How to completely get rid of MAF on de-EGR'd TD5

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Originally Posted by DiscoDB

You know you are having fun when the EGT alarm is your prompt to change gears.......

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My problem is towing and not paying attention. The 4BD1T boost compensator gives full fuel by 7psi boost, I'm tuned to ~750C at 20psi but I don't get 20psi until about 1900rpm.

So towing (90km/hlimit = 1800rpm in 5th) and not paying attention it's easy to get far more fuel than I can use. Winding the VDO to the end of the dial.:eek: The fix is to redesign the boost compensator. A job way down the priority list.


But I've had the head off since and no thermal damage. But I'm not willing to try 900C sustained intentionally. I'm happy to pull 750C for minutes on end

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Originally Posted by sierrafery

i "pushed" it uphill today a bit but got scared when it went to 750 and i took it easyer..., plugged back the MAF just to be on the safe side... i'll make other tests in the winter when there will be -25*C outside not +35 like there were today:cool:

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Perfect time to do the same comparison with the MAF connected. That is you want to compare under the same load and ambient temp conditions. You may be surprised and find you get the same high temps with the MAF connected.

i'll drive it today again without fear then.... this EGT thing is very new to me, it'll take some time untill i get used to it but thought about it and realised that ignorance is a bliss :) ... my car has 244.000km on board without any serious engine problems(not even one HG failure) and seen 100*C coolant temp not once ... God knows what EGT could have been then but yesterday i got scared at 750 albeit the cooant temp was only 93 then :(

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Originally Posted by sierrafery

maybe my car is strange but just made an interesting test... bridged the MAP's signal to MAF input and seems more responsive than with the original MAF ...no EGT difference so far.... dont blame my curiosity and insistence in this MAF emulating thing it's a kinda obsession of mine :) ... i've previously compared the signals with two voltmeters on both(MAF and MAP) outputs with running engine but revved it to 4000rpm only stationary didnt watch voltages under load just drove it few miles:cool:

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Speaking of strange tests, I drove mine home with the properly functioning MAP disconnected (having previously tested disconnecting the MAF). As with my "cooler dense air, at sea level MAF disconnection test", pretty much saw no change in performance most of the time, except peak turbo boost hit when you first floor the accelerator was about 4 psi lower and my standard 4th gear 60-100 test was about 1 second slower. Nanocom also showed the inlet air temp defaulting to 120degC instead of the normal 25-27degC. This time I did get an ECU fault code (unlike my test with the MAF disconnected) although the fault code was "Driver Demand Problem" (ironic) and "Inlet Air Temp Circuit" fault. Presumably again the ECU is defaulting to look up tables to enable it to run so well in most conditions. In fact if I did not push to the limit I would not have detected the difference.

OffTrack's post which shows that the mass air load calculation from the MAF traces near exactly to the calculation from the MAP/IAT with the exception at idle got me thinking that one of the reasons the look up tables are so effective in cooler climates and at sea level is because of the built in redundancy of having two ways to calculate the mass air load. Which has been the source of most of the debate at the core of this topic given RAVE's references to the MAP/IAT calculation being used for the mass air load and presumable input for the fuel maps and no reference to the MAF's role in this.

Before OffTrack went off track, he was in the process of testing how to use the two mass air load calculations for the early detection of MAF faults. Also makes you wonder why if the ECU has two ways to calculate the same input why it would not discount the faulty reading and just use the more likely to be correct reading for the mass air load input into the fuelling maps rather than look up tables. That is defaults to 1 out of 2 voting and goes with the reading that is within acceptable tolerances. The MAF could be a cross check to ensure the MAP/IAT calculation is correct. Certainly has the information needed to do this and enable reliable running in the event of one failing. Of course losing the turbo boost input would explain the conservative limit in total fuelling to drop the peak boost.

So do I now test disconnecting both....

.....to be continued.

nice one... IMO disconnecting the MAP/IAT has much more bad effect cos you mix up two signals instead of one and i think you are right that as RAVE sais the management uses mainly the MAP/IAT input to calculate the inlet air mass in the cylinder but it doesnt completely neglect the MAF input cos this one gives it the intake air flow which can't be calculated on the MAP signal whatsoever ... if i saw many cases when disconnecting the MAF haven't made any noticeable difference on MAP or IAT fault there has been always running issues.... IMO it will run like sh*T with MAP unplugged

OK silly testing time now.

This time I disconnected both the MAF and the MAP/IAT. Started Ok, and under partial throttle low speed conditions drove OK. Pulled out onto an 80kph road and definite flat spot with the acceleration. Selecting lower gear and higher revs and was able to get up to 110kph once out of the 80 zone.

With the electronic tuning box compensating with additional fuel, able to get about 16psi boost and cover 60 to 100 in 4th about 7 seconds slower (15secs versus 8secs).

So for an EU3 Manual Td5 D2 under cool dense air conditions at sea level:

Disconnecting the MAF had no impact (under the conditions I tested).
Disconnecting the MAP/IAT had a small impact (most likely around not seeing how much boost is being generated).
Disconnecting both had a significant impact.

IMO - the ECU is able to calculate the mass air load from either the MAF or the MAP/IAT. If either fails or is disconnected the ECU deals with this very well (providing one is still working). If both are working then either will give the correct mass air load. If there is a discrepancy between the two then an error code may be generated but then the ECU must decide or have coding to determine which value to run with. If both fail then it must go into an ultra conservative mode to deal with this but still allow the engine to run and get you home.

nice one...i love all kind of tests:), and this test of yours seems quite relevant, any change in EGT? ...and by the way, did you try only with MAP/IAT unplugged and MAF connected?

The second test was with the MAP/IAT disconnected and MAF connected (post #174).

No increase in EGT, but with the last test with both MAF and MAP/IAT disconnected obviously saw lower temps.

Thanks Sierrafery for a well descriptively educational post!
Kept me reading until gone 3am :-)
I recently bought an aftermarket MAF (on advise from local LANDROVER "specialist") and noticed increased fuel consumption... Black smoke... But more responsive up to 3,000 rpm.
It has EGR removed remapped (now on nanocom) & boost resistor....
Now after recent remap (properly) this time with nanocom, it is cutting power just over 3k rpm!
With high air flow readings. I was told there is a three wire resistor mod on these forums which will cap the max MAF reading to prevent this happening (should have payed the extra for a genuine LR, I know!) due to after market MAF.
Now I think I might give this mod of yours a try.
Impressed with the egt readings at the end ;-)
With MAF unplugged it revs right through to max!
Will be interesting to see how this mod deals with it.
Cheers
Nick

IMO as long as you keep watching the EGT and the engine will run OK you have nothing to worry about, i made many more tests on this and i've realised that it's very dependent on what variant of fuel map is involved