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OHV MAF voltage low DTC

thcscubajohn

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EEC code 157 I think
I had a bad alternator which I changed and still got this code
I cleaned the MAF sensor and the elements looked fine but were dirty so this led me to believe that I have a bad ground or maybe vacuum leak I have checked all the vacuum lines with brake cleaner with the engine running and there was no response maybe I missed a hard to access one or maybe it's because the hinge on the back of my airbox is broken and letting dirty air in?
I also checked the negative cables (grounds) and did not seem to find the problem

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RonD

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I think the code was..................is worse than no code at all, lol :)

Anyway look here: http://www.therangerstation.com/tech_library/index.shtml
Good page to bookmark

Click on Engines section
Then on the right find and click on MAF Cleaning
It has the voltages to look for/test on the MAF wires
 

thcscubajohn

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FORD
Engine Type
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Engine Size
247ci
Transmission
Manual
2WD / 4WD
4WD
Total Lift
4"
Tire Size
31x10.50r15
My credo
Smog is for pussies.
I know it was a MAF low or no voltage code I am just not sure of the number

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thcscubajohn

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FORD
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4"
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My credo
Smog is for pussies.
I've got a 157 code I checked it again
and I've got 14.5 volts between A and B and 5.2 volts between C and D

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thcscubajohn

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157- R,M) Mass Air Flow signal is/was low or grounded - MAF

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RonD

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I've got a 157 code I checked it again
and I've got 14.5 volts between A and B and 5.2 volts between C and D

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If engine is idling 700-1,000RPMs you should see 0.34-1.96 volts between C and D.

A and B are the heater circuit so should show battery voltage, 13.6v-14.9v engine running, so that is correct
C and D is the actual MAF sensor
MAF sensor gets 5 volts from computer, and sends back .3 to 4.9volts, depending on air flowing passed the sensor.
Idle air is low flow so low voltage, WOT(wide open throttle) is high air flow so above 3.5 volts usually, never seen over 4 volts.

Your sensor reads like it has a short
Retest with engine idling but this time Ground the meter to the battery Negative or engine metal, then test each wire, C and D, one should be 5volts the other 0.34-1.96 volts
If both are 5volts then replace sensor
 

thcscubajohn

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Location
Antarctica
Vehicle Year
1994
Make / Model
FORD
Engine Type
4.0 V6
Engine Size
247ci
Transmission
Manual
2WD / 4WD
4WD
Total Lift
4"
Tire Size
31x10.50r15
My credo
Smog is for pussies.
If engine is idling 700-1,000RPMs you should see 0.34-1.96 volts between C and D.

A and B are the heater circuit so should show battery voltage, 13.6v-14.9v engine running, so that is correct
C and D is the actual MAF sensor
MAF sensor gets 5 volts from computer, and sends back .3 to 4.9volts, depending on air flowing passed the sensor.
Idle air is low flow so low voltage, WOT(wide open throttle) is high air flow so above 3.5 volts usually, never seen over 4 volts.

Your sensor reads like it has a short
Retest with engine idling but this time Ground the meter to the battery Negative or engine metal, then test each wire, C and D, one should be 5volts the other 0.34-1.96 volts
If both are 5volts then replace sensor
Okay also normally when it is cold it will not hold idle I does not do this all the time also even when it's warm if I'm driving and disengage the clutch it will sometimes stall or sometimes idle I've noticed that it does this more so when it is cold so I thought maybe a vacuum line but I couldn't find a leak

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thcscubajohn

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FORD
Engine Type
4.0 V6
Engine Size
247ci
Transmission
Manual
2WD / 4WD
4WD
Total Lift
4"
Tire Size
31x10.50r15
My credo
Smog is for pussies.
Is this problem possibly caused by a bad MAF

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RonD

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Cold and warm idle involve a few things and the MAF is not one of them but it can cause issues.

When you turn on the key the computer boots up and runs a self test, it then opens the IAC(idle air control) Valve all the way for starting.
Computer checks coolant temp via ECT(engine coolant temp) sensor
And checks air temp via IAT(intake air temp) sensor

If coolant temp is under 140degF the computer runs Choke Mode, a Richer fuel mix and higher idle, the colder the coolant temp the Richer the mix and the higher the idle.

If you don't touch the gas pedal, when engine starts it should REV a bit, 1,400rpm briefly, then computer will start to close the IAC Valve to set desired idle RPM based on coolant temperature, 1,100 cold, 700 warmed up

I would clean IAC Valve as first step, and replace ECT SENSOR, $8, as second step.
4.0l OHV will have 2 coolant temp detectors, a 2 wire sensor, and a 1 wire SENDER, sender is only used by the dash board temp gauge.
They are located next to each other on lower intake just above thermostat housing


Now the MAF data is important and could get computer "confused" which is why it set the MAF code, the "low voltage" doesn't always mean "low voltage" all the time, lol, computerese.
Computer is programmed for a 4 Liter engine, which will use 4 liters of air every 2 RPM at wide open throttle, so at any specific RPM and throttle position the computer "knows" the range(voltage) the MAF sensor should be reporting and if that voltage is low for that specific RPM then computer would set that low voltage code

You can test the MAF sensor voltage and raise the RPM while watching the voltage, you should see a steady increase of voltage matching RPM increase, and voltage drop as RPMs decrease
 
Last edited:

thcscubajohn

Active Member
Joined
Nov 23, 2014
Messages
147
Reaction score
31
Points
28
Location
Antarctica
Vehicle Year
1994
Make / Model
FORD
Engine Type
4.0 V6
Engine Size
247ci
Transmission
Manual
2WD / 4WD
4WD
Total Lift
4"
Tire Size
31x10.50r15
My credo
Smog is for pussies.
Cold and warm idle involve a few things and the MAF is not one of them but it can cause issues.

When you turn on the key the computer boots up and runs a self test, it then opens the IAC(idle air control) Valve all the way for starting.
Computer checks coolant temp via ECT(engine coolant temp) sensor
And checks air temp via IAT(intake air temp) sensor

If coolant temp is under 140degF the computer runs Choke Mode, a Richer fuel mix and higher idle, the colder the coolant temp the Richer the mix and the higher the idle.

If you don't touch the gas pedal, when engine starts it should REV a bit, 1,400rpm briefly, then computer will start to close the IAC Valve to set desired idle RPM based on coolant temperature, 1,100 cold, 700 warmed up

I would clean IAC Valve as first step, and replace ECT SENSOR, $8, as second step.
4.0l OHV will have 2 coolant temp detectors, a 2 wire sensor, and a 1 wire SENDER, sender is only used by the dash board temp gauge.
They are located next to each other on lower intake just above thermostat housing


Now the MAF data is important and could get computer "confused" which is why it set the MAF code, the "low voltage" doesn't always mean "low voltage" all the time, lol, computerese.
Computer is programmed for a 4 Liter engine, which will use 4 liters of air every 2 RPM at wide open throttle, so at any specific RPM and throttle position the computer "knows" the range(voltage) the MAF sensor should be reporting and if that voltage is low for that specific RPM then computer would set that low voltage code

You can test the MAF sensor voltage and raise the RPM while watching the voltage, you should see a steady increase of voltage matching RPM increase, and voltage drop as RPMs decrease
Thanks Ron after beating around the bush I finally bought a MAF sensor and put it in took about a minute of some WOT for it to idle on its own again or even start up I guess it was bad for a while


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thcscubajohn

Active Member
Joined
Nov 23, 2014
Messages
147
Reaction score
31
Points
28
Location
Antarctica
Vehicle Year
1994
Make / Model
FORD
Engine Type
4.0 V6
Engine Size
247ci
Transmission
Manual
2WD / 4WD
4WD
Total Lift
4"
Tire Size
31x10.50r15
My credo
Smog is for pussies.
That was last year and it has been running great

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