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Originally Posted by ohioboxster
Interesting, you described a popping sound. Have you done anything else to the car lately? When I had a popping sound it was due to a vacuum leak. Its a big long boring story but it ended up being a broken oil tube. I tought my maf was bad too and as it turns out it probably wasnt. Does your car have a rough idle? When the car is cold it takes readings from the maf until the 02's heat up. The car switches back and forth between 02's and maf. Another question, do you get a check engine light? If so another board member turned me on to running the car to Autozone and getting them to tell me the code for free. I bought a code reader on e-bay since then so I can read my own codes now.
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Hi,
Sorry, the car does not rely on MAF readings when the engine is cold. It takes only approx. 10-15 sec. for the OČ Sensors to come up to operating temperature, they are heated sensors with an induction coil or heater to do this. Until then, the DME operates in what is termed an
Open Loop, meaning that it isn't sampling anything, just operating on a default MAP.
The MAF Sensor and OČ Sensors work in conjunction with the DME in
Closed Loop operation where the Air Mass measured (along with other variables like Engine Temp, Load, Speed, Fuel Quality, etc.) determines which Fuel/Timing MAP is selected.
The Pre-Cat or Primary OČ Sensors verify or corroborate this selection with post combustion Oxygen Sampling, which is further refined by the Post-Cat, or secondary, OČ sensors sampling the same exhaust pulse to determine the Cats efficiency in managing the Emissions requirements.
One of the reasons (but not the only one) why an engine with a failed MAF will exhibit
popping is that the DME gets an unrecognizable signal (including no signal) from the MAF. If the MAF has failed, the signal is interpreted as too much Intake Air and the DME enriches the mixture, which then does not fully combust inside the combustion chamber and passes through to the hot exhaust where it spontaneously combusts causing the
Pops. On primarily a dirty MAF, the dirt/oil acts as insulation not allowing the Intake Air to extract any heat from the Hot Film. The resistance or voltage (depending upon type) doesn't change which the DME interprets as a lesser Air Mass. Consequently, it leans out the Fuel Mixture, often resulting in poor starting, low performance, hesitancy. Just FYI...
Happy Motoring!... Jim'99