Proper MAF Testing Procedures?

[erykv1]

Hey guys,

Could someone please let me know if the following test procedures I found apply for hitachi MAF's on the 2.7's?

I am trying to find out if I have a inherent issue with my MAF sensor wiring / MAF sensor or if its the MAF housing / intake. I am logging about 4.5V's on the MAF sensor voltage at around 18psi which is almost the limit of the sensors capability. Fuel trims are still wonky and there are no leaks in the system (unless it is coming from the intake manifold gaskets, the only thing I have not replaced).

Checking MAF sensor function

Internal resistance check.

* Disconnect MAF sensor harness connector.
* Switch DVOM to 200 ohm range.
* Connect multimeter (using VW 1594 connector test kit) to MAF sensor terminals 1 and 2.
* Record resistance value.
* Disconnect test leads from MAF sensor, and connect test leads together.
* Display value must equal value recorded previously.

If difference is greater than 0.1 ohm :

* Replace MAF sensor.

Output signal check.

* Re-connect MAF sensor harness connector.

Mass Air Flow Sensor Connection


* Peel back rubber boot on back of harness connector to expose terminals.
* Switch multimeter to 20 Volt range.
* Connect multimeter to (exposed) terminals 1 and 3.
* Switch ignition ON.
* Must be 1.2 - 1.5 Volts .
* Start engine and let idle.
* Must be approx. 2.5 Volts .
* Increase Engine Speed (RPM) briefly.
* Voltage must increase to 3.0 - 5.0 Volts
* All of the specified voltages must be obtained.

If not:

* Replace MAF sensor.

Checking MAF sensor burn-off

Note : The sensing element of the MAF sensor must be clean to function properly. To accomplish this, the element is heated to 100°C (183°F) for one second, each time the ignition is switched OFF.

Burn-off occurs only under the following conditions:

* Engine Coolant Temperature (ECT) above 60°C (140°F) .
* Engine Speed (RPM) has exceeded 2000 rpm for at least 3 seconds .
* MAF sensor wiring is OK.
* Injector valve circuit breaker S72 is OK.
* Disconnect MAF sensor from air cleaner housing and position far enough back so that burn-off process can be observed.

Note : Do not disconnect the intake air hose or the MAF sensor connector.

* Start engine and let idle above 2000 RPM for minimum of 3 seconds .
* Switch ignition OFF.
* Observe burn-off process.
* Heating wire glows for about 1 second.

Thanks

[erykv1]

bump bump. anyone?

this is a long shot, but if anyone has the ECU pin outs from the MAF pigtail to the ECU box, I would love to know which the pins go to.

[phila_dot]

ECU -> Hitachi MAF
Pin 53 +5v -> pin 1
12v -> pin 2
Pin 27 ground -> pin 3
Pin 29 signal -> pin 4

[erykv1]

ECU -> Hitachi MAF
Pin 53 +5v -> pin 1
12v -> pin 2
Pin 27 ground -> pin 3
Pin 29 signal -> pin 4

awesome!
thank you.

While you're still here, is there any parameters in the tune that directly affect MAF voltage (ie voltage scaling)? MAF voltage is a result of of the airspeed passing the sensor right?

My sensor almost pegs the max voltage in the operating range at only 17-18 psi so its impossible to tune it for higher boost levels. I've tried multiple sensors and theres no difference in trims, some read slightly worse than others but at the end of the day they all go out of normal range.

Unless there is some crazy black hole inside my intake / maf housing, I am starting to think this is harness related (harness is 100% stock though).

[phila_dot]

Stock hitachi? Intake setup?

uhfm_w is direct voltage from the A/D converter, so nothing tuning wise will affect it.

Post MAF leak lowers restriction which can allow excessive airflow. Also, the MAF is fed 5v and pulled down to ground. The signal wire is tied to ground and voltage will be much higher if this is loose or missing.

[erykv1]

Stock hitachi? Intake setup?

uhfm_w is direct voltage from the A/D converter, so nothing tuning wise will affect it.

Post MAF leak lowers restriction which can allow excessive airflow. Also, the MAF is fed 5v and pulled down to ground. The signal wire is tied to ground and voltage will be much higher if this is loose or missing.

Running a 89mm custom intake w/ an 034 MAF weld in bung and a hitachi sensor. It pretty much resembles the intake that SRM sells.

I will check the wiring before going any further. Thanks for your help.

[Monty23]

Really seems like you have a boost leak with all your symptoms

[erykv1]

Really seems like you have a boost leak with all your symptoms

I agree, but I've pressure tested again and again with no signs of a leak. System holds pressure for a good amount of time before it bleeds down. I've changed all internal check valves to rule out an internal leak.

Lets say there is a leak in the system, it wouldn't cause these voltage readings at moderate PSI levels.

[christianb5s4]

I agree, but I've pressure tested again and again with no signs of a leak. System holds pressure for a good amount of time before it bleeds down. I've changed all internal check valves to rule out an internal leak.

Lets say there is a leak in the system, it wouldn't cause these voltage readings at moderate PSI levels.

Which internal check valves have you checked? Have you smoke tested the vacuum lines?

[erykv1]

Which internal check valves have you checked? Have you smoke tested the vacuum lines?

Both green check valves on the intake manifold, the check valve from the brake booster line, the check valve in the spider hose, the pancake valve on the spider hose, and i even put in stock DV's to rule my 034 DV's out.

Blown through / sucked each valve to make sure they were 100% functional. all vac lines were rebuilt / replaced when the motor was out. been chasing this issue for 1+ month and its driving me insane.

I wanted to say it was tune related, but even if it was the tune / some vac / boost leak I am completely overlooking, my MAF voltage readings are way off.

[axnjaksn]

the frustration continues!!!!!! we'll get it man, sooner hopefully before later

[erykv1]

Stock hitachi? Intake setup?

uhfm_w is direct voltage from the A/D converter, so nothing tuning wise will affect it.

Post MAF leak lowers restriction which can allow excessive airflow. Also, the MAF is fed 5v and pulled down to ground. The signal wire is tied to ground and voltage will be much higher if this is loose or missing.

Can you verify if my understanding is correct...

The ecu takes the voltage reading @ the MAF, then references the MLHFM table to convert those values into a g/s value for the ECU to do its thing with?

KRKTE values are used in part throttle and idle conditions, but not during WOT correct?

If I swapped MAF sensors to troubleshoot, and the car was still warm... is it safe to assume that it was still in closed loop mode when I restart? I swapped MAFs (again) the other night and it registered the partial adaptations almost immediately (within 0.3miles)... I thought that was kind of odd.

[phila_dot]

Yes, MLHFM converts voltage to airflow.

KRKTE converts relative fuel mass to injector on time. It's used at all times, but it's greatest influence is during part throttle.

Yes, most likely it would be in closed loop. Not due to motor temp, but due to sensor temp.

Adapted fuel trims are stored in non-volatile memory and would remain unless memory was cleared.

[erykv1]

OK, update / troubleshooting check...

Since it is a hitachi, I will reference the table on the right.



With the key in the ignition, I am getting the following at the harness (with the sensor unplugged):

- 5V when testing pins 1 and pin 3.
- 3.48V when testing pins 2 and 3.

Is this normal? I thought pin 2 was the 12V line... or does the car have to be running for it to read 12v?

[Monty23]

Was the key on when you tested pin 2?

[erykv1]

Yes, key was on. I was speaking to someone else and they said I shouldn't have had my MAF disconnected during this procedure. Thoughts?

[Monty23]

pin 2 should be +12V from the battery, so if you are not getting +12V at pin2, you need to figure out why. Check your harness and make sure someone didn't splice wires and screw something up.

I don't know what the guy was talking about by having the maf plugged in.... that would make testing difficult and I don't see why results would be different either way if testing at the plug/connector.

[erykv1]

pin 2 should be +12V from the battery, so if you are not getting +12V at pin2, you need to figure out why. Check your harness and make sure someone didn't splice wires and screw something up.

I don't know what the guy was talking about by having the maf plugged in.... that would make testing difficult and I don't see why results would be different either way if testing at the plug/connector.

well, from what I was told, the car has to be running for it to read the full 12v? not just with the key on.

if this isn't the case, then I may have found my issue.

[erykv1]

pin 2 should be +12V from the battery, so if you are not getting +12V at pin2, you need to figure out why. Check your harness and make sure someone didn't splice wires and screw something up.

I don't know what the guy was talking about by having the maf plugged in.... that would make testing difficult and I don't see why results would be different either way if testing at the plug/connector.

The harness is 100% factory.

I had 2 other b5 s4 owners test theirs, and the pins 2&3 both read 2.5V with the key on and the MAF disconnected. Mine reads 3.84V... which may be why my MAF reads high.

Can anyone else verify this for me or check theirs?

[Aragorn]

The harness is 100% factory.

I had 2 other b5 s4 owners test theirs, and the pins 2&3 both read 2.5V with the key on and the MAF disconnected. Mine reads 3.84V... which may be why my MAF reads high.

Can anyone else verify this for me or check theirs?

Some engine power feeds are fed from the fuel pump relay and are only live when the ECU signals that relay to close. (IE cranking, pump prime or engine run)

A quick look on the wiring diagram for the AGB motor shows that the MAF and most of the engine sensors are powered in this way. N75/N80/N249, lambda sensor heaters etc are all fed from the same supply as the MAF, which is sourced from the fuel pump relay.

The 2.5/3.7v your seeing is probably just a phantom voltage from somewhere else, feeding down into that line. These things happen when one end of a circuit is left floating.

Pretty sure the hitachi sensor has no voltage offset either. The bosch sensor can measure negative airflow, and thus 0g/sec isnt 0v, it reads 1v at 0 airflow. The hitachi sensor cant measure negative flow, and reads 0v output when no airflow is present.

[erykv1]

Some engine power feeds are fed from the fuel pump relay and are only live when the ECU signals that relay to close. (IE cranking, pump prime or engine run)

A quick look on the wiring diagram for the AGB motor shows that the MAF and most of the engine sensors are powered in this way. N75/N80/N249, lambda sensor heaters etc are all fed from the same supply as the MAF, which is sourced from the fuel pump relay.

The 2.5/3.7v your seeing is probably just a phantom voltage from somewhere else, feeding down into that line. These things happen when one end of a circuit is left floating.

Pretty sure the hitachi sensor has no voltage offset either. The bosch sensor can measure negative airflow, and thus 0g/sec isnt 0v, it reads 1v at 0 airflow. The hitachi sensor cant measure negative flow, and reads 0v output when no airflow is present.

so to accurately check for 12v, my MAF should be connected and the car should be running or turned over?

[Aragorn]

unplug it if you like, the car will run fine with it unplugged so long as the tune is decent, just start the engine first.

[erykv1]

With the MAF disconnected, does block 032 still log fuel trims? Does anyone know?

[humblelittlea4]

Did you ever figure this out?

[erykv1]

Did you ever figure this out?

Yeah after going through 3 new MAFs, replacing every check valve / hose on the car... it turned out the MAF was poorly positioned in the intake tract. The flow to the sensor was too turbulent and was throwing the readings off.
A flow straightener could have possibly mitigated this, but I ended up going back to an OEM rs4 accordion, 85mm MAF housing, and RS4 airbox.

[humblelittlea4]

I’m going through the exact same problem. My maf readings are all over the place because of turbulence. I need to find a flow straighter to fix this. The problem started when I misplaced my previous flow straightener. What behavior did your car have while this maf turbulence issue was there? I have a little hiccups while cruising with minimal throttle and I suspect it’s because of the turbulence.

[humblelittlea4]

My cars building 18 psi at most has small sputters/lean spikes on minimal throttle. And I’m hoping the flow straightener will fix this. But if not, at the very least it will fix my readings all over the place.

[phila_dot]

My cars building 18 psi at most has small sputters/lean spikes on minimal throttle. And I’m hoping the flow straightener will fix this. But if not, at the very least it will fix my readings all over the place.

It’s misfiring, check ignition system