ambient air pressre sensor

I don't own a scan tool for the TD5 but is there any ways of checking with a multi metrer and if so what values should I see
I have a funny feeling the ambient sensor has failed .my max boost limit is now 1 bar any thing over 1 bar I hit boost limit and surges

the AAP sensor is very hard to be ruled out without tester, you can hook a voltmeter set on DC across the ECU red plug's pin 30(-)(pink/black wire) and 10(+)(white/yellow wire) using needles as to reach the pins from behind to measure on them... at idle you should get a voltage up to 4V(i dont know exactly how much cos it's pressure dependant), you must watch the voltmeter while driving and see the voltage dropping under heavy throttle ...if it's not so the sensor is fubar'd but it can behave like that and give erratic readings... if you dont get any voltage only then you know it's certainly gone...concentrate to measure on the correct pins, this view is from the ECU side

sierrafery said:

the AAP sensor is very hard to be ruled out without tester, you can hook a voltmeter set on DC across the ECU red plug's pin 30(-)(pink/black wire) and 10(+)(white/yellow wire) using needles as to reach the pins from behind to measure on them... at idle you should get a voltage up to 4V(i dont know exactly how much cos it's pressure dependant), you must watch the voltmeter while driving and see the voltage dropping under heavy throttle ...if it's not so the sensor is fubar'd but it can behave like that and give erratic readings... if you dont get any voltage only then you know it's certainly gone...concentrate to measure on the correct pins, this view is from the ECU side

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thanks mate
today going to work was pretty poor .but it came life a a few times .I'm suspecting a loose connection on a connector or maybe there is a break in the wire
tomorrow I'm going to clean all maf map ambient sensor electrical plugs and also try and close the pins up on the female side of the electrical plugs

for a quick test coming home I thought **** with it I disconnected both MAF and ambient sensors knowing the car will be in limp mode for a few seconds on start up
and I never had any issues driving home my boost gauge was hitting 18 to 19 psi with out any surge ...so its looking to be either maf or ambient I will take it for a run tomorrow with only one of the 2 disconnected .to try and narrow it down

Are you sure that your wastegate is not sticking? if your defender is fitted with a wastegate modulator that can be at fault as well or the MAP to read high, proper diagnose is only with tester for such symptom

test drove this morning with a few different combinations of the ambient sensor and maf sensor plugged and unplugged
it appears that when the maf sensor is plugged in I have issues

without the maf sensor plugged in my analogue boost gauge fitted at the manifold sees a boost of 17 to 18 psi

when the maf is plugged in the engine surges when boost levels go over 15 to 16 psi

just come back from a bit of a drive got the engine up to operating temps and also flogged hell out the engine even used my LPG system more than normal I tried to get the engine to surge ..this is with the maf sensor unplugged and ambient sensor plugged in

up to now I'm just going to leave the maf unplugged and monitor it over the next few days if it wont surge or over boost looks like a may need a new maf

Strange... what was the boost level before that symptom? like with MAF unplugged now or higher? and what year is the vehicle(NNN or MSB ECU)? if it has wastegate modulator try with MAF plugged and modulator unplugged too

sierrafery said:

Strange... what was the boost level before that symptom? like with MAF unplugged now or higher? and what year is the vehicle(NNN or MSB ECU)? if it has wastegate modulator try with MAF plugged and modulator unplugged too

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update I have cleaned the maf sensor with contact cleaner and installed ..took for drive ..really need to feather the throttle on hard acealration my boost gauge showed the bunny hopping at about 16 psi so I pulled over and quickly disconnected the maf sensor with engine still running
the car drives perfect hard acceleration and a few hill inclines I also slightly pulled up my hand brake up an incline to minuupulate some load it pulls like a train

when my last maf sensor failed it only put the engine in limp mode for about 30 seconds until the ecu set a set value this time my symptoms are different
my boost modulator has been disconnected for about 5 years I run a manually boost controller that tricks the waste gate ..this just is a quicker way instead of adjusting waste gate rod length

in regardless how much LPG or fuel enters the engine my manually boost controller bleeds off air and the waste gate still opens as normal

my over boost issue has only just appeared

unsure what ecu I have as all numbers and stickers have been rubbed off from the previuse owner ..but its a 2002 disco 2 if that is any help



from monitoring boost levels seems like I cant reach my 18 psi with maf sensor plugged because if I do the the engine will surge and this is without using my LPG system

Ok, i thought it's a defender... if it's D2 without wastegate modulator let the MAF plugged in and remove fuse F2 from engine bay fusebox and see then... i presume you dont have the EGR still on do you? ...if the wastegate modulator is still there disconnect it's electrical plug ...these are to rule out a wiring issue on that circuit if possible as the MAF, wastegat emodulatorn and EGR modulator are all on F2, as i said for this kind of symptom the only accurate way to troubleshoot is with tester

a 2002 modell should be Eu3... the Eu3 calculates the airmass for injection control based on MAF readings first and swaps to MAP/IAT sensor if the MAF is unplugged so a bad reading MAF can mix up the fuelling but as long as we can't see the live readings it's the "swap it and we'll see" method.

ok a little bit more update in low boost situations between 8 and 10 psi @ 50 KPH
when the maf sensor is plugged in I have noticed my throttle position feels further down to maintaine speed while going up the hill out side my house it feels like the engine has lost performance or it feels like I'm towing or dragging something

my neghbours must think I'm crazy LOL doing laps around the block all day long

with the maf disconnected my throttle position is less and it pulls up the hill with out a struggle it feels more alive while sitting at the same boost levels but it feels like I don't need to push down more on the peddle as much compared to using the MAF

Yes...it seems like you need a new one, it can fail in more ways creating different symptoms... try the F2 removal thing too just to be ruled out once more

sierrafery said:

Ok, i thought it's a defender... if it's D2 without wastegate modulator let the MAF plugged in and remove fuse F2 from engine bay fusebox and see then... i presume you dont have the EGR still on do you? ...if the wastegate modulator is still there disconnect it's electrical plug ...these are to rule out a wiring issue on that circuit if possible as the MAF, wastegat emodulatorn and EGR modulator are all on F2, as i said for this kind of symptom the only accurate way to troubleshoot is with tester

a 2002 modell should be Eu3... the Eu3 calculates the airmass for injection control based on MAF readings first and swaps to MAP/IAT sensor if the MAF is unplugged so a bad reading MAF can mix up the fuelling but as long as we can't see the live readings it's the "swap it and we'll see" method.

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yes your correct mate I wish at this time a had a tech tool but in the mean time doing it by feel and working off anologue gauges

its a d2 with the boost modulator but this has been disconnected for aproxx 5 years with no ill side affects the boost modualtor is still there but not connected up at all

I reconnected the MAF sensor and removed F2 fuse ..I have limp mode on start up but it drives like a dream once the ecu detects this

the EGR system has a full delete this is actuators removed blanking plates and also solenoid's removed ..the egr cooler is still in place with coolant running through it but blanked on both ends on exhaust ports .... I opted to leave the cooler in place as it sits in the direct path of air flow (every little helps when it comes to cooling the engine via engine coolant

So do you see any difference between MAF unplugged and F2 removed? ... if no then buy a new MAF(only genuine is reliable) but if tere is any difference then it might be a wiring issue on that circuit, the loom used to rub against the engine where it crosses beneath it it... you can make some rudimentary check with multimeter but not 100% relevant

sierrafery said:

So do you see any difference between MAF unplugged and F2 removed? ... if no then buy a new MAF(only genuine is reliable) but if tere is any difference then it might be a wiring issue on that circuit, the loom used to rub against the engine where it crosses beneath it it... you can make some rudimentary check with multimeter but not 100% relevant

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thanks sierraferry
with the f2 fuse removed the engine seem to react the same as me doing my tests by disconnecting the MAF
the MAF sensor was from landrover barbeggello here In perth buts its about 2 years old now and its the hot wire type

thanks for the vid I will check some voltage readings I'm guessing if don't have enough power supplying the sensor it wont work correctly but unsure the values coming out the sensor ...

i might just try a continuity tests on the wire harness but unsure what pins the ecu run for the MAF

any ways thanks for the help

ozzyboydeano said:

i might just try a continuity tests on the wire harness but unsure what pins the ecu run for the MAF

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from MAF pin 1 goes to ECU red plug pin 20(pink/black wire) and pin 2 to pin 11(brown/orange wire), you have the pin disposals in my first post