Disco 2 Td5 no power, changed loads and at a loss.

sierrafery said:

In the morning after a night rest watch the ECT, FT and IAT inputs immediately from cold start at idle(no need to record just report), then these readings should be close to each other cos the vehicle is quite equalised wit the ambient temp, i've checked about 10 logs i have from more vehicles and none of them has such IAT behaviour though i think it wasnt so cold outside when all of those files were recorded

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OK, I still have the old map sensor so I'll record another run tommorow with each one from cold.

Ok, we'll see tomorrow but if everything checks out well then on the next drive when it's loosing power in 5'th or 4'th change back in 3'rd and if it accelerates well that way and those huge tyres were always on i'd be about 75% convinced that those tyres are a very important part of the problem. If it loses power in lower gear too then further investigation is needed. You must understand that an untuned and old Td5(which might have a worn turbo too) with such tyres(especially if it's loaded with steel bumpers or other extras) can't behave well as the ECU was mapped from factory for std dimension tyres which are 235/70R16 (10% less than your's). I've studied deeply and for long time the impact of tyre dimensions on the Td5's management, made many live tests as well and i can tell for sure that 5% bigger tyres is the extreme accepted limit without proper tuning/remap. I've explained this many times and i'lll not repeat, just in a nutshell: the gist of it lays in the following (+ some other things) ..from the WSM/management's operation :
"Vehicle Speed Signal (VSS)
The VSS is an integral part of the ECM's overall adaptive strategy. The ECM receives the signal direct from the
SLABS ECU."
and now imagine that at a certain throttle position/gear/rpm/boost and torque which are all correlated with a calculated IQ(injected quantity) based on the fuel map the vehicle must reach a certain VSS and your ECU receives a 10% lower signal than expected due to those tyres so it will behave like when you are starting to climb a steep hill in 4'th and when it slows down you just keep pushing the throttle without changing the gear in lower... it's a very long and complicated story so i rest my case for now cos maybe we find some other explanation

Here is the new sensor from cold https://www.dropbox.com/scl/fi/ubspip1nhuqhvi29s0u0g/New.xlsx?rlkey=38050bzv3vroj9p9bd8ch21gb&dl=0
And this is the old sensor straight afterwards.

Sadly the injector seals that were done yesterday didn't seem to fix my cold start issue and it would seem there's still air getting into the fuel system.
Only thing left is the fuel filter housing.
(had to crank it many times for it to fire and stay running & it only happens from cold)
This still makes me think it's a fuel issue and not the tyres & besides the tyres were on there when I got it and it was fine before that.
Someone has suggested to me just to get a map and hope that what's broken will present it self but I think that's just hiding the problem.

The old sensor is definitely fubar cos that's when it shows 120 from start, ... i'll go for a night shift today and check the cold start readings on mine cos i dont like how those temps look on your's as there is toomuch difference between the ECT and FT.

as about hard starting, replace the air bleed valve in the filter head's rear outer port (WJN500110) you should rule this out too

I was too curious so went out and checked... outside was -1*C but in my garage which is not heated was +1.7*C and when i started it the ECT was close to 10, FT to 6 and IAT to 2 so presuming it was colder at you i can't blame the sensors ...at least i learned something new and i know now how these temps are in reality from really cold start which has never occured to me to ckeck

In conclusion IF the power loss problem is not caused by the tyres there is a fuel supply issue and that's not covered by diagnostics, though if it's that then it should lose power in lower gears too IMO. The relevant thing would be if you could bring into the cabin a fuel pressure gauge and watch it when the symptom occurs but that's not easy cos you can't simply plug it instead of the FT sensor as usual cos the FT sensor must be there for the management to work well under load ... Good luck cos seems that i'm out of ideas other than the injectors might be worn eventually

So sorry you have not been able to narrow this down.

as it'll cost you nothing, more or less, I'd still change the turbo even though hard starting is a problem. I think you have two separate problems, and the lack of power at high revs could still be it going into limp mode.
Best of luck.

sierrafery said:

I was too curious so went out and checked... outside was -1*C but in my garage which is not heated was +1.7*C and when i started it the ECT was close to 10, FT to 6 and IAT to 2 so presuming it was colder at you i can't blame the sensors ...at least i learned something new and i know now how these temps are in reality from really cold start which has never occured to me to ckeck

In conclusion IF the power loss problem is not caused by the tyres there is a fuel supply issue and that's not covered by diagnostics, though if it's that then it should lose power in lower gears too IMO. The relevant thing would be if you could bring into the cabin a fuel pressure gauge and watch it when the symptom occurs but that's not easy cos you can't simply plug it instead of the FT sensor as usual cos the FT sensor must be there for the management to work well under load ... Good luck cos seems that i'm out of ideas other than the injectors might be worn eventually

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Following some other advice I found on the forum I couldn't blow through that air bleed valve so I temporaryly removed the gauze filter from it and put it back in to to see if she starts in the morning, as for the top end power I think I'll just get it mapped and see what fails. I'm not convinced it's the turbo & think it's either fuel or ecu related at this point. & I don't really see there being a problem with the fuel system after changing everything.

Stanleysteamer said:

and the lack of power at high revs could still be it going into limp mode.

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there is no "limp mode" for manuals

CallumP227 said:

I'm not convinced it's the turbo & think it's either fuel or ecu related at this point. & I don't really see there being a problem with the fuel system after changing everything.

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I'd not blame the turbo as well as long as you get up to 230 map reading. What about the boost pipes? are you sure they are not delaminated or some crack which leaks only under load? also check if there are no smoke traces around the exhaust manifold gasket

sierrafery said:

there is no "limp mode" for manuals

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oops, never realised it wasn't an auto.
today is yet again a school day.

CallumP227 said:

think it's either fuel or ecu related at this point

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I just remembered something which would be good to rule out: go with nanocom in "inputs switch" and see what happens with the brake switch and clutch switch inputs when you push the pedals and report cos if the brake switch's N/C contact is not closed or the clutch switch is closed with pedal released the fuelling is reduced and it's noticeable only under load

sierrafery said:

there is no "limp mode" for manuals

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Actually, thinking about it, Inever knew this anyway, so manual or auto I'd never have known this.
Ta again my knowledgeable friend!!

sierrafery said:

I'd not blame the turbo as well as long as you get up to 230 map reading. What about the boost pipes? are you sure they are not delaminated or some crack which leaks only under load? also check if there are no smoke traces around the exhaust manifold gasket

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He did say, among the long list of things he'd changed, that he'd changed the intercooler and the hoses.
But I had a brand new silicone hose slip off last christmas, i.e. 2022, on holiday in Yorkshire! So, good advice! and yes it did produce similar symptoms!

sierrafery said:

I just remembered something which would be good to rule out: go with nanocom in "inputs switch" and see what happens with the brake switch and clutch switch inputs when you push the pedals and report cos if the brake switch's N/C contact is not closed or the clutch switch is closed with pedal released the fuelling is reduced and it's noticeable only under load

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I shall try this in a bit when I pop out.

My newly acquired TD5 behaves similarly, but I'm not hijacking this thread for a diagnosis... However, I simply must commend Sierrafery for his knowledge of the TD5 management system.

sierrafery said:

I just remembered something which would be good to rule out: go with nanocom in "inputs switch" and see what happens with the brake switch and clutch switch inputs when you push the pedals and report cos if the brake switch's N/C contact is not closed or the clutch switch is closed with pedal released the fuelling is reduced and it's noticeable only under load

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I did try this yesterday and I shall probably have to do it again as I cant remember which way around they were but they both read open until pressed then they swapped to closed or vise versa (can't remember which way around but they were both the same).

CallumP227 said:

I did try this yesterday and I shall probably have to do it again as I cant remember which way around they were but they both read open until pressed then they swapped to closed or vise versa (can't remember which way around but they were both the same).

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In this thread you will find @sierrafery 's copy of the wiring diagram and his comments on it!

CallumP227 said:

I did try this yesterday and I shall probably have to do it again as I cant remember which way around they were but they both read open until pressed then they swapped to closed or vise versa (can't remember which way around but they were both the same).

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Concentrate when you'll do it cos it's important, for the clucth switch is OK off-on but for the brake switch nr 1 must do the opposite of nr 2, i'll check with nanocom on mine cos it's possible to have a glitch in this area as when i had a problem with the brake switch i used hawkeye which has a different software, the gist is that one of brake switch inputs iirc nr 2 should be "on" with pedal released otherwise the ECU "thinks" that brake is applied and reduces the IQ hence low power under load... would be good to fully depress the pedal and pull the switch's plunger to the maximum you can.... though if you have cruise controll and it's working this one is ruled out as well so no need to bother with it, here's the theory:

sierrafery said:

there is no "limp mode" for manuals

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Wellll......

Theres the overboost "limp mode" that clears after restart or clearing the code while driving..

Dervishi said:

Wellll......

Theres the overboost "limp mode" that clears after restart or clearing the code while driving..

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As this is what I meant, and @sierrafery told me there isn't one for manuals, I now don't know what to think!