1. If the MAF sensor is faulty, will it always set a trouble code or can it send out incorrect info and not set a signal?

2. What are the symptoms caused by a bad MAF sensor?

I am *still* trying to track down the reason my car is eating gas, and I'm running out of ideas. Thought maybe this sensor could be a contributor?

 

Age of engine
Worn engine
Poor sealing-compression
all cause poor gas milage.
Engine electronics don't cause the gas problems (except lousy/weak ignition).
If incorrect, educate me.

 

check the oil and make sure there is no fuel in it. Thats what happened to me... lots o' internal leakage

 

Karl: This has only been happeneing for about eight months or so, before that it got great mileage, so I doubt age is to blame. Unless something broke I can't see it going suddenly downhill like that. My theory on this is that if the Maf sensor were giving faulty info to the ECM, then the ECM would not be able to correctly adjust the fuel mixture, thus causing it to run lean or rich. If I am wrong about this, please explain why (I am still learning).

nj88v6: Guess I'll be sniffing my dipstick tomorrow..what kind of leakage was yours exactly?

Thanks for answering!

 

Usually when a MAF sensor goes south, MPG is not the only problem. Every one that I have seen go out (including mine but it was just a bad connection) causes the car to run poorly (bad idle,hesitation,surging, etc.).

As far as MPG, have you checked for any vacuum leaks? Even a small leak can drop MPG significantly. How about the O2 sensor? Cap and Rotor? Plugs and Wires?

Dale

 

Around town gas milage or freeway milage.
How is car performance during this "problem" period...

DALE
MANY THANKS, AGAIN!!

 

I wouldn't think that the maf would cause bad milage. It's my understanding that the O2 sensor is the primary input for the ECM to compute the A/F ratio, so you might want to check that. As for it setting an error code, it may not. The ECM guesses at the MAF reading if you disconnect it, so you might have a broken wire/bad connection somewhere. Have you checked your spark plugs? They may be partially fouled or at the very least will confirm if you're running rich all the time.

 

Like Dale said, a bad MAF could cause poor driveability- and that would affect gas mileage.

And yes, the MAF can go bad without setting an error code. Some tips; you can perform a visual inspection of the MAF sensor. Remove the sensor, and look inside. The orange frequency film should be perfectly FLAT- not warped or bent or kinked. If the film is NOT flat, you need to replace the sensor. You can also, with the sensor in place and connected and the engine running, tap on the outside of the MAF housing with a screwdriver. If the motor stalls, the MAF is bad.

Some un-obvious things causing bad mileage that I can think of: a TPS that fell out of adjustment, exhaust leak near the manifold/y-pipe connection, one bad spark plug wire, dying fuel pump. And the obvious, spark plugs, deposits on inside of distributor cap/rotor, misadjusted timing (has the 0 degree mark on the balancer slipped?), clogged fuel filter, clogged air filter, etc- basically, all the major tuneup parts.

 

Exhaust leak I do have..it has been there since before I bought it, but I forgot about it because it didn't seem to make any difference and my dad told me it wouldn't. According to the inspection paper "L/S exhaust manifold leaks; two broken bolts." Two years having passed since then, it probably has gotten worse. Which brings up the next question: could that be responsible for the RPMs to drop 50-100 when the car gets quite warm (above 50*C)?
Last full tune-up was exactly one year ago, time for plugs again I know but that'll have to wait til I can coerce someone unwary into helping me. I strongly doubt the plugs are the culprit though.
Anyways tomorrow I'll ramp the car and see what can be seen from below.

 

I had any exhaust leak very similar to yours and when I got it fixed they said that it was probably affecting the O2 readings because it could be allowing air into the exhaust which would cause a false lean condition. They also said that cold air might have been able to get in and damage the exhaust valve. It also hurt performance a bit, so it's a good idea to get it fixed.