Hello, my Cayman 987.1 152K miles is giving me a CEL with codes P0491 and P0492, secondary air injection system insufficient flow.

I my AOS failed and was replaced a few weeks ago, and was running great since then, with a smooth idle. The weird thing I got this after the car was already warmed up.


I searched the forums for ways to fix but seen no real clear resolution but replacing eveything in that system one at a time, Also are there two air pumps(one for each side/bank) and how can they both be bad at same time,

I live in CA and cannot just reset the CEL, block off and disregard.

any more insight or experience would be greatly appreciated thanks

 

Think the following applies to your car:

P0491 Secondary Air Injection System, Bank 1 - Insufficient Flow
P0492 Secondary Air Injection System, Bank 2 - Insufficient Flow

Possible cause of fault
- Electrical fault in power supply or line between relay and secondary air injection pump
- Secondary air injection pump relay mechanically faulty
- Mechanical fault in electrical secondary air valve
- Pneumatic secondary air valve faulty/sluggish
- Electrical fault in secondary air injection pump
- Mechanical fault in secondary air injection pump or secondary air injection pump blocked
- Vacuum system leaking
- Air hose to secondary air injection pump slipped off or constricted



Given the error codes appeared after the AOS was replaced I'd lean towards the last two possible faults. A vacuum hose was disturbed and failed due to age or an hose hose was disturbed and failed due to age

 

thanks for the info Macster, and will look into the hoses,

a clue into my issue,
today I noticed going uphill on canyon road the revs would surge a little every five seconds which was weird and new. but was fine crusing on level ground and when stopped...

 

Surging or any change in RPMs from idle in my experience has been either due to a bad AOS or in one case a bad VarioCam solenoid/actuator. In the case of the VarioCam issue there was no CEL, but there was a pending error code which pointed to the VarioCam solenoid/actuator.

Assuming the AOS and VarioCam hardware is ok, any change in how the engine runs when going up (or down) hill vs when on flat ground suggests a fueling problem. (How does the engine behave under hard cornering?)

My experience with my 2002 is the fuel pump fits right to the bottom of the tank. That is the housing does and the level has to be pretty low for the fuel pump to be starved -- even a little -- for fuel. The fuel pump is held in place with some kind of plastic catches. If one failed or of the pump was eplaced but not done correctly the fuel pump may not be properly secured. It could then be affected by low fuel level. I could imagine a fuel pump moving about on the floor of the tank too.

But it doesn't have to be a real low fuel level or a loose fuel pump. A in tank fuel line may have a crack/split in it that opens up a tad and affects fuel supply and pressure. This was a problem with the Turbo with its saddle tank with two separate basins and two separate fuel siphons to pull fuel out of its basin. One develops a split/crack and the siphon would not be able to pull fuel out of its basin. The car would run out of fuel at around 1/2 tank.

 

under hard cornering the idle is fine, but I did not think about the fuel or actuator.
I did the oil cap test while running and it there was no extreme suction so I am ruling out the AOS for now... but have heard some sad tales of new AOS installs that went south quickly,
my AOS failure was a bad one that got oil into intake, plugs, and probably cats so im thinking the oil must be in a air line or something

 

A very bad/advanced AOS failure can load the intake with oil. In fact it can oil the throttle body. My first AOS experience before I even knew there was an AOS to fail advanced to the point the exhaust tips were dripping oil. Very bad. I removed the TB from my Boxster's intake and it was heavily oiled, there was a drop of dirty oil hanging off the bottom of the butterfly valve.

There might be some benefit to cleaning the throttle body. In this case I might even be on board with cleaning the MAF. Under normal operating conditions these never have to be cleaned but a very advanced AOS failure is not normal. Cleaning these is something relatively easy to do and doesn't require you throw expensive parts at the behavior.

You must be sure you handle the TB with care. Drop it and its toast. Be sure you get it properly bolted down but do not over tighten. IIRC my cars TB had an o-ring for a seal and I did nothing but ensure the o-ring and TB mating surfaces were clean.

Likewise handle the MAF with care. Be sure you do not static discharge into either the MAF or the engine wiring harness connectors. Like the TB you drop the MAF you buy a new one.

Use MAF cleaner. Non-residue cleaner. The hot film surface is inside the passageway but MAF cleaner sprayed in there will remove any "dirt" on the hot film. Do not insert anything in the passageway.

Given the reason you are cleaning the MAF you may want to give it a couple of cleanings with some time between them to let the cleaner soak the dirt some. The hot film runs "hot" and it can to some degree cook dirt/oil if it gets on it.

IIRC the MAF has an o-ring that seals it to the intake. Be sure you install the MAF in the right direction -- it is "keyed" but pay attention nonetheless -- and secure the connector. It has a catch/latch that to separate the connectors requires the latch be pressed enough to let the connectors separate. IIRC this requires the two connectors be forced together a bit to release the pressure on the latch. And when you connect the connectors be sure the latch catches and is secure.

 

thanks Macster for the wise advise, and I will check those areas for oil and clean the MAF. It cant hurt since I dont know how good of a Job the mechanic did cleaning up all the oil. Its very possible some of the missed gunk got loose from the intake and TB and is fouling the MAF.

 

The MAF is a ways from where the AOS tube connects with the intake. The connection, at least for my 2002, was just after (downstream) of the throttle body.

But the throttle body was quite oiled. The amount of oil vapor a failed AOS can allow into the intake is quite a bit. In all 3 failures the final failure stage has the engine smoking something fierce.

The increase in "air" flow through the hose from the AOS can cause under low throttle opening conditions the vapor/fumes from the AOS to flow the wrong way which then can foul the throttle body with oil. And even though the MAF is a good ways upstream of the throttle body the MAF can also get fouled with oil.

After my car's first AOS the service manager told me it can take some time for the effects of the AOS failure to go away. The service department doesn't unless specifically requested attempt to address any collateral "damage". By "damage" I mean the intake is not removed and cleaned. The throttle body is not cleaned. The MAF is not cleaned. The plugs are not changed. The exhaust system is not flushed with solvent to remove any oil.

The SM told me it could take 50 miles of driving for the after effects of an AOS failure to go away. And not just any kind of driving. Just 50 miles on the freeway may not suffice. Given the first AOS failure for my car occurred in early 2003 it was still quite cold being winter. I knew from experience the engine doesn't get very warm at all when driven at freeway speeds even for some distance.

To really help the oil leave the various surfaces the surfaces must get hot. To get hot the engine must get hot. To this end around town driving, just a mix of idling, followed by within the law acceleration up to the legal speed limit, some cruise time, followed by another stop, more idling. Repeat. This will have the engine get pretty warm. It helps if one can drive the car with the A/C off so the radiator fans do not run all the time. And then when the radiator fans do come on that's a good sign the engine is indeed getting "hot".

While I did not have the benefit of observing oil temperature back then with one of my current cars it has an oil temperature gauge and when driven in the above manner the oil temperature can climb to 212F and above -- I've seen it climb to 230F (the coolant temperature staying at 217F or lower (at 217F the radiator fans come on). With the oil this hot the engine is "hot" and the heat soaks into the intake and any oil in the intake and on the throttle body surfaces gets hot and this works to remove the excess oil.

The oiled surfaces will of course retain some oil but the worst of it leaves.

The entire exhaust system gets plenty hot too and this works to burn any residual oil out of the exhaust system. The portion of the exhaust nearest the engine of course loses its oil pretty soon after engine start. The heat of combustion gases sees to this. Likewise the plugs and combustion chamber surfaces lose their oil. The Porsche plugs are of the extended tip type and tend to run "hot" at low engine speeds, which works to keep the plug from fouling and "cool" at high engine speeds which works to keep the plug from burning it tip.

 

great stuff Macster, this is my weekend car and I dont think I did much more than 80 miles since AOS failure, and much of that was traffic w AC on and not much running hot.
so I have yet to get the oil out of the system...the mechanic did say they cleaned the intake and some of the upstream hoses as well as fowled plugs but I need to get in there and really check myself. I was told that the cats may be toast after the AOS failure but I dont think that may be the case for now

 

My car suffered 3 AOS failures. Each one ended with the engine smoking like a coal power plant chimney. The first failure was the worst and I was told at the dealer the engine suffered hydraulic lock which fortunately did not harm the engine. The point is the engine was "flooded" with oil and of course so too were the sensors and converters.

After some usage, in the case of the first failure considerable usage, the converters were fine. The O2 sensors were fine. 'course, this doesn't guarantee there will be no issues with these items in your car.

But the converter and O2 sensors are pretty heavily monitored components and if there is a problem the engine controller will make it known via the CEL and one or more error codes. Assuming there is no CEL no active or pending error codes, nothing you can really do now.