Will the original MAF increase gas Mileage

[oldshoman]

I am giving my 94 ATX to my daughter. Will removing the 73MM C&L and replacing it with the stock 55MM cause the injectors to inject less gas and result in better MPG?

 

[NoSlo]

You probably already know the answer if you are asking the question...
There is no theoretical reason why a larger MAF should cause worse mileage as long as it accurately reports flow. The C&L MAF however is reportedly one of the worse as far as accurately metering air and replicating the transfer function of the original MAF. By misreporting air flow it could use more gas. I believe one of the problems with it is it actually leans out under high flow; that could cause the engine to learn a richer strategy that would also be used under low load conditions.
Probably nothing better than the original MAF, well cleaned, with a clean air filter. Other maintenance such as properly gapped spark plugs, good O2 sensors, maybe even new brake lines if there is a hint of brakes dragging, is also important. Then you can keep the tires properly inflated (or a little over-inflated) and use 5w-30 oil to eek the last bit of mileage out of the car. And tell her to keep her foot out of the gas pedal...

 

[oldshoman]

Jay,
Thanks for the quick feedback. Now I have to find it in my garage! You hint the nail on the head with the brakes. My left rear brake was grabbing, and after changing the caliper and new pads I found that it I could not bleed the brakes without the engine running. Turns out the brake line was shot internally. My tires are getting to the end of their cycle. I am going to downsize from 225 to 215's. Less rubber on the pavement = less friction.

 

[doclees]

My 89 has the 73mm and 30mpg highway, 24 mixed. My wife's 93 atx, stock MAF, gets lead buld up on the gas peddle - her foot. She gets 18 to 20 mpg mixed, I get 25 mixed

 

[93rev2sev]

Fuel economy.

My understanding is that Automatic transmissions are inherently less efficient than MTX trannies. The numbers you gave were consistent with my experience.
20+ mixed with MTX (no matter how you drive it)
16-18 mixed with ATX (depending on torque converter lock-up functionality)

Most 100,000 mile+ SHO ATX torque converters stop locking up at some point.

This is noticable when cruising up or down your 45MPH roads. When you flatten out to 45MPH the tachometer will drop a 5th time from about 1800+ to 1500. At this point your torque converter is locked up. A worn torque converter is diagnosable if A. It dosent lock up. or B. if (while locked) you let off the gas and the tach jumps up slightly (less than 100rpm).

Correct me if I'm wrong.

 

[93rev2sev]

As for larger throttle body/MAF...

If all components/sensors are working correctly, you can bet that the original MAF will increase Fuel Economy slightly.

Larger MAF theory: The EEC in the SHO is constantly adjusting the amount of fuel fed to the cylinders based on the amount of oxygen the engine is using. There are several reasons why the amount of oxygen changes.
Cold air is more dense (has more oxygen).
Low altitude air is more dense also.
Larger throttle bodies flows more air.

This just means that the engine computer will sense the changes and make slight adjustments to the mixture. There is only one "strategy" burned into the computer-the baseline factory strategy, it learns as it goes by sensing (o2 sensors) the effect of the latest mixture changes. The o2 sensors need to warm up to operating temp before working properly so short trips will hinder fuel economy because the engine runs rich until the o2 sensors heat up (to help them heat up faster).

Problems with a Larger MAF: A larger MAF will flow more air but not as much as you might think. a 20% larger MAF will not flow 20% more air because the same 3.0 liter engine is sucking the air in. A larger MAF will actually SLOW DOWN the intake charge, lowering manifold vacuum, which makes low end torque suffer - not to mention brake booster/all other things that use vacuum at low RPM.

Advantages of larger MAF: A larger MAF will increase power output on engines that are modified to use more air/fuel such as running the engine at a higher average RPM (lowering the final drive ratio) or boring/stroking the engine.

Think of this: Ford/Yamaha engineers are smart and well funded. They are told to produce a product for a specific purpose. In the case of the SHO engine, performance was the purpose (they handed the entire engine to Yamaha to keep it away from the Ford Bean Counters). On the other hand...the 3.8L standard P.O.S. engine that other Fords have, the purpose was cheap/reliable/torque. If a larger MAF would increase power without a cost to fuel economy, why would they not use it stock?

If you think this is complete BS don't tell me...I would rather go on believing the lies...

 

[Axianator]

I am giving my 94 ATX to my daughter. Will removing the 73MM C&L and replacing it with the stock 55MM cause the injectors to inject less gas and result in better MPG?

As Jay has noted, the chances are greater that you will experience better gas mileage and improved power output with a cleaned factory 55mm MAF, a clean air filter and other up-to-date maintenance items. Furthermore, depending on the sample tube (SHO or Mustang) that is paired with your C&L 73mm MAF, your WOT mixture could be running anywhere from somewhat rich to dangerously lean.

Check out this thread for more information about the C&L 73 and other aftermarket MAFs:

http://www.shoforum.com/showthread.php?t=61242

Correct me if I'm wrong.

Ok, but remember that you asked for it ...

My understanding is that Automatic transmissions are inherently less efficient than MTX trannies.

While the '93-'95 AX4S transmission is certainly no marvel of engineering, it is easily more efficient than a lot of other FWD trannies out there. Moreover, when properly modified with the right components and when coupled with a lightweight synthetic fluid, the transmisison comes very close to matching it's '89-'95 MTX-IV brother in the realm of "overall efficiency".

20+ mixed with MTX (no matter how you drive it)
16-18 mixed with ATX (depending on torque converter lock-up functionality)

Gas mileage, like most automotive measurements, can and will vary between vehicles of the same make or model. Case in point - I can easily attain 18-20mpg in mixed driving (with plenty of full-throttle action) or 29-30mpg of highway driving with my "lightly modified" LC 3.3L ATX using nothing more than a stock 55mm MAF, stock airbox, a standard-issue paper air filter and a TwEECer.

Most 100,000 mile+ SHO ATX torque converters stop locking up at some point.

While it is theoretically possible for a torque converter to eventually wear out it's clutch lining (given enough time), this is rarely the typical (or even contributing) cause of transmission trouble for most '93-'95 ATX SHOs. In fact, most of these vehicles will experience some type of severe, internal transmission failure long before their converter ceases to provide reliable lockup operation.

This is noticable when cruising up or down your 45MPH roads. When you flatten out to 45MPH the tachometer will drop a 5th time from about 1800+ to 1500.

It should be noted that this behavior will only occur if a) the transmission fluid temperature (as indicated by TFT/TOT sensor readings back to the EEC) have reached a certain stabilized temperature, and b) the vehicle speed (as indicated by VSS readings back to the EEC) is high enough at a given throttle voltage for the EEC to command converter lock in that gear. It should also be noted that too much throttle application will actually cause the EEC to keep the converter unlocked until a) the vehicle has gained sufficient speed for the EEC to command a relock, or b) the driver eases off the throttle and the throttle voltage has dropped below a certain point.

A worn torque converter is diagnosable if A. It dosent lock up.

Not necessarily, as there are several other electrical components that can cause a converter to remain unlocked.

B. if (while locked) you let off the gas and the tach jumps up slightly (less than 100rpm).

Actually, what you have just described is a sign of a perfectly-functioning converter.

A larger MAF will actually SLOW DOWN the intake charge, lowering manifold vacuum, which makes low end torque suffer - not to mention brake booster/all other things that use vacuum at low RPM.

While an overtly-large MAF could reduce overall air velocity (which, in itself, can affect a number of things relating to engine power output), rarely will it have a significant or measureable effect on engine vacuum readings. Even if there was a significant and/or measureable loss of engine vacuum, it is highly unlikely that such a loss would result in a reduction of low-end power output.

For more information on this subject, I submit the following two excellent articles:

http://en.wikipedia.org/wiki/Manifold_vacuum
http://www.aa1car.com/library/vacleak.htm

If you think this is complete BS don't tell me...I would rather go on believing the lies...

Normally, I might, but there's already been enough misinformation spread throughout the community over the past few years.