Incorrect Fuel Reading/Idle Consumption High

[Righteousness]

Hey all,

I recently serviced the following on my Diesel engine and concerned about the latter: MAF sensor clean with Liqui Moly MAF sensor cleaner, air filter change, fuel filter change, and Liqui Moly 500mL fuel system purge via fuel lines.
All of these were done successfully with no problems encountered. I kept the fuel line in the mason jar when purging the system without sucking in air at all. No leaks coming from fuel lines either when engine is running.

Results:
- My idling was at 0.6l/h and is now 0.8-1.0/h… does not change.
- Average fuel consumption was 5.9l/km and is now 7.2-8l/km with 50-60km/hr speeds.
- When idling, the 0.0l/km reading increases every 10 seconds, doesn’t stop and can keep going until it maxes out. I recall is wouldn’t change values until I acc understand this is not a reliable source of readings, but a change has developed since the recent service that I have performed so I’ve done something wrong here.
I’ve disconnected the battery to reset the ECU but hasn’t helped.

Is the MAF sensor faulty? Does this go away when the liqui moly is depleted from the system? I sprayed the MAF sensor without contact and allowed it to dry.

Appreciate the upcoming feedback.

[Righteousness]

Plugged in the VCDS and was presented with the following:

Address 01: Engine Labels: 03G-906-016-BKD.clb
Control Module Part Number: 03G 906 021 KK HW: 03G 906 021 KK
Component and/or Version: R4 2,0L EDC G000AG 9970
Software Coding: 0000078
Work Shop Code: WSC 20117 959 97404
VCID: 72B6B0B228A39D6B897-8026
1 Fault Found:

000258 – Mass Air Flow Sensor (G70)
P0102 – 000 – Signal too Low – Intermittent
Freeze Frame:
Fault Status: 00110000
Fault Priority: 2
Fault Frequency: 1
Reset counter: 255
Mileage: 119589 km
Time Indication: 0
Date: 2000.00.00
Time: 14:03:14

Freeze Frame:
RPM: 1218 /min
Speed: 0.0 km/h
Load: 0.0 %
Duty Cycle: 79.7 %
Bin. Bits: 00101000
Mass Air / Rev.: 615.0 mg/str
Mass Air / Rev.: 0.0 mg/str

Readiness: 0 0 0 0 0

[Lucas_R]

Its possible that the MAF sensor has died and may need replacement. Otherwise, check that you have it installed facing the right way and the plug is plugged in properly.

If the engine does not know how much air is being sucked in, then it wont know how much diesel it needs to achieve its desired air:fuel ratios, so it will default to a safe air:fuel combination which is always rich to be safe. Rich = using more fuel than usual/necessary.

Cleaning the MAF is safe and you have used a correct MAF cleaning product. The product evaporates very quickly so the product dries within 10-15 seconds of spraying on the MAF.

Try unplugging the MAF and see if the car behaves any differently. If not, then the MAF needs replacing. (assuming its not incorrectly installed)

[Righteousness]

Its possible that the MAF sensor has died and may need replacement. Otherwise, check that you have it installed facing the right way and the plug is plugged in properly.

If the engine does not know how much air is being sucked in, then it wont know how much diesel it needs to achieve its desired air:fuel ratios, so it will default to a safe air:fuel combination which is always rich to be safe. Rich = using more fuel than usual/necessary.

Cleaning the MAF is safe and you have used a correct MAF cleaning product. The product evaporates very quickly so the product dries within 10-15 seconds of spraying on the MAF.

Try unplugging the MAF and see if the car behaves any differently. If not, then the MAF needs replacing. (assuming its not incorrectly installed)

I have done as you suggested with unplugging the MAF sensor and no difference was noted. Idling was at 0.8l/km still. I will use another MAF sensor on this car to see if it resolves it but how in the world would cleaning the MAF sensor cause a fault?! I left it out to dry for 30 minutes and plugged it back in.

[Lucas_R]

How in the world would the MAF sensor from me cleaning it?!

Could just be coincidence. They do tend to have a lifespan though.

A few weeks ago I helped my neighbour to troubleshoot an issue with his Mercedes van - turns out it was a dodgy MAF. That was a 2013 model Sprinter van (ex Ambulance and has done 340,000kms). The van had heavily reduced power and error codes for a bad MAF. New MAF sourced from overseas (for about 1/3 of the price of getting it locally) installed and the van is running like new again. I tried cleaning it before buying a new MAF but it didnt do anything.

[Righteousness]

Could just be coincidence. They do tend to have a lifespan though.

A few weeks ago I helped my neighbour to troubleshoot an issue with his Mercedes van - turns out it was a dodgy MAF. That was a 2013 model Sprinter van (ex Ambulance and has done 340,000kms). The van had heavily reduced power and error codes for a bad MAF. New MAF sourced from overseas (for about 1/3 of the price of getting it locally) installed and the van is running like new again. I tried cleaning it before buying a new MAF but it didnt do anything.

$3-400 for a new BOSCH MAF sensor.. the car has only done 120,000kms at the moment.

[Lucas_R]

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[bluey]

In my reading, chip based MAF sensors are very reliable.

Most likely cause seems to be failing lambda sensor.

Apparently there are some measurements in measuring block 30 via VCDS that may indicate this, but i haven’t found a good diagnostic guide.
Bosch suggests lambda sensors could be good for 160,000 km.

Old Bosch Australia oxygen sensor catalog 2013-4 has the most useful diagnostic and technical info i have found. Failing sensor reports oxygen closer to atmospheric causing computer to compensate with richer mixture. Tailpipe smell test indicated rich. That has corrected with new sensor.

Got a new Bosch lambda sensor and reported fuel consumption has dropped to lowest ever for daily drive. Only done half a tank.

[bluey]

In my reading, chip based MAF sensors are very reliable.

Except maybe they are not. There are traces of oily residue in the intake ducting from some hose upstream. Maybe that has contaminated the sensor. MAF sensor cost about $135 and swapping is a 5-10 min job. Would swap out MAF sensor before oxygen sensor knowing whst i do now.

Have disassembled the old MAF sensor and can’t see any visible evidence why it is misbehaving.

My brother had dealer swap lambda sensor in UP for $800!