38mpg at 70mph. 2004 C5 estate 110bhp

[myglaren]

MAPs are for petrol not diesel so nothing applies I'm afraid.

Acording to the Citroën parts catalogue, the dw10ated engine has a MAP sensor. It's hosed to the top of the intercooler, part no 1920gh.

Agreed - my local dealer has it listed as a boost pressure sensor.

[KevMayer]

Why not try some Wynns EGR3 spray. This can clean all the crud out of the inside of your inlet manifold and off your inlet valves.

I tried it and it made quite a difference.

[cachaciero]

MAPs are for petrol not diesel so nothing applies I'm afraid.

Acording to the Citroën parts catalogue, the dw10ated engine has a MAP sensor. It's hosed to the top of the intercooler, part no 1920gh.

Quite correct, on a turbo equipped engine a diesel injection system needs to know the inlet pressure as much as a petrol injection system does.
In the case of a diesel the pressures it will measure are all positive and are effectively a measure of the turbo pressure. If this sensor was defective in the sense that it indicated a higher pressure than actually existed the injection system would tend to overfuel the engine. However I would expect there to be a monitor loop within the logic that would check the sensor output against engine revs and maybe throttle position this loop would have a map of expected manifold pressure for these values, if the sensor was outside this map it would post an error. Well that's how I would write the software anyway

cachaciero

[Paul-R]

Mmmm, well I suppose you could say that if we're talking about absolute pressure then that can be either positive or negative relative to normal atmospheric pressure. However, the MAP in the link is for vacuum measurement which is then used to provide data for the petrol injection. The pressure sensor in the DW10ATED engine measures the pressure of the Turbo above atmospheric norm.

[cachaciero]

Mmmm, well I suppose you could say that if we're talking about absolute pressure then that can be either positive or negative relative to normal atmospheric pressure. However, the MAP in the link is for vacuum measurement which is then used to provide data for the petrol injection. The pressure sensor in the DW10ATED engine measures the pressure of the Turbo above atmospheric norm.

Oh! so a turbo charged petrol engine doesn't have positive pressure in the manifold then ? I believe that your first sentence was the correct one, it measures absolute pressure that way it takes into account altitude as well.

cachaciero

[Paul-R]

There aren't that many turbocharged petrol engines around and I wonder whether they have two pressure sensors, one for positive pressure and one for vacuum. It would probably be easier than engineering a sensor that could cope with both positive and negative pressure.

Coming back to PSA I believe that altitude in the HDi is measured by a sensor in the ECU.

[torq]

This evening I

Unplugged the MAP and MAF while the engine was running. The idle went rough when the MAF was unplugged. Plugged back in and ignored the EML, I'll Lexia it at the weekend. Drove home at an average of 67mph for 17miles and got a reported 47.1mpg from the OBC, my best to date!


The bosch book gives the following sensors and set point generators

Road speed sensor
Crankshaft speed sensor
Camshaft sensor
Engine temperature sensor
Intake air sensor
Boost pressure sensor(MAP)
Hot film air-mass meter (MAF)

[cachaciero]

There aren't that many turbocharged petrol engines around and I wonder whether they have two pressure sensors, one for positive pressure and one for vacuum. It would probably be easier than engineering a sensor that could cope with both positive and negative pressure.

Coming back to PSA I believe that altitude in the HDi is measured by a sensor in the ECU.

At the end of the day a pressure sensor is a pressure sensor it's how you calibrate it that counts.
If the sensor has a voltage output you can arrange for it to have an output of say 0Volts at 1013mb and say 12V @ 3000mb such a calibration would only give you an output for pressure above 1013mb. On the other hand you could calibrate the same sensor to give you an output voltage of say 3Volts @1013mb such an arrangement would give you a meaningful output for pressures positive and negative about normal atmospheric.

Not aware of a separate sensor in the ECU, which doesn't mean there isn't one but I can't see why one would be needed, the engine is only interested in the absolute amount and pressure of air going into the engine which the ECU can calculate from Mass Flow (MAF) and manifold Pressure (MAP) altitude per se is irrelevant, the effects are already taken into account.

cachaciero

[BX]

The atmospheric pressure sensor is part of the ECU in both the SID and EDC controlled HDIs.

[cachaciero]

The atmospheric pressure sensor is part of the ECU in both the SID and EDC controlled HDIs.

So it is. You made me go away and do some more studying Still can't work out why they would need it though.

cachaciero

[myglaren]

We don't really have this in the UK so it may not be immediately obvious but some countries - America is the one that springs to mind first, there are many regions that are significantly above sea level* and the normal barometric pressure consequently lower which has a huge impact on performance.
Perhaps the sensor in the ECU detects the ruling barometric pressure and compensates for the deviation from standard sea level pressure of 14.696 psi.

*I may be wrong here but I have the feeling that some regions in Utah are below sea level.

[cachaciero]

We don't really have this in the UK so it may not be immediately obvious but some countries - America is the one that springs to mind first, there are many regions that are significantly above sea level* and the normal barometric pressure consequently lower which has a huge impact on performance.
Perhaps the sensor in the ECU detects the ruling barometric pressure and compensates for the deviation from standard sea level pressure of 14.696 psi.

*I may be wrong here but I have the feeling that some regions in Utah are below sea level.

You are correct even in Europe we have high mountain ranges e.g. the Alps which can make a big difference to engine performance.
I was writing an explanation on how altitude was irrelevant as things such a MAP and MAP would automatically take care of it which they do as far as fueling is concerned but it suddenly occurred to me that as the inlet pressure falls what you really want is for the turbo to compensate for this auto magically, with a separate barometric sensor this becomes possible at least with a variable geometry turbo, not sure how this could be achieved using a non variable geometry turbo. Another very useful feature of a separate barometric sensor is that it enables a calibration check of the Manifold Pressure sensor, with engine stopped i.e at switch on the output of both sensors should indicate the same pressure.

cachaciero

[torq]

Today I bypassed the MAP. Drove 20miles at 70mph and 2.3k rpm with no effect. Temp stayed the same as did performance and I got 41.5mpg. Will try another 40miles tomorrow to see but it appears the MAP has no input at steady engine speeds.

T

[Citroenmad]

Today I bypassed the MAP. Drove 20miles at 70mph and 2.3k rpm with no effect. Temp stayed the same as did performance and I got 41.5mpg. Will try another 40miles tomorrow to see but it appears the MAP has no input at steady engine speeds.

T

So is it even working?

Ive replaced a few on 2.0HDi 110 C5s, often they don't store a fault code but fitting a new MAF sensor restored performance and economy. On one occasion it did store a fault code.

Cheap MAF sensors are not worth anything in my opinion, you might as well stick with an old and broken one. I had to replace a cheapy with a genuine one as it just wasn't working correctly.

[cachaciero]

Today I bypassed the MAP. Drove 20miles at 70mph and 2.3k rpm with no effect. Temp stayed the same as did performance and I got 41.5mpg. Will try another 40miles tomorrow to see but it appears the MAP has no input at steady engine speeds.

T

How did you bypass the MAF? mechanically or electrically? I found on my 2.2 that bypassing the MAF (air bleed downstream of MAF) made quite a substantial difference much more than I was expecting, acceleration was much poorer and power seemed to be down over much of the low / mid rev range.

Edit
Edited to reflect what I was thinking, which actually had little to do with the post I was responding to.........

cachaciero