Map sensor readings

[wuzerk]

I have managed to take the readings from my MAP sensor (not the MAF) and, since I do get varying voltages I assume that it is working ok but comparison with somebody elses figures would be useful.
The White lead is 5.0V supply
Green/Brown is chassis
readings taken between the Blue/White lead and chassis.
Ign ON =1.77V
Tickover =1.81V
1000 rpm=1.81V
2000 rpm=2.06V
3000 rpm=2.80V
4000 rpm=3.25V

[grivas]

So what do the readings actually mean, and how are these values used to tell us what is going on?

[chrissyboy]

I have managed to take the readings from my MAP sensor (not the MAF) and, since I do get varying voltages I assume that it is working ok but comparison with somebody elses figures would be useful.
The White lead is 5.0V supply
Green/Brown is chassis
readings taken between the Blue/White lead and chassis.
Ign ON =1.77V
Tickover =1.81V
1000 rpm=1.81V
2000 rpm=2.06V
3000 rpm=2.80V
4000 rpm=3.25V

long time since i had a lesson on sensors but im sure its the other way round .good sensor volts fall the faster the engine runs should said 4volts dropping to 1 volt ,but as i said LONG TIME since i hd any sort of lesson

[wuzerk]

Chrissy: I would tend to agree since it is normally the higher the vacuum the lower the voltage which I why I await someone elses readings on a 75. For all I know the system could be reversed on our diesels. Then again I would expect maximum vacuum when the revs are dropping down on a petrol engine but probably not on a diesel.
Grivas: The MAP sensor measures the amount of vacuum in the inlet manifold and sends the appropriate info to the brain which adjusts things to suit.
According to the writeups a faulty one can cause surging and excessive fuel consumption.

[spyder]

Chrissy: I would tend to agree since it is normally the higher the vacuum the lower the voltage which I why I await someone elses readings on a 75. For all I know the system could be reversed on our diesels. Then again I would expect maximum vacuum when the revs are dropping down on a petrol engine but probably not on a diesel.
Grivas: The MAP sensor measures the amount of vacuum in the inlet manifold and sends the appropriate info to the brain which adjusts things to suit.
According to the write ups a faulty one can cause surging and excessive fuel consumption.

I will check mine in the light over the week-end.
Question though, why Vacuum ? Its a diesel and the manifold is been pressurized by the turbo-the higher the revs the more pressure ergo the higher voltage readings.

I have replaced mine with no difference in performance or MPG.

[Mike Noc]

Yes there is no vacuum to be had in the CDT. That's why they fitted a separate vacuum pump. :D

Mike

[wuzerk]

OK so the Map sensor on the diesels doesn't measure vacuum so what does it measure? Pressure? I used the word vacuum because the posted link to 'testing the Map sensor' uses a vacuum gauge to check that the sensor is working. I still await another owners readings please because there is much talk about the Map but nobody seems to know what readings we should see on a working one. If SPYDER had known what readings to look for he would not have wasted his money on a new one.

I would imagine that MAP stands for something close to Manifold Absolute Pressure'?

http://www.youtube.com/watch?v=B8EVhFc5Yqw&feature=related

[chrissyboy]

[QUOTE=wuzerk;1215027]OK so the Map sensor on the diesels doesn't measure vacuum so what does it measure? Pressure? I used the word vacuum because the posted link to 'testing the Map sensor' uses a vacuum gauge to check that the sensor is working. I still await another owners readings please.

http://www.youtube.com/watch?v=B8EVhFc5Yqw&feature=related[/QUOTE
The MAP sensor is usually found attached via a vacuum line or directly to the intake manifold and measures the VACUUM (or negative pressure in relation to the calibrated pressure in the transducer) that is being created by the flow of air as it is being PULLED through the manifold and into the cylinders.

[RichB]

At the risk of stating the obvious....

MAP stands for manifold absolute pressure.

On normally aspirated cars, this is generally measuring a vacuum. The smaller the throttle opening and hence the higher vacuum, until you get it to wide open throttle and it reads roughly ambient pressure.

For turbo charged cars, you measure both vacuum and positive pressure. During light load / small throttle openings, the turbo doesn't do much so you will read a vacuum. For higher loads when the turbo is forcing air into the engine, you will see positive pressure.

The MAP sensor will be rated to the boost levels of the turbo. A 1 bar MAP sensor reads upto 1 bar (14.7psi) of positive pressure. Not sure about our cars, but would expect the sensor to be 1.5 or 2 bar.

You can't really check a MAP sensor at static rpm levels as different loads produce different MAP readings. You really need to take the readings at different load/boost levels, either using a boost gauge or (possibly?) using the OBD.

Rich

[Mike Noc]

[QUOTE=wuzerk;1215027]OK so the Map sensor on the diesels doesn't measure vacuum so what does it measure? Pressure? I used the word vacuum because the posted link to 'testing the Map sensor' uses a vacuum gauge to check that the sensor is working. I still await another owners readings please.

http://www.youtube.com/watch?v=B8EVhFc5Yqw&feature=related[/QUOTE
The MAP sensor is usually found attached via a vacuum line or directly to the intake manifold and measures the VACUUM (or negative pressure in relation to the calibrated pressure in the transducer) that is being created by the flow of air as it is being PULLED through the manifold and into the cylinders.

Chris that's for petrol engines mate, which are air throttled so you will get a vacuum. With diesel engines there is no air throttling - they run on a full charge of air every cycle. You may get a slight drop in pressure as air is drawn in at idle but as the turbo spools up the whole inlet is pressurised. You can see this on the CDT by the intercooler pipe swelling up when you rev the engine.

But depending on whose definition you use I suppose you can call a pressure drop a partial vacuum, but the diesels do have a separate vacuum pump to make up for the fact that they can't draw a vacuum at the manifold.



OK so the Map sensor on the diesels doesn't measure vacuum so what does it measure? Pressure? I used the word vacuum because the posted link to 'testing the Map sensor' uses a vacuum gauge to check that the sensor is working. I still await another owners readings please because there is much talk about the Map but nobody seems to know what readings we should see on a working one. If SPYDER had known what readings to look for he would not have wasted his money on a new one.

I would imagine that MAP stands for something close to Manifold Absolute Pressure'?

http://www.youtube.com/watch?v=B8EVhFc5Yqw&feature=related


I'd agree it is measuring pressure within the manifold as its name implies. The absolute zero pressure for practical purposes is a complete vacuum, so everything else is measured as a positive value above that.



Mike

[Jules]

Sensors can be configured either way.
ie
Pressure increasing can be given an increasing or decreasing resistance & vice versa.

Same goes with temp sensors .
All depends what input the comparitor/amplifier in next module is designed to receive .

Negative coefficient is the usual term for resistance decreasing with an increase temp/pressure etc.

The alternative solution is to have a 3 pin output sensor.
Like a potentiometer so if you measure between pin 1& 2 you will find opposite readings on pins 2 & 3

[wuzerk]

The alternative solution is to have a 3 pin output sensor.
Like a potentiometer so if you measure between pin 1& 2 you will find opposite readings on pins 2 & 3

Interesting Jules, I will take the readings between chassis and WHITE lead instead of chassis and Blue/White and see if the readings drop instead of rise
but, either way, if proven on more than one engine should be enough for future references for those who wish to check their MAP because, at the moment there is no standard on which to compare.

[Jules]

Just found these readings from a new MAP.

Figures emailed to myself on 11/11/2007 !


Rover 75 M47R engine senors readings:


Manifold pressure /turbo boost sensor
Pin V - Pin G = 4k
Pin G- pin O 6k ohms
PinV - Pin O = 2.1k ohms

[wuzerk]

Just found these readings from a new MAP.

Figures emailed to myself on 11/11/2007 !


Rover 75 M47R engine senors readings:


Manifold pressure /turbo boost sensor
Pin V - Pin G = 4k
Pin G- pin O 6k ohms
PinV - Pin O = 2.1k ohms

Confused now! My Map read Blue to chassis 56.9 Ohms and White to chassis 1.1 Ohms
EDIT: Your readings across the Map Mine across the unplugged connector! I wasted my time!

[Jules]

Was that connected or disconnected?
I'll check another one later in week.

What is the reason you are fettling round there anyway?!

[wuzerk]

Jules, I am desperately searching for the reason that my diesel rattles the seats,windows, and steering wheel on tickover! It drives beautifully just bad on tickover. Having exhausted the usual suspects I am looking for rarer reasons. For instance the intercooler is so low that it has worn a hole in the undertray!

[HarryM1BYT]

Chrissy: I would tend to agree since it is normally the higher the vacuum the lower the voltage which I why I await someone elses readings on a 75. For all I know the system could be reversed on our diesels. Then again I would expect maximum vacuum when the revs are dropping down on a petrol engine but probably not on a diesel.
Grivas: The MAP sensor measures the amount of vacuum in the inlet manifold and sends the appropriate info to the brain which adjusts things to suit.
According to the writeups a faulty one can cause surging and excessive fuel consumption.

The manifold is not under vacuum, it will be under pressure from the turbo. The higher the voltage, the greater is the pressure - a least judging by those readings.

[wuzerk]

The manifold is not under vacuum, it will be under pressure from the turbo. The higher the voltage, the greater is the pressure - a least judging by those readings.
Yes Harry I know that from my figures but they were the reverse of what was expected after seeing the U tube Map sensor test. Two owners are now going to check their readings so we should finish up with a reliable table of what you should see if you wish to check.

[chrissyboy]

At the risk of stating the obvious....

MAP stands for manifold absolute pressure.

On normally aspirated cars, this is generally measuring a vacuum. The smaller the throttle opening and hence the higher vacuum, until you get it to wide open throttle and it reads roughly ambient pressure.

For turbo charged cars, you measure both vacuum and positive pressure. During light load / small throttle openings, the turbo doesn't do much so you will read a vacuum. For higher loads when the turbo is forcing air into the engine, you will see positive pressure.

The MAP sensor will be rated to the boost levels of the turbo. A 1 bar MAP sensor reads upto 1 bar (14.7psi) of positive pressure. Not sure about our cars, but would expect the sensor to be 1.5 or 2 bar.

You can't really check a MAP sensor at static rpm levels as different loads produce different MAP readings. You really need to take the readings at different load/boost levels, either using a boost gauge or (possibly?) using the OBD.

Rich
it measures pressure , the clue is in the name .manifold absolute pressure :D maf measures flow ,mass air flow ;)