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MAF sensor too sensitive

 
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Old 11-07-2018, 04:37 PM
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Default MAF sensor too sensitive

I know this sounds silly, but I am trying to see what is going on with my car. the issue that I am having is I find that one of two MAF sensors appears to be responding faster than the other (I have dual air boxes). It only seems to affect things when I am getting off of the gas. So, what happens is if I am say trying to follow someone and I am adjusting the gas pedal to maintain distance behind someone (ie, get on the gas some, let off, get on the gas some, get off, ......), if I do this too many times, the check engine light comes on with a P0101 code (ie, MAF sensor problem). When I hook up my code reader to monitor the air flow, I can step on the gas as hard or soft as I want and the car will do what I am after. But, if I get the air flow up a little bit from idle and then let off the gas, it will tell me that right after letting off the gas, the air flow changed too fast, resulting in an error. As long as you only get a limited number of these over time, the car doesn't care. I have replaced both of the MAF sensors (one at a time) and this does not seem to change anything. It does seem to be a bit more sensitive to tripping the CEL if I remove the intake tubes on the upstream side of the air box (ie, the ones that suck the cold air from in front of the radiator).

Anyone experienced something like this? The only thing that I can think of is I have something goofey with a MAF sensor (kinda ruled this one out by swapping around the sensors) or my throttle body has too strong of a spring (resulting in it shutting too fast, never heard of this being a problem, but......). Interested in hearing what others may have experienced.
 
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Old 11-07-2018, 04:38 PM
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If it matters, the engine is a naturally aspirated 5.0L engine in a 2012 XJ.
 
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Old 11-07-2018, 05:03 PM
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Could it be a problem with your engine air filters? On the XK I have heard problems where air filters did not come from the same batch and varied the airflow enough between each side to cause a CEL.
 
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Old 11-07-2018, 08:17 PM
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amcdonal86, I have contemplated that, but it does it with both the paper filters and K&N filters. So, that doesn't seem to be related to the issue. Doing a little bit of reading, it did mention that you could have an air leak on one side and that could cause this problem. But, I would think under heavier acceleration, the leak would be enough to trigger something. I know the MAF sensors are fairly equal in flow at idle because I have disconnected one at a time while watching the air flows and it drops by half regardless which one I pull. May have to play a little bit by revving the engine with one disconnected to see if I can notice a difference.
 
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Old 06-07-2019, 05:33 AM
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Older post but....

I have experience tuning. The MAF sensors input (volts) is referenced against a chart called a "mass airflow transfer function". In hi-po tuning this is one of the first things you adjust. And it has a big effect on throttle response as well as transmission function.

For it to do what you describe its either a vacuum leak between the MAF and intake valve...or.... the MAF output doesn't match the trans function (which would be poor engineering)
 
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Old 06-07-2019, 11:05 AM
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wydopnthrtl, I finally figured out the problem and it completely blew my mind. It turned out to be the throttle body that was the issue. In short, after cleaning the throttle body, all my problems went away. All I can figure out is the butterfly valve was sticking slightly and that was causing a mismatch. But ,I have been driving for about a month now with no further issues. the interesting part is that the throttle body was not that bad and I cleaned it more out of curiosity than anything else.
 
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Old 06-07-2019, 11:38 AM
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Interesting...

I tuned fords and I just don't know anything about Jag tuning.
IMO the TPS ought to see open throttle. But maybe it was just closed enough to read 0% but yet there was a higher air flow rate. (like a vacuum leak would have given)

If your Jag has a wideband then the ECU will be reading those values live. (traditional narrow bands are only used with a much lower weighting. Kinda uses them to learn short term trends more than immediately commanding A/F and timing)

One thing you can do w/the newly cleaned TB is to disconnect the battery and then after re-connect and *before* starting.. floor the throttle twice. This makes the ECU learn TPS full range.
 

Last edited by wydopnthrtl; 06-07-2019 at 11:46 AM.
 
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