TD5 MAP sensor ECU pin voltage

[Grant.]

Hi all,

Got a slight electrical problem with my TD5

on Live data, the MAP pressure is a lower value than the barometric pressure by about 25 kPa, when i unplug the sensor i get a default value of 100kPa (same as ambient). even when you pick up the rev's the MAP pressure only climbs a small amount.

I replaced the sensor, and the values stayed the same.

I've got continuity through the earth to the correct ECU pin (pin 17) and i have the 5 volt feed to the MAP sensor (pin 8).

However, when i compare to my discovery, the voltage value is 3.99v back to the ECU (pin 6), and on the defender i get a voltage back of 1.40v. (pin 6)

absolutely confuddled at the moment.

Is it just another dodgy sensor? or am i missing something?

thanks in advance!

[Aragorn]

Isnt that expected? There will be a lower pressure in the manifold at idle than atmospheric, because the turbos not doing anything, theres yards of intake pipework/intercooler etc creating restriction and potentially the EGR flap will have partially closed too?

Not sure why your getting such a discrepancy on the readings between two cars though, however 3.99v isnt anywhere near the right value for an idling engine, if anything i'd say the disco is the faulty one here.

Given 1.2bar of boost clocks in around 4-4.5volts, theres no way the sensor should be outputting that when idling.

Heres a graph for a range of bosch map sensors:

Not sure the TD5 uses a bosch sensor, but its probably going to be pretty similar to the 2.5bar plot in that chart, which suggests that just below atmospheric pressure you should be in the 1.4-2v range

[Grant.]

Hi there,

as far as i understood the Baromatric and the inlet pressure should be nearly identical at idle, as they were on the other vehicle aswell.

Yep they are bosch sensors.

Thankfully found the problem, turns out it was the boost box which had a fault that was reading low on the MAP pressure, not sure what caused it, bypassed it. So now it goes like a train! Just gotta get a replacement box now...