How to Test a MAP sensor - Manifold Absolute pressure / Manifold Air Pressure sensor
I started looking at the MAP sensor as I initially thought it may be leading to a low turbo pressure and smoke from the exhaust. I even bought a new MAP sensor but it didn’t make any difference, so I did this test to check the sensor. It’s fairly easy, confirms it’s operating correctly or not and should save you arbitrarily buying a new part!
Just compare your sensor output voltages at a particular pressure with the graph of volts versus pressure (in psi) shown in the video.
If you want a better printable copy of that MAP pressure/voltage graph I’ve made a download area, with just a small charge for my time - £1.99 via PayPal (nice and safe) use the link below and you’ll get instant access to the document in 3 formats. The files are in universally readable pdf format, the Apple ‘Numbers’ and ‘Excel’ format. No material is posted, just download access. The payment link is set up to accept PayPal or any credit card and so is very safe. You will be directed to the files after you have paid and clicked on “return to merchant” it will take you to a page by Dropbox, then just click on “continue to website” (or download Dropbox app if you want) and you will then see the files which you can open up to view or you can download them to your device.
If you do find after testing that you need a new MAP sensor then see here for the best price on eBay U.K.:
When talking about pressure please note the difference between absolute and relative pressures. The normal atmosphere pressure at sea level is about 15 psi. That graph I showed of pressures is absolute pressure, i.e. the pressure relative to a vacuum. So that is why the MAP sensor reads 1.77 volts when it is just open to the air as that is the voltage for 15 psi of absolute pressure. When you use a tyre gauge to pressurise it, the tyre gauge reads relative to atmospheric pressure (i.e. the amount over atmospheric pressure), so 15 psi on the tyre gauge is about 30 psi absolute pressure.
This video is part of a series of investigations I did to try and improve and eventually remove the exhaust smoke coming from this TD4 (BMW engine) freelander. Hence I suppose you could call this “smoke reduction stage 6”.
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