Td5 Engine Surging

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Originally Posted by sierrafery

IMO option 2 from Tombie's last post is not neglectable at all, cos watching very carefully the readings we'can see that first time when according to the throttle track 1 reading(and the others) you floored it the MAP went up to 217(i'll "round" the readings to be easyer) and second time again close to 217 and both times the MAF was around 670...but the AAP reading shows that it was serious suction there as it dropped from 101 to 95/96

if we extract the AAP from MAP both times the boost is around 1.2(120KPa) Bar and based on the infos from "LUCAS Td5 Diagnostic" in Nanocom files the maximum MAP allowed by the overboost protection is 210 for Defender and 230 for D2 considering the AAP 100 so you are very at the limit...and as we know we can consider a 10% margin in these cases

now based on the fact that it's a serious suction there it's possible that the MAF's circuit has some limiter too and when it reaches the 5V to cut the feed... i'm up to open one and make some measurements there in the near future

i saw this kind of happenings on several forums and not just for D2, that's why the market is full of all kind of MAF enhancers/limiters, here is a not very old thread from this forum http://www.aulro.com/afvb/electronic...nipulator.html ... i'm not gonna go deeper into this to not be named idiot again but it'a something to think about in case the new MAF will not fix things...or to find the reason why that huge suction under load.... by the way did you replace the depression controll valve?

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Thanks Sierrafery,


This is all way over my head in terms of competence level.


I did exactly the same test with a different MAF and have attached the file - does this show the same symptoms on paper?


I need to sort this before Saturday when we are due to leave on a 7,000km outback trip and am a little stressed about not being able to fix this.

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Originally Posted by sierrafery

.... by the way did you replace the depression controll valve?

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No, I did not but did remove and inspect it - looks fine and allows air through from either end. I the only way to check its functionality by replacement?

this second file looks good to me, the MAF didnt cut out at all and at the same maximum MAP it was at 650 so the MAF readings (and all the others were OK, not even the AAP dropped so much), so didnt this second MAF fix things?

afaik that depression valve can't be tested just like that... it is loosing it's qualities in time

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Originally Posted by sierrafery

this second file looks good to me, the MAF didnt cut out at all and at the same maximum MAP it was at 650 so the MAF readings (and all the others were OK, not even the AAP dropped so much), so didnt this second MAF fix things?

afaik that depression valve can't be tested just like that... it is loosing it's qualities in time

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The surging above 3,000 rpm does not occur with the MAF used in this test and I have not been able to reproduce the original symptoms either.


Fingers crossed that it was a combination of the boost control valve and dodgy MAF sensor that caused both problems. I guess time will tell.


I'll purchase a new MAF tomorrow and post up a file with the results.


Thanks for looking over the files - I have no real idea as to what to look for!

yes, according tpo the readings everything went OK, IMO it will be quite the same with the new MAF too, keep this second MAF for spare and get rid of the other one, if i was you i'd replace the depression valve too with a new one cos a "tired" DCV can stress the MAF and make it fail sooner

New MAF installed today and she is running well and will hopefully continue to do so for a long time.


Thanks to all for your input and support.


I've attached the file with my latest test.

Fery - just FYI terminology wise - in Aus at least the "depression valve" is commonly known as a PCV (Positive Crankcase Valve)