car is falling flat on its face at like 3500-4k. - Page 15

texas_stang02 · 07-03-2009, 04:10 PM

Quote:

Originally Posted by Smokin04

I saw this and had to say something. For the folks that are new to the game...when cruising at a steady rpm your A/F ration should NEVER be stable. You should normally read 13.0-17.0 (constantly fluctuating) and down to 11.0-15.0 on the hotter days. This is completely normal. What's causing the "bouncing" is your O2 sensors working properly. They're always talking to the PCM adjusting A/F ratio for the optimum MPG. If your A/F doesn't bounce around, it usually signifies a bad sensor. This is also the importance of having a dual bank (one wide band per side) Wideband system. You could have a bad O2 sensor on your pass. side and not know it because your wideband is in the drivers side. You wouldn't even notice a problem until you fill up and notice that your MPG is really crappy. Also a PCM correction for a bad O2 sensor is max rich. Rich is always safer than lean. When I went to my PLX setup, that's when I finally noticed I had a bad O2. Drivers side was bouncing from 13-17 while pass side was holding at 10.0 (<--PCM MAX RICH). Swapped O2 sensors and all was well.

Only when you go into open loop (WOT, max load) should your A/F ratio be steady. Even then it will move around a bit, but only until it reaches desired (read: comanded) A/F ratio.

EDIT: After reading a few previous posts...

Guys, long gone are the old 5.0 days of just getting a bigger MAF and running it with correct injector calibrations. A lot of you guys are wasting your money of un-needed parts. A MAF is a very needed part (obviously), but changing them isn't always necessary. A stock meter is fine in almost EVERY application. I still have a stock MAF in my car (albeit with a MAFia). A MAF is just a sophisticated sensor...nothing more. It's job is to tell the PCM the criteria (density, volume, BARO, etc.) of the incoming airflow. Why people "upgrade" MAF's is often due to resolution issues. Meaning how "clean" the meter reads/interprets the data. By changing MAF's you're doing nothing for your performance without telling the PCM what you're doing...in other words, you need a tune. Keep in mind, the MAF doesn't "control" anything. It's just a communication device just like every other sensor. So by swapping meters and injectors, you just added more fuel capacity by upping injectors, but the PCM doesn't know unless you tell it what you did. It can "hypothesize" due to the adaptive learning tables, but the combination will never be dialed in without a tune. That's why all you guys are running rich. Spend the money on a tune, not a MAF. Stock MAF's are good for tons of power and can be run in any configuration, draw-through/blow-through. So hang onto them and just get a bigger housing if you're worried about airflow.

i can see you didn't read very many of my previous posts.. i just had it tuned (waiting for you to tell me my tuner doesn't know what he's doing), it ran fine for a while before it started doing this. my car sucked in a bunch of water a few months back (which is why i had to rebuild the motor) and my a/f never jumped around this much before. it did vary anywhere from 13:1 to 15:1 under cruising and idle conditions, but it never idled at 10:1 and then jumped up to 13.5:1, and it never felt like i hit a rev limiter at 4k on one pull and then pulled fine to redline on the next. i also already replaced the front O2 sensors, still having problems so that wasn't it. and since my last post, i've had the maf tested and it does need to be replaced.

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Smokin04 · 07-03-2009, 11:03 PM

I said I read a few. I don't know who your tuner is, so I wouldn't make a statement like that without some facts or knowledge of who you used. The statements I made were not directed at any one person. They are just general statements about MAF's and A/F ratios. I apologize if you think they were directed at you.

lizzyfan · 07-04-2009, 11:39 AM

Quote:

Originally Posted by Smokin04

Stock MAF's are good for tons of power and can be run in any configuration, draw-through/blow-through. So hang onto them and just get a bigger housing if you're worried about airflow.

Absolutely incorrect!

Smokin04 · 07-04-2009, 04:49 PM

How so?

lizzyfan · 07-05-2009, 10:42 AM

Quote:

Originally Posted by Smokin04

How so?

Because on a stock MAF or even some aftermarkets, you hit the electronic capacity of the sensor and nothing to do with airflow restriction

texas_stang02 · 07-05-2009, 01:05 PM

does anyone know of a good technical web site or book on tuning EFI cars? i read so much conflicting data on the forums that it's hard to make heads or tails of all the stuff i see/hear. i've been building and tuning carbureted race engines for years but when you throw in all the electronics involved with the EFI Mustangs i'm still a bit confused.

Smokin04 · 07-05-2009, 06:55 PM

Quote:

Originally Posted by lizzyfan

Because on a stock MAF or even some aftermarkets, you hit the electronic capacity of the sensor and nothing to do with airflow restriction

You can run any voltage extension device...(MAFia, MAFextender, whatever...) on a stock meter. I still have the stock meter...with a MAFia.

Smokin04 · 07-05-2009, 06:56 PM

Quote:

Originally Posted by texas_stang02

does anyone know of a good technical web site or book on tuning EFI cars? i read so much conflicting data on the forums that it's hard to make heads or tails of all the stuff i see/hear. i've been building and tuning carbureted race engines for years but when you throw in all the electronics involved with the EFI Mustangs i'm still a bit confused.

Look here:

http://www.hptuners.com/

texas_stang02 · 07-05-2009, 07:08 PM

Quote:

Originally Posted by Smokin04

You can run any voltage extension device...(MAFia, MAFextender, whatever...) on a stock meter. I still have the stock meter...with a MAFia.

i've heard of the MAFia before, but i'm not sure exactly what it is... so you're saying that if the voltage on my 90mm Lightning maf is maxed out (forgive me if i'm using the wrong terminology here), i can run a MAFia and still run that maf at higher power levels?

Smokin04 · 07-05-2009, 10:11 PM

Correct. The factory MAF voltage runs to 5V. By adding a MAFia it extends the voltage range to around 15V depending on setting. The PCM obviously needs to be told its there via tune, but all it does is take the factory voltage, and converts it into an appropriate amount that the PCM can interpret.

So by literal definition, it doesn't "extend" the voltage range of the factory MAF, it simply changes the voltage signal above 5V's into values the PCM can recognize. So in essence your stock (or aftermarket) MAF can now communicate 3-4 times the amount of airflow to the PCM.

My MAF is just a 95mm (4 inch) housing with the factory MAF sensor and a MAFia. I'm well over 700 rwhp with the turbo's, and the MAFia is only on setting 3. It goes to 10.