Baffling Engine Fault

So, I have a 2010 Disco 4, 3.0 TDV6. A while back I was cruising on the M40 at 75 mph with cruise on, and the car started to struggle to maintain a steady speed. It was as if the car was having momentarily breathing issues. Eventually the "Reduced Performance" warning and red triangle came on. I stopped the car for 10 mins, restarted and it cleared.. for a while. Anyway, I took it to the dealer who suspected the EGR Valves. They removed them but they looked ok, so they tested them, decided they were not at fault, gave them a clean and re-fitted. Car ran fine for 3 days, then same symptom again. This time the dealer thought it was a turbo issue. Again, turbo removed, no fault found, and re-fitted. Breather pipe found blocked so replaced and off I went again. This time the car went fine for 2 weeks, and then.. You guessed it. Having tested it out, it seems to be in warm weather (Above 20 degree ambient), between 70 and 80 mph.

Anyone had this or got any ideas?? Dealer flumoxed and I don't want to just throw good money after bad.

The problem is its not a continuous fault, unfortunately it's those random faults that are the worst to find.

Something is obviously upsetting the ECU, and I would have thought it'd leave a code. Did the garage read any codes, maybe it's listed as a pending code, which normally refers to a temporary one.

Nodge68 said:

The problem is its not a continuous fault, unfortunately it's those random faults that are the worst to find.

Something is obviously upsetting the ECU, and I would have thought it'd leave a code. Did the garage read any codes, maybe it's listed as a pending code, which normally refers to a temporary one.

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Garage did read codes - Which is what pointed them at the EGR and then Turbo lines of enquiry.

As you say, intermittent faults are a real PIA, which is why I thought I'd ask around here on the off chance.

Matelot87 said:

Garage did read codes - Which is what pointed them at the EGR and then Turbo lines of enquiry.

As you say, intermittent faults are a real PIA, which is why I thought I'd ask around here on the off chance.

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Have you tried doing the same journey at the same speed without using cruise control? Just a thought, good luck

Are the hoses in good order and not collapsing under high load when they get warm?

Does the D4 TDV6 have a DPF system? If it is getting clogged the ECU may be putting it into limp mode..

Si Click said:

Does the D4 TDV6 have a DPF system? If it is getting clogged the ECU may be putting it into limp mode..

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then you should get a DPF light on the dash

Si Click said:

Does the D4 TDV6 have a DPF system? If it is getting clogged the ECU may be putting it into limp mode..

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if it has (I am sure it does) cruising along on the motorway should keep it clean. As they do their own burn off thing.

J

marjon said:

if it has (I am sure it does) cruising along on the motorway should keep it clean. As they do their own burn off thing.

J

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That's correct and the car tells you when you need to do it.
That's why I suggested that it might be something to do with the cruise control maybe.

Madman2Swords said:

That's correct and the car tells you when you need to do it.
That's why I suggested that it might be something to do with the cruise control maybe.

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it’s a good point, But
Ours has never said do “this or that” it just does it. DPF will burn off at a constant speed above xx/mph if needed all by itself.
Is the cruise control interfering with this? I doubt it, but it is a LR product so who knows. It’s worth a free shot.

J

marjon said:

it’s a good point, But
Ours has never said do “this or that” it just does it. DPF will burn off at a constant speed above xx/mph if needed all by itself.
Is the cruise control interfering with this? I doubt it, but it is a LR product so who knows. It’s worth a free shot.

J

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I doubt it too but he said the problem started when he was cruising at 70 mph using CC at that speed it wouldn't be the DPF anyway, as it's an intermittent fault if it were me I wouldn't rule anything out.

marjon said:

if it has (I am sure it does) cruising along on the motorway should keep it clean. As they do their own burn off thing.

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Yes they will - once you have been at 60 mph for at least 20 minutes or so, but they need this regularly. If most of your driving is around town then it may choke up quite quickly and it could take more than an occasional motorway run to clean it. You cannot rule out DPF just because it happened at 70 mph. We need to understand what the OPs driving practices are. If this was the first time on the motorway in a couple of months then DPF could be the cause.
That said, if there is a DPF light and it is not on, then it makes it much less likely.

Doesn't a dpf regen need to be done over a certain rpm for an uninterrupted time period?
The filter doesn't last forever either, sometimes a chemical clean will help, sometime you just need a new one

Get the inlet manifolds smoke tested.

kermit_rr said:

Doesn't a dpf regen need to be done over a certain rpm for an uninterrupted time period?
The filter doesn't last forever either, sometimes a chemical clean will help, sometime you just need a new one

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Yes, normally the cycle will not start until the car has reached at least 60 mph and been at that speed for at least 20 minutes. But it needs to regenerate fairly frequently. If you buy a diesel and potter around town you will run into problems, with the car occasionally going into limp mode particularly when you do eventually take it on a motorway.