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Old 10-20-2009, 11:39 AM   #1
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Quote:
Originally Posted by stateofidleness
sounds logical. i'll give that a try! googling some more and I keep coming across people stating the MAF.. yada yada... When I looked at mine, it looked BRAND NEW! Does a failed/failing MAF have any visible signs of failure or do they just "not work" after some point? also, during reinstall of it, could that have introduced a vacuum leak where it connects? I've read that if you get BOTH codes, it is most likely the MAF, one code and it means something is wrong on that side... (might go along with the 02 sensor theory, but i haven't had ANY indicators up to this point that an O2 was on the way out)

Also, and this may be far-fetched, but I have been using 92 octane (Valero) gas for the past few weeks only because my Shell (only 93 octane in town) is not on my daily route. Could this cause some kind of lean issue as well?

Would filling up with 93 and maybe some additive do anything for me?
Well, I just changed my MAF on Friday.
The old one was just as clean as the new one I put on.

In fact, when using the Durametrics program, I was getting the same Air Flow readings and Air temp readings with the new sensor as the old sensor. The only difference was in the Voltage reading, which was 1 volt constantly across the rpm range, while the new sensor increases as the rpms rise.

As for the gas, it would affect both banks, not just one.

If you wanted to get technical, we could break down the different fuel systems piece by piece:

MAF sensor - tells computer amount of air being ingested by the entire engine (doesn't differentiate between cylinder banks)

Air temp sensor (in MAF) - Tells computer temp of air being ingested by the entire engine (doesn't differentiate between cylinder banks)

Throttle body - Controls amount of air ingested by entire engine (doesn't differentiate between cylinder banks)

Vario-cam valve timing - Adjusts opening and closing of valves in relation to crankshaft position and engine speed. Both banks are activated at the same time at certain rpm points, but controls just an individual cylinder head. Should not affect fuel mixture in any way.

Fuel injectors - Each one is assigned to a cylinder. If one was sticking open, could cause a bank of O2 sensors to report an error, but would also be associated with a cylinder misfire, and bad engine performance. (opposite of what you are experiencing)

Spark plugs and Ignition coil sticks - One per cylinder. If one is failed, cylinder misfire, bad engine performance, and too rich of a mixture would be reported on that bank of cylinders. (opposite of what you are experiencing)

Cat converters - Two per bank - the second set of O2 sensors will be able to point out if the primary cat converter is not scrubbing the exhaust optimally.

O2 sensors - Two per bank. First set of O2 sensors controls the mixture as the computer uses its signal to determine the Oxygen content of the exhaust stream. Second set is primarily used to check the efficiency of the cat convertor, and determine if it has fully warmed up, based on the differences between the two sensors in that bank.

The O2 sensor swap is probably your best bet for quick and easy, with no cost involved.

BC.
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Old 10-20-2009, 12:01 PM   #2
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wow great info!

ill try to swap them when i get home tonight.

any thoughts on what the "thunking" sound is on cold starts? like hitting the side of an empty 50 gallon drum with a hammer.. or a low steel drum.. i hear it randomly about 3 times on cold (not driven in 10+ hrs) starts, if i turn car off and then restart, it's fine, but idles at 1k steady. When i put it in R, it goes down to 500 like normal.
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Old 10-20-2009, 03:47 PM   #3
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Quote:
Originally Posted by stateofidleness
wow great info!

ill try to swap them when i get home tonight.

any thoughts on what the "thunking" sound is on cold starts? like hitting the side of an empty 50 gallon drum with a hammer.. or a low steel drum.. i hear it randomly about 3 times on cold (not driven in 10+ hrs) starts, if i turn car off and then restart, it's fine, but idles at 1k steady. When i put it in R, it goes down to 500 like normal.
That I don't know.
I would have to hear the noise from the cabin to hazard a decent guess.

Personally, I would check the condition of the engine mount first, because if it is really bad, the engine could be flopping around when the engine cranks to life. That's easy to do just by removing the engine cover, and driving up and down the street in first gear, flooring the car to see how much the engine moves.

Do you park on a slight incline of decline when it makes the noise?

BC.
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Old 10-20-2009, 05:29 PM   #4
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flat surface when parked and Tiptronic trans. I might try cold-starting it with the engine cover off and viewing it topside to see if I can better place the source of the noise. Wouldn't I hear the noise on warm starts too though if it was the engine mounts?

seen a lot of posts recently about engine mounts so I was getting curious about mine.. I might try to get a "look" at them if it is even possible without dismantling stuff.
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Old 10-21-2009, 07:58 AM   #5
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Again, I had more or less the same problems. The new O2 sensors fixed everything. I actually could not believe how much the computer relies on their readings for the air fuel mixture. If they are bad they also throw other electronics out and cause multiple error codes.

Try changing them and see what happens.
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Old 11-19-2009, 12:08 PM   #6
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it's back!

car running fine for quite some time (since last post) with no CEL (only thing is it seems like the idle might be high at startup, 1k)

driving to school like normal today and raced a yellow light
when i stepped on it (read, accelerated real fast) about a minute later, the solid CEL came on... I haven't had a chance to read the codes yet, but I will when I get out of class

again, I started scouring the net for symptoms.. I have a pre-existing exhaust leak that is "minor" but should be noted. Is there any way to "bench test" an MAF? mine looked brand new when taken out to inspect, so I'd hate to replace a good one..

also, my mechanic has offered to smoke the exhaust system and attempt to fix the leak.. what does it cost to have this 'smoking' done?

thanks!

EDIT: I should note that the AOS was replaced since last post as well. Wasn't sure if I mentioned it. No smoke is present now.

Last edited by stateofidleness; 11-19-2009 at 12:10 PM.
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