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

Hi, believe me i did very serious reading but maybe the wrong manuals... it's stated somewhere in the many posts that mine is a 2000 Td5 manual but i might have not mentioned that it's Eu2 map, i dunno the map's exact number/variant cos it was made by somebody who works in the re-mapping business... i can accept also that my approach might not be the best with this mod i also admit that when it comes exclusively about the engine's physical behaviour i have serious lacks of knowledge... maybe my problem is that i've studied how an aircraft must fly safely and i've learned that from official manuals, schemes, diagrams, etc...so it seemed obvious to me that an official workshop manual must contain accurate data...even if RAVE is vague at some points i consider that where it explaines something it explaines it at least close to reality.

i'm wondering how would i understand better how a system or sensor works than making tests on it with quite proffesional tools...so all i've said about MAF SENSOR cos that's the main issue here i've tested in various ways from the electric point of view ... as you see i've already ordered a EGT gauge cos some of the statements here looked logical to me even if i insisted about it's futility in this particular engine management(for de-EGR'd TD5, now i complete: manual)... no harm done untill now cos neither me nor those who did this mod dont have a melted engine...YET

i'll stand corrected and make public right away any problem which might be caused by this mod when it becomes certain to me..i've already took steps and warned the guys with auto gearboxes on the other forums to not go for it untill everything will be clear and unfortunately nobody has WEGT gauge fitted from those who i speak with ... so keep up the arguments against it cos i dont mind but dont expect me to instantly accept some statements which are completely against what i know and i believe it's right... like e.g. how the MAF sensor works cos it's only about two temperature sensitive variable resistance pieces of wire ...it;s a completely different discussion how would that sensor affect the Td5 engine management and here i'll accept any well argumented guidance

to prove that i'm not considering RAVE a bible i declare here that i think it's wrong when it names the MAF Mass air flow sensor cos IMO it should have named it simply Air flow sensor

Originally Posted by sierrafery

thanks for the clue ... i think you confuse the MAF sensor with a computer though,...it's a simple resistance setup and outputs an analogue VOLTAGE signal, if doesnt "compensate" anything, as the heated element in it is cooled by the air flow it's resistance drops and the voltage rises... it's about air flow drawn into the engine

A MAF is absolutely not two variable resistors hanging in the air.

I'm not the confused one here.
I don't know what flavour Engineering degree you've got, but it appears to be one with no heat-transfer or thermodynamics involved.

Cooling effect is proportional to the mass flow of air. Not volume flow. This is why they are Mass AirFlow sensors. Not Volume Air Flow sensors.
If volume air-flow with external temp compensation was the aim they could us a pressure based pitot system with much lower cost.

The average MAF sensor runs on three wires. Power, earth and voltage signal out. There is no additional temperature output on the ones I have personally used, because there is no need. The cooling of the hot-film and the internal signal conditioning compensate for temperature change and the output signal is all about mass flow of air.

It is not volume flow and never will be.

Originally Posted by sierrafery

(if we can rely on the book and on reality)... here i have a contradiction to the book(to show that i'm not blindly following it when i think it's wrong) cos IMO it's exagerated to be named mass air flow meter cos in reality it's just an air flow meter ... if it's like you said that "It measures mass flow already compensated for temperature difference" , i'm asking temperatrure difference compensated by what?

Mass flow and volume flow are related by air density. The biggest factor in air density (at a constant altitude) is temperature. A hot-wire or hot-film MAF sensor measures using two hot surfaces which give a mass reading already compensated by temperature and hence density.

The cooler the air through a MAF the more current is required to sustain the hot film and the more mass flow is recorded.
The faster the air through a MAF the more current is required to sustain the hot film and the more mass flow is recorded.

It's a very clever and simple device. Far more useful than volume flow.

Originally Posted by sierrafery

... and then why on those cars where the book sais the MAF is mainly used for engine management there is a IAT on the same port? i say cos the ECM calculates the mass based on the air flow and the temperature readings and the built in software "compensates" for that...
V8 description: The MAF/ IAT sensors are combined into a single unit and located between the air filter housing and the inlet manifold.
The ECM receives input signals from the MAF/ IAT sensor to calculate the mass of air flowing into the engine inlet
manifold.

The description is sound, but you are interpreting it wrongly. MAF sensors can run without any external temperature compensation. The MAF is a nice place to put an additional IAT temperature sender but it isn't required for mass airflow calculation. The IAT has many engine control uses, like startup where MAF flow isn't enough to work properly.

Originally Posted by sierrafery

maybe i dont know how the MAF works but then everything about it in RAVE is inaccurate so we could bin it without remorse.

You don't throw a book away when someone finds an error. Don't compare it a bible, that stuff is pure fiction.

Ok sir, no thermodinamics involved in my studies... it's not the first time when somebody proves me that avionics is not very compatible with diesel engine management... please dont be mad at me that i sustained my findings... i didnt make it public untill i drove my car much this way especially cos i know my limitations when it comes about diesel engine behaviour, i interpreted everything from pure electronic point of view then when i saw that it works i believed it's ok... that's the first time since this thread started when you explained as to be understandable for me too...i stand corrected and i apologise for being stubborn but from my point of view(electronically speaking) i was convinced that what i'm saying is correct...also without the engine attached but ECM connected to everything and fed like in reality with all the inputs when i modified the MAF input from the generator independently by the throttle input i've got an image on the oscilloscope from the outputs to injectors which was the same with the bridged signal(with very slight 1.2% variations in pulsation from time to time) but got serious variations on the EGR modulator output, these things corroborated with the description from RAVE reinforced me the ideea that on(at least on my) Td5 the MAF is mainly for EGR and has no major impact in engine management, my whole theory was based on that...i'm glad i came here with it and it was contested cos the last thing i want is to create trouble to somebody...that's why i've already ordered a EGT gauge cos i wasnt so subjective to stick blindly to my ideea

thank you for explaining the MAF thing and i hope we can continue a friendly polemic on this cos even if i dont contest anymore your MAF theory i'm still not convinced about it's such great involvment in Td5 engine management

convince me with clear arguments about that too and i'll publicly recognise that this mod is crap

with my full respect Fery

P.S. ..i have a degree in philosophy too so i'm not a big fan of the bible... it meant RAVE more to me......... untill now

I must say to those involved, what a great and well debated thread.


It was so good to read a topic where different points of view, both backed by very well put reasonings, but never stooped to personal attacks and from my perspective think many who read this have learnt greatly how these type of sensors on our engines work.


Great stuff and full credit to both Sierrafery and Dougal , and I personally look forward to reading any further outcomes in this thread.


Cheers Ean

Originally Posted by sierrafery

convince me with clear arguments about that too and i'll publicly recognise that this mod is crap

All the evidence has been presented and the operation of the MAF is clear. It appears you are just choosing to ignore it simply because yours still runs after 30,000km.

Your conclusions were reached before you started this thread and nothing anyone says or does will change them.

why would you think i'm such a loggerhead though...i've just admitted that i was wrong about what the MAF sensor does and i apologised sincerely, about how the sensor works you convinced me... that is crystal now ...but between the "brute" sensor and the actual engine behaviour there is a complex electronic system named ECM(which you are perfectly aware of...and even if i'm dumb in all the other areas at least when it comes about electronics i know some things) ... what i'm asking is the evidence of the fact that RAVE is wrong when it comes about Td5 but accurate when it comes about all the other engines in it... and how do you explain the similarity of injector outputs between the independent and bypassed MAF?

Your conclusions were reached before you started this thread and nothing anyone says or does will change them.

that was a bit harsh though... why did i order a EGT gauge then? ...and if you'll check the other forums where i'm a respected member(i'm not gonna make publicity here for them) you'll see that i've already launched warnings about the possibility of increased EGT just based on what you and DiscoDB said...if we can't have a friendly debate then that's it

Originally Posted by sierrafery

what i'm asking is the evidence of the fact that RAVE is wrong when it comes about Td5 but accurate when it comes about all the other engines in it... and how do you explain the similarity of injector outputs between the independent and bypassed MAF?

Evidence:

Exhibit 1.
TD5's without EGR still have a MAF.
Exhibit 2.
A bad MAF causes all sorts of running issues not related to EGR.
Exhibit 3.
The injector signals in your test were running against one of the (many) other limiters in the ECU and therefore changes in the MAF signal will not affect them in that part of the operation.

Originally Posted by Ean Austral

I must say to those involved, what a great and well debated thread.


It was so good to read a topic where different points of view, both backed by very well put reasonings, but never stooped to personal attacks and from my perspective think many who read this have learnt greatly how these type of sensors on our engines work.


Great stuff and full credit to both Sierrafery and Dougal , and I personally look forward to reading any further outcomes in this thread.


Cheers Ean

just a little early in your praise Ean.

Dougal.....disappointed.....you spoiled the tone of this thread...didn't you?

It wasn't necessary.