SAI bypass for P0410; alternate idea
12-23-2013, 05:09 PM
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SAI bypass for P0410; alternate idea
I made a minor contribution to the circuit shown in flying_low's posts to "Recap of the SAI circuit" (FETs instead of bipolar transistors).
This circuit has worked for several Forum members. It bypasses the O2 sensors while the SAI pump is running.
I may have a simpler solution and would appreciate some info so that I can refine my idea.
As I understand, the SAI pump runs for a specific time (two mins?) and runs ONLY when the engine is below a certain temperature, like cold morning starts. The fuel mix is enriched to heat the CAT more quickly, thereby reducing emissions. After the specific run time, the SAI pump shuts off. If the SAI ports are clogged, the pump sees back pressure (or the O2 sensors show excessively rich) and you get the dreaded CEL P0410.
My idea is to trick the temp sensor, so that the SAI pump never comes on, and the SAI test is ignored by the computer. The minor downside is that the CAT won't heat up as fast. I'd do this every time the ignition is turned on, and trick the temp sensor to think the engine is at a temp above the temp that would turn the SAI on.
If you see a flaw in this thinking, let me know some details.
If this may work, someone please tell me where to find the temp sensor, and if you have the resistance values for cold and hot, let me know.
I'll be happy to post results of this when/if I get it working.
Ron
This circuit has worked for several Forum members. It bypasses the O2 sensors while the SAI pump is running.
I may have a simpler solution and would appreciate some info so that I can refine my idea.
As I understand, the SAI pump runs for a specific time (two mins?) and runs ONLY when the engine is below a certain temperature, like cold morning starts. The fuel mix is enriched to heat the CAT more quickly, thereby reducing emissions. After the specific run time, the SAI pump shuts off. If the SAI ports are clogged, the pump sees back pressure (or the O2 sensors show excessively rich) and you get the dreaded CEL P0410.
My idea is to trick the temp sensor, so that the SAI pump never comes on, and the SAI test is ignored by the computer. The minor downside is that the CAT won't heat up as fast. I'd do this every time the ignition is turned on, and trick the temp sensor to think the engine is at a temp above the temp that would turn the SAI on.
If you see a flaw in this thinking, let me know some details.
If this may work, someone please tell me where to find the temp sensor, and if you have the resistance values for cold and hot, let me know.
I'll be happy to post results of this when/if I get it working.
Ron
12-23-2013, 06:35 PM
#4
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Here's my thoughts.
What else reads that temp sensor? Could having a fixed value as opposed to a 'true' value make problems in other areas?
Could this make the car hard to start if you park it outside on a cold morning?
I would do the port cleanout myself if I got the problem. But I'm following with interest too!
What else reads that temp sensor? Could having a fixed value as opposed to a 'true' value make problems in other areas?
Could this make the car hard to start if you park it outside on a cold morning?
I would do the port cleanout myself if I got the problem. But I'm following with interest too!
12-24-2013, 02:25 PM
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JB:
Good question on ease of starting. I don't know of other cars with FI that employ this method, so I'm hopeful starting will not be an issue.
I'm told that cleaning the ports is not a trivial job. I'd like to avoid it completely. I'm told that even if the ports become clogged, it does not affect emissions during normal operation, i.e., the car would pass smog test, even in Calif(!) with clogged SAI ports.
Good question on ease of starting. I don't know of other cars with FI that employ this method, so I'm hopeful starting will not be an issue.
I'm told that cleaning the ports is not a trivial job. I'd like to avoid it completely. I'm told that even if the ports become clogged, it does not affect emissions during normal operation, i.e., the car would pass smog test, even in Calif(!) with clogged SAI ports.
12-24-2013, 03:27 PM
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JB:
I'm told that cleaning the ports is not a trivial job. I'd like to avoid it completely. I'm told that even if the ports become clogged, it does not affect emissions during normal operation, i.e., the car would pass smog test, even in Calif(!) with clogged SAI ports.
I'm told that cleaning the ports is not a trivial job. I'd like to avoid it completely. I'm told that even if the ports become clogged, it does not affect emissions during normal operation, i.e., the car would pass smog test, even in Calif(!) with clogged SAI ports.
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12-25-2013, 07:44 AM
#9
QUOTE:
"On cold start, the fresh air from the secondary air pump creates a very lean condition at the pre cat O2 sensor. The ECU compensates by injecting more fuel resulting in a fuel rich condition in the exhaust after the combustion chamber. That unburned fuel in the exhaust combines with the oxygen from the SAI system and burns thereby heating the catalyst quickly to operating temperature.
In an OBDII car the ECU checks for the presence of the pump by O2 sensor signal as it goes through the stoichiometric, lean, rich, stoichiometric cycle with the SAI."
In other words, the ECU knows the pump is working when it sees the O2 sensor cycle from lean to rich to stoichiometric during the warm up time interval.
The sole purpose of he SAI system is to heat up the exhaust catalytic converter quickly. The cat needs to be hot to function properly.
This is probably why that circuit card that was created to fool the ECU during the SAI period did not really work. The ECU needs to see the O2 sensors cycle to know the pump is delivering air to the exhaust.
"On cold start, the fresh air from the secondary air pump creates a very lean condition at the pre cat O2 sensor. The ECU compensates by injecting more fuel resulting in a fuel rich condition in the exhaust after the combustion chamber. That unburned fuel in the exhaust combines with the oxygen from the SAI system and burns thereby heating the catalyst quickly to operating temperature.
In an OBDII car the ECU checks for the presence of the pump by O2 sensor signal as it goes through the stoichiometric, lean, rich, stoichiometric cycle with the SAI."
In other words, the ECU knows the pump is working when it sees the O2 sensor cycle from lean to rich to stoichiometric during the warm up time interval.
The sole purpose of he SAI system is to heat up the exhaust catalytic converter quickly. The cat needs to be hot to function properly.
This is probably why that circuit card that was created to fool the ECU during the SAI period did not really work. The ECU needs to see the O2 sensors cycle to know the pump is delivering air to the exhaust.
Last edited by Wolfk; 12-25-2013 at 08:06 AM. Reason: clarify
12-25-2013, 07:37 PM
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"John Coffin, aka flying_low, claims he had success; Mike Damen, aka MDamen, said he did not."
I forgot to clarify this: John and Mike used the FET circuit that bypasses the O2 sensors when the SAI pump is running.
I forgot to clarify this: John and Mike used the FET circuit that bypasses the O2 sensors when the SAI pump is running.
12-25-2013, 11:21 PM
#12
"I'm told that even if the ports become clogged, it does not affect emissions during normal operation, i.e., the car would pass smog test, even in Calif(!) with clogged SAI ports."
Not really! Affecting the temp to prevent the SAI tests may help avoid the
0410 fault code, but what about completing the ODBII monitors for
an emissions tests? The SAI test is necessary for completion of ODBII
monitors. If one prevents the test, then one will not pass an emission test
that requires the completion of the monitors (readiness tests).
Read here under 'Porsche 993 Cycle Flag Basics';
http://www.systemsc.com/codes.htm
Not really! Affecting the temp to prevent the SAI tests may help avoid the
0410 fault code, but what about completing the ODBII monitors for
an emissions tests? The SAI test is necessary for completion of ODBII
monitors. If one prevents the test, then one will not pass an emission test
that requires the completion of the monitors (readiness tests).
Read here under 'Porsche 993 Cycle Flag Basics';
http://www.systemsc.com/codes.htm
12-25-2013, 11:45 PM
#13
"I'm told that even if the ports become clogged, it does not affect emissions during normal operation, i.e., the car would pass smog test, even in Calif(!) with clogged SAI ports."
Not really! Affecting the temp to prevent the SAI tests may help avoid the
0410 fault code, but what about completing the ODBII monitors for
an emissions tests? The SAI test is necessary for completion of ODBII
monitors. If one prevents the test, then one will not pass an emission test
that requires the completion of the monitors (readiness tests).
Read here under 'Porsche 993 Cycle Flag Basics';
http://www.systemsc.com/codes.htm
Not really! Affecting the temp to prevent the SAI tests may help avoid the
0410 fault code, but what about completing the ODBII monitors for
an emissions tests? The SAI test is necessary for completion of ODBII
monitors. If one prevents the test, then one will not pass an emission test
that requires the completion of the monitors (readiness tests).
Read here under 'Porsche 993 Cycle Flag Basics';
http://www.systemsc.com/codes.htm
Having just performed the drive cycles to reset my monitors, I was wondering how tricking the SAI system would affect other portions of the system, and I think Loren hit at least one, if not the most important nail, right on the head!
Not knowing the system and its inter-relationships/dependencies; I was hesitatant to ask the question...Thanks for your knowledge and clarification, Loren
12-26-2013, 07:21 AM
#14
[QUOTE=rpaitich;11002679]Wolfk,
Where does that quotation come from? I'd like to learn more.
It came from my own post in the RECAP OF THE SAI thread. I can no longer remember where it originally came from.
I was amazed at how many people bought those SAI bypass circuit cards but with so little feed back on their success or not.
With the SAI thing, I resorted to ensuring the check valve is functioning, periodically pulling exhaust manifolds and performing a quick port flush. Do this couple of times and it becomes pretty easy. My 2c.
Wolfgang
Where does that quotation come from? I'd like to learn more.
It came from my own post in the RECAP OF THE SAI thread. I can no longer remember where it originally came from.
I was amazed at how many people bought those SAI bypass circuit cards but with so little feed back on their success or not.
With the SAI thing, I resorted to ensuring the check valve is functioning, periodically pulling exhaust manifolds and performing a quick port flush. Do this couple of times and it becomes pretty easy. My 2c.
Wolfgang
12-26-2013, 10:23 AM
#15
Rennlist Member
"If one prevents the test, then one will not pass an emission test
that requires the completion of the monitors (readiness tests)."
Maybe!
But in the Great State of Texas, one may pass an emissions test in a 96-98 OBD2 993 with up to two non constant monitoring codes in the not-ready state. Is the law not the same in the peoples republic?
For the record, I am still officially on the port clean out team, but I am also in the pro-enthusiast tinkering camp.
that requires the completion of the monitors (readiness tests)."
Maybe!
But in the Great State of Texas, one may pass an emissions test in a 96-98 OBD2 993 with up to two non constant monitoring codes in the not-ready state. Is the law not the same in the peoples republic? For the record, I am still officially on the port clean out team, but I am also in the pro-enthusiast tinkering camp.