Consequences of disabling MAF on 2.5 Diesel

The DHSE has been standing this year as I really prefer driving the (now tatty old banger) remapped DSE, decided to give it an airing a couple of weeks ago and had to turn back at the bottom of the hill (I live at the top), no acceleration, easy on the pedal, nor floored, pedal position seemed not to influence the motor, but after a delay would feel a slight momentary surge, too brief to affect road speed, then drop back. Removed Spider inline power chip thinking it had failed, that made no difference, checked EGR valve, cleaned it thoroughly although it wasn't jammed open, refitted and blanked it off just to be sure. road tested same route and returned for the same reason, no improvement. Drained fuel filter, no water, so replaced as I had a spare new one, road tested again, still no better. Tonight I unplugged the MAF and road tested again, it initially didn't start as instantly as normal, but did start, out on the road it flew, much better than with the power chip fitted previously, ran it through cold to hot, on the level and up hill for 10 miles, through the gears and using kick-down. I began feeling it was as good as the remapped DSE, so I went back and swapped to the DSE for comparison, it is better, but not enough to make me remap the DHSE, which now feels lively and an enjoyable drive as is.
What I would like from the rest of you is, anecdotally, theoretically or real life, what is likely to be the consequential result of leaving the MAF disabled, I will however remove it, check it and clean it, when I find where I put the MAF cleaner I used a few years ago.

Cheers John

Here you are Keith answer this one.

wammers said:

Here you are Keith answer this one.

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:hysterically_laughi:hysterically_laughi:hysterically_laughi





and op knock knock:emps1:

wammers said:

Here you are Keith answer this one.

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You answer it. I know that the MAF affects fueling, without it the ECU runs the default maps. There are now 3 people reporting the same thing.
You cannot clean a Pierburg MAF IMO as it's a hot film device unlike the Bosch which is hot wire.

Datatek said:

You answer it. I know that the MAF affects fueling, without it the ECU runs the default maps. There are now 3 people reporting the same thing.
You cannot clean a Pierburg MAF IMO as it's a hot film device unlike the Bosch which is hot wire.

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You know a lot more than BMW do then.

wammers said:

You know a lot more than BMW do then.

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But not more than Bosch who designed the system.

Datatek said:

But not more than Bosch who designed the system.

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Ok carry on. Think what you want to i am really past caring. I have explained how it works believe what you want to.

"The Mass Air Flow Sensor (X105) is a hot film sensor which has a heated surface maintained by an electrical current at a constant temperature. With cool air flowing past the sensor, the volume of air drawn into the intake manifold is measured by the electrical current required to keep the temperature of the hot film sensor constant."

"This data is used to calculate the INJECTED FUEL VOLUME and the rate of Exhaust Gas Recirculation (EGR)."

"The intake air temperature is measured by a thermistor with a negative temperature co–efficient and measures the actual temperature of the turbo booster air entering the engine. The ECM (Z132) uses this information, in conjunction with the manifold absolute pressure sensor, to determine the volume of air being drawn into the engine."

Quoted directly from Rave.

Jovial John said:

"The Mass Air Flow Sensor (X105) is a hot film sensor which has a heated surface maintained by an electrical current at a constant temperature. With cool air flowing past the sensor, the volume of air drawn into the intake manifold is measured by the electrical current required to keep the temperature of the hot film sensor constant."

"This data is used to calculate the INJECTED FUEL VOLUME and the rate of Exhaust Gas Recirculation (EGR)."

"The intake air temperature is measured by a thermistor with a negative temperature co–efficient and measures the actual temperature of the turbo booster air entering the engine. The ECM (Z132) uses this information, in conjunction with the manifold absolute pressure sensor, to determine the volume of air being drawn into the engine."

Quoted directly from Rave.

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What happens if you don't haves egr valve ???????

if there was never one fitted, then you don't have a MAF sensor fitted, if there was, but it has been removed, then there will be no exhaust gas mixed with the intake of atmospheric air, a good thing IMO as the density of air is greater at lower temperatures, the exhaust gas is re-circulated with the raw intake and therefore will increase the air temperature, thereby reducing the air density = less oxygen = less efficient combustion as I understand it.

But a turbocharger will effectively 'compress' the air making it more dense,but by 'compressing' it the air the temperature is raised, so when an intercooler is fitted the air charge is cooled back to a more desirable temperature, thus again increasing the density.

Going back to the original question, as the MAF is used on this engine setup to monitor and feedback on the EGR operation, I suppose that having no MAF connected will mean the EGR is not being operated. The engine ECU will still have engine load information via the MAP sensor, but not being able see any airflow through the MAF it will keep the EGR closed, and then ultimately ignore the lack of MAF signal as it will be a reading outside of it's expected parameters.
I imagine a fault code would be logged, but I havent had too much experience playing around on this engine set up yet.

I stand to be corrected, but that is my guess.

N5Fav said:

But a turbocharger will effectively 'compress' the air making it more dense,but by 'compressing' it the air the temperature is raised, so when an intercooler is fitted the air charge is cooled back to a more desirable temperature, thus again increasing the density.

Going back to the original question, as the MAF is used on this engine setup to monitor and feedback on the EGR operation, I suppose that having no MAF connected will mean the EGR is not being operated. The engine ECU will still have engine load information via the MAP sensor, but not being able see any airflow through the MAF it will keep the EGR closed, and then ultimately ignore the lack of MAF signal as it will be a reading outside of it's expected parameters.
I imagine a fault code would be logged, but I havent had too much experience playing around on this engine set up yet.

I stand to be corrected, but that is my guess.

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That may or may not be correct, I have not checked that situation. EGR operation is also dependent on engine load (accelerator) speed and manifold pressure and maybe engine temperature.

The MAF does not monitor the operation of the EGR, it is fitted up stream of the EGR, which therefore has no sense of EGR operation, it signals to the ECM the volume and temperature of the air passing through it to the manifold via the turbo then through the intercooler then the EGR, the ECM uses this information to decide whether to add exhaust gas via the EGR and to what extent + the fuel quantity required as indicated by the various other sensors such as road speed and accelerator pedal etc. The MAF sends only, it receives no instructions from any source, also it's signals sent are unaffected by turbo pressure, which is further down stream and therefore only affect MAP.

Jovial John said:

The MAF does not monitor the operation of the EGR, it is fitted up stream of the EGR, which therefore has no sense of EGR operation, it signals to the ECM the volume and temperature of the air passing through it to the manifold via the turbo then through the intercooler then the EGR, the ECM uses this information to decide whether to add exhaust gas via the EGR and to what extent + the fuel quantity required as indicated by the various other sensors such as road speed and accelerator pedal etc. The MAF sends only, it receives no instructions from any source, also it's signals sent are unaffected by turbo pressure, which is further down stream and therefore only affect MAP.

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Close, but when the EGR opens, it will marginally reduce the air drawn in via the MAF, thus there is an indication from the MAF when the EGR is open.

valid point.

Hi guys , I'm sorry if this is deemed hijacking a thread, but I think my question is related and will expand on the vast amount of knowledge quoted already.

Does the MAF sensor provide the ECM a percentage of the information it requires to adjust fuelling with regard to boost pressure/compressed air flow?

Also if you haven't got a MAF sensor but only have a MAP sensor, does the ECM use that and throttle position sensor/engine temp etc to achieve fuelling?

Finally if you have a vacuum operated EGR valve with a position sensor on it, and you remove it, does the ECM function ok without it?

Sorry again if this is seen as hijacking the thread guys

many thanks

Matt

Datatek said:

Close, but when the EGR opens, it will marginally reduce the air drawn in via the MAF, thus there is an indication from the MAF when the EGR is open.

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Under certain conditions the induction charge can be 50% exhaust gas i would not say that was a marginal reduction in airflow through the MAF. After all that is what the MAF is for to tell the ECU how much exhaust gas is being ingested so the ECU can modulate the EGR solenoid valve to control it. To much exhaust gas you will get smoke and soot to little you will get NOx production.

wammers said:

Under certain conditions the induction charge can be 50% exhaust gas i would not say that was a marginal reduction in airflow through the MAF. After all that is what the MAF is for to tell the ECU how much exhaust gas is being ingested so the ECU can modulate the EGR solenoid valve to control it. To much exhaust gas you will get smoke and soot to little you will get NOx production.

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The MAF could only indicate the level of exhaust gas being injected via the EGR if there was a sufficient reduction in airflow to be detectable, as the turbo will still be stuffing air into the engine based on the fuel being injected how would that be accurate?

Datatek said:

The MAF could only indicate the level of exhaust gas being injected via the EGR if there was a sufficient reduction in airflow to be detectable, as the turbo will still be stuffing air into the engine based on the fuel being injected how would that be accurate?

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EGR only works under certain conditions. It is not operational at all times. There is always more air in the cylinder than the engine needs to maintain any particular power setting. A lot more at lower RPMs less at higher RPMs. EGR works in the lower RPM power setting spectrum to reduce the amount of oxygenated air not needed for combustion. Think of a normal non turbo diesel engine. There is always the same amount of air in the cylinder no matter what the power setting. Air never varies. It is the amount of fuel injected into that air that causes the RPM/power level to rise and fall. Not airflow. One would wonder with all this reduction of fuel due to airflow via EGR why the MPG of the EGR engine is not greatly higher than that of the non EGR engine. In fact they are the same as far as i am aware.

The pre EGR/MAF P38s are reputed to be both more frugal and livelier than the EGR version and I did notice this in my own before remapping the non EGR DSE. Fuel consumption was only marginally better pre EGR, but power was really lower with the EGR irrespective of the stated spec of the two models. Currently checking fuel consumption with MAF dissed (definitely duff, cleaned thoroughly, ok for a while, then acting up again), runs much better without, gut feeling mpg down. Anyone know if BMW or Vauxhaul MAF is compatable (same Pierburg Pt No. 2246084).