Disco Td5 15p Runs sweeter with AAP sensor unplugged

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Discodevon

Discodevon

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1,448
Hi guys back again :doh:

Had a starting problem with my disco, she starts first turn if I turn the ignition on for a couple of seconds then turn. if I leave it until the glow light goes out that's when I have starting issue.

Also I had a misfire at light throttle unplugged AAP sensor and she sounded sweeter than ever with that lovely td5 noise at light throttle.

Got another used sensor from a 2004 put it on now I have to drive say 3 miles until shes sweet and doesn't misfire but unplugged shes still abit better :(

anyone who can shed some light would be much appreciated
 
on 15P engines the AAP has two purposes, to give ambient pressure and ambient temp inputs to ECU, the most important is the pressure reading for which the ECU will go on default value if the sensor doesnt work well, the engine might run better with it unplugged than with it plugged if faulty but it's risky for the engine as theres no turbocharger overspeed protection... if the EGR is bypassed it's influence is not so noticeable in the engine running though

the AAP reading is "linked" to the MAP reading cos the ECU extracts the boost from the MAP reading usnig this formula: MAP=AAP+turbo boost

IMO it's good to have a well working AAP to be on the safe side... with it unplugged the wastegate modulator is bypassed too and there's no active boost controll so the engine will work like on the defender... make sure the wastegate modulator is working aswell, complete info attached
 

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Hi guys iv still got this problem.. I changed for another used off ebay and it helped abit something still was not right.. anyway whilst it was running the other day I unplugged the aap revved the engine abit and my disco sounded lovely.. im guessing like its meant to sound.. plugged the sensor back in again and revved the best way I can describe it is a cackle noise (not misfire) but not that beautiful music a td5 produces on light throttle :(.. Any what do you think? Devon 4x4 are about 15 miles up the road so may just have to bite the bullet and leave her there.. Also I sometimes have a tapping noise underneath from cold start but goes after a min idling.. sounds like a little pin hammer hitting a bit of loose metal? any ideas people?
 
without tester and with used sensor nothing is certain... with unplugged AAP it's on a default mode with limited boost so with good sensor must run better not worst...check fuse F2 in engine bay just to rule it out

i can't tell you much about that noise...might be hydraulic tapped, missadjusted rocker or god knows what
 
Yeah that noise is not a nice one unfortunately, but doesn't do it all the time, has its moments, its almost underneath I think not a knock but a tap tap tap tap. I have a hawkeye and no faults are found with aap sensor plugged in. obviously when I unplug it a fault comes up then. when unplugged I get faults coolant temp high and coolant fault which will not delete. uneven idle is still faintly there sometimes aswell
 
put hawkeye on live data and read ambient temp and pressure, the temp reading must be very close to the real ambient temperature there and the pressure as well(around 100kPa) but it must drop 2-3 units if you floor the throttle... cos it's possible that the AAP sensor is not completely gone just gives wrong readings and the ECU might not log a fault for that
 
Iv tested live data and aap sensor does drop units when I floor the throttle :( at a dead end with this now.. I still have the cold start issue aswell.. This morning it was about -3 here and my dad started my land rover, Started right up first turn, ran for about 20 secs while he moved it. then he switched off.. all ok. I come and start it half hour later and it turned over fired then just kept turning fast for 3 seconds. so I let go of the key turn again to start it shes running first turn.. hmmm.. and because it was cold out this morning the idle was at about 1000rpm for a minute and I couldn't here the tapping noise until the engine settled to normal tap.. so the tap almost goes when I rev it. seems to be on idle??
 
I didn't read it this morning but did the other day and seemed about right.i plugged it in for a cold start the other day it was running a little shakey and not nice and smooth injector 4 jumped up to +10 which I never seen before. Normally + ~1 to 3
 
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