Is this a MAF problem?

I've got a 96 Disco 300tdi. When driving normal speeds its sluggish but when you let off the throttle or if u just touch the throttle it kind of misses (or maybe goes into 'limp home' mode) and the check engine light comes on, it goes off as u accelerate or back off completely.

Think i've narrowed it down to the MAF, if i disconnect it the performance is the same but the power loss/missing problem stops and the check engine light stops flashing on. I have searched endlessly for a replacement new part (bosch unit 0281 002 092) and cant find one for less than £360!! went second hand and got one for £30, fitted it yesterday and didn't work!! not sure now if its another faulty part i bought or if i'm barking up the wrong tree! anyone got any idea how to test these things?

mark george said:

I've got a 96 Disco 300tdi. When driving normal speeds its sluggish but when you let off the throttle or if u just touch the throttle it kind of misses (or maybe goes into 'limp home' mode) and the check engine light comes on, it goes off as u accelerate or back off completely.

Think i've narrowed it down to the MAF, if i disconnect it the performance is the same but the power loss/missing problem stops and the check engine light stops flashing on. I have searched endlessly for a replacement new part (bosch unit 0281 002 092) and cant find one for less than £360!! went second hand and got one for £30, fitted it yesterday and didn't work!! not sure now if its another faulty part i bought or if i'm barking up the wrong tree! anyone got any idea how to test these things?

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Hi there, can I just ask, is this a manual or auto gearbox car?

Hi Big Lad, its Auto

mark george said:

Hi Big Lad, its Auto

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Ok Mark that's fine.

It could be the throttle potentiometer. To test for this, start the engine, get it warmed up, then very slowly and very carefully increase the tickover speed by using the throttle and listen carefully for any engine misbehaviour.

There's a possibility that it could also be being caused by the number 4 injector. This has the inductive sensor in it.
I've just had all sorts of problems as a result of this damn thing.
Mostly misfires though.
It finally ended up as the CEL flashing on at about 1200 rpm and off when I revved up to 2000 rpm. I could repeat the fault several times on the trot.
Get your alarm codes read though, they could save you costly attempts to chase the fault. Even when I had mine done, they only showed "Engine Speed". Initially pointing to the crank sensor.

I found a s/h injector and replaced the number 4 injector and it seems to have done the trick. I haven't posted the full fault details on the forum yet 'cos I've still got my fingers crossed!!

mark george said:

, if i disconnect it the performance is the same but the power loss/missing problem stops and the check engine light stops flashing on.

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thebiglad said:

It could be the throttle potentiometer. To test for this, start the engine, get it warmed up, then very slowly and very carefully increase the tickover speed by using the throttle and listen carefully for any engine misbehaviour.

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I too thought throttle potentiometer, but shirley with the MAF disconnected the problem would remain if that was the fault.......Wouldn't it?

I went round to Marks last night and of course a 96 Disco isn't OBD II compliant so nothing came up. :doh:

Did seem to be a bit underpowered though and couldn't hear the turbo. Oh and before anyone says EGR it's been blanked off and decatted.

If anyone has any idea what the problem is or.
If anyone close by has a 300tdi that there willing to let Mark borrow the MAF sensor off, just to compare I'm sure he'd apreiciate it

I didn't think the 300 had a MAF??

Yes the MAF is a large cast Bosch unit, with a flap device in it, probably why the price of a new one is up to £400 compares to a £50 plastic MAF!!

Big Lad, tried the throttle thing and seemed fine, i have got the MAF disconnected though, should i reconnect and try?

Hey Mark have a look here

http://www.landyzone.co.uk/lz/f9/maf-repair-so-whats-trick-then-32013-4.html

Not sure where you can get a MAFAM from now Roverron seems to have vanished

Bromsgrove Defender said:

Hey Mark have a look here

http://www.landyzone.co.uk/lz/f9/maf-repair-so-whats-trick-then-32013-4.html

Not sure where you can get a MAFAM from now Roverron seems to have vanished

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hey, bromsgrove defender, Found roverron products but only do freelander TD4 MAFAM

tempted to buy another second hand unit and chance my arm again, what do you think?

..........Mark

mark george said:

Yes the MAF is a large cast Bosch unit, with a flap device in it, probably why the price of a new one is up to £400 compares to a £50 plastic MAF!!

Big Lad, tried the throttle thing and seemed fine, i have got the MAF disconnected though, should i reconnect and try?

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YEsssssssssss !!! What you are trying to do is to ascertain whether the pedal potentiometer is the cause of the problem - and if the problem only occurs with the MAF connected then it would seem sensible to have it connected whilst doing the throttle tests, wouldn't it?

thebiglad said:

YEsssssssssss !!! What you are trying to do is to ascertain whether the pedal potentiometer is the cause of the problem - and if the problem only occurs with the MAF connected then it would seem sensible to have it connected whilst doing the throttle tests, wouldn't it?

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:doh: durr yes of course!! reconnected the MAF went through the throttle test as you describe Big Lad.... not a murmour, revs smoothly up and down without so much as a hiccup!

Seems to only happen when the vehicle is moving and a small ammount of throttle is applied.

mark george said:

:doh: durr yes of course!! reconnected the MAF went through the throttle test as you describe Big Lad.... not a murmour, revs smoothly up and down without so much as a hiccup!

Seems to only happen when the vehicle is moving and a small amount of throttle is applied.

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You did move the pedal very slowly (especially in the first half of the pedal travel) and attentively didn't you?

mark george said:

hey, bromsgrove defender, Found roverron products but only do freelander TD4 MAFAM

tempted to buy another second hand unit and chance my arm again, what do you think?

..........Mark

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I still think yr best bet is find some kind soul who will either let you try their's to compare, or who's selling one and will let you try it first.

Did you have a look at the turbo?

thebiglad said:

You did move the pedal very slowly (especially in the first half of the pedal travel) and attentively didn't you?

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Just a quick question. ( again )

If when the MAF is disconnected there is no acceleration hesitation,
and when it's connected there is.

How can that be the throttle potentiometer being faulty?

Bromsgrove Defender said:

Just a quick question. ( again )

If when the MAF is disconnected there is no acceleration hesitation,
and when it's connected there is.

How can that be the throttle potentiometer being faulty?

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I don't know for sure but the EDC system on the TDi auto is a very basic one with only few components: throttle potentiometer, MAF, crank sensor and temp sensor from memory.

So it MAY be that by disconnecting the MAF the ECU uses a default mode which changes the way the throttle potentiometer signals are treated.

I believe you said earlier that the misfire only occurs on light throttle openings - it is a known fact that the slides on the pot. (potentiometer) wear only in the area they are most used, which leads me to suspect the pot, that's all.

If you were able to drive the car and get it to misbehave consistently, you might find that it is in the same throttle pedal position each time, which would give more weight to the problem being in the pot.

thebiglad said:

I don't know for sure but the EDC system on the TDi auto is a very basic one with only few components: throttle potentiometer, MAF, crank sensor and temp sensor from memory.

So it MAY be that by disconnecting the MAF the ECU uses a default mode which changes the way the throttle potentiometer signals are treated.

I believe you said earlier that the misfire only occurs on light throttle openings - it is a known fact that the slides on the pot. (potentiometer) wear only in the area they are most used, which leads me to suspect the pot, that's all.

If you were able to drive the car and get it to misbehave consistently, you might find that it is in the same throttle pedal position each time, which would give more weight to the problem being in the pot.

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Slightly new twist guys, i drove it today as i have been with the MAF disconnected and guess what? the missfire and engine light came on!! this is the first time this has happened while the MAF is disconnected.

Its not as bad as when the MAF connected but definitly the same problem at the same point in acceleration. Could a dodgy potentiometer be effected by the MAF in this way? and is it possible the pot is getting worse?

thebiglad said:

I don't know for sure but the EDC system on the TDi auto is a very basic one with only few components: throttle potentiometer, MAF, crank sensor and temp sensor from memory.

So it MAY be that by disconnecting the MAF the ECU uses a default mode which changes the way the throttle potentiometer signals are treated.

I believe you said earlier that the misfire only occurs on light throttle openings - it is a known fact that the slides on the pot. (potentiometer) wear only in the area they are most used, which leads me to suspect the pot, that's all.

If you were able to drive the car and get it to misbehave consistently, you might find that it is in the same throttle pedal position each time, which would give more weight to the problem being in the pot.

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Thanks that makes sense now

mark george said:

Slightly new twist guys, i drove it today as i have been with the MAF disconnected and guess what? the missfire and engine light came on!! this is the first time this has happened while the MAF is disconnected.

Its not as bad as when the MAF connected but definitly the same problem at the same point in acceleration. Could a dodgy potentiometer be effected by the MAF in this way? and is it possible the pot is getting worse?

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YES

Well done the Biglad

raise:

Looks like its part number STC1734 to me....... £250 on ebay!!! !! is there any other way to test it to be sure before i part with "mega bucks"?