Freelander 1 Overfueling

Nodge68 · Oct 17, 2016

Alibro said:
If unplugging the MAF makes no difference don't that mean the MAF is knackered?

Can do on the TD4. If the MAF signal is below a preset minimum, the ECU substitutes a fixed fuelling strategy, based on throttle position and engine speed.
So unplugging a failed MAF can conceivably make no difference to the way the engine runs, giving a false good MAF result.

S1monm · Oct 17, 2016

wammers said:
That is it's primary function.

And another function would be to assist the ECU in controlling fuelling to minimise black smoke, maybe just before full boost?

wammers · Oct 17, 2016

GrumpyGel said:
OK from Rave TD4....

Mass Air Flow/ Inlet Air Temperature (MAF/ IAT) Sensor

The MAF/ IAT sensor is located on the engine intake air manifold, it combines the two functions into one unit.

The MAF sensor works on the hot film principle. The MAF sensor has two sensing elements contained within a film. One element is at ambient temperature e.g. 25 °C (77 °F) while the other is heated to 200 °C (392 °F) above this temperature e.g. 225 °C (437 °F). As air passes through the MAF sensor it has a cooling effect on the film. The current required to maintain the 200 °C (392 °F) differential provides a precise, although non-linear, signal of the air drawn into the engine. The MAF sensor output is an analogue voltage proportional to the mass of the incoming air. The ECM utilises this data, together with information from the other sensors and the fuelling maps, to determine the correct fuel quantity to be injected into the cylinders. It is also used as a feedback signal for the EGR system.

So according the LR, looks like MAF is used as an input to fuelling levels on TD4.

Dear god in heaven. Look up how a diesel works and then work out how that can be so.

Alibro · Oct 17, 2016

wammers said:
The MAF sensor can influence fuel, but only in the sense that if a throttle request is made, were the fuel would exceed the available combustible air as measured by the MAF and relayed to the ECU. The ECU would not inject that fuel to go to the throttle demand until there was enough combustible air for clean burn.

Don't that mean a dodgy MAF can cause the car to put too much fuel in therefore sending unburnt fuel out the exhaust and causing black smoke?

Diesel Do · Oct 17, 2016

GrumpyGel said:
OK from Rave TD4....

Mass Air Flow/ Inlet Air Temperature (MAF/ IAT) Sensor

The MAF/ IAT sensor is located on the engine intake air manifold, it combines the two functions into one unit.

The MAF sensor works on the hot film principle. The MAF sensor has two sensing elements contained within a film. One element is at ambient temperature e.g. 25 °C (77 °F) while the other is heated to 200 °C (392 °F) above this temperature e.g. 225 °C (437 °F). As air passes through the MAF sensor it has a cooling effect on the film. The current required to maintain the 200 °C (392 °F) differential provides a precise, although non-linear, signal of the air drawn into the engine. The MAF sensor output is an analogue voltage proportional to the mass of the incoming air. The ECM utilises this data, together with information from the other sensors and the fuelling maps, to determine the correct fuel quantity to be injected into the cylinders. It is also used as a feedback signal for the EGR system.

So according the LR, looks like MAF is used as an input to fuelling levels on TD4.

Think I've posted that before. Was told it was wrong

S1monm · Oct 17, 2016

Do I sense some missing posts?

Nah it's me phone playing up

GrumpyGel · Oct 17, 2016

wammers said:
Dear god in heaven. Look up how a diesel works and then work out how that can be so.

Don't shoot the messenger!

wammers · Oct 17, 2016

GrumpyGel said:
But exactly the same could be said of any sensor. At the end of the day, it is controlling the amount of fuel injected.

No not in the sense that it controls fuelling which it certainly does not. It does not work in the same way as the MAF in a petrol engine works. That is what some fail to understand. A diesel is throttled by fuel NOT by air. So the air going in through the MAF other than as already explained does not influence fuelling. There is ALWAYS more air than is needed in a diesel engine. The only thing that changes to accelerate it or reduce power is the amount of fuel injected.

Alibro · Oct 17, 2016

Wammers, I'm getting very upset your not answering my questions.

Nursey says I'm very naughty too.

Diesel Do · Oct 17, 2016

The engine management system uses the maf sensor to measure the mass of air entering the engine. At low rpm when the turbo is not working efficiently and there isn't an abundance of air available, it is important for performance, emissions and fuel consumption that the air is accurately measured. If the maf signal is below par the fuelling is reduced and performance suffers, if it is too high, fuelling is increased leading to smoke, and poor mpg, as well as lumpy, hesitant, juddery running. In extreme cases stalling or bad starting can occur.

Above about 2000rpm on most car and van engines, the turbo is within its full operating range and there is a surplus of air available so the maf signal assumes less importance because the ecu can simply use predetermined fuel maps to control the torque. i.e the assumption is made that there is more than enough air available so it need not be measured accurately.

Nodge68 · Oct 17, 2016

wammers said:
The MAF sensor can influence fuel, but only in the sense that if a throttle request is made, were the fuel would exceed the available combustible air as measured by the MAF and relayed to the ECU. The ECU would not inject that fuel to go to the throttle demand until there was enough combustible air for clean burn.

About time.

The MAF will affect power, if it returns a lower signal than the ECU wants to see. The ECU will only inject enough fuel to burn cleanly in the available measured air.
So the MAF signal is important to the way the ECU fuels the engine.

Diesel Do · Oct 17, 2016

Back pedal

S1monm · Oct 17, 2016

So to cap this off before I go to bed. The MAF on a TD4 is not used solely to control fuelling but it does assist the ECU in determining the amount of fuel to be injected, so a duff one could cause black smoke, possibly.

Just run it on pure veg oil then it'll smell like a chippy and no one will mind the clouds of wonderful smelling black smoke

wammers · Oct 17, 2016

Nodge68 said:
About time.

The MAF will affect power, if it returns a lower signal than the ECU wants to see. The ECU will only inject enough fuel to burn cleanly in the available measured air.
So the MAF signal is important to the way the ECU fuels the engine.

Only in the scenario described.

Diesel Do · Oct 17, 2016

wammers said:
Only in the scenario described.

The engine running scenario?

wammers · Oct 17, 2016

S1monm said:
So to cap this off before I go to bed. The MAF on a TD4 is not used solely to control fuelling but it does assist the ECU in determining the amount of fuel to be injected, so a duff one could cause black smoke, possibly.

Just run it on pure veg oil then it'll smell like a chippy and no one will mind the clouds of wonderful smelling black smoke

The amount of fuel to be injected is determined by the throttle power request. Nothing to do with air going through the MAF. Listen carefully i will say this only once more. THERE IS ALWAYS MORE AIR IN THE CYLINDERS THAN IS NEEDED.

Nodge68 · Oct 17, 2016

wammers said:
Listen carefully i will say this only once more. THERE IS ALWAYS MORE AIR IN THE CYLINDERS THAN IS NEEDED.

No true. Off boost there's the very real possibility that the fuel injected can exceed the available oxygen to burn it. This is why the ECU needs the MAF signal

wammers · Oct 17, 2016

Diesel Do said:
The engine management system uses the maf sensor to measure the mass of air entering the engine. At low rpm when the turbo is not working efficiently and there isn't an abundance of air available, it is important for performance, emissions and fuel consumption that the air is accurately measured. If the maf signal is below par the fuelling is reduced and performance suffers, if it is too high, fuelling is increased leading to smoke, and poor mpg, as well as lumpy, hesitant, juddery running. In extreme cases stalling or bad starting can occur.

Above about 2000rpm on most car and van engines, the turbo is within its full operating range and there is a surplus of air available so the maf signal assumes less importance because the ecu can simply use predetermined fuel maps to control the torque. i.e the assumption is made that there is more than enough air available so it need not be measured accurately.

There should ALWAYS more air in the cylinders than is need for combustion.

Alibro · Oct 17, 2016

OK, for the benefit of the OP and me.
OP is getting black smoke on acceleration and someone suggested MAF.
OP disconnects the MAF and gets the same issue.
I suggested that means the MAF could well be at fault. My thinking was if the MAF was working correctly it would prevent the issue.
All hell then breaks loose and we get conflicting descriptions for how the MAF works.

So can a faulty MAF cause the car to belch out black smoke or not? And if it still belches out black smoke with the MAF disconnected what does this mean?

wammers · Oct 17, 2016

Nodge68 said:
No true. Off boost there's the very real possibility that the fuel injected can exceed the available oxygen to burn it. This is why the ECU needs the MAF signal

Nonesense.

Freelander 1 Overfueling

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