MAF Sensor

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Having hesitation and stumbling problems with my 2007 Nissan Spec-V with 25,000 miles, no check engine light, took it to the dealer and they couldn't find any problems or codes stored and had nothing else to offer, I read that the MAF sensor can cause drivability issues without throwing a code/check engine light so I took it out and cleaned it with CRC MAF cleaner, it looked clean to begin with and it didn't solve the problem. I'd like to rule out the MAF sensor once and for all and I also read that if you disconnect it and drive the car and the problem goes away it indicates a faulty MAF, and if the problem persists it rules out the MAF as the cause. Is that true? Thanks!
 
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Disconnecting it might throw it into "limp home" mode and it would run even worse--but different. I would try disconnecting the battery for as few minutes and go through the auto reprogramming-while-driving sequence (if any) listed in the owners manual. Don't forget your radio codes if you do that. See what the manual says about battery disconnection. Sometimes I've had the above help when the 'puter just gets glitchy for some reason. But I'm not a mechanic.
 

MADMIKE

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Thanks river rat, that sounds like a good idea, it's certainly easy enough to do, can I just disconnect the negative terminal or do I need to do both? Thanks!
 
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You know what stinks, if got a problem and it doesn't throw a code the dealer can't do jack. Got an 03 2.5 Altima that would occasionally hiccup, felt like a momentary cut out, on the highway. Scary. Luckily it finally did throw a code. But, I tried the same thing you did, cleaning the MAF sensor first, not difficult. Didn't help, so I finally bit the bullet, took it to the dealer, he read the code which said I needed a throttle actuator control. They were going to want some ridiclous price, to which I said, this is a part that should never go bad, especially not with only 52k. They charged me 100 bucks and fixed it under goodwill. This is apparently a common problem because the part was a remanufactured part. Two suggestions for possible cause of your issue, crank angle sensor and/or camshaft postion sensor. These are two noted issues with some Nissans, might relate to you. They replaced my crank angle sensor when they did the throttle actuator control. Also you can go to Nissan boards and/or google it to check for like problems.
 

MADMIKE

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I agree--I thought all this computerization and all these electronics and sensors were supposed to make diagnostics easier than ever! I was surpised when they told me everything checked out and there was nothing more they could do unless I got a check engine light.
 
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 Originally Posted By: MADMIKE
I agree--I thought all this computerization and all these electronics and sensors were supposed to make diagnostics easier than ever! I was surpised when they told me everything checked out and there was nothing more they could do unless I got a check engine light.
The mechanics just got dummer as a result. Most, even dealerships are nothing more than code readers and parts replacers. If there's no code they can't help you. I had to hold the tech's hand and walk him though his own diagnostics when I took the Murano in for a pinging problem. He tried the old "it doesn't have any codes". In my GN I know that it typically pulls 6gm/sec through the MAF at hot idle. I've had that number change and I got a hesitation with no codes. After seeing that it only pulled half the normal airflow I replaced the MAF and all was fine. The moral of the story is it doesn't have to set a code to have a problem and the techs aren't educated enough to troubleshoot. You can unplug it, if the hesitation goes away I would say it's the MAF. Keep in mind it won't run perfect, but it will be different.
 

MADMIKE

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Thanks Grand National, I agree, without a code the guy seemed genuinely not to have any ideas on his own. First I think I'll try disconnecting the negative battery terminal for a couple of hours and let the computer "re-learn" the fuel trim, etc over a few drive cycles and see if that helps. If not, then I'll disconnect the MAF and see what that does. In the end I'm afraid I may have to just replace the MAF at my expense and see if that's it but I hate to do that as it's expensive (around $260) and It's just a guess.
 

MADMIKE

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One other thing I forgot to mention, don't know if it's of any significance or provides a clue, it doesn't start hesitating and stumbling until I've been driving about 15 minutes, and if I shut the engine off for 5 minutes and go into a store or something like that when I restart it the problem is gone for a while and it runs great, like the engine "resets" itself or something as a result of shutting it off and restarting it. Odd.
 
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I wish I were more educated on your particular car. It may be that when it goes into closed loop it gets the hesitation which would likely be an 02 sensor issue.
 
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 Originally Posted By: BuickGN
 Originally Posted By: MADMIKE
I agree--I thought all this computerization and all these electronics and sensors were supposed to make diagnostics easier than ever! I was surpised when they told me everything checked out and there was nothing more they could do unless I got a check engine light.
The mechanics just got dummer as a result. Most, even dealerships are nothing more than code readers and parts replacers.
Yes. Usually the dealership shop foreman (if he's good) knows the fix before the tech gets the vehicle. If the tech can't figure it out, they call an 800 number to talk to the factory techs. Getting back to the MAF, I was traveling and my Aerostar threw about 8 codes at once and it was almost undriveable. Matter of fact, the guy at Auto zone told me that he had never seen so many codes from one vehicle. About 6 of them were really crazy codes and really none of them were related to each other. None of the codes pointed to the MAF. I took some aerosol cleaner and it didn't help. On a guess, I replaced it and it fixed my problems. Sometimes OBD1 is a little vague on the codes.
 
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Could be egr. I think that system only starts doing its thing after certain other tests have run on the engine. The trick to understanding all this stuff is actually knowing how it works(*). Sometimes the factory manual says, sometimes it doesn't. If the tech hasn't taken the time to understand the system as a whole, he's just a code + part = fix. Like so many other things, it's all in the documentation. (*) Like in this case, it might have to get up to temperature again, run some o2 sanity checks, run some other tests, and then if the engine is running correctly, it will start doing egr. Just guessing, but half-way educated.
 
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 Originally Posted By: BuickGN
The mechanics just got dummer as a result. Most, even dealerships are nothing more than code readers and parts replacers.
Some shop manuals don't even give any specs for the sensor outputs. It's plug a scantool in, if there's no code, sensor good, code, sensor bad. Extremely dumbed down. The shop manual for my Saab 93 is very good in this regard, it gives pretty detailed information about the sensor outputs so you can test them with a multimeter or an oscilloscope. How many dealerships still have an oscilloscope...if they ever did?
 
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The barometric pressure sensor on Ford vehicles with a MAF (the newer ones, anyway) is software that uses MAF readings to calculate the barometric pressure. Apparently, if the calculated barometric pressure readings are wrong that means the MAF is bad.
 
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swalve is right, you sometimes run into chicken and egg situations. Some cars don't run the OBDII I/M monitors b/c of falsely low coolant temp... which starts a chain reaction... Lets say for grins you have low fuel pressure and it's running lean, you disco the MAF and it's running a rich failsafe that is now "better"... Best thing is to look at the raw data, a $50 ebay scan tool will show you MAF flow.
 
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