Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Any one done this?

Ok, first, let me ask that you read the entire thing before you start asking questions, as I will try to be as complete as possible.

All right, here goes.

Let me start with a description of the mod. This mod has typically been called "gutting the MAF" and is mostly common in the Mustang community. It consists of removing the center post of the MAF, and/or further polishing/smoothing/"porting" the MAF sensor flow area.

Many people seem to notice power improvements after doing this mod, which is very possible, but still not a good idea. There are a couple of things you are doing by "gutting the MAF"

1. Removing the center post and/or "porting" the MAF will marginally increase airflow through the MAF. Though this airflow increase is minimal, and has little part in any power increase.

2. You also artificially lean the a/f ratio. This is where the power increase comes from, and also where the real problems lie.

Now a word about the MAF design. Many of the Ford MAF sensors (including the ones used in the contours) are designed with a post running through the center of the flow area. (the post we are talking about removing) Now, this post is designed in as part of the sampling tube (the part that actually measures the air) and the size of the sampling tube (and the way it works) are carefully controlled vs. the rest of the flow area in the MAF. The sampling tube is actually what is called a venturi, in that it accelerates the air through the sampling tube, and is an integral part of the MAF sensors that are designed to have them. This design may not be ideal for ultimate performance, but it does offer many advantages from an OEM perspective (actually, from most any perspective) This design allows decent flow, while still maintaining an accurate measurement of the incoming air charge, even under low flow conditions, ie idle etc.

When the post is removed, you instantly "recalibrate" the sensor to an unknown condition. Typically reading less air than is actually coming in, but to what degree is completely unpredictable. It also reduces the ability of the sensor to even get a worthwhile reading at low flow rates. The reduced ability in low flow conditions can lead to idle and low speed drivability problems, as at least on person has noted in this thread. This part is actually not that big of a deal, because the effect is merely annoying, and doesn't always happen, it's the rest that is really bad.

Now, the bad part. Now that the MAF is "recalibrated" to an unknown state, it will tell the PCM that less air is coming in to the engine than there really is. This will cause the PCM to inject less fuel, creating a lean condition (this lean condition can vary from only a little lean, to really lean) a lean condition that the PCM knows nothing about.

Now before anyone freaks out, let me interject a few things about factory oxygen sensors.
1. Factory oxygen sensors or notoriously inaccurate at anything away from stoich conditions.
2. The factory oxygen sensors are used as an emissions control device for the most part, and are more or less ignored under several important conditions, especially WOT.
Bottom line is, that factory O2 sensors cannot be relied upon for anything other than what the factory PCM mainly uses them for, fine-tuning the a/f for emissions purposes.

Ok, back to the lean condition. This lean condition can cause a myriad of problems, both long-term and short term. The main concern in short term is severe detonation. Severe detonation is pretty noticeable, for even the most non-technical of folks, and it carries the possibility of severe engine damage in a VERY short period of time. Thankfully, this modification rarely causes a severe enough lean condition for severe detonation. Long-term effects are far more subtle, but do carry with them potential for expensive repairs down the road. A persistent lean condition can cause minor detonation (severe detonation conditions w/ a knock sensor, like the SVT turns into a minor detonation condition) which over the long-term can also cause pretty heavy damage to the internal engine components. A lean condition also elevates engine temperatures, particularly the exhaust gas temps. High exhaust gas temps can cause valve problems, and other things like melted cats.

To make a long story short, doing this sort of thing to your MAF causes an undeterminable and uncontrollable lean condition in your engine, which can and does lead to long-term damage. The only way you could legitimately do this, is if you had a flow bench and electrical testing equipment to test and recalibrate the MAF sensor after modification, and I know that none of us has that sort of equipment handy. If you really feel that your particular setup requires more airflow through the MAF, I highly suggest purchasing a quality unit from a reputable aftermarket company that has the equipment and technical expertise to calibrate their MAF sensors properly. I mean really, they aren't all that expensive.

And on a side, but related note, to all those using something like the Apexi S-AFC and SHM Mafterburner, or Pro-M Optimizer, you are effectively doing the same thing that gutting the MAF does, only you have more control over what is going on. I urge you guys, do NOT depend on the factory O2 sensors for your tuning, Ford doesn't, the good aftermarket tuners don't, and neither should you! Do it right, use either a wide-band O2 sensor, or even EGT sensors to develop your tuning, and please make the effort to understand what you are actually doing before you start doing ANY tuning. It isn't that hard, go do some real research before you fool w/ the critical aspects of how your engine runs.