Challenge for Diesel Experts!

[icogger]

Hoping some of you 'good guys' on here can help. Friend of mine has a Freelander TD4 Automatic that was exhibiting all the symptoms of a faulty MAF. I advised him to unplug the MAF which he did and all the performance came back but with the engine management light on.
So, he bought a genuine Bosch MAF, plugged it in but had no effect, in fact the thing was worse!
He then took it to the local Landy dealership who checked the following list of things.
T4 Check - no faults
Replaced MAF with known working one.
Check all turbo hoses
Clean and chech EGR
Clean MAP Sensor
Smoke test intercooler
Fit new fuel filter
Vac hose to turbo actuator
Change turbo actuator
Check exhaust for blockages.

I'm sure it cannot be turbo related as the thing goes like the proverbial poo off a shovel with the MAF unplugged. With it plugged in, the engine will only rev very slowly to 2200 rpm and no further! :shrug:
The dealer has told him the only thing they think it can be now is the ECU but they can only fit one at a non-returnable charge of £700 and they're not sure that will fix it - I'm pretty sure it won't!
Now the EML is on all the time!
Any help / suggestions greatly appreciated even though it's not a 75 or ZT, just a close relative!

[klarzy]

Hoping some of you 'good guys' on here can help. Friend of mine has a Freelander TD4 that was exhibiting all the symptoms of a faulty MAF. I advised him to unplug the MAF which he did and all the performance came back but with the engine management light on.
So, he bought a genuine Bosch MAF, plugged it in but had no effect, in fact the thing was worse!
He then took it to the local Landy dealership who checked the following list of things.
T4 Check - no faults
Replaced MAF with known working one.
Check all turbo hoses
Clean and chech EGR
Clean MAP Sensor
Smoke test intercooler
Fit new fuel filter
Vac hose to turbo actuator
Change turbo actuator
Check exhaust for blockages.

I'm sure it cannot be turbo related as the thing goes like the proverbial poo off a shovel with the MAF unplugged. With it plugged in, the engine will only rev very slowly to 2200 rpm and no further! :shrug:
The dealer has told him the only thing they think it can be now is the ECU but they can only fit one at a non-returnable charge of £700 and they're not sure that will fix it - I'm pretty sure it won't!
Now the EML is on all the time!
Any help / suggestions greatly appreciated even though it's not a 75 or ZT, just a close relative!

Have you checked the inlet manifold to engine seals for tightness and the MAP sensor? that's the other half of the MAF equation?

[DMGRS]

Check the pipe connecting the airbox to the turbocharger is on properly, and that the rubber bung inside the pipe where it pushes onto the turbo is still there.
Also check the smaller breather pipe is connected at both ends - this also connects to the turbo inlet pipe.

The reason is that unmetered air will enter if anything above is missing or disconnected - the car will think no air is getting to the engine, and will slow the fuelling to suit.
I know this because a friend bought 2 MAFs before we found the sealing bung was missing!

[icogger]

Thanks for your quick replies guys! According to the Landrover Techs report, he 'removed and cleaned the MAP sensor' and 'Removed and checked turbo hose on turbo NFF'?
Also 'Replaced Vacuum hose from turbo valve to actuator' and 'Change turbo actuator valve'. Would the 'bung' have been in one of these? Will check these tomorrow morning.

[rich17865]

Where did the new maf come from, is there a possibility it could be a dodgy copy?

[icogger]

Where did the new maf come from, is there a possibility it could be a dodgy copy?

Was deffo a genuine MAF and anyway the dealer tried one from a vehicle that was working ok - all very puzzling for me but air bypassing the MAF makes sense although wonder if you could hear air being drawn in by the turbo?

[rich17865]

Ah well, any suggestion can be a help :)

[icogger]

Ah well, any suggestion can be a help :)

Absolutely, all suggestions much appreciated as I'm stumped at the moment :}

[klarzy]

As DMGRS said I would suspect an air imbalance throwing the mixture calculation off

[clf]

I would also go along with DMGRS. 'Looking' at it logically, with the MAF unplugged, the ECU will revert to a failsafe setting for air flow metering. With the MAF replaced, it goes back to 'bad' running.

I would suggest something with the wiring, though.

When the MAF is plugged in, the ECU receives an electrical signal. In this case, one telling the ECU faulty readings, then the ECU reacts accordingly.

When the MAF is unplugged, the ECU does NOT receive an electrical signal, so as said, it reverts to a failsafe.

Is it possible, the plug or the wiring when disconnecting or reconnecting has become damaged, causing a short or something else wrong with the wiring?

As regards the ECU, could its map be checked to make sure there have been no corruptions of the data? (or perhaps a battery reset been tried) - Again with the ECU, could a salvaged one be tried and programmed? Cheaper I am sure than £700

[Mike Noc]

As DMGRS said I would suspect an air imbalance throwing the mixture calculation off

With a diesel there is no mixture calculation. ;) These engines aren't air throttled, so the full charge of air is drawn into each cylinder during every induction stoke, and a regulated amount of fuel injected depending on demand.

The fuel takes what oxygen it needs to burn. At idle the air to fuel ratio can be well in excess of 100 to 1. The MAF is fitted to ensure there is always enough air available for the injected amount of fuel. The mass of air will vary depending on temperature, elevation and how hard the turbo is working.

Worth checking out the MAF wiring, and as mentioned that there aren't any leaks anywhere in the inlet pipework or manifold. If that's all OK then send the ECM to Marinabrian for a health check and a wave of his magic wand. :bowdown:


.

[spyder]

Iirc this vehicle gave a lot of trouble with the connection on the common rail due to water ingress??

[ArsenalDes]

Hi
This may be totally off the mark and may have already been done but have you tried disconnecting the battery long enough to clear the ECU. The only reason for saying this is I changed the stereo in a Citroen last week and the on board computer wouldnt recognise it infact gave an ECU error reading disconnected battery for 30 mins reconnected and all was ok. So could it be the new MAF sensor is not being recognised correctly ????

[icogger]

Thanks to all for your helpful suggestions - knew I could rely on you :}


I would also go along with DMGRS. 'Looking' at it logically, with the MAF unplugged, the ECU will revert to a failsafe setting for air flow metering. With the MAF replaced, it goes back to 'bad' running.

I would suggest something with the wiring, though.

When the MAF is plugged in, the ECU receives an electrical signal. In this case, one telling the ECU faulty readings, then the ECU reacts accordingly.

When the MAF is unplugged, the ECU does NOT receive an electrical signal, so as said, it reverts to a failsafe.

Is it possible, the plug or the wiring when disconnecting or reconnecting has become damaged, causing a short or something else wrong with the wiring?

As regards the ECU, could its map be checked to make sure there have been no corruptions of the data? (or perhaps a battery reset been tried) - Again with the ECU, could a salvaged one be tried and programmed? Cheaper I am sure than £700

Spent about an hour last night discussing this with another Freelander owner and what you have said is basically what we concluded. This morning going to check the plug connections and wiggle the wiring a bit :shrug: Might do something! Also will try a reset and the owner has been quoted £30 to check the ECU. Is there a wiring diagram available that shows the ECU connections?

Once again thanks for all suggestions - everything helps to narrow the search - will let you know how we get on. :}

[Kwakykarl]

I had something like this and it was a wire on the common rail pressure plug had pulled out a little bit pushed back in and jobs a god one

[Avulon]

With a diesel there is no mixture calculation. ;) These engines aren't air throttled, so the full charge of air is drawn into each cylinder during every induction stoke, and a regulated amount of fuel injected depending on demand.

The fuel takes what oxygen it needs to burn. At idle the air to fuel ratio can be well in excess of 100 to 1. The MAF is fitted to ensure there is always enough air available for the injected amount of fuel. The mass of air will vary depending on temperature, elevation and how hard the turbo is working.

Worth checking out the MAF wiring, and as mentioned that there aren't any leaks anywhere in the inlet pipework or manifold.


.

True to a point, the system inputs fuel dependent on what it sees the car doing and the throttle demand. However if there is more air coming in than it 'sees' due to a leak post MAF then it won't put as much fuel in as you would normally expect in the same conditions without a leak: this means less power and possibly an inability to rev as high as normal - the engine speeds up but according to the MAF doesn't pull more air in so the fuel is reduced to prevent excessive fueling (wasted black smoke out the exhaust). What I'm saying is that there is still a correlation between the air being sucked in (as measured by the MAF) and the amount of fuel injected, there is indeed a mixture calculation just not in the same way as in a petrol engine...:getmecoat:

[Mike Noc]

However if there is more air coming in than it 'sees' due to a leak post MAF then it won't put as much fuel in as you would normally expect in the same conditions without a leak: this means less power and possibly an inability to rev as high as normal - the engine speeds up but according to the MAF doesn't pull more air in so the fuel is reduced to prevent excessive fueling (wasted black smoke out the exhaust).

The MAF is connected to the turbocharger by a short elbow, and if there are any induction system leaks after that the air will leak out of the system, not get sucked in, so you will get overfuelling. Don't take my word for it - ask anyone who has had an intercooler pipe or O ring let go.

What I'm saying is that there is still a correlation between the air being sucked in (as measured by the MAF) and the amount of fuel injected, there is indeed a mixture calculation just not in the same way as in a petrol engine...:getmecoat:

Whilst there is a correlation between the mass of air entering the cylinders and the maximum amount of fuel that can be injected, there is no mixture calculation.

This is one of the fundamental differences between how petrol and diesel engines work. The others are of course type of fuel used, method of ignition, and that the diesels run with no air throttling and petrol engines do. That's why a separate vacuum pump is fitted to the diesels.

With a petrol engine the fuel is mixed with the air to form the mixture that is ignited by the spark. With a diesel engine fuel is injected into the mass of air in the cylinders and ignited by the heat of compression.

The term mixture is redundant because the diesel fuel only takes the amount of air it needs to combust, so say at idle, there is plenty of air left over that hasn't mixed.

The reason you need a MAF on the diesel is to make sure there is always enough air available for the amount of fuel injected. That is why you can get away with disconnecting the MAF on the diesel and not on a petrol engine where it is needed to determine the mixture, and why, unlike a petrol engine, you can't run a diesel engine too lean.