MAF and MIL light

[NikTheGeek]

Just trying to diagnose a failing/failed MAF. However, when I unplug it and run the engine with it disconnected, the engine warning light doesn't come on. Surely it should do? I haven't actually driven it, just run it on the drive.

Any thoughts?

tnx

Nick

[kiowa]

No you wont get any warnings on the dash it's self.You will find that the car will run fine without it but will be heavy on fuel

[NikTheGeek]

No you wont get any warnings on the dash it's self.You will find that the car will run fine without it but will be heavy on fuel

Well thats the symptoms I already have! :) No warning light, car runs fine but mpg has dropped right down to around 27-28!

I've had it out and cleaned it so I'll see how that goes, I don't really fancy spending £170 on a new one only to find its something else!

tnx

Nick

[Hodgy]

Does the car run better with the maf disconnected or is it the same. If there is no difference, then its likely not the maf sensor at fault. It could be something as simple as a clogged air filter?

[wuzerk]

Most Maf faults do NOT show up as a faliure. There is no way you can see if unplugging the Maf makes any difference by 'running it on the drive'
nor is that any way to check the fuel consumption. An auto diesel used for purely local trips will only show around 28mpg any way.

[NikTheGeek]

I unplugged the MAF last year and the mpg dropped to 26mpg on a brim-brim. I check every time I fill up and I have been getting 31-32mpg but this last couple of weeks its dropped to 27mpg. No other changes - apart from new tyres at xmas. The air filter is 12 months old and black so I'm going to change it anyway, I've took off the white cover to expose the paper element for now.

FWIW, when I did unplug the MAF last year and ran it for a tank, I noticed no difference in performance other than the drop in MPG.

Not sure if all that helps with any diagnosis! :)

Nick

[wuzerk]

NICK, I ran for three months with my Maf disconnected with no problems and didn't really notice an increase in consumption. I get over 50mpg on a motorway run but am only seeing around 28 on purely local runs. If unplugging your maf makes no improvement in performance then it would appear to be ok but they can overfuel as well as the more usual fault of ruining the low down performance. Are you seeing any black smoke and is the exhaust
leaving a black deposit on the rear bumper?

[NikTheGeek]

Just done a brim to brim again and the mpg has dropped to 21 !!

Help! What can I look for, it's driving fine. I did clean the maf yesterday so hopefully it'll improve, but what can I look for? It seems to be driving better today - but I might be imaging it and I can't believe cleaning a maf would make much of a difference.

FWIW, there is no soot on the bumper, but the inside of the tail pipes are covered in a thick powdery black soot - however I presume that would be normal. No idea about black smoke, none I can see whilst driving.

Help :)

tnx

Nick

[Jules]

Carry out Leakback test.
Worst scenario is HP pump seals.
Check oil level isn't rising!

Wiring fault from MAF ??
Do continuity tests from MAF to ECU.
Sounds like your MAF isn't functioning

[NikTheGeek]

Tnx Jules

Oil level spot on high mark. What would it mean tho if it did get higher? Diesel in the oil?

No fuel leaks.

Not sure how to perform a leak-back test, I'll do a search.

We have a T4 at work (a college), but no one to operate it. How hard can it be? :) Can I just hook it up myself and go through some menus? I've never even seen one, are they small enough to borrow and take home for the weekend?

No MIL light

I'll get it hooked up and then replace the MAF if needed

Nick

[NikTheGeek]

Just had the OBD display running engine temp on a 12 mile journey in to work this morning. Outside temp 3.5'c, internal heater and air con off, speed mainly 40mph, a little stop start then a couple of miles flat out at 70mph - ish ;)

Engine temp never got above 86'c and it took around 9 miles to get to that. It slowly rose from 60 through to 70, even slower from 70 to 76 and took ages to get from 76 to 86.

So, is the thermostat shot? If it is, would it make much difference to fuel economy? Just 10-20'c difference in temp?

Finally, I gather the MAF has a temp sensor on it that if it goes it defaults to -5'c and overfuels the engine. How would I check this temp with the IPK?

tnx

Nick

[Jules]

Your stat does sound out of spec but a true test is :
Will it maintain 88C in top gear at 50MPH?

MPG typically only reduces by 4-6 with temps you have.

Again T4 may tell you what is going on.

Oil level rises if HP pump seals fail

[para999]

Just had the OBD display running engine temp on a 12 mile journey in to work this morning. Outside temp 3.5'c, internal heater and air con off, speed mainly 40mph, a little stop start then a couple of miles flat out at 70mph - ish ;)

Engine temp never got above 86'c and it took around 9 miles to get to that. It slowly rose from 60 through to 70, even slower from 70 to 76 and took ages to get from 76 to 86.

So, is the thermostat shot? If it is, would it make much difference to fuel economy? Just 10-20'c difference in temp?

Finally, I gather the MAF has a temp sensor on it that if it goes it defaults to -5'c and overfuels the engine. How would I check this temp with the IPK?

tnx

Nick

I had the same problem recently. Disconnected the MAF and performance went back up to normal, but the MPG went down drastically! The temp gauge also took froever to move and never reached midway. I think I've read on this forum that with the MAF disconnected, the ECU thinks the outside temp is -5, so fuels for that. At the time of my problem, it was -10 most of the time so wasn't too bothered!

I replaced the MAF with a Pierburgh one and fitted a Synergy 2 tuning box from Roverron... http://tuning-diesels.com/Products/prod2.htm

The result was fantastic...increased power and torque depending on which setting you put the box on. The temp gauge is back to normal too and warms up as quickly as before. I wouldn't spend £170 on a replacement MAF and certainly not but one from Fleabay....never know what you will get or how reliable it will be!

You will also need a 5 sided Torx bit (most are 6 sided) which is also availablefrom Roverron...or you could cut slots in the screw heads with a saw and then use a flat bladed screwdriver.

:)