Re: loss of power : (

I replaced my AOS about six months ago everything went well but after and more so now i have experienced a loss of power mainly around 4k to 6k rpm. I think it might be the cats..???
any ideas? this is a very frustrating problem for me. I cleaned the throttle body and ran some techron through the gas but it has made little difference I also replaced a MAF sensor but only as a result of my ignorance about AOS failures. the power will come and go sometimes

please help

Do you have a CEL?
If so, what code?
Check the hose that connects the AOS to the intake tee.
It needs to be perfectly sealed.
Check for any other air leak in the system.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

When you replaced your AOS, had it failed completely? You mentioned you cleaned the throttle body and replaced the MAF at the same time, however if oil entered the intake system, there could be residual oil that fouled the MAF after it was replaced. When my '99 had about 30k miles, I had the same problem, cutting out at ~5500 rpm, as if it hit a rev limiter. I replaced the MAF and never looked back. It couldn't hurt to clean the MAF.

As Pedro mentioned, a CEL code can help the diagnosis if you have one.

Since the MAF is upstream of the AOS.

of the TB and got some oily residue on the paper towel. Now I did clean the MAF and the cleaning fluid ran clear from the MAF so while there was some signs oil vapor had managed to make it part way the wrong way in the intake system, the MAF was clean, not comtaminated.

While it is unlikely the MAF could become comtaminated I believe this might occur in the very late stages of an AOS failure.

Sincerely,

MarcW.

and since the business end of the MAF is suspended in the top of the intake pipe, the only way oil coming from downstream could possibly get on the MAF is if the entire intake pipe filled with oil. That is pretty much impossible. So perhaps oil got into your intake from the outside but it did not come from the AOS.

Quote
Boxsterra
and since the business end of the MAF is suspended in the top of the intake pipe, the only way oil coming from downstream could possibly get on the MAF is if the entire intake pipe filled with oil. That is pretty much impossible. So perhaps oil got into your intake from the outside but it did not come from the AOS.

when the engine is shut off oil vapor can flow upstream in the intake. Since the AOS is not working properly the engine crankcase is experiencing higher pressure than it does otherwise. Additionally the crankcase air is loaded with oil vapor naturally, but of course since the AOS is not working properly this normal vapor load is not removed from the crankcase air.

When the engine is shut off, most of the cylinders and their valves block any flow of any vapor into the chamber and out again, thus the intake pipe is the only path this over pressurized oil vapor ladened crankcase air can flow.

As I mentioned earlier when my car's AOS was going bad rather early on I found a bit of oily residue in the intake between the MAF and the TB. The TB was quite oily with the butterfly valve

However, I cleaned the MAF and the cleaner fluid ran clear. That was before the AOS went really bad. At the end -- that is when I gave up my efforts to diagnose the problem (at the time I didn't know it was the AOS) because the engine was smoking constantly and I was afraid of hydraulic lock -- I never bothered to remove the TB nor the MAF.

Thus under the latter stages of AOS failure, at least the failure mode that results in the engine emitting continuous billows of oil smoke, fouling the MAF with oil from oil vapor is a possiblity.

An AOS repair job replacing an obviously sick AOS would not be complete without a check of the TB and a cleaning if it is found needing it and a check/cleaning of the MAF.

Sincerely,

MarcW.

Also, when you shut off the engine there is a vacuum in the system, not positive pressure.

Quote
Boxsterra
Also, when you shut off the engine there is a vacuum in the system, not positive pressure.

condition in the intake manifold but the intake system's pressure quickly reverts to atmospheric pressure almost as soon as the engine stops.

Additionally the heat of the engine continues to increase as the heat soaks through and this will help drive engine crankcase air out through whatever passage there is to the outside. One such passage is past the TB and into and through the intake pipe. The other way down through the engine is blocked unless one piston happens to stop at just the right time that both the intake and exhaust valves are open.

But there is heat in the engine and the combustion chambers and this heat would tend to cause air flow away from the hotter area and this would tend to add incentive for any vapor that comes out of the crankcase through the bad AOS on out through the intake system.

Sincerely,

MarcW.

... on an engine that's backfiring generally due to an air leak.
I've seen it a few times where the air intake tube is very oily.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Quote
wyatt-peake
I replaced my AOS about six months ago everything went well but after and more so now i have experienced a loss of power mainly around 4k to 6k rpm. I think it might be the cats..???
any ideas? this is a very frustrating problem for me. I cleaned the throttle body and ran some techron through the gas but it has made little difference I also replaced a MAF sensor but only as a result of my ignorance about AOS failures. the power will come and go sometimes

please help

put forth by BoxsterBob suggesting the MAF might have gotten fouled with residual oil from the previosly failed AOS.

Also, the integrity of the new AOS has to be questioned -- a new one can fail prematurely -- or the installation of the new one.

But in the case of a failing AOS or a bad AOS installation I would expect to read the CEL was on and then of course see you post the error codes.

If the engine is down on power and not acting up in other ways you can disconnect the MAF at the wiring harness and clear/erase the error codes (even if the CEL is not on this resets the long term fuel trims (among other things) to their defaults which will undo the long term fuel trims having possibly been goofed up by a bad MAF) then just using the car as you do normally.

You want to drive the car a distance. My experience is that generally a 30 mile drive with mixed driving will been enough.

If the engine perks up then the MAF is suspect. You can of course clean it before trash canning it.

If the engine remains flat as before... probably not the MAF. What it could be then well, you can try the above first and depending upon the results...

When you reconnect the MAF, clean it, or replace it, you should still erase the error codes again to of course undo any long term fuel trim learning that was done prior so the engine controller starts out unburdened with learning that may be way out of line.

Be aware that depending upon various things the engine might initially run a bit rough, have a more ragged idle, as it has had its cold start/idling adaptation erased.

My experience though with my 02 Boxster is the engine's behavior is not scary upon that first start after the error codes have been erased.

Sincerely,

MarcW.

I dont think it would be the maf,as it is near the air filter and up stream of the motor. is your car an e gas car or a cable throttle. It would may be good to check to see if your cams are advancing, . How is the idle speed , fuel economy any strange noises. The more you tell us the more things we can check off. make sure you installed the Aos correctly.

okay i checked the connections and i think one might have been loose, so i took the whole throttle body off and reconnected the intake tee. I need to find my torques tools to take the MAF off and inspect/clean it.

It has an E throttle body
* it has been throwing some CEL but i have to wait for it to come back on and i will read it

I was dumb and replaced the MAF before i was wise about the AOS once its was a huge embarrassing smoke machine

I got some home work to do. will get back with the error code

There is no need to reinspect it. If the problem happened before and after MAF replacement it is almost certainly not the MAF causing it.

Chances are that the problem is in the area of the AOS. Check the vacuum lines in that area. It is also possible that you cracked one of the lines going into the AOS. And definitely check the code (or if you don't have a code reader, have it checked for free at your local auto part store) and report it here. We will help you find the problem.