Think I need a new Mass Air Flow Sensor

[imartin]

My car is a 2003 2.0 hdi estate.

Over the last few months the acceleration has been dire.
Engine runs smoothly and no black smoke.

Garage has so far replaced timing sensor on the cam shaft as they saw a timing error code.

Also recently had fuel filter replaced.

EGR valve cleaned and checked.

After the EGR - the mechanic said that further investigation could be pricey, so today I thought I'd unplug the MAF sensor to see what would happen and there was a considerable improvement - more like back to its old self.

Rather than clean the sensor I have - the car is 14 years old - I thought I'd just go and buy a replacement MAF Sensor.

From looking on the web I think the one I'm looking for is a Siemens 5WK9621Z.

Could anyone please tell me whether this is correct?

I'm looking at the 3rd party rather than OEM for this. Ebay has them from £25.

Also any recommendations as to where it's best to get from?


Thanks in advance

[fattail95]

Please learn from my mistakes, I sent months hunting down my poor performance issue before, having replaced the MAF with two different cheap eBay parts with no success. Finally, I splashed out on a genuine MAF as a last hope and that fixed all my problems! The cheap eBay MAF's are sh*te and report incorrect data to the ECU as they are made of cheap, inferior components.

Part number: 1920 7S



Best Regards,
Ben

[Doggy]

+1 shop around for the cheapest OE / Siemens unit

[PeterN]

I have had success with second hand units, most in the scrap yard still work OK and are probably original equipment. If you are handy with a multimeter you can check them yourself. The only effect I have noticed with a duff MAF is poor acceleration below 2000 rpm, doesn't seem to make much difference to anything else, try disconnecting it and see if it makes any difference, if it doesn't the chances are its not working.

Peter

[GingerMagic]

+2 for a new genuine MAF.
Look online for various deals at local factors - some have free delivery too...

For example, go into ECP website, type in your reg and look for a Siemens MAF, then open a second window and type in ECP discount code - do this for cp4l, gsf etc to find the best deal.

I do have a couple of old MAFs here, you are welcome to try them out before you buy a new one.

[trufflehunt]

I've bought a genuine Siemens second user MAF on eBay.
About £20 ish, and it worked fine for me.

One on there right right now for about £12.

May depend on how much you're willing to spend. New or s/h, stick to genuine Siemens.

[imartin]

Many thanks for all the helpful advice.

I'll report back how I get on!

[piglet]

+3 on genuine or OEM
I bough a chinese one and then had to buy a proper one as well, thus negating any saving.

[imartin]

I'll confess to having gone for a 3rd party one before getting all your comments on OEM.

I hadn't thought I would have been able to reanimate my old PC with the parts database on it (unable to transfer to my new one it seems) - but was able to confirm with the database.

The problem had been going on for a while and I guess I just got impatient.

I ordered my from Ebay - it said the unit is UK made. It was just a shade under £26.

However the acceleration has improved considerably. Whether it is "as good as new" it's hard to tell - the problem had been going on for some months now.

If there is a way to confirm this more accurately then I'd be happy to hear it.

However if the car runs alright without a MAF sensor fitted - what is the point of it? Does it help reduce emissions?

[dirtydirtydiesel]

I'll confess to having gone for a 3rd party one before getting all your comments on OEM.

I hadn't thought I would have been able to reanimate my old PC with the parts database on it (unable to transfer to my new one it seems) - but was able to confirm with the database.

The problem had been going on for a while and I guess I just got impatient.

I ordered my from Ebay - it said the unit is UK made. It was just a shade under £26.

However the acceleration has improved considerably. Whether it is "as good as new" it's hard to tell - the problem had been going on for some months now.

If there is a way to confirm this more accurately then I'd be happy to hear it.

However if the car runs alright without a MAF sensor fitted - what is the point of it? Does it help reduce emissions?

There mass air flow sensor is critical to the correct running of your engine,
It measures a infinite amount of information & see's over 75 thousand miles worth of air before crying enough.
Ebay/Chinese cheepys will get your car running ok, so will disconnecting it
It'll just go into limp mode/factory base settings.
Buy a genuine bosch one from ECP or the main steelers, you won't regret it.

I said this before & I'll say it again MAF sensors should be considered a consumable item
At least you haven't got to worry about DPF'S

[frog]

However if the car runs alright without a MAF sensor fitted - what is the point of it? Does it help reduce emissions?

If the MAF sensor is unplugged, the engine management computer (ECU) will detect it, and switch to running on air pressure instead (MAP sensor).

That works fine, but... it just hasn't got that kick in the back that you get with a good MAF sensor. And it seems to be consuming just a bit more fuel.

Says someone who has been driving around a while first with MAF then without (only MAP) then back to MAF.

The emissions thing is a good point. My experience was that less smoke came out when driving on MAP only. But i think that is because of a special effect in the tuning of the ECU. This is my theory:

The MAF is at the intake side, just after the air filter but before the turbo. When running on MAF, the increase of air flow is seen before that air actually reaches the cylinders. The ECU reacts by already increasing the fuel injection. This gives a short time of "too much" fuel, giving a small puff of smoke but a rich mixture which increases exhaust gas temperature (EGT) which in turn is helpful to spin up the turbo.

The MAP sensor, on the other hand, is situated after the turbo. It sees the amount of air increase only after the air pressure has gone up due to a spinning turbo. So the ECU is always late in increasing the fuel injection. This leads to slower response to the accelerator pedal, but also to less puff at the exhaust.

[imartin]

Thanks once again for the advice and explanations.

I'll run the car on the ebay MAF for a while - and may try and find a way of testing the old one off car.

But it's as like as not I''ll do as suggested and buy a 'proper' one. Which makes are used here - Siemens/Bosch?

In the meantime I'd like to ask whether the photo here showing a cable tie on the air intake pipe is a 'bodge' ?

There is a proper Jubilee clip on the other side - so shouldn't it also have one in place of the cable tie too?

I've a Haynes 406 manual - but the photo is too bad to really see and I've also the Peugeot SEDREAP software but I can't fathom that out either.

[dirtydirtydiesel]

Yes,
That should have a jubilee clip on it, but it's on the air intake/low pressure side.
So not critical.
With regards to which MAF you have, it should be on the old one.
It's on the opposite end of the intake pipe in your pictures.

Mines a VDO SIEMENS, done via a reg check with ECP, at the moment these are £112.99,
But with there current discount code it's down to £73.44.

[imartin]

Thanks again for the very helpful advice.

Mine is a VDO too.

I got it for £67.64 from Car Parts 4 Less.

Made some further improvement but stil not accelerating as well as I remembered.

Yesterday I it dawned on me that the accelerator pedal was sitting rather low - I could pull some slack up with my foot underneath it.

I've just checked the engine bay and found that the throttle cable retaining clip had come off.

Luckily it had been caught by a tray below.

I've replaced it and now it's (almost) like a new car!

It does look like I'll need to replace the cable at some poiint as it's almost at the limit of how far it can be adjusted.

Once again thanks all.