mass air sensor

[711sdekick]

trying to research a p0174 code on a 97 explorer. one of the things to check is the mass air filter, voltage going in and signal voltage. my sig volt is .84. is this above normal, and is there a way to lower it?

 

[imp]

trying to research a p0174 code on a 97 explorer. one of the things to check is the mass air filter, voltage going in and signal voltage. my sig volt is .84. is this above normal, and is there a way to lower it?

P0174 is "System Too Lean, Bank 2". This is being picked up by an oxygen sensor. Mass Air SENSOR (not a filter) would affect BOTH BANKS EQUALLY, not just one. If the oxygen sensor were at fault, the PCM (computer) would likely call that out. So, this points to something the computer can't "see", but causes one side of the engine to be seen as not getting enough fuel- lean. What could cause that?

Fuel pressure? No. Low pressure would affect both banks.
Fuel injector problem? Yes. A clogged injector, just one, on Bank 2, would cause a LEAN condition. A DEAD injector, in other words electrically inoperable, shorted or burned out coil in the injector, PCM would "see" as an electrical fault. Bad connection at injector, broken wire in connector? NO. PCM can "see" that.

But, it can't see if the fuel is getting injected in enough quantity, or at all. I would look for that as the problem. How badly is the engine running, or are you responding to a check engine light, and the engine "feels" OK? imp

 

[koda2000]

P0174 is "System Too Lean, Bank 2". This is being picked up by an oxygen sensor. Mass Air SENSOR (not a filter) would affect BOTH BANKS EQUALLY, not just one. If the oxygen sensor were at fault, the PCM (computer) would likely call that out. So, this points to something the computer can't "see", but causes one side of the engine to be seen as not getting enough fuel- lean. What could cause that?

Fuel pressure? No. Low pressure would affect both banks.
Fuel injector problem? Yes. A clogged injector, just one, on Bank 2, would cause a LEAN condition. A DEAD injector, in other words electrically inoperable, shorted or burned out coil in the injector, PCM would "see" as an electrical fault. Bad connection at injector, broken wire in connector? NO. PCM can "see" that.

But, it can't see if the fuel is getting injected in enough quantity, or at all. I would look for that as the problem. How badly is the engine running, or are you responding to a check engine light, and the engine "feels" OK? imp

or an intake manifold vacuum leak.

 

[imp]

or an intake manifold vacuum leak.

How right you are! Now, why would the PCM programmers, knowing what level of intake manifold vacuum should be present given all the parameters being fed to PCM, i.e., engine speed, engine load (based on TPS), barom. temp. & pressure, mass of air entering engine via MAF, included the programming conclusion that intake vacuum numbers ain't what they ought to be (that is, a leak is introducing air unaccounted for, and throw a CEL for probable intake gasket leaks? imp

 

[2000StreetRod]

no baro pressure or vacuum sensors

How right you are! Now, why would the PCM programmers, knowing what level of intake manifold vacuum should be present given all the parameters being fed to PCM, i.e., engine speed, engine load (based on TPS), barom. temp. & pressure, mass of air entering engine via MAF, included the programming conclusion that intake vacuum numbers ain't what they ought to be (that is, a leak is introducing air unaccounted for, and throw a CEL for probable intake gasket leaks? imp

On my 2nd generation Explorer there is no barometric pressure sensor or vacuum sensor that connects to the PCM. I suppose the PCM having access to intake air temperature and air mass flow could compare that to typical stored data and compute a barometric pressure. I've wondered why a vacuum sensor is not incorporated into our fuel injected Fords. The data would be very helpful in detecting and isolating malfunctions.

 

[imp]

On my 2nd generation Explorer there is no barometric pressure sensor or vacuum sensor that connects to the PCM. I suppose the PCM having access to intake air temperature and air mass flow could compare that to typical stored data and compute a barometric pressure. I've wondered why a vacuum sensor is not incorporated into our fuel injected Fords. The data would be very helpful in detecting and isolating malfunctions.

Barometric Pressure sensing was IMPERATIVE with the old "Speed Density" system, which assumed the engine inhaled an amount of air equivalent to it's displacement (not true, unfortunately, but close enough for beginnings into EFI). Vacuum is highly variable due to uncontrolled engine parameters; worn-out engines produce less vacuum, for example. For that reason, I suspect the use of vacuum sensing is still "on the horizon". You are absolutely correct, it WOULD be very helpful; however, in order to implement it, the system would have to store data containing vacuum values when the vehicle was released for general sale, and compare them against some sort of "wear-out" tables, to determine when/if a vacuum leak had produced a glitch in expected numbers.

In EEC-V, barometric pressure is actually still an important input, as fuel/air mixes must be adjusted to compensate for mountain-driving (high-altitude). imp

 

[2000StreetRod]

mass air flow sensor

. . . In EEC-V, barometric pressure is actually still an important input, as fuel/air mixes must be adjusted to compensate for mountain-driving (high-altitude). imp

I agree except for possibly the above. The MAF sensor measures the flow of air mass instead of just the velocity of air entering the engine. Changes in barometric pressure due to altitude or weather are reflected in the mass of the air. The PCM uses stored tables to adjust the pulse width of the injectors for the measured air mass flow. Vehicles driven at high altitudes have less power because less air mass is entering the engine for a given engine speed. However, the air to fuel ratio should remain near optimum. I have no first hand experience but I've read posts that the system works well at high altitudes.

 

[imp]

I agree except for possibly the above. The MAF sensor measures the flow of air mass instead of just the velocity of air entering the engine. Changes in barometric pressure due to altitude or weather are reflected in the mass of the air. The PCM uses stored tables to adjust the pulse width of the injectors for the measured air mass flow. Vehicles driven at high altitudes have less power because less air mass is entering the engine for a given engine speed. However, the air to fuel ratio should remain near optimum. I have no first hand experience but I've read posts that the system works well at high altitudes.

Sharp cookie, ain't ya? I may have been thinking of the latter EEC-IV, but am still not sure the Mass Air Sensors are capable of accurately gauging the mass flow of air given that air density varies with temperature, altitude, and relative humidity contained. But, they likely DO NOT still use a barom. press. input, anymore, just as you say. I stand corrected, proly.

How the hell did you learn so much about the intricacies of EFI? imp

 

[2000StreetRod]

My second volvo

My first Volvo was a PV-544 with dual side draft carbs.

My second Volvo was a 142S with Bosch fuel injection.

I bored the block 10% (had thick cylinder walls) and had a modified fuel injection controller (analog) that allowed me to vary the richness from stock from 10% lean to 25% rich from the driver position. I spent a lot of time reviewing Bosch fuel injection documentation.

For my Sport I have a copy of the Ford strategy (source code listing of Ford generic PCM) that I periodically search thru (over 8,000 pages).

 

[SoNic67]

...but am still not sure the Mass Air Sensors are capable of accurately gauging the mass flow of air given that air density varies with temperature, altitude, and relative humidity contained...

This is how:
http://en.wikipedia.org/wiki/Mass_flow_sensor#Hot_wire_sensor_.28MAF.29