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Help diagnosing possible SAI problem.


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2000 2.7L

 

 

I've been getting regular (about every 2 weeks or so) CEL for the SAI system P 0410 "signal implausible" as well as 1128 and 1130 which indicate the fuel trims are at full rich. The MAF is reading lowish, around 10-11 when it should be at 15. This leads me to believe that I am getting a vacuum leak somewhere in the SAI system.

Does that sound right and if there is a vavuum leak from the SAI, what are the usual suspects?

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If you can hear the SAI pump running, you may have a vacuum leak e.g., one of the vacuum lines is disconnected or cracked, or the vacuum reservoir is cracked, etc. 

 

Since you have a scanner that can read real-time sensor data, you may want to monitor the O2 sensors and use the following diagram on a cold start to check if the exhaust actually sees any air. If not, that means even the pump is running, the air is not getting to the exhaust. That points to vacuum line or changeover valve issue.

 

post-5282-0-28626300-1421174121_thumb.jp

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Looks like throttle body, cross-over tubes, the oil fill tube, and the alternator http://986forum.com/forums/319050-post13.html

 

BTW, once you can access that area, you can hook up a vacuum pump to the black/white one-way valve (pic #4) to see if the whole system holds vacuum. You can also test the valves individually by supplying vacuum and power from a 9v battery. You should hear them click and hiss. You *may* be able to access that black/white valve for a quick check even before you remove anything. You could for a 996 but not sure for a Boxster.

Edited by Ahsai
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I ran the diagnostic and everything checked out.  Both pre cat O2 sensor voltages went to near 0 after I started the car, the post cat sensors straight lined at a higher voltage than the pre cat sensors and after a few seconds, also wnet down to near 0.  Then, once the pump shut off, the pre cat sensors started to track sine waves and the post cat sensors went up and tracked slightly wavering straight lines.

 

So I'm thinking its an intermittent problem with one of the components, but it still doesn't explain the low MAF readings, which is still around 10-12.

Edited by san rensho
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Agree your SAI system seems to be working properly at this time. Also agree that 10-12 kg/hr sounds low. I think you really need to give it a more thorough check for air leak. The usual suspects include cracked oil filler tube (a crude test is remove the oil cap and see if you hear any engine idle change), faulty purge valve (remove valve and try to blow through it), vacuum lines, etc. The most complete leak test is of course using a smoke machine. If no air leak is found, the MAF will be a strong suspect.

 

Any mods to the intake?

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No mods.  I recently replaced the valve that goes from the EVAP canister to the throttle body, so I guess I better check that again.  When it was bad, I diagnosed it by pinching off the connection at the throttle body and the MAF reading, which was low at  around 9-10 went back up to within spec, so I guess I'll start there since its an easy diagnosis.  Is this the purge valve you mentioned?  I hate messing with the evap system, its real pain.

 

When I remove the cap at the filler tube, the idle stumbles and changes, so I think I'm ok with the tube.

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Yes, that's the purge valve I was talking about. Do you have Durametric? If you do, you may want to check the RKAT (or TRA) values (fuel trims at idle) and see how bad they are.

 

Hope you know someone who can swap in a known-good MAF for further diagnosis.

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2000 2.7L

 

 

I've been getting regular (about every 2 weeks or so) CEL for the SAI system P 0410 "signal implausible" as well as 1128 and 1130 which indicate the fuel trims are at full rich. The MAF is reading lowish, around 10-11 when it should be at 15. This leads me to believe that I am getting a vacuum leak somewhere in the SAI system.

Does that sound right and if there is a vavuum leak from the SAI, what are the usual suspects?

san rensho, remember this thread? http://986forum.com/forums/general-discussions/49666-p0410-secondary-air-injection-system-cylinders-1-%96-3-a.html

Check the air ports on the heads... You will have to drop the three-way catalytic converters to inspect the ports.

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2000 2.7L

 

 

I've been getting regular (about every 2 weeks or so) CEL for the SAI system P 0410 "signal implausible" as well as 1128 and 1130 which indicate the fuel trims are at full rich. The MAF is reading lowish, around 10-11 when it should be at 15. This leads me to believe that I am getting a vacuum leak somewhere in the SAI system.

Does that sound right and if there is a vavuum leak from the SAI, what are the usual suspects?

san rensho, remember this thread? http://986forum.com/forums/general-discussions/49666-p0410-secondary-air-injection-system-cylinders-1-%96-3-a.html

Check the air ports on the heads... You will have to drop the three-way catalytic converters to inspect the ports.

 

Ah yes, remember it well.  I was hoping that was not the problem.  But in your case, the Durametric trace shows the SAI system was not working, Correct?  At start the voltages should go to near zero until the pump shuts off and then they should track as shown in your trace.  In my case, the trace shows the SAI system is working, so i guess I'll take alook at the SAI components before I tear into air passages.

 

By the way, if the SAI system works on vacuum, how can it inject air into the exhaust, or am I not understanding how the system works.

Edited by san rensho
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