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Old 11-05-2008, 08:29 AM   #1
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Mass Air Reads Lean, Check Engine Light is On

LONG TIME NO TALK EVERYBODY. Well I have a question for anybody that wants to help. I just fabricated my OWN Cold Air Intake . I didn't have $249.99 to buy one so I figured I would be awesome and make my own. I did a superb job and when I get a chance I will post pictures for anyone to drool at lol. My question is, after I installed this one of a kind CAI my check engine light came on, so my first thought was to check it with a computer and see what the reading was for. It told me my air flow was too lean (too much air to gas.) so I went to auto zone to reset the Mass Air Flow sensor and they did . I drove for about 30min and the light came back on. I took it back just to be safe and it was the same thing . He reset it again but it came back on. HOW DO I GET IT TO REGISTER THAT THERE IS A NEW FILTER SYSTEM SO IT WILL MAKE THE RIGHT MIXTURE FOR AIR AND GAS?????? I hope anyone here can help me because I have completely lost hope and figured I would just drive it as is. Oh and I tinted my windows this last weekend!!!!! YAY ME!! LOL sorry I haven't been on lately I've been really busy!!


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Old 11-05-2008, 10:09 AM   #2
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I kinda did the same thing before I got my CAI. My check engine light came on once and my friend at work reset it. The only thing I could suggest would be to un hook your battrie for about 15 min. That will reset your ECU to stock...but I can't promise it will not come back. The problem isn't your MAF sensor the problem is your AFR (air to fule) is off now and your MAF sensor is throwing a flag up. The sensor is doing what it's supose to...no need to reset it. I would try maybe a smaller filter...did you check all the band clamps to see if your leaking air...or in this case sucking it in.....let me know if this helps you I would also suggest posting in the Duratec section I hink you'd get a bit more feed back from them.
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Old 11-05-2008, 11:14 AM   #3
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You will also want to make sure that you MAF is not upside down wil cause the same style problem (that is if you took it out) does the car run fine or is it hesitating on accel? I found that out when I put mine in up side down.
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Old 11-05-2008, 01:58 PM   #4
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You indeed can get to much air into the TB. The ECU will adjust the a/f ratio as far as it can and then throw the CEL when it can't compensate any further.

My Steeda SRI still has the insert installed which restricts the air-flow. Steeda warns not to remove the insert without a tune or the engine will run "dangerously" lean.

Here's more than you probably want to read from my 08' manual.

The fuel system monitor is an on-board strategy designed to monitor the fuel control system. The fuel control system uses fuel trim tables stored in the powertrain control module (PCM) keep alive memory (KAM) to compensate for the variability that occurs in fuel system components due to normal wear and aging. Fuel trim tables are based on air mass. During closed-loop fuel control, the fuel trim strategy learns the corrections needed to correct a biased rich or lean fuel system. The correction is stored in the fuel trim tables. The fuel trim has 2 means of adapting: long term fuel trim and a short term fuel trim. Refer to Powertrain Control Software, Fuel Trim in this section. Long term fuel trim relies on the fuel trim tables and short term fuel trim refers to the desired air/fuel ratio parameter called LAMBSE. LAMBSE is calculated by the PCM from the heated oxygen sensor (HO2S) inputs and helps maintain a 14.7:1 air/fuel ratio during closed-loop operation. Short term fuel trim and long term fuel trim work together. If the HO2S indicates the engine is running rich, the PCM corrects the rich condition by moving the short term fuel trim into the negative range, less fuel to correct for a rich combustion. If after a certain amount of time the short term fuel trim is still compensating for a rich condition, the PCM learns this and moves the long term fuel trim into the negative range to compensate and allow the short term fuel trim to return to a value near 0%. Inputs from the engine coolant temperature (ECT) or cylinder head temperature (CHT), intake air temperature (IAT), mass air flow (MAF) sensors are required to activate the fuel trim system, which in turn activates the fuel system monitor. Once activated, the fuel system monitor looks for the fuel trim tables to reach the adaptive clip (adaptive limit) and LAMBSE to exceed a calibrated limit. The fuel system monitor stores the appropriate DTC when a concern is detected as described below.


1. The HO2S detects the presence of oxygen in the exhaust and provides the PCM with feedback indicating air/fuel ratio.
2. A correction factor is added to the fuel injector pulse width calculation and the mass air flow calculation, according to the long and short term fuel trims as needed to compensate for variations in the fuel system.
3. When deviation in the LAMBSE parameter increases, air/fuel control suffers and emissions increase. When LAMBSE exceeds a calibrated limit and the fuel trim table has clipped, the fuel system monitor sets a DTC as follows: The DTCs associated with the monitor detecting a lean shift in fuel system operation are P0171 (Bank 1) and P0174 (Bank 2). The DTCs associated with the monitor detecting a rich shift in fuel system operation are P0172 (Bank 1) and P0175 (Bank 2).
4. The MIL is activated after a concern is detected on 2 consecutive drive cycles.
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Old 11-05-2008, 02:42 PM   #5
 
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i had the check light to and my car would like stutter it was do to maf being in wrong cause i had messed with it flipped it back and took off the neg battery post it was just like new
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Old 11-05-2008, 07:17 PM   #6
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Yep, 99% of the time when someone installs a CAI/SRI and there's a CEL it is caused by the MAF being installed wrong.

I just wanted to point out that it is possible to get too much air also. Which I would think would be easier to do with a homemade unit rather than a commercial one.
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Old 11-05-2008, 08:51 PM   #7
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Moved to FORD FOCUS TECHNICAL CHAT.
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Old 11-05-2008, 09:31 PM   #8
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pictures could possibly help on this one.
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Old 11-06-2008, 01:22 AM   #9
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Well at first like a I put the MAF in completely wrong, it was turned sideways completely blocking the air from coming into the engine So once I figured out what I did wrong I checked the old intake tube where the MAF was located to see what way the MAF was installed originally. When I determined that I had to rotate it just right to get the right position of it it seemed to be working right. The only different change I see in my engine other than a little gain in horsepower and noise is when it starts to drop down RPM from driving (say I put in clutch to stop) It dips down a little lower than it use to almost sounding like it wants to die but it just jumps right back where it should be.

PS I will try to post pics tomorrow so I can give you guys a little more advantage to the situation. Thanks everybody for your help!!!!
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Old 11-06-2008, 05:29 AM   #10
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^^ Do an A/F reset on the computer.
1) drive car until engine is warm
2) remove neg terminal from battery for 10 mins or so
3) connect terminal, and start engine. DO NOT touch accel, allow engine to idle.
4) time engine idle for 6 mins after engine drops out of start-up mode and idle drops.


You will notice fluctuations in the idle during this time if you have a tach. Once it finishes, you'll see the idle drop slightly and even out.

These are all little tests that your ECU will do while you drive the car to reset the fuel trim and curve, doing the first one just reduces the time it takes for the computer to reset itself.
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