TD5 air flow meter test

hello boys and girls

a friends TD5 T reg D2 is running realy low on power, and was talking about a remap to get some power back. But after i took it for a run i told him it doesnt need a remap, it needs something sorting on the engine as it shouldnt be that gutless. Ive drove 2 300 TDI's and they both had loads more power than this TD5, plus ive also drove a good TD5 and it was great on power even tho it weighs more, so i knew the engine wasnt running right

i looked at the MAP sensor and yes it was cover in crap (all clean now tho)

i checked the EGR was working and that it fully closed off

i noticed the fuel pressure regulator was leeking so a new one is on its way

BUT i realy think that the main problem is the MAF (air flow meter), ive drove an alfa 156 2.4 JTD with a dodgy MAF and it felt the same as this. I know like the alfa if you unplug the MAF it goes into a base setting and usualy improves by 500% if the MAF is at fault.....

...... BUT i also own a new alfa 156 1.9 16V JTD EURO4 engine and if the MAF is unplugged the engine light comes on and doesnt go off if the MAF is plugged back in again, only if you wipe the fault code from the ECU


SO BASICALY I WANT TO UNPLUG THE MAF ON THE TD5 TO SEE IF IT IMPROVES ANY, BUT IM WORRIED THAT THE ENGINE LIGHT MAY STAY ON, AND IVE GOT NO SOFTWARE FOR LANDROVERS SO WONT BE ABLE TO TURN IT OFF MYSELF

has anybody unpluged the MAF on a TD5 and noticed if the engine light stayed off???

regards
adam

Standard TD5 test, unplug it and power is restored,its quicker than plugging in Testbook - you have a knackered MAF.No CEL,just a logged fault which can be cleared at any later date.

eightinavee said:

Standard TD5 test, unplug it and power is restored,its quicker than plugging in Testbook - you have a knackered MAF.No CEL,just a logged fault which can be cleared at any later date.

Click to expand...

cheers bud, just the test i wanted to do, just worried the CEL was going to stay on

have you done this test yourself???


on an alfa forum im joined with, my motto was "if in doubt MAF it out" they are the most unreliable sensor on any car, and they can cost a couple of hundred quid aswell..... alot of people always say dont buy cheap and always buy genuine bosch, but they dont last that long, so i prefer to buy several cheap ones for less money than a bosch one

thanks for the reply :bounce:

Yes,countless times.I have many customers running around with them permanently disconnected.They will go through the smoke test like this.Fitting a new unit,(Forget aftermarket - they are shi-e) just gives a little more top end poke,and I guess better mpg - but I only diagnose them,I dont run the rubbish.

from RAVE:

The MAF sensor can fail the following ways or supply incorrect signal:
l Sensor open circuit.
l Short circuit to vehicle supply.
l Short circuit to vehicle earth.
l Contaminated sensor element.
l Damaged sensor element.
l Damaged in wiring harness.
l MAF supplies incorrect signal (due to air leak or air inlet restriction).
In the event of a MAF sensor signal failure any of the following symptoms may be observed:
l During driving engine speed may dip, before recovering.
l Difficult starting.
l Engine stalls after starting.
l Delayed throttle response.
l EGR inoperative.
l Reduced engine performance.
l MAF signal out of parameters.
The MIL will not illuminate in a MAF sensor failure, and the ECM will use a fixed default value from its memory.

hi i have just had mine in for a diagnostics check due to driving like crap when warm in stop start traffic, just trying to crawl is a nightmare when its warm the revs jump from 600 to 1200 with the slightest pressure on the pedal after maybe a second delay of course, it really isnt nice to drive, from cold it is spot on now the faults that have been logged are:

mass air flow low
egr stuck open

also 2 other faults relating to cruise control although i dont have cruise on mine

could the egr be causing the maf to record a fault also

no1smytho said:

hi i have just had mine in for a diagnostics check due to driving like crap when warm in stop start traffic, just trying to crawl is a nightmare when its warm the revs jump from 600 to 1200 with the slightest pressure on the pedal after maybe a second delay of course, it really isnt nice to drive, from cold it is spot on now the faults that have been logged are:

mass air flow low
egr stuck open

also 2 other faults relating to cruise control although i dont have cruise on mine

could the egr be causing the maf to record a fault also

Click to expand...

best to remove egr altogether, then fit new maf sensor, or un plug yours if it feels better then change maf

EGR would not affect the MAF reading though a MAF fault could affect the EGR ... if it's stuck open it might be due to excessive muck in it which would "choke" the engine cos it doesn get any oxygene through the inlet manifold... also if it's stuck open due to dirt not due to a management or modulator issue by unplugging it wont help at all cos it will stay opened.

as said...remove the EGR and replace the MAF

The EGR valve WILL massively affect the airflow reading if its stuck open.(In some cases will cause poor or non start situations)It will mean that the engine is constantly recirculating its own combustion gases and not taking in enough fresh air - hence a low maf reading.Repair or remove the EGR valve and the airflow reading will be restored.Guideline values for the airflow are 55-65KG/hr at idle and approx 330KG/HR at 3000rpm,engine hot,all loads off.(When the EGR is functioning properly you can see the reduction in airflow,from memory just off idle it drops to about 35KG/HR when the EGR is at around 80% open)

eightinavee said:

The EGR valve WILL massively affect the airflow reading if its stuck open.(In some cases will cause poor or non start situations)It will mean that the engine is constantly recirculating its own combustion gases and not taking in enough fresh air - hence a low maf reading.Repair or remove the EGR valve and the airflow reading will be restored.Guideline values for the airflow are 55-65KG/hr at idle and approx 330KG/HR at 3000rpm,engine hot,all loads off.(When the EGR is functioning properly you can see the reduction in airflow,from memory just off idle it drops to about 35KG/HR when the EGR is at around 80% open)

Click to expand...

i always like to speak about things with you believe me... cos i might learn things, and not just me, everyody who's reading it so please dont be offended that i contradict you on this... cos AFAIK the EGR valve is controlled by the ECU based on MAF readings and i can't see how these readings are affected by the EGR valve's behaviour(as long as it's just an EGR valve fault not a ILT valve fault, which is just for the EU3 systems.)...it might affect the MAP reading maybe
IMO on this logic all the cars with bypassed EGR(or with stuck closed EGR) would have "Mass air flow high" fault codes in the ECU.
But to cut a long story short on all sites where there are fault code descriptions nobody speaks about MAF reading error due to EGR missbehaviour

here are two examples from OBD-II description... the fact that the D2 is not OBDII compliant is irrelevant cos it's only about a diagnostic protocol encryption not functionality of the car's systems, and as we speak about OBDII/EOBD we can't presume that those cars dont have EGR fitted:

1. OBD-II Trouble Code: P0102 Mass Air Flow (MAF) Circuit Low Input

2. OBD-II Trouble Code: P0103 Mass Air Flow (MAF) Circuit High Input

Off course if i'm wrong i'll stand corrected and accept my apologies in advance

no1smytho said:

hi i have just had mine in for a diagnostics check due to driving like crap when warm in stop start traffic, just trying to crawl is a nightmare when its warm the revs jump from 600 to 1200 with the slightest pressure on the pedal after maybe a second delay of course, it really isnt nice to drive, from cold it is spot on now the faults that have been logged are:

mass air flow low
egr stuck open

also 2 other faults relating to cruise control although i dont have cruise on mine

could the egr be causing the maf to record a fault also

Click to expand...

As you have had the EGR stick open I'd also pull the MAP sensor and give it a clean as it will be covered in black sticky gunge. Simple to do and makes a big difference when working properly. I think Ratty did a "how to" on the MAP but its not rocket science and lives midway on the inlet manifold. Two 10mm (may be 8mm can't recall) bolts and it should pop right out. the O ring seal may make it stick a bit but take your time and it will wiggle free. Dont poke anything down the sensor when cleaning it out though. I used oven cleaner but you can soak it in brake cleaner to loosen the crap then flush with parafin or petrol.

sierrafery said:

i always like to speak about things with you believe me... cos i might learn things, and not just me, everyody who's reading it so please dont be offended that i contradict you on this... cos AFAIK the EGR valve is controlled by the ECU based on MAF readings and i can't see how these readings are affected by the EGR valve's behaviour(as long as it's just an EGR valve fault not a ILT valve fault, which is just for the EU3 systems.)...it might affect the MAP reading maybe
IMO on this logic all the cars with bypassed EGR(or with stuck closed EGR) would have "Mass air flow high" fault codes in the ECU.
But to cut a long story short on all sites where there are fault code descriptions nobody speaks about MAF reading error due to EGR missbehaviour

here are two examples from OBD-II description... the fact that the D2 is not OBDII compliant is irrelevant cos it's only about a diagnostic protocol encryption not functionality of the car's systems, and as we speak about OBDII/EOBD we can't presume that those cars dont have EGR fitted:

1. OBD-II Trouble Code: P0102 Mass Air Flow (MAF) Circuit Low Input

2. OBD-II Trouble Code: P0103 Mass Air Flow (MAF) Circuit High Input

Off course if i'm wrong i'll stand corrected and accept my apologies in advance

Click to expand...

Fairly simple,the ecu can command as much as it like to open or close the EGR valve,in this case the logged fault is EGR valve stuck open.The fault will be logged as an assumption of the ecu because of lower than expected maf readings and a higher than expected inlet air temp.The valve sticking is then beyond the control of the ecu,which uses a PWM signal to progressively use vacuum to pull on the EGR valve to open it.(Rest state is closed)
So it stands to reason that if the valve is stuck open,(Not uncommon) the engine ecu is going to see value back from the Maf and inlet air temp sensors that it doesnt like - it then will assume the valve is stuck open,and also complain about lower than expected airflow readings.
All this is a big problem to combustion when driver demand increases at low revs,the low airflow reading will limit the amount of fuelling the ecu will allow.(Thinking it will limit black smoke,when actually its already smoking badly due to the lack of fresh air) As the revs increase the amount of EGR is gradually overcome by increasing mass of air boosted in from the turbo,power output will increase,airflow readings will increase and the driver will be less aware of the issue.
BTW, those links to the OBD site are very generalised - not much help at all in a real world situation,far better to use specific data from a trusted one make site or forum like this,esp when as on this site there are plenty of people who have experience of faults such as these.

ok, i can't argue on that, just a question... on the same logic why the "EGR stuck closed" fault doesnt come together with the "air flow too high" code then?

... or why there are cases of "EGR stuck open" codes without the "air flow too low" at the same time?

sierrafery said:

ok, i can't argue on that, just a question... on the same logic why the "EGR stuck closed" fault doesnt come together with the "air flow too high" code then?

... or why there are cases of "EGR stuck open" codes without the "air flow too low" at the same time?

Click to expand...

Ok,firstly the EGR valve only operates normally under idle and light load/cruise conditions.So if it sticks shut firstly the driver will notice no difference at all,secondly the valve being stuck shut will mean that the engine will only injest fresh air.Air flow high faults are usually caused by a sticking wastegate,which in turn boosts too much air - more air than normal,equals an overly high maf reading.
The second example can be because the EGR valve may be stuck partially open,increasing the inlet air temp,but not open enough to put the maf reading below the threshold to log a low reading.

irrefutable ... thanks