How to Test if MAF is working correctly

[MNBoxster]

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.

Hi,

Sorry, the car does not rely on MAF readings when the engine is cold. It takes only approx. 10-15 sec. for the O² 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 O² 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 O² Sensors verify or corroborate this selection with post combustion Oxygen Sampling, which is further refined by the Post-Cat, or secondary, O² 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

[Sammy]

Another good way to test the MAF:

1) Start car and drive around while taking notice of performance.
2) Remove MAF and smash with sledge hammer.
3) Reconnect what remains of the MAF.
4) Start car and drive around. If car runs worse with broken MAF than the MAF was probably okay prior to step number 2.

[ajgray925]

Originally Posted by Sammy

Another good way to test the MAF:

1) Start car and drive around while taking notice of performance.
2) Remove MAF and smash with sledge hammer.
3) Reconnect what remains of the MAF.
4) Start car and drive around. If car runs worse with broken MAF than the MAF was probably okay prior to step number 2.

Sounds like the caveman method...this is usually the way I handle my car problems..ha ha.

[ajgray925]

Alright guys, here's the update:

I replaced the MAF as well as the air filter and reset the CEL. After two weeks of driving, the P1128/P1130 codes have never reappeared and the cars appears to be driving well (no more popping/back firing sounds), BUT I have a new problem:

When at idle, the rpms jump from 850 down to 400-500 rpms and then back up over and over (looping). The lights on the dash even dim/flicker when the rpms drop. The car hasn't yet died because of a low idle, but it sure does come close. I DO NOT have any CEL now, so I'm not sure where to start. I have read that it might possibly be an O2 sensor or a vacumm leak, but who knows. Any suggestions are highly appreciated.

[CJ_Boxster]

I get that same hunting idle even with no CEL... It could be a number of things from plugs, cats, o2's, throttle body cleaning, compression that could cause this.

[blue2000s]

Originally Posted by MNBoxster

Hi,

Sorry, the car does not rely on MAF readings when the engine is cold. It takes only approx. 10-15 sec. for the O² 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 O² 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 O² Sensors verify or corroborate this selection with post combustion Oxygen Sampling, which is further refined by the Post-Cat, or secondary, O² 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

The ECU will use the MAF when the engine is cold to determine load conditions. The MAF is used with and without inputs from the O2 sensors.

In fact, even when the car's hot, it will go into open loop mode during transient conditions because of the lag in O2 sensor feedback. The load data comes from throttle position and the MAF.