Contour Enthusiasts Group Archives Forums General Troubleshooting Bad MAF = bad emissions?

Fuel mixture is so rich, I failed emissions. Also having trouble starting on cold mornings. This problem could even be the cause (?) of my O2 sensor failure.

I dropped it off at the dealer and they said they think it's the MAF because the A/F curve is wrong. Well, yes, the A/F ratio is definitely wrong, but is the MAF the cause? They also said that they need to reprogram the PCM afterward. I asked him if this was different from disconnected the battery. He said it was different; the computer had to be configured for the new part. Does this sound right???

Also, if I should replace my MAF, should I just upgrade to a Pro-M/Pro-Flow for the money? What size is appropriate if I plan on doing a 3.0L conversion?

A bad MAF can easily cause an incorrect A/F ratio since the PCM uses the MAF signal to calculate the air charge entering the cylinders. Thus, it directly bears on the 'A' in the A/F calculation. Assuming that the dealer replaces the MAF with stock, there shouldn't be any need to reflash the PCM. My guess is that he just wants to upgrade you to the latest calibration for your vehicle at the same time as he replaces the MAF. Basically, he gets paid for pressing a button and waiting around for a few minutes.

If you are still under warranty, I'd tell him to go ahead with both the MAF and reflash. If it isn't under warranty, I would want to have them read the infered barometric pressure from the PCM (or better yet, buy/borrow a scanner and read it yourself). The PCM infers BP from the MAF signal and if the MAF is bad, the BP calculation will be well off the actual BP (usually >5" low). If the BP reading is fine, your MAF is probably fine and they need to do some real troubleshooting instead of just throwing parts at the vehicle.

Can't a bad O2 sensor cause the same problem?

Based on your description, did the richness cause the O2 sensor to fail, or was it a bad O2 sensor that caused the car to run rich...

Not to this degree, no. If the O2 sensor is failing, the PCM starts to ignore it, goes open loop and lights the CE light.

-Lance

If that's the case, why wouldn't he do it when I asked him to upgrade the computer without replacing the MAF? He actually told me to come and get the car. Must have figured I was either a difficult customer or onto him. :p



i wholeheartedly agree with that statement, so i replaced the MAF myself; however, the autotap is showing similar numbers (airflow and fuel injector pulse width) for the new MAF. i'm not sure what to do now. i've done more reading in the Ford service manual, and have discovered a host of sensors that play into the A/F equation.

redhawk: i get your point. i had a CEL stating the O2 sensor was dead. car was rich. i replaced the O2 sensor and the CEL went away. car is *still* rich. emissions place said the problem was due to more than a bad O2 sensor.

lance: apparently the O2 sensor directs the PCM to trim the fuel levels back 25% or up 35%. if more trim is needed, then the CEL is thrown.

thank goodness for record highs in winter! i just passed my emissions inspection , but threw a CEL. :rolleyes: good thing i hadn't made plans for this weekend...

Do you have a cotton gauss style filter?

The MAF element may be dirty and need cleaning.