If I disconnect one or both of the MAF sensors on my TDV8 will the ECM just 'see' a default value and run the engine safely?

To put it another way, would doing this risk any damage to the engine if I run it like that for a test run of 20 or so miles?

I only want to try this temporarily to test a hypothesis. 2008 MY Java Black TDV8 HSE

I think you might get some odd issues. Here's what the manual says about the MAF and what happens when it fails (which is effectively what the car will think if you remove them):

Quote:

MASS AIR FLOW/INTAKE AIR TEMPERATURE (MAF/IAT) SENSOR
Two MAF/IAT sensors are located on the intake air duct directly after the air filter box. Each sensor is housed in a plastic molding
which is connected between the intake manifold and the air intake pipe.
• NOTE: The MAF/IAT which monitors the LH bank intake does not use the IAT portion of the sensor.
The MAF sensor works on the hot film principle. Two sensing elements are contained within a film. One element is maintained at
ambient (air intake) temperature, e.g. 25°Celsius (77°F). The other element is heated to 200°Celsius (392°F) above the ambient
temperature, e.g. 225°Celsius (437°F). Intake air entering the engine passes through the MAF sensor and has a cooling effect on
the film. The ECM monitors the current required to maintain the 200°Celsius (392°F) differential between the two elements and
uses the differential to provide a precise, non-linear, frequency based signal which equates to the volume of air being drawn into
the engine.
The MAF sensor output is a digital signal proportional to the mass of the incoming air. The ECM uses this data, in conjunction with
signals from other sensors and information from stored fueling maps, to determine the precise fuel quantity to be injected into the
cylinders. The signal is also used as a feedback signal for the EGR system.
The IAT sensor incorporates a Negative Temperature Coefficient (NTC) thermistor in a voltage divider circuit. The NTC thermistor
works on the principle of decreasing resistance in the sensor as the temperature of the intake air increases. As the thermistor
allows more current to pass to ground, the voltage sensed by the ECM decreases. The change in voltage is proportional to the
temperature change of the intake air. Using the voltage output from the IAT sensor, the ECM can correct the fueling map for
intake air temperature. The correction is an important requirement because hot air contains less oxygen than cold air for any
given volume.
The MAF sensor receives a 12V supply from the Battery Junction Box (BJB) and a ground connection via the ECM. Two further
connections to the ECM provide a MAF signal and IAT signal.
The IAT sensor receives a 5V reference voltage from the ECM and shares a ground with the MAF sensor. The signal output from
the IAT sensor is calculated by the ECM by monitoring changes in the supplied reference voltage to the IAT sensor voltage divider
circuit.
The ECM checks the calculated air mass against the engine speed. If the calculated air mass is not plausible, the ECM uses a
default air mass figure which is derived from the average engine speed compared to a stored characteristic map. The air mass
value will be corrected using values for boost pressure, atmospheric pressure and air temperature.
If the MAF sensor fails the ECM implements the default strategy based on engine speed. In the event of a MAF sensor signal
failure, any of the following symptoms may be observed:

Difficult starting
Engine stalls after starting
Delayed engine response
Emission control inoperative
Idle speed control inoperative
Reduced engine performance.

If the IAT sensor fails the ECM uses a default intake air temperature of -5°Celsius (23°F). In the event of an IAT sensor failure,
any of the following symptoms may be observed:
Over fueling, resulting black smoke emitting from the exhaust.
Idle speed control inoperative

What is your hypothesis? Do you think there's a problem your MAF meter? Visiting from DISCO3.CO.UK
2006 Discovery 3 TDV6 Auto HSE Zambezi Silver

Thanks, perhaps disconnecting them wouldn't help much then.

As they say in all the best magazines: regular readers will be aware of my strange drive line shunt that occurs when on the open road just as the engine reaches full operating temperature and then again about 20 minutes later and after that at longer intervals if at all.

Monitoring the live value for the TC reveals that the shunt coincides with it unlocking momentarily.

I've replaced the brake light switch, TPS, engine oil temp sensor, torque converter and battery. The MAF sensors can also tell the ECM to unlock the TC it seems so the hypothesis was one may be sending spurious values. If that was true then maybe disconnecting may stop the shunt even if the engine runs a little rough.

My shiny new upgraded IID Tool (now BT version) just arrived so new plan is to record multiple live values and look for a spike coinciding with the shunt.

BTW the car runs perfectly with smooth gear changes the rest of the time. 2008 MY Java Black TDV8 HSE

Could be an EGR issue. The EGRs don't operate until the engine has warmed up which fits. If you ask for throttle and the EGR is tardy in closing you'll have the engine increasing revs with little effect until, bang, the EGR closes and the engine starts pulling. It's a bit like turbo lag and would likely cause some driveline shunt as the torque hits the transmission.

Be worth checking EGR operation if the new IID allows it. If the BT IID does do that, then I'll buy one because I think I have the same issue. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Lost for Words wrote:

What is your hypothesis?

It's a joy to find someone using the correct word for once...  2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

I used the 'h' word first and the ironically named LFW gets the plaudit?

Have considered the EGRs as the source but no related fault codes with the old IID Tool plus the issue hasn't become more frequent over 20k plus miles. To me that suggests an electronic problem rather than a mechanical one?

Will figure out the new live recording function and see what transpires.



Is your issue same as mine RRSTDV8 or different in some way? 2008 MY Java Black TDV8 HSE

Sorry Paddi!

I have an issue that the engine feels v. laggy at times. However, it's not lag as the revs seem to rise without any power and then suddenly there's a surge and it gets going. Doesn't do it all the time, usually when I've been at steady throttle e.g. in steady traffic on an A road. Sometimes it feels like drive line shunt when it gets going.

My "old" IID doesn't give any live info about the EGRs. There are no EGR related errors recorded either. But it feels like an EGR issue from what I've read over the last couple of years in here and Disco3. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Paddi wrote:

I used the 'h' word first and the ironically named LFW gets the plaudit?

It had me confused when I read it.

Have you tried a transfer box calibration?

No gearbox fault codes presumably?

 Visiting from DISCO3.CO.UK
2006 Discovery 3 TDV6 Auto HSE Zambezi Silver

Yes - had the transfer box calibrated by an indie some time ago and did it again last week myself using IID Tool (beta version firmware). No change.

There are no gearbox fault codes.

And yes I have had the engine and gearbox software updated again with no change.

Also had the mechatronic removed and tested on a rig. It passed but the specialists changed a few parts of the valve bodies (that were showing almost imperceptible wear) before reinstallation. The TCM however was not changed so it could perhaps be still harbouring a minor fault. 2008 MY Java Black TDV8 HSE

RRSTDV8 wrote:

My "old" IID doesn't give any live info about the EGRs. There are no EGR related errors recorded either. But it feels like an EGR issue from what I've read over the last couple of years in here and Disco3.

If you install the latest beta firmware for your non BT IIDTool you will find it is possible to display live EGR values. I was doing this yesterday. The live values are not quite what you might expect since the EGR valves seem to spend most of their time open to some degree. Only on throttle does the EGR valve close and then the value changes to 4% even at WOT.

At steady throttle on the flat with fully warmed up engine the value settles to the high 50s. Interestingly when cruising on the flat and the transmission jolt occurred if I quickly glanced at the value it had momentarily changed from the high 50s to 4% and then quickly returned to the high 50s again.

Would be great to hear from any other users who have tried this on a TDV8 and see if they see similar values. 2008 MY Java Black TDV8 HSE

That all makes sense now. The EGR (for some reason) opens, the engine looses power and you feel the effect of engine braking. The TC then unlocks itself as it's still under throttle and isn't expecting this.  Visiting from DISCO3.CO.UK
2006 Discovery 3 TDV6 Auto HSE Zambezi Silver

LFW - Well not quite.

On steady throttle on the flat we are cruising along and the EGR position is 56% or so which is partly OPEN then the EGR position changes suddenly to 4% which is CLOSED and the jolt occurs and then the EGR position immediately changes back to about 56%.

This was using my old non BT IIDTool which only reads one live value at a time so I monitored EGR 1 on the outbound journey and EGR 2 on the return trip. There didn't seem to be any difference between the behaviour so whatever is causing the issue appears to affect both valves equally.

From looking at previous posts by our resident experts such as Robbie and Disco Mikey it seems fully open is 75% and fully closed is 4%.

So the question is - where do I go from here? Why is the ECM telling the EGRs to close inappropriately? What values should I log using the new BTIIDTool that I just set up yesterday? Presumably it would make sense to suspect a faulty sensor: coolant temp, exhaust temp, intake pressure etc? 2008 MY Java Black TDV8 HSE

Ahh, yes. Sorry, just re-read your post. So basically it's the reverse effect. Have you been getting smoke/low on power?

I'd graph various values. Naturally, do one with both EGRs and the TC state. I'd have a look at the accelerator position, engine speed and EGT sensor too. No doubt there are other things to add to the list too. Don't select too many at once though - You'll get a better sample rate with fewer.  Visiting from DISCO3.CO.UK
2006 Discovery 3 TDV6 Auto HSE Zambezi Silver

No smoke and power is not a problem either. I buried the throttle at about 30 to see what the EGR value did and she was up around 90 in no time. On my private test track obviously  2008 MY Java Black TDV8 HSE