SAI issues, codes P0491, P0492
11-29-2016, 07:38 AM
#1
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SAI issues, codes P0491, P0492
Today I checked again my car with durametric and saw the following codes
P0491: Secondary Air Injection System, Bank 1: Insufficient Flow
P0492: Secondary Air Injection System, Bank 2: Insufficient Flow
I checked the satus of the SAI pump. When I toggle it I hear it running.
I disconnected the hose from the pump, to check if it blows enough air. To me it seems the flow rate is good. I know I need to look further down the lines and valves of the SAI sytem to see if there is something blocked. For this I came accross other threads on the forum that go into detail where to look when these codes appear.
However I noticed the following
1. recently, when coming to a stop, i.e. when leaving the highway. I hear a whirring sound kicking in for some seconds. It sounds to me as it is the SAI pump. But I am not 100% sure. At the same time with the whirring sound I see the RPM at idle going 100rpm or so higher. When the sound disappears Idle rpm falls back to normal. Is this possible? I thought that the SAI only kicks in at cold start to speed up heating of the cats.
2. Further I notice at cold start, car sits overnight, that the exhaust smokes for 3-10 seconds (warm or cold ambient temperature, makes no different, it smokes). To me it is not oil burning. Had that before and know how oil fumes look and smell. Water I doubt it is, as in warm ambient temperature it also smokes. It is whitisch but doesn't smell like burnt oil. It smells more as fuel, could that be white too? Could this be related to the SAI malfunction? As if at cold start the ECU injects more fuel to heat up cats but the SAI does not provide the necessary extra air to burn te rich mixture? Unburnt fuel exits the exhaust as white smoke?
Engine is further running Idle very stable at all times, cold or warm start.
Besides that I also had the P0420, P0430 codes pending
They read as: Cat conversion Efficiency bank 1 & 2
No CEL light in the dash; those two codes are coming most probably from the 200cell cats of the x-pipe. So unrelated to the above issues, I suppose?
P0491: Secondary Air Injection System, Bank 1: Insufficient Flow
P0492: Secondary Air Injection System, Bank 2: Insufficient Flow
I checked the satus of the SAI pump. When I toggle it I hear it running.
I disconnected the hose from the pump, to check if it blows enough air. To me it seems the flow rate is good. I know I need to look further down the lines and valves of the SAI sytem to see if there is something blocked. For this I came accross other threads on the forum that go into detail where to look when these codes appear.
However I noticed the following
1. recently, when coming to a stop, i.e. when leaving the highway. I hear a whirring sound kicking in for some seconds. It sounds to me as it is the SAI pump. But I am not 100% sure. At the same time with the whirring sound I see the RPM at idle going 100rpm or so higher. When the sound disappears Idle rpm falls back to normal. Is this possible? I thought that the SAI only kicks in at cold start to speed up heating of the cats.
2. Further I notice at cold start, car sits overnight, that the exhaust smokes for 3-10 seconds (warm or cold ambient temperature, makes no different, it smokes). To me it is not oil burning. Had that before and know how oil fumes look and smell. Water I doubt it is, as in warm ambient temperature it also smokes. It is whitisch but doesn't smell like burnt oil. It smells more as fuel, could that be white too? Could this be related to the SAI malfunction? As if at cold start the ECU injects more fuel to heat up cats but the SAI does not provide the necessary extra air to burn te rich mixture? Unburnt fuel exits the exhaust as white smoke?
Engine is further running Idle very stable at all times, cold or warm start.
Besides that I also had the P0420, P0430 codes pending
They read as: Cat conversion Efficiency bank 1 & 2
No CEL light in the dash; those two codes are coming most probably from the 200cell cats of the x-pipe. So unrelated to the above issues, I suppose?
11-29-2016, 09:39 AM
#2
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I would check out Part #'s 9 and 11 first here: http://www.autoatlanta.com/porsche-p...section=108-05
The check valve is prone to getting gummed up.
Also, there are two changeover valves Part # 18. Known to go bad.
It is not unusual for the SAI pump to kick in after a highway run. Just seems to be one of the quarks of the system.
The smoking exhaust is not all that uncommon either. If you are not losing oil or coolant, it most likely is a result of the error codes and SAI system. How many miles on your AOS?
The check valve is prone to getting gummed up.
Also, there are two changeover valves Part # 18. Known to go bad.
It is not unusual for the SAI pump to kick in after a highway run. Just seems to be one of the quarks of the system.
The smoking exhaust is not all that uncommon either. If you are not losing oil or coolant, it most likely is a result of the error codes and SAI system. How many miles on your AOS?
Last edited by DBJoe996; 11-29-2016 at 10:56 AM.
11-29-2016, 01:12 PM
#3
This thread should help https://rennlist.com/forums/996-foru...not-ready.html
The SAI pump kicks in after highway run is normal and is by design. The DME does that if it didn't have a chance to check the SAI operation during cold start (e.g., if you drive the car off immediately without much idling). The drop in the rpm was because of current draw (a lot) from the SAI pump, which loads up the alternator, then in turn the engine raises its rpm to compensate.
The SAI pump kicks in after highway run is normal and is by design. The DME does that if it didn't have a chance to check the SAI operation during cold start (e.g., if you drive the car off immediately without much idling). The drop in the rpm was because of current draw (a lot) from the SAI pump, which loads up the alternator, then in turn the engine raises its rpm to compensate.
11-29-2016, 02:48 PM
#4
I had the same codes. I replaced basically everything shown in Ahsai's picture, and haven't had problems since. To me it was easier to replace all the hoses/joints etc. than figuring out which one leaked. Plus if one was cracked, the others probably wouldn't be far behind.
11-30-2016, 06:02 AM
#5
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Thx Ahsai and Joe ... Your input has been as always very appreciated!
Will have a look at those valves pointed out.
The links posted contain a whole lot of detailed info for analysis. Especially the read-out of the pre-cat O2 sensors at cold start. Will try to have a graph with durametric.
In two weeks I will have the transmission and torque converter out for a rebuild and modifaction so I will have time and space enough to inspect the whole SAI system.
Will have a look at those valves pointed out.
The links posted contain a whole lot of detailed info for analysis. Especially the read-out of the pre-cat O2 sensors at cold start. Will try to have a graph with durametric.
In two weeks I will have the transmission and torque converter out for a rebuild and modifaction so I will have time and space enough to inspect the whole SAI system.
11-30-2016, 08:41 AM
#6
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