can’t imagine that the large bore SAI piping can get plugged. Cleaning the SAI channels in the heads is what I did to solve the problem.
When the 987.2 first threw the P0491/P0492 CEL codes, I ordered a new check valve. I removed the air pump and tested it with a battery. The pump was bad (brushes were worn down ). Porsche wants about $1,000 for this pump and I couldn’t find an aftermarket. Unwilling to pay that amount for an air pump, I found an SAI pump for a 987.1 Cayman for less than $200 and ordered it even though it was not a direct bolt on for my 987.2. I removed the new motor from the new pump (which seemed identical to my 987.2 motor) and rebuilt the 987.2 pump with that motor. You should be able to find a VW, Audi or Porsche SAI pump for a reasonable price from which you can harvest parts for a rebuild. I installed the rebuilt pump, cleared the codes, and drove the car for several weeks before the codes came back. I made a post about this a while ago.
After some additional research, I tumbled to the conclusion that the SAI channels in the heads were likely clogged. While discussions for the 987.2 SAI are hard to find (at least I had trouble), there is a lot of general information on other Porsches and other cars. Here are some YouTube links on this issue.
(For a 987.1 or 986);
(Audi, not Porsche).
My general plan was to clean the channels in three stages: first, remove the top of the engine. Second, remove the bottom of the engine. Third, chemically clean the SAI system from the top. For the first, I left the car on the ground, disconnected the battery, and pulled the front engine access panel, the top access panel, the plenum (“distribution tube”), right side intake runners (“intake air distributor”), SAI pump, alternator and SAI check valve. For the second step, I raised the car (jack and stands), removed the wheels, disconnected the exhaust pipes from the mufflers and removed the exhaust manifolds from the heads. Once all that was done, I started cleaning the SAI piping and channels.
STAGE ONE
Here is the engine bay with the plenum seal clamps removed. A flexible, magnetic screw pick up (blue tool in picture) is a must have for me especially when dealing the intake runners.
I find one of the biggest hassles are the vacuum lines under the plenum. From previous work, I made a “quick” disconnect for these vacuum lines at the front of the engine behind the access front cover. By pulling the hard plastic vacuum line from the piece of flexible vacuum line I previously installed, removing the plenum without disturbing the vacuum lines underneath is possible. This picture shows the disconnect.
Once the plenum seals are moved fully onto the plenum, the plenum can be wrestled out. Because I was going to remove the right-side intake runner to give me more room to remove the air pump, I loosened the intake bolts first to give me some wiggle room when I removed the plenum.
I had replaced the Air/Oil Separator a while ago with an OEM AOS. Thus, I was surprised to find what I consider to be an excessive amount of oil in the intake manifolds and in the air supply to the mass air sensor. The oil on top of the oil cooler in this picture came from the plenum/manifold. Going forward, I think I will drop the normal oil level to one bar below the top mark. This picture shows the engine with the plenum removed. The SAI check valve is shown with the arrow.
This picture shows the right-side intake ports after the intake runner was removed. I was surprised at how clean the ports were considering the amount of oil in the plenum and air supply.
With the intake runner removed, you have clear access to the SAI pump, as shown below.
Unplugging and removing the SAI pump is straightforward and only has two hold down bolts (shown above). The pump, which I had previously rebuilt, is shown below.
This view shows the top of the engine with the SAI pump removed and paper towels protecting the intake ports. The SAI check valve is held with two 8mm bolts fore and aft. The aft bolt is easy to get to. The fore bolt is hard to access. You can reach it with your fingers, but it’s a lot easier to remove if you remove the alternator – which I did.
This view is from the front engine access with the alternator removed. The arrow shows the fore bolt on the SAI check valve.
Once the check valve is removed, you have access to the SAI check valve manifold (“console”), which feeds the Bank 1 (right side) head and the Bank 2 (left side) SAI channels.
STAGE TWO
I raised the car fairly high off the ground (for a floor jack and stands) and removed the rear wheels. My FabSpeed exhaust has a wedge clamp where the post-Cat pipe enters the muffler. I loosened but did not remove the clamp. Next, was unbolting the exhaust manifolds from the heads.
Once the headers were unbolted, I removed the wedge clamp to the mufflers and was able to position the headers/Cat/pipe mostly out of the way. I didn’t want to remove the O2 sensors or unplug the 02 sensors.
Compare the exhaust ports above for the 987.2 with the exhaust ports for the 987.1/986 shown below. The arrows indicate the SAI channels on the 987.1/986 heads.
After removing the headers, I placed old sheets on the garage floor underneath the exhaust ports to collect all the crap I was hoping to dislodge.
STAGE THREE
Now I was ready to attempt cleaning the SAI channels. First, I created a rubber adapter that would seal against the SAI manifold opening and allow me to use an air compressor to “blow out” the channels. This picture shows the rubber adapter and air gun.
This picture shows the adapter position on the SAI manifold.
The compressor was set at about 90 psig and I blew out the SAI piping and channels. I heard escaping air and checked the sheets beneath the exhaust ports – NOTHING.
Moving on to chemicals. I picked up some carb cleaner and brake cleaner. Chemtool B-12 is mostly Toluene and Acetone. Straight MEK (available at paint stores but not big box stores) or straight Acetone also should work. PEA-based cleaners like Techron or Regane are also suitable.
I first used the liquid (rather than spray) Chemtool. I used a funnel to pour the Chemtool cleaner into the SAI manifold, then waited about 5 minutes before I used the air gun to blow out the channels. The next picture shows the results.
Only the Bank 1 channels blew out. Nothing happened to the Bank 2 channels. On further inspection, you can see that the Bank 1 SAI piping has a lower maximum elevation than the Bank 2 piping. In other words, pouring the cleaner in the manifold preferentially flows to Bank 1. My solution was to find the right size tubing to allow me to feed cleaner preferentially into each bank.
This is the result of using this system followed by the air gun. The splatter is not accurately located as I moved the sheets around to clean up some messes before this picture.
It took me most of a Sunday to get to this point. I used two cans of liquid B-12 Chemtool and 1 can of spray Chemtool. I did a final spray and let it sit overnight, then did a final blow out.
The exhausts ports looked cleaner, but not as clean as the intake ports. I reinstalled the headers, exhaust, wheels and dropped the car. I reinstalled the top of the engine, connected the battery and cleared the OBDII codes. It fired up with no problems and there have been no SAI codes for over 4 months.
Hope this can help someone with SAI issues.
Just incredible,
@ABD
- what a write-up. Really nice work here and I expect to have to deal with this at some point down the road.
