MAF Problem?

[doc]

Unfortunately I only have the Haynes manual for my Mk4 Bora. I have had higher than average fuel consumption and some black exhaust smoke when hot. This is not all the time. Sometimes it runs ok but then others it chews through the fuel. My shareware vag shows faults in the MAF and the Lambda sensor.
The manual is next to useless for the petrol engine emissions but in the diesel section, it says there is supposed to be 12 volts between terminal 2 and 3 of the MAF connector and around 5 volts between terminals 3 and 4. I have the 5 volts but nothing between terminals 2 and 3. Both terminal 2 and 3 seem to be earths as the multimeter shows battery voltage when connected between each terminal individually and the battery.
Any suggestions?

Thanks in advance

doc

[dylan8]

Have no idea about the voltage stuff sorry.

How many Km on your car, what year? has it had any other sensors etc changed in the past?

Can show up as being MAF on checkers but from my past experience it may not always be.

Have you tried disconnecting the battery to reset the ecu? Also hows the temperature gauge after 5-10mins of the motor running?

[h100vw]

What engine doc?

Coolant temp sensor and Lambda more likely to cause symptoms in my experience.

If you can't get a better scan from the ECU with another VAG-COM. The temp sensor is a cheaper speculative replacement.

Gavin

[doc]

It's the 2 litre with an auto. I replaced the coolant sensor about 4 months ago. It does seem to show a bit low at times.
The car has 113000k's and I'm not sure whether any other sensors have been changed in the past.
I have disconnected the battery for a while to reset the ecu but it didn't seem to make a difference.
I got a new catalytic converter 2 days ago as the old one was rattling. I saw inside the old one and it was starting to block up. It does seem to be using less fuel since then and I haven't seen any smoke but it could be my imagination. Maybe I should just take it to the local vw place for a proper scan.
Thanks for the replies.

[Jmac]

Thermostat is stuck open then mate, this will have the same characteristic of a failing temp sensor, engine will run cool and the injection pulse width will then be longer thus more fuel consumption, changed heaps of stats on these mate. What is the heater like on hot mate , is it like an oven or luke warm that will geive you a good idea too
Cheers
Jmac

[Transporter]

Unfortunately I only have the Haynes manual for my Mk4 Bora. I have had higher than average fuel consumption and some black exhaust smoke when hot. This is not all the time. Sometimes it runs ok but then others it chews through the fuel. My shareware vag shows faults in the MAF and the Lambda sensor.
The manual is next to useless for the petrol engine emissions but in the diesel section, it says there is supposed to be 12 volts between terminal 2 and 3 of the MAF connector and around 5 volts between terminals 3 and 4. I have the 5 volts but nothing between terminals 2 and 3. Both terminal 2 and 3 seem to be earths as the multimeter shows battery voltage when connected between each terminal individually and the battery.
Any suggestions?

Thanks in advance

doc

Look in my post in here how to test MAF
Let us know how did you go.

[doc]

Thanks for the replies. It came good for a few days so I thought it may have been a bad connection. (I checked all connections and jiggled them)

Jmac
I was thinking the thermostat may be playing up as as times it takes a while to warm up and the heater is not at hot as it used to be. I didn't think that would effect the ECU as my last car was a 1976 Holden Ute. The closest to a computer in that was electronic ignition.

Transporter

I followed your test as best I could as remembering I only have the Vagcom shareware. It logged
P1570
P1544
P0134
P1128
P0171
P0102
It turns out I do actually have 12 volts at the MAF and everything else appears to be OK.

I VCDS under group 03 I didn't have mg/stroke. The closest was g/ms or similar. That was about 5.2 if that means anything. I can't take it for a drive as I don't have a laptop. Only a hardwired jobby

The problem is when it's at operating temperature but I'll try a thermostat first and see how it goes. If not, down to Volkwerke for a scan and some work.

doc

[Jmac]

Yeah it affect the running condition, doesnt upset the computer as such its merely doing what its told, engine is cooler so the injection pulse is wider thus lots richer, done a few now, so really when the stat is playing up and the engine is cool its doing what a faulty temp sensor would do ( tell the ecu the engine is cold) if you catch my drift.
See how you go. Fit it, bleed it and clear all your faults and go for a blast, whilst you are there check all induction system is in good order, vac lines or splits.
Good luck
Jmac

[h100vw]

Rev the engine and the MAF output will change. Drivng it would be a better test though.

Gavin

[Transporter]

I have to check the rest of the OBD2 codes but I know for sure that P0171 is lean mixture and P0102 is MAF low output.
Can you log the data in VCDS?
You should also check your oxygen sensor.

[Jmac]

Ok if you check your O2 sensor and the stat is stuck open it will be reading rich along with a longer duty cycle on the injectors, all checkable with measured blocks on Vagcom. If you still query the o2 sensor pull the vac line off the fuel pressure reg then itll richen, blanking off the vac at the same time. Now check it for lean switching, create an air leak. All very checkable with Vagcom. You mention the fact its at op temp well the system is on closed loop then.
good luck with tests
Jmac

[Transporter]

Ok if you check your O2 sensor and the stat is stuck open it will be reading rich along with a longer duty cycle on the injectors, all checkable with measured blocks on Vagcom. If you still query the o2 sensor pull the vac line off the fuel pressure reg then itll richen, blanking off the vac at the same time. Now check it for lean switching, create an air leak. All very checkable with Vagcom. You mention the fact its at op temp well the system is on closed loop then.
good luck with tests
Jmac

Hey there, Jmac.
All we need now is his car.

[Jmac]

Hey there, Jmac.
All we need now is his car.

Haha true story mate
cheers
Jmac