407 very intermittent surging

[GiveMeABreak]

19 & 20 are the particle filter pressure pipes, 2 is the gas temp. sensor	1 is the Diff Pressure Sensor, 6 the particle filter pressure pipes

[EDC5]

My downstream temp sensor always shows 100 degrees or thereabouts even when stone cold. It must be the minimum reading of the sensor.

[MikeT]

Yes, the exhaut temp count only starts at 100c, Pete. Mine shows <100c (less than) until it exceeds it.
If you have seen the pressure fluctuating, at least it's showing it's working of sorts so I'd not be concerned any more with it at this point.

[moizeau]

So the downstream temp is fine. Thanks for the confirmation. I saw a reading on the diff pressure twice from 6/7 revs, the first 2. Thanks for the pics Marc, Is the noted '2' on the first diagram the '2' on the second 'cause 2 on the first looks like a gasket and I can't see '1' on the second, unless it's '2'? I've got onto Service Box now but have to do it through a VPN in the UK or it asks for my Siret No. (business No.), not sure if it's checked? But hey it it works 'if I'm in the UK!' I'll have a look, but can't teleport whilst writing! I think I need to get under the car, to have a look if nothing else. Just need to figure out why it's in a constant state of regen, though if it does a regen on a non motorway run that will, at least, have sorted the initial issue.
We will see
Oh and Mike, when I read it through this morning I realised you were just pulling my p......r, just too tired last night to realise.

[GiveMeABreak]

No Pete the component numbers are not the same. These are 2 different diagrams. On the left hand diagram 19 & 20 are the pressure pipes, but 2 on the right hand diagram is the Exhaust gas temperature sensor. If you look closely along side the particle filter on the right diagram you can see the pressure pipe running alongside.

[moizeau]

Cheers Marc

[moizeau]

Beer o'clock. Just been on a drive at 50 mph (speed limit here) with the 'puter plugged in. It got to 77% soot then regenned back to 1% with absolutely no hiccups. Revs were at 1700 ish as well. Did notice that the diff pressure is almost always at 0, very occasionally increasing to 25 ish if I accelerate then once the speed levels out it goes back to 0 and the state of regen is still 'regeneration'? Need to get under the car to check the pressure pipes next.

[EDC5]

I still suspect there might be something up with your differential pressure sensor.

If the sensor is accurate is it possible that someone has 'holed' the DPF as there will always be some sort of back pressur surely?

[moizeau]

I agree, do you know where the sensor is and if it's checkable? I've checked underneath and there isn't any obvious damage. It's been through the French MOT on the new regs so I don't think the DPF has been played with, also the previous owner had it for the last 100000m and isn't the sort. It does seem odd that 'apparently' it's in a permanent state of regen, however it doesn't keep the soot down to zero ish which is what I would expect if that was really the case, fuel consumption is good also. I'd guess that a high diff pressure would force a regen? What else would ask for a regen?
This a copy of the CT with the emission values, it would be interesting to compare the figures.

[EDC5]

To be fair, a bashed through DPF would probably give a better running engine and higher economy. It may have been remapped to prevent any error codes (from low diff pressure) from turning up.

Could you get an assistant to floor the throttle whilst you look at the exhaust? There should be no hint of black smoke with a fully functioning DPF.

I can't really see that picture as it's a bit pixelated.

[moizeau]

Elis, click on the image then you get a plus sign, or at least I do, just checked it my Diag laptop as well. No smoke what so ever, I watched during a rev test on the CT, I will do it again though, to do it with an auto, better in park or neutral?

[EDC5]

Ok, I can see it now, however I should probably brush up on my french!

If there's no smoke then I assume all is well, just my suspicious mind

On my C5 the Diff pressure sensor is located on the bulkhead in the engine bay with the tubes running down to the exhaust tunnel.

[moizeau]

Cheers Elis, I'll have a poke tomorrow.

[moizeau]

Found it, centre top of the bulkhead. It's got the factory fitted pipe clips so I'm not going to touch it until I've got some replacements, the spring loaded clips that hold the fuel lines on mowers look the job. I'm presuming once I've unclipped them I should be able to blow down them easily. That should see they're blocked at the exhaust end, and then if I unscrew the metal pipes from the exhaust and block them up, blow again and I shouldn't be able to. Not going to do anything until I've taken my daughter to Wales though, every things working and I don't want to compromise anything. I say every things working, the ABS ecu is not talking to the 'puter, no warning lights, but I've found a broken wire in the front rh w/arch, guessing it will be that then. Something else to stop be getting bored!
Is there any way of testing the sensor or is it just a swap job?
Thanks

[MikeT]

Clic clips? They're actually very good and worth re-using as they're sized to the pipe diameter. A small bladed screwdriver can unclip them and a pair of pliers will refit them but it's better to use dedicated clic clip pliers as they're not expensive and make the job very quick!

I have these as they've got articulated heads allowing wider angles of access than fixed pliers.
https://i.ebayimg.com/images/g/icsAAOxy ... -l1600.gif

One easy way to test the sensor is to simply blow into the upstream port or pipe (depending which you detach) and observe the live data (key-on, engine-off).