ECU Question, how often does it check for problems?

Hypothetical question: Let�s say my MAF is dead or dying, and I get a cel to warn me about it. I am lazy so I unhook the battery to reset the cel. How long does it take for the ecu to perform another test to see the MAF is bad and throw another cel? Is there a set time or mileage that the ecu waits to perform another �systems check� or would it be instantaneous? How or when does the ecu know when to issue a cel for a minor issue? Just curious. Thanks Drew

When using my durametric tester it just takes a 20-30 sec to throw another CEL after resetting the CELL, but if the problem part is marginal it may take it alittle longer. I have not seen a marginal MAF it either works or does not.

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How do you like the Durametric software? I looked at their website and it looks quite in depth. Which package did you go with?

The original MAF on my car was marginal. It began tripping P1123 codes in certain driving patterns (e.g., interstate cruise followed by a stop on an exit ramp) and then started adding P1125 to this code, and then began generating more frequent instances of both those codes in a wider variety of driving patterns. Replacing the MAF solved the problem. To the OP's question: the DME is constantly evaluating everything it sees and will generate a code if something is out of spec.

"how often does it check for problems?" Constantly - depending on the conditions it sets a pending code or sets a code and turns on the CEL. Not all fault codes turn on a CEL.

What are the consequences of having a bad MAF?

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Why don't you just share with the forum what your problem is instead of speaking in hypotheticals, going about it in a rather circuitous manner? This may help you find a quicker resolution to the problem you're having with the car.

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I am not having issues. I am thinking about buying a K&N filter(not the CAI) and want to be prepared encase it breaks the MAF due to over oiling. I have read so much contradicting info on this filter and the only ECU experience I have is on my Subaru. So to gain some knowledge on the Porsche ECU and to avoid posting another "CAI Thread" I posted this thread. Thanks for your concern.

Knowing that even the K&N intake doesn't do much for power and there's much discussion around the pains of oiling it (over/under), why in the hell would you go for the aftermarket filter when there's the good OEM filter available?

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If you're not going to address the questions I posted, why are you responding to this thread?

Because I can and the question I'm asking of you certainly is related to the original question. Having a bad day?

Sorry for the digression, back to the original question. What are the consequences/symptoms of having a bad MAF? What exactly does the MAF do? I mean I know it measures the amount of air entering the engine and the ecu uses that info to change the fuel mixture. What else does the car rely on the MAF for? Thanks Drew

Don't forget who had your back even after you internet stalked me, don't know where all this sensitivity is coming from, but do what you do https://rennlist.com/forums/showthre...=407966&page=4

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Air mass and intake charge temperature are the only things the MAF measures. When either of those things are not properly measured, the engine will not run correctly. You may notice hard starting, surging under partial or full throttle, poor performance, rough or erratic idle, stalling, or other symptoms, depending on the failure mode.

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....depending on failure mode? I am not sure I follow. The MAF can have more than one failure point? Thanks for the reply by the way.

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from harness CEL may not be set for minutes maybe longer if my memory of when I did htis some years ago is accurate. Even if MAF acting up, it may not act up right after engine start. It may take time to start acting up and it may upon an engine shut down even if followed by an almost immediate engine restart may self correct, temporarily. The ECU constantly moitors its various sensor population for problems but some and dare I say most problems aren't clear failures, but readings that drift out the normal range over time. For instance say the engine has an air leak . At idle the air leak admits considerable air that is not measured by the MAF and the engine controller will adjust for the air leak by adding extra fuel. If this condition continues too long ECU will cross a threshold that esssentially says it has gone too far to the rich end of its adjustment range and this will cause a CEL. However, if the idling state doesn't last long at higher engine speeds the amount of air from the leak drops to insignifiance compared to the huge amount of air being admitted by the throttle. So the engine controller may undo its enrichen action. And the MAF doesn't have to be the source of the problem. Sincerely, Macster.

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OK, I think I get what you said. So basically the ecu must "learn" that the maf is bad or faulty and adjust accordingly, just like the ecu will "learn" that you have installed a new intake or exhaust, and this "learning" may take some time. If I read this right then its not much different from the Subaru ecu. Depending on how you drive the WRX, you can gain or lose up to +/- 20hp after an ecu reset.

To the OP, disconnect your MAF harness and drive around, this is what it will do and answer your question. It takes 4 driving cycles to reset the CEL, or you can start and stop the motor 4 times and it will do the same.

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Thats kinda weird. Exactly 4? Good to know though. Thanks!

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I ordered the cheapest one which is made for porsche and is used for the private owner and not the pricer one for businesses which can be used for multiple cars . If you have some knowledge of cars then this is priceless. As then engine ages and you can save a base file and compare to later files to see how you car is doing or just use to find out that your O2 sensor and MAF are bad etc and then just replace and reset system. I have some EXCEL data sheets from the durametric at this link: http://www.webbspot.com/Porsche/fvdvideo.html or this thread for more on MAF workings: https://rennlist.com/forums/showthre...percharger+fvd

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Thanks for the info. I remember following your thread, sorry about your engine. Any updates?

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Called porsche in scottsdale today and they want $10,330 for rebuilt and yet suncoast is 5K cheaper, so to say the least I was upset on the price difference between dealers. I was hoping for same cost and save on shipping charges of core and new engine. At a loss now.

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monitors inputs from a variety of sensors and from this knows the air/fuel mixture is ok the converters are working the o2 sensors are working/etc, sort of... Unless a sensor fails outright or in such a way the failure is readily apparent, the ECU can only adapt until it succeeds or fails by going outside of its adaptability limits. For instance if the coolant sensor is faulty, the ECU may believe the engine's colder than it really is and feed the engine a richer than normal mixture. However, it will know by the oxygen levels in the exhaust that something's not right and possibly override the enrichening triggered by the erroneous coolant sensor input and go leaner until the O2 sensors are reading within acceptable limits. Only if the coolant sensor reads -40 might the ECU then have to go too far towards its leaner adjustment that a CEL would be set. It might even report O2 sensor diagnostic error when in fact the coolant sensor is the real problem. Anyhow, the ECU will know something's amiss and of course attempt to adapt. If it is successful, no one is the wiser. If coolant sensor so far gone, or gets worse, or varies its misbehavior (probably the most common case) the ECU will swing back and forth as it tries to compensate. Same applies to the MAF. The ECU has to have some room to adjust/adapt to deal with variations in engines and engine components, driving styles, climatic conditions, fuel differences, etc. I do not know what driving cycle or cycles are required for the ECU to relearn. Maybe not much, but since the ECU must deal with a variety of operating conditions, engine speeds, cold/warm/hot starts, etc., a goodly mix of driving may be necessary. Even more difficult is if the check engine light is extinquished and its associated error code is erased this resets all readiness monitor tests to incomplete. These require some effort to see them all set to complete. Engine restarts are not sufficient. For your Subie, chances are you could have gained the HP (or at least the sensation of additional HP) by making a pass or two down the quarter mile. Generally for those that drag race modern cars, the first and sometimes 2nd pass is to give the ECU the chance to 'relearn' a new set of fueling/ignition parameters under the driving conditions (quarter mile blasts) the car is being exposed to. (One just hopes one doesn't undo all that learning by sedate driving back to pits and lumbering around in car visiting other attendees until one's next pass is up.) And when the car is driven from the track back home the ECU unlearns all it learned at the track and learns all it needs to learn for the street. If you're not at the track and couple of hard acceleration runs up through the gears can suffice. If the engine picks up more performance with a ECU reset, then somethings amiss (I would hazard a guess) which is causing it to adjust at the expense of engine performance for possibly emissions compliance or converter safety. Sincerely, Macster.

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WOW, thanks. Great explanation!