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Old 12-12-2013, 03:56 PM   #1
Ravel36
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I have an issue with my MAF sensor returning low readings to the ECU. My tuner has been working for weeks now with me trying to get to the bottom of this. I have swapped the MAF sensor with one from another car that has about 60k on it. My current sensor has 120k. Everything else seems to be fine. I have performed a smoke leak test and there was a leak at the stock OEM post MAF hose, but I fixed that by replacing it with a COBB Post MAF hose. It still shows low readings. It has been cleaned using MAF sensor cleaner. The readings are approx. 100 g/s off. For instance right now it is reading 4.14v @190 g/s. It should be reading a lot higher. Any thoughts on what we could be missing?
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Last edited by Ravel36; 12-12-2013 at 04:04 PM.
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Old 12-12-2013, 03:58 PM   #2
Ravel36
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04 sti turbo back exhaust, 1 step colder ngk, cobb sri. Perrin EBCS, AEM UEGO Wideband, 255lph Walbro.
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Old 12-12-2013, 05:42 PM   #3
OldManRed04
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Quote:
Originally Posted by Ravel36 View Post
04 sti turbo back exhaust, 1 step colder ngk, cobb sri. Perrin EBCS, AEM UEGO Wideband, 255lph Walbro.
While I will agree 190g/s seems low, I don't think the setup you listed will show 290g/s. 260-270 perhaps.
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Old 12-12-2013, 06:02 PM   #4
Ravel36
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Yea I don't know, but right now we have it at stock boost. Does that sound like a bad MAF? I am considering spending the 200 bucks to get a new one.
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Old 12-12-2013, 06:10 PM   #5
OldManRed04
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Quote:
Originally Posted by Ravel36 View Post
Yea I don't know, but right now we have it at stock boost. Does that sound like a bad MAF? I am considering spending the 200 bucks to get a new one.
I'd need to look at the stock map scaling.
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Old 12-12-2013, 06:21 PM   #6
Ravel36
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I am not sure if the mapping that I have is stock or not, and I don't have the original oem map. The tune is not stock, but I don't know if the MAF scaling or map scaling is stock.
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Old 12-12-2013, 06:22 PM   #7
OldManRed04
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Quote:
Originally Posted by Ravel36 View Post
I am not sure if the mapping that I have is stock or not, and I don't have the original oem map. The tune is not stock, but I don't know if the MAF scaling or map scaling is stock.
Well without knowing what maf scaling you are using and knowing that it's not stock, I'd say you need to start there. It could be rescaled and doing exactly as it's told.

Do you have the ability to flash the ecu?
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Old 12-12-2013, 06:32 PM   #8
Ravel36
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I do, the tuner, who in my opinion seems to be pretty competent, stated that it's not the scaling that's the concern. We have been tuning, so I take logs and email the, to him, he sends me a revised ecu map and I reflash.
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Old 12-12-2013, 07:35 PM   #9
OldManRed04
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Quote:
Originally Posted by Ravel36 View Post
I do, the tuner, who in my opinion seems to be pretty competent, stated that it's not the scaling that's the concern. We have been tuning, so I take logs and email the, to him, he sends me a revised ecu map and I reflash.
Well I show 4.1volts would be right around 190g/s. On a stock maf scale. Perhaps you have a pre turbo leak? Somewhere post maf...
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Old 12-12-2013, 07:48 PM   #10
Ravel36
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No leak. I had that checked. We'll not pressurized, but with a smoke machine.

If the readings I have match what you have for a stock scale, then it seems to me that there is no issues. Your thoughts?
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Old 12-12-2013, 07:51 PM   #11
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you sure you don't have a map that has the "half maf hack?"

basically to get the maf to support higher g/s someone somewhere figured out to scale the maf and injectors differently to get the maf to support more power on the 16bit ecus. In turn the maf readings will appear lower than they really are.
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Old 12-12-2013, 08:06 PM   #12
Ravel36
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How do I tell if it is a half MAF? My ecu is 32 bit
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Old 12-12-2013, 09:33 PM   #13
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Quote:
Originally Posted by Ravel36 View Post
How do I tell if it is a half MAF? My ecu is 32 bit
I think the person who posted the half MAF comment missed that you had an 04 STI. All the STI's had 32 bit ECU's which are scaled to 348g/s stock. Of course the CEL limit is 300g/s stock, but that's easy to change. The 16 bit WRX ecu's were limited to 292. Im not too familiar with the whole "half MAF" deal, but I would assume you would need to run a larger diameter MAF housing and then rescale the MAF to where a lower voltage indicated are higher airflow value. The ECU uses the airflow measured from the MAF sensor to calculate injector pulsewidth needed to hit the target AFR in your maps. Anyways, I digress. I am pretty sure this is not your problem.

G/s flow is generally accepted as a rough calculation for horsepower to the wheels. A stock STI in good health has been shown to dyno typically in the 240-255ish range. That being said, stock I would be looking for flow figures in this range. If your only showing 190 on a stage 2 STI, I would say for sure something is "wrong".
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Old 12-12-2013, 09:55 PM   #14
Ravel36
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Ok thanks for the input. I think I will go ahead and by a new MAF and see what happens, before I do so, does anyone happen to know how to test a MAF sensor to see if it is good or bad.
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Old 12-12-2013, 10:09 PM   #15
bluemax189
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Quote:
Originally Posted by OldManRed04 View Post
I think the person who posted the half MAF comment missed that you had an 04 STI. All the STI's had 32 bit ECU's which are scaled to 348g/s stock. Of course the CEL limit is 300g/s stock, but that's easy to change. The 16 bit WRX ecu's were limited to 292. Im not too familiar with the whole "half MAF" deal, but I would assume you would need to run a larger diameter MAF housing and then rescale the MAF to where a lower voltage indicated are higher airflow value. The ECU uses the airflow measured from the MAF sensor to calculate injector pulsewidth needed to hit the target AFR in your maps. Anyways, I digress. I am pretty sure this is not your problem.

G/s flow is generally accepted as a rough calculation for horsepower to the wheels. A stock STI in good health has been shown to dyno typically in the 240-255ish range. That being said, stock I would be looking for flow figures in this range. If your only showing 190 on a stage 2 STI, I would say for sure something is "wrong".
that I did miss sorry.
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Old 12-12-2013, 10:10 PM   #16
bluemax189
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Quote:
Originally Posted by Ravel36 View Post
Ok thanks for the input. I think I will go ahead and by a new MAF and see what happens, before I do so, does anyone happen to know how to test a MAF sensor to see if it is good or bad.
I'd find a local guy(look in your areas' sub forum) with a known working maf and see if they'd can swap their maf in temporarily and see if you have the same issues.
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