• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

testing a mass air flow sensor.


mitch4712

New Member
Joined
Jun 15, 2014
Messages
57
Reaction score
0
Points
0
Location
Kiefer
Vehicle Year
1994
Make / Model
Mazda
Engine Size
3.0L
Transmission
Manual
I have a rough idle ( worse when cold). Also hesitation (worse when cold). If I remember correctly the truck is supposed to idle at 1000RPM till warmed up and after warmed up till your under 10MPH. My symptoms are it idles around 1200 till the truck has stopped. Then it idled down to 750rpm. Same for hot and cold.

I have checked and double cheacked for a vacuum leak. I have plugged all the vacuum lines at the intake manifold. I have used carb cleaner to try and find leaks. I have not done a smoke test yet. I have changed the spark plugs (set gap to .042"), plug wires, cap , rotor, and fuel filter.

I was next going to start testing sensors. First the mass air flow sensor. Anyone now the voltage parameters for the mass air flow sensor?
 


RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,292
Reaction score
8,298
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Have a read here: http://www.therangerstation.com/tech_library/CleanMAF.shtml

You will probably have a 6 wire MAF connection, the 2 outside wires are for the built-in IAT(intake air temp) sensor, the 4 inside wires are the MAF wires.

Yes, on cold start idle should jump up to 1,500+ and then drop down to 1,000-1,200RPM based on engine temp, colder engine higher RPM.

As engine warms up idle should slowly drop to 700-800 depending on manual/auto trans.
Warm up should be within 5 to 10 minutes of cold start, other wise your thermostat is stuck open.
Always use a 190 to 195 degF thermostat, 160 or 180 t-stat will make for dirty oil and lower MPG.

Coasting to a stop, warmed up, idle will stay at about 1,000 until you stop, at least until below 5mph, on manual trans idle will stay high while clutch pedal is in, as least for a few seconds.
Both of these behaviors are to save fuel and lower emissions.

Computer only has one sensor to test engine temp, the ECT sensor, it has TWO wires.
Computer sends the ECT sensor 5volts on 1 wire, this 5volts passes thru the ECT's temp variable resistor and returns a lower voltage, 3 volts cold, under 1volt warmed up, as resistor warms up it blocks more voltage, like most resistors.

There is a similar looking device often near the ECT sensor, it is the ONE wire temp SENDER, this is used for engine temp gauge on dash.

ECT sensors rarely fail, but rarely is not never.
 
Last edited:

mitch4712

New Member
Joined
Jun 15, 2014
Messages
57
Reaction score
0
Points
0
Location
Kiefer
Vehicle Year
1994
Make / Model
Mazda
Engine Size
3.0L
Transmission
Manual
Thanks ronD. I checked the voltage on terminal c and d . It had 1.15 volts at idle. So it in spec and shows to be good. I guess I'll test the coolant temp next.
 

mitch4712

New Member
Joined
Jun 15, 2014
Messages
57
Reaction score
0
Points
0
Location
Kiefer
Vehicle Year
1994
Make / Model
Mazda
Engine Size
3.0L
Transmission
Manual
Have a read here: http://www.therangerstation.com/tech_library/CleanMAF.shtml



Computer only has one sensor to test engine temp, the ECT sensor, it has TWO wires.
Computer sends the ECT sensor 5volts on 1 wire, this 5volts passes thru the ECT's temp variable resistor and returns a lower voltage, 3 volts cold, under 1volt warmed up, as resistor warms up it blocks more voltage, like most resistors.
I tested the ECT with the engine at normal operating temp. the first terminal had .85 volts and the other had .09 volts. I used different grounds and tested a couple of times. any thoughts?
 

RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,292
Reaction score
8,298
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
.85v would be about right for warmed up engine, but .09v is odd, since that would be the "return voltage" as it is lower.

I would remove the connector and test one of the wires for 5volts.
Then test the .85v wire when engine is cold, should be above 2v at that time.

If you have 5volts when connector is removed and then .85v when connected I would think the ECT has a short inside, replace it.

This is the Computer(EEC-IV) pin out assignments: http://www.auto-diagnostics.info/ford_eec_iv
Good page to bookmark or save

Pin 26 is the 5volt sensor reference voltage that should be seen at the ECT, IAT and TPS(throttle position sensor), it can be 4.6-5.0v, it is a "reference voltage".
On most systems the 5volts passes thru the TPS first then to the ECT and IAT, so could resemble a Ground(.09v)

Pin 7 is the return voltage from the ECT

Pin 25 is the return voltage for the IAT

Pin 47 is return voltage for TPS

Test IAT and TPS for the 5volts as well if ECT doesn't have it, could be a loose wire at the splice or at the ECT connector.
 
Last edited:

mitch4712

New Member
Joined
Jun 15, 2014
Messages
57
Reaction score
0
Points
0
Location
Kiefer
Vehicle Year
1994
Make / Model
Mazda
Engine Size
3.0L
Transmission
Manual
I disconnected the connector from the ECT and test the voltage. the green/red wire had 4.75 volts and the other had 0 volts. When I plugged it back in the voltage dropped to 1.2 and slowly kept dropping as the engine warmed back up. could this cause the rough idle and hesitation?
 

RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,292
Reaction score
8,298
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
That could cause the symptoms but ONLY cold or warm, not both

If engine is cold but ECT tells computer it is warm then it would idle rough and even stall until it warmed up, but it would run fine warm.

If ECT tells computer engine is colder than it is then engine would run good cold and then start running rough as it warmed up, MPG would be bad and you would often get CEL since ECT is not changing voltage, computer has a cold start timer that monitors ECT changes.
 
Last edited:

mitch4712

New Member
Joined
Jun 15, 2014
Messages
57
Reaction score
0
Points
0
Location
Kiefer
Vehicle Year
1994
Make / Model
Mazda
Engine Size
3.0L
Transmission
Manual
ok Ill change it and see what happens. thanks ROND
 

mitch4712

New Member
Joined
Jun 15, 2014
Messages
57
Reaction score
0
Points
0
Location
Kiefer
Vehicle Year
1994
Make / Model
Mazda
Engine Size
3.0L
Transmission
Manual
I have not. got to wait till payday to buy the ECT sensor.
 

mitch4712

New Member
Joined
Jun 15, 2014
Messages
57
Reaction score
0
Points
0
Location
Kiefer
Vehicle Year
1994
Make / Model
Mazda
Engine Size
3.0L
Transmission
Manual
I remeber reading somewhere on here if you have a rough idledue to a vacuum leak you lift the top of the air filter housing and partially cover the inlet and the idle should smooth out. is this true. I tried it on mine truck and i barely started to cover it and the engine started really missing, sputtering, shaking.
 

RonD

Official TRS AI
TRS Technical Advisor
Joined
Jun 2, 2012
Messages
25,292
Reaction score
8,298
Points
113
Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
I have not. got to wait till payday to buy the ECT sensor.
I would test the ECT sensor first.
Simple way is to unplug it and then start cold engine.
Having it unplugged should turn on the CEL(check engine light), and it also forces the computer to be in Open Loop mode(no O2 sensors) which runs fuel slightly rich from preprogrammed data tables.

See how it runs.

Then shut off engine(key to OFF) and plug ECT back in, restart and see how it runs.

Do the same test with engine warmed up.
 
Last edited:

mitch4712

New Member
Joined
Jun 15, 2014
Messages
57
Reaction score
0
Points
0
Location
Kiefer
Vehicle Year
1994
Make / Model
Mazda
Engine Size
3.0L
Transmission
Manual
Ok ill give it a shot thanks.
 

mitch4712

New Member
Joined
Jun 15, 2014
Messages
57
Reaction score
0
Points
0
Location
Kiefer
Vehicle Year
1994
Make / Model
Mazda
Engine Size
3.0L
Transmission
Manual
oh I forgot to mention one more thing. the filler neck for the fuel tank is starting to dry rot. thus causing a vacuum leak in the evap system. so I capped off the vacuum line that runs to the solinoid just behind the charcoal canister. any thoughts?
I plan on replacing the filler neck sometime. would having this capped off cause any issues?
 

mitch4712

New Member
Joined
Jun 15, 2014
Messages
57
Reaction score
0
Points
0
Location
Kiefer
Vehicle Year
1994
Make / Model
Mazda
Engine Size
3.0L
Transmission
Manual
I unplugged the ECT and ran the engine while it was cold and warmed up. I didn't notice a change in the symptoms.
 

Sponsored Ad


Sponsored Ad

Members online

Today's birthdays

Member & Vendor Upgrades

For a small yearly donation, you can support this forum and receive a 'Supporting Member' banner, or become a 'Supporting Vendor' and promote your products here. Click the banner to find out how.

Latest posts

Truck of The Month


Kirby N.
March Truck of The Month

Recently Featured

Want to see your truck here? Share your photos and details in the forum.

Follow TRS On Instagram

TRS Events

25th Anniversary Sponsors

Check Out The TRS Store


Sponsored Ad


Sponsored Ad

Sponsored Ad


Amazon Deals

Top