Thread: THE PROCESS OF ELIMINATION - ADVICE PLEASE GUYS

I've just posted a very similar fault in the Discovery 2 section. My TD5 has a hunting throttle as well. I'll bet whatever is faulty we have the same fault. I've heard the MAP sensor needs cleaning sometimes, maybe this is the fault symptom.

Unfortunately this kind of fault is very hard to be diagnosed without tester and the process of elimination can be expensive and irrelevant some times

for example you can unplug the MAP but being double purpose MAP/IAT sensor both values(the manifold pressure and the inlet air temp) will go on default and the engine's performance will be seriously reduced... so at such reduced preformance maybe the initial symptom dissapears too but exactly due to the reduced performance not cos the fault was eliminated so you might replace the MAP/IAT sensor in vain

if there was oil in the red plug and the injector loom was replaced the oil will keep coming from the harness and needs cleaning untill it dries out cos the oil can act like an insulator and mix up some inputs, in this case the crank sensor inputs are very important too and the input is in the red plug, give electric contact spray in both ECM plugs and in the TPS plug too

there are many other issues which can cause such symptoms which are almost impossible to reveal without tester

Originally Posted by sierrafery

Unfortunately this kind of fault is very hard to be diagnosed without tester and the process of elimination can be expensive and irrelevant some times

for example you can unplug the MAP but being double purpose MAP/IAT sensor both values(the manifold pressure and the inlet air temp) will go on default and the engine's performance will be seriously reduced... so at such reduced preformance maybe the initial symptom dissapears too but exactly due to the reduced performance not cos the fault was eliminated so you might replace the MAP/IAT sensor in vain

if there was oil in the red plug and the injector loom was replaced the oil will keep coming from the harness and needs cleaning untill it dries out cos the oil can act like an insulator and mix up some inputs, in this case the crank sensor inputs are very important too and the input is in the red plug, give electric contact spray in both ECM plugs and in the TPS plug too

there are many other issues which can cause such symptoms which are almost impossible to reveal without tester

time to buy a nanocom then..

Originally Posted by Jazzman

I've just posted a very similar fault in the Discovery 2 section. My TD5 has a hunting throttle as well. I'll bet whatever is faulty we have the same fault. I've heard the MAP sensor needs cleaning sometimes, maybe this is the fault symptom.

im gonna work through them all methodically, i have a new cooler and ECU coming for upgrades so id like to sort this out before i go adding more horses as it seems it often makes the surging worse.

ill stick with it and let you know how i get on as we progress. If i find my fault it may help lead you to yours perhaps or at least give you some things to rule out.

What about a problem with the throttle itself? the accelerator pedal just moves a potentiometer which are known to fail not sure if the would deliver the symptoms you describe but its worth checking.

Originally Posted by Leyland1980

What about a problem with the throttle itself? the accelerator pedal just moves a potentiometer which are known to fail not sure if the would deliver the symptoms you describe but its worth checking.

"It doesnt seem to be behaving like a faulty TPS as its not dependant on throttle position/pedal position but rather engine revs/ maintaining revs and its the same for high and low gear."

i wrote this originally, but i haven't ruled out oil in the throttle harness. have a full day tomorrow and some more time this week to do some more fault finding. will report back on what i find guys, seems like there are a few threads on this problem but not too many definitive answers ill try add some results to the data available.

Originally Posted by blackapache

im gonna work through them all methodically, i have a new cooler and ECU coming for upgrades so id like to sort this out before i go adding more horses as it seems it often makes the surging worse.

ill stick with it and let you know how i get on as we progress. If i find my fault it may help lead you to yours perhaps or at least give you some things to rule out.

I'd appreciate that. I'll do the same.


Disco W.A mentioned he had a similar fault with a bad earth at the ECU.


http://www.aulro.com/afvb/showthread...08#post2301308

So one other interesting possiblity.



What year is your Defender? If it's post 2003 it's an EU3 engine. I've heard that if you have to replace and ECU on a Defender, and you use a factory ECU with a EU2 map in an EU3 engine or vice versa it will surge under light throttles.