Bad news,well first off i need to say that i got all the emissions crap hooked up so every one doesn't have a cow,anyways when i step on the gas its like its sucking in too much air it bogs down then picks up,and i fixed the maf so its centered in the tube,and when it does get up to speed it down shifts then up then down and up agin,is my intake tube too big its only 3in,any one have an idea why its doing this,its worse insted of better!!!

 

It sounds like the Mass Air Flow isn't calibrated for the tube you just put on. You can't go wild installing a tube that's bigger than the MAF because it's going to detect so much air incoming to the sensor and when it gets to the throttle body and into the engine it's completely different. That'd be my best educated guess.

 

hmm what can i do about that?

 

Get a bigger MAF.

 

You can't just put the sensor in any size tube. It is, as was mentioned earlier by John Gehrig, designed for a given diameter tube. That's why it's mounted in the housing it is.

To fix it, you either need to know exactly what the flow curve is for your new setup and get a custom program for your PCM, or put a real MAF back on it. That's why I asked where your MAF was -- the housing was not there.

MAF stands for "Mass Air Flow". Basically, in order to calculate that you need a cross sectional area of the tube you're in, the velocity of the air flow, and the density of the air. Density is a function of temperature and pressure.

The MAF does all the calculating for you basically. But it already "knows" the cross sectional area of the tube it's in (the one it was designed for) and uses that value to produce a correct output after it uses a hot-wire meter that can measure the velocity and density of the air flowing past.

You changed one of the two biggest variables: cross sectional area. Another big one is velocity but you change that when you change the throttle. The other one (density) doesn't change all that much.

That's why it doesn't work. If you're going to do these sorts of things, do more homework on how things work -- otherwise you have the possibility of making some mods that will do real damage. On this one you got off easy.

 

ditto what has been said. These are not real numbers but will simplify what is going on.
Air flowing through the maf at 50 mph is sending 90 Cubic ft per minute into the engine. Now with the larger maf housing 50 MPH equals 180 cubic ft per minute, because a greater volume of air is moving at the same speed. It's too much for the computer to self adjust to. Smaller housing at the MAF or a retune is in order.

 

To additionally expand on Wayne's example:

At a given engine RPM the engine will try to "pump" more or less the same amount of air regardless of your tube -- but because of the larger diameter of the new tube it can do so with a lower velocity.

So the MAF reports a very low velocity and too little fuel is injected. The O2 sensors report this, but the allowable range of correction is rapidly exceeded and the computer throws you a code.

Your honor, we rest our case.

 

An aftermarket/DIY intake that doesn't perform as expected? That's shocking!

 

well good news i fixed it and it runs good as hell! all i did was cut off the part of the air box where the MAF goes in to stuck it in the tube bolted it together! ill put a new pic up tomorrow.

 

Except, this is not now a MAF works. It measures the MASS of air, in pounds (or equivalent, grams, oz, etc). The EEC then calculates the mass of fuel to add to achieve the right mixture, according the fuel map. MAF sensors are superior to 80's style MAP (absolute pressure) sensors, because they don't need correction for temp or ambient pressure.

You only need a bigger diameter, if the pounds of air the engine ingests is off the scale of the existing MAF.

 

If you read the posts, I already explained calculating mass air flow.

MAF sensors inherently compensate for density variation because of the way they work. So velocity, density and cross sectional area are still the controlling variables in measuring the mass of air.

Perhaps you should read ALL the posts, lol.

You aren't measuring properly if you simply change the diameter without changing the scaling of the sensor. Your last statement is entirely wrong without compensation. Simply changing tube diameter makes the problem WORSE by throwing off the entire range scale, which is what happened in the case of this homemade intake.

 

so what happens if you put a snorkel onto a stock airbox?