Why...how else can you explain it.....

 

You explain it as a fluid flow through a pipe.

 

CRH, post a link to something that I can read that would explain why his MAF is reading more than what it is taking in. I want to learn it. That's what I like do.

 

For sake of the issue at hand.....

Assume that

1 Temp is constant
2 Air consumed by the engine is the same in both models
3 No Venturi effects are occurring at the site of the MAF...constant tube diameters

This leaves us with the same mass of air being rammed into two tubes of differing cross sectional areas....the flow will be different in the different tubes....the small one will have more volume/area than the larger one

Anyone got a problem with that....

Anyone see how the flow could be smaller in the small tube..ie less per unit area???

I don't....so the MAF will read higher flow in the small tube.....ie Higher MAF Voltage

And read smaller Voltage in the larger tube

 

If the volume of air in going through the tubes is the same, the smaller tube will have a lower pressure and the MAF will see less air density. The larger tube will have a higher pressure and the MAF will see more air density. The amount of air going through will be the same(volume).

That's with no venturi effect, ie constant tube sizes. LOOK AT THE ANIMATION OF BERNOULLI'S PRINCIPAL. That's what we're talking about. That animation assumes constant temperature and volume of air.

 

As A goes down V will go up. The smaller tube will have a higher velocity. Density will be constant and the same for both since we're not in the compressible regime (>mach0.3) I tend to agree that Velocity will have a larger affect than stagnation pressure on the cooling of the hotwire.

 

well depending on the vaccum and pressure in the MAF tube, if you went with a larger tube, the flow rates would change. the larger tube would be better at WOT or while in boost, but in low rpms and high vaccuum, the larger tube would have a negative effect on the amount of air entering the engine.

 

Please do. I said that I hate Wikipedia, but if that's correct, then it make perfect sense why the MAF would read higher than what's actually flowing through the pipe.

 

It doesn't...that's the whole argument It should read lower on a larger tube

 

Celronx:

When you use the animation you posted, which is very cool btw, you notice that when you make a large straight tube and then a small straight tube the change in pressure is very small compared to the change in velocity ~10x less.

From this I agree with Dan that velocity will have the largest impact on the accuracy of the MAF hotwire cooling, not the pressure change. This is in line with the assumption at low velocities that gases are incompressible when looking at fluid flow in a pipe.

 

Ahahahahahah. That's funny. OK, I correct myself. In my understading of flowing gasses, it makes perfect sense.

 

if anyone's still interested in talking about the accessport...

how's your cruise afr's? at light throttle, does the afr stay solid, or does it bounce around +/- 1 afr?

 

I finally received my AccessPort today. Yippe!

I will be checking my email 40X per day hoping to receive my maps from Jeff!!!

 

just 40? sounds like you don't really care.

 

I agree, that's 3 pages of talking about this. If someone can describe this to me other than just saying that a bigger pipe will flow more air (I know that) please PM it to me because I really do want to know. Again, I want to know why his MAF sensor would show more air entering the engine than is actually entering it.


On subject, my AP is GREAT. My LTFT is solid under light throttle, but the STFT varies pretty wildly while driving.
At idle they are solid 1 and -1 respectively

 

cel, i can tell you, just give me a minute.

 

how about your afr's on light throttle cruising?

I'm always second guessing if I have a dying engine or not (having had a few cases of detonation in the past), so I guess I look too deeply at many things.

Yesterday and today I noticed my afr's at light cruising was 14.5 and it bounced to 16 afr and back repeatedly - once or twice per second. So I checked the factory o2 sensor and it reported the same thing as my uego wideband. I then checked the MAF airflow and the airflow was constant. My intake is nicely setup, nothing lose. So I am basically looking to see if others see something similar or if I should keep digging. The car is very quick and feels perfectly fine. The bouncing AFR was just worrying me.

 

also I have two maf sensors. So I took the other sensor, cleaned it out with electrical cleaner spray, and installed that this morning. The afr's were bouncing still. So I don't think the maf or intake is causing it. I only started noticing this yesterday, but it might have well have been happening earlier.

 

That's pretty much what I'm seeing. The crusing AFR's for me are about 14.7 up to about 15.7, and they randomly change. I have seen some 16's while driving. I imagine that your's would be a little lower since you're turbo.

 

when i'm not in boost, my car should be pretty much the same as yours

So you're saying your afr bounces too? Not the range, but moving between the two values repeatedly?.

 

I did have one strange thing happen yesterday. I came off a cruise of about 45mph or so in 4th gear. I slowed down to about 20 or so for a 90 deg. bend in the road and hammered it in 2nd and got a weird rattle. It didn't really sound like detonation and it didn't sound like the intake rattle, but it definately came from the engine at about 4k. I didn't have time to check the AFR's before it was gone. It didn't seem to have any bad effects on the car at the time and no problems now.

 

Oh ya, absolutely. Multiple times a second. Just about the time it regesters in my head what the AFR reading says it changes.

 

your AFR's should bounce. the PCM view the engine in standstill mode where it is so fast in making changes, that it has time to read all sensors, compare them to what a chart says based on load, TPS, and rpms, and correct the injector pulse width and ignition timing as the intake air flow fluctuates.

 

Sounds like a ping...... that would be an area that would ping easily (4-5K) if too lean at WOT

 

good. When I tested it today going into boost, the afr's quit bouncing and moved to a solid number. It's still too lean though since installing the CAI. I require a richer map.

Funny since a few days ago I was asking Jeff for a much leaner map (before the CAI)