It's official....MAF ends are the Devil.
 

For those of you that followed my other thread where I was getting STFTs of -40+, here is the latest update. I re-installed my stock MAF ends (that's why you buy ported ends and don't port your stockers) and used a MAF table from a 2000 Holden and magically all my problems went away. Apparently my fueling was all F-ed up because of the ends. It was so bad, that yesterday when I started my car the LTFTs actually put my O2 sensor readings at idle to 1100mv+. It also caused it to run so rich that I threw a P0161 code because I drove off before I came out of open loop and the PCM thought the O2 sensor did not heat up. Totally weak. So the lesson of the day is; no matter how much tuning you do, MAF ends cannot be tuned for. The readings are not reliable or steady enough at cruise and low rpms. Weak. It's a shame. The MAF ends are a work of art. Soooo....85mm MAF will be my next step.

I got ported MAF ends. I was going to put it on the flow bench and measure the freq vs flow. And put this data in the the MAF table. Will this work?

I expect you will be able to flow it just fine. Just don't expect your readings to be reliable in anything other than a test environment. You forget also, the MAF readings depend a LOT on the shape of your intake tract. You can find out how much a ported MAF will flow, but don't expect to gather any data you can use to build a new MAF table with.

I think that the intake in the f-body-LS1 is somewhat strait. Do you think adding a throttle body to the set up and pulling air thru it will help? If not why?

Thanks for the help

You would have to mimic the complete intake tract, from the FTRA (if installed) to the throttle body ... including the lid, filter and couplers.

Great info to know Another_User, sorry you had to be the guinea pig.

Yeah...it happens. It sucks because the ends are so well made. I would love to use them, but it doesn't look like a good idea. It is funny that somebody mentioned the throttle body. I have been putting a lot of thought into the intake system on these cars, and I noticed something else that is hurting us. The TB is really close behind the MAF. REALLY close. So, even if your intake is perfectly straight you are screwed. Because the TB is going to pull air:
a) from the IAC at the top
b) above and below the blade at less than WOT

So with a screenless MAF it greatly increases the amount of unmetered air because airflow will be biased above and below the sensors. Just another wrench to throw into the works for you guys to consider. It would probably be easier to calibrate if there was a 90 degree angle before the TB because it would likely yield more predictable results (always biased more or less in the same side of the intake). I think that this was probably considered in the Z06, since their intake is different in a way that could probably give more reliable results for calibration.

I am not entirely sure I agree with you AnotherUser (not to start a battle :) ). It is an interesting theory though about the airflow being biased. I am not sure it biased (or at least enough to make a difference). The screen just straightens the airflow and does not really bias it towards any side. The MAF has that diverter in the middle of it, which purpose is to allow the little resistors to see the greatest amount of airflow (center of the tube theory). But the diverter is shaped like a wedge to restore smooth airlow after it. Basically it splits the airflow and then puts it back together again after the MAF. So after the MAF you have a "wall" of air heading towards the TB. Feel free to comment on what I said, I can confuse myself sometimes.

Now the diverter is vertical in the MAF, and the TB blade opens horizontally. I think this is to help offset the bias you metioned, especially at idle. But you also have the small hole drilled in the TB blade at the bottom to compensate for bias to the IAC port.

Now at part throttle I don't think any bias would matter. Air is incompressible below 0.9 mach, so its a case of what comes into the MAF goes into the engine, whether it is biased or not. At part throttle enought air is moving through the MAF to negate any biasing at the TB.

I was only referring to using a ported MAF without a screen. That is what the screen is there for, to ensure laminar airflow.

Back to the question. What if I took everything from the air filter to the TB and put it on the bench and calibrated with that would it work. If we all used the same MAF ends it would be one test.

You can try it, but I doubt you will get any further than I have already gotton. I can send you a log if you like, and everything will make more sense. It is not that my MAF table is not properly calibrated. On a flow bench you can more or less get consistent airflow, and I can't say for sure how you could flow it under various TB% openings, etc. The problem is at light cruise there is turbulence and irregularities in the airflow, caused by the plastic divider (and lack of a center air foil) and the throttle body being cracked. Especially with a cam, there are certain to be irregular pulses in your intake system that will cause irregular readings as well. So even though my MAF table was properly caibrated, sometimes (only sometimes) while driving my trims would drop as far as they could because the MAF started reading additional air that it should have been reading. I will post a log, gimme a few minutes.

Sorry to hear bout your woes AU... :( Seems like you're always gettin the shaft eh??? First the 98 junk, now the MAF won't behave for ya... :bang: Finally got mine where it needs to be though, and took care of that horseshit low end trimming we discussed once upon a time. It was all ariflow related... :eyes:

I think you deserve the award for shit luck AU. Good to see that you figured out your issues.

Ha ha ha. Nice. My luck is not all bad. Somebody has to figure this stuff out, and I don't mind doing a little leg work on these problems. Below is a link to my log for those that are interested...
http://users.adelphia.net/~someoneelse/log.zip

yeah i had ported ends on before and the car ran like shit. put the stockers on and got more power back. this was before hp tuners though so i never logged, just with predator.

airflow can be so inconsistant even with the stock maf ends on the car. your right the screen is there to create laminar flow but normally a larger section of strait pipe is required to get truer readings.

Yeah...I started tinkering with my MAF table and the stock ends, and I think I was able to re-create the same problem I saw with the aftermarket ends

I thought you were loving your sd tune. Are you just running a maf now for research or what?

I ran into some off-idle driveability issues caused by irregular dynamic airflow readings at idle. Putting the MAF back in fixed the issue, unfortunately at a cost. I put my ported MAF ends back in today and I am going back to the drawing board tomorrow. I have noticed that the PCM does a better job of recovering from a lean condition than it does from a rich condition. What a PITA.

Another_User:

I came into the same situation you're in about 3 months ago. I did a search on ebay and picked up a screened 85mm MAF from an '02 Yukon for $23 shipped to my door. This included the entire intake track from the filter connection to the TB connection.

One thing I found very interesting is that the SLP lid I have has the same ID as the 85mm MAF - so, no need to buy a new lid for the new MAF.

Here is the thread I posted about it.