MOT failure on emissions

[Tim451]

My THP failed it's MOT on emissions today. The garage used the term "failed spectacularly" and said the emissions are at a level they'd expect to see from a dodgy remap. The only mods are an induction kit (the filter is clean and in perfect condition) and a resonator delete and back box. The car hasn't been running well for a while with hesitation, juddering and persistent pending fault codes for rich fuel mixture. It seems to bog down when pulling out of junctions followed by a noise similar to turbo flutter on occasion when it picks up again (the diverter valve diaphragm is intact and it appears to be functioning correctly). Fuel consumption has gone through the roof too. I've replaced the plugs and coils already, as well as the coolant temperature sensor but it's still running rich. My next port of call is the upstream lambda sensor and both map sensors in an effort to cure the issue. I replaced the temperature sensor as the gauge never reads more than a quarter of the way up but its still reading low. I'm presuming this will increase fuelling due to the engine running cooler but surely not to the extent that it has. Either way a new thermostat housing is also on the to do list in case the thermostat is stuck in the open position. A walnut blast is also on the cards as it's now done just over 30k so is probably in need of one.

Sorry for the long post but does anyone have any suggestions for anything else that could be causing the issues? I love the car when it works but at this point in time I'm wishing I'd bought something else.

[BenS]

Sounds exactly like it's getting choked by carbon - rich fuel mixtures because the air's restricted and it's pumping in even more fuel to try and get the same power out of it. Sounds as if the fuel pump is still working so that's an expense saved. Get it in for a blasting ASAP

[Owd git]

Replacing the thermostat housing with the upgraded version sounds like a good plan. My partner's VTi hasn't been warming up at all since it was recently recalled to have the coolant temp sensor replaced. The diagnosis by the dealership was that a new thermostat housing was needed - at her cost too! It was done yesterday and now all seems well.

The amount of fuel injected must be partly based on the engine temperature; which might explain your symptoms.

Just for info my 2010 THP has 43000 miles on it and hasn't been blasted, or had new plugs yet for that matter.

[BenS]

Just for info my 2010 THP has 43000 miles on it and hasn't been blasted, or had new plugs yet for that matter.

Plugs should be changed at 40k, mine were done at about 44k and were fouled to the verge of misfires, and the VTi does not make carbon anything like the THP.

You should really be considering some sort of valve clean, be that a walnut blast or manual disassembly and scrubbing - it's not a luck-of-the-draw thing like the timing chain and HPFP, all THP engines get heavy carbon buildup and if a chunk breaks off and goes through your engine and out the turbo, then it can cause a hell of a lot of damage. Probably write off the turbine blades in the turbo.

[Tim451]

Sounds exactly like it's getting choked by carbon - rich fuel mixtures because the air's restricted and it's pumping in even more fuel to try and get the same power out of it. Sounds as if the fuel pump is still working so that's an expense saved. Get it in for a blasting ASAP

Funds are tight at the moment so looks like I'm going to be busy with some carb cleaner, a brush and a mirror over Christmas lol.

[Tim451]

Replacing the thermostat housing with the upgraded version sounds like a good plan. My partner's VTi hasn't been warming up at all since it was recently recalled to have the coolant temp sensor replaced. The diagnosis by the dealership was that a new thermostat housing was needed - at her cost too! It was done yesterday and now all seems well.

The amount of fuel injected must be partly based on the engine temperature; which might explain your symptoms.

Just for info my 2010 THP has 43000 miles on it and hasn't been blasted, or had new plugs yet for that matter.

Yeah a new thermostat housing is definitely on the to do list. When I did the sensor it had already been upgraded to the one that fits in where the bleed screw goes but I swapped it anyway as it was cheap and easy to try. I've been putting off doing the housing to be honest as the access doesn't look great. The gauge has always read slightly on the cooler side long before this issue developed though.

[Owd git]

I've been putting off doing the housing to be honest as the access doesn't look great. .

Needs a lot of stuff removed to get at it I gather.............including disconnecting the gear linkage did I read somewhere?

[haceracen]

Give it a 10 minute (ish) bash of >3k revs to rid the valves of some carbon buildup, cheap and fun method. Probably a little broscience but there was a test done showing it can knock off a significant amount of carbon when operating at a high temperature.

[BenS]

Give it a 10 minute (ish) bash of >3k revs to rid the valves of some carbon buildup, cheap and fun method. Probably a little broscience but there was a test done showing it can knock off a significant amount of carbon when operating at a high temperature.

Was that testing done on a THP engine though? Or just a VAG TSi or similar engine. As far as GDi engines go, the THP is well above the average for carbon buildup and driving it hard is unlikely to counter the formation of deposits, just slow it.

[lfcrule1972]

According to SP Tuning the EA888 TFSi engines are not an issue for this Ben

[BenS]

Older ones still had it, the mk5 GTi was known for it I think. The new generation of GDi engines seem to have taken into account the horrible carbonisation problems of earlier models and either rerouted the PCV internally rather than through the intake, or have added a spray into the intake to wash away the oil droplets, or have catch cans etc. etc.

[Bill the Badger]

Faulty fuel pressure sensor? If its reading lower than actual it will ‘tell’ the HPFP to increase the pressure which will lead to more fuel being injected into the cylinder than expected which will lead to mre unburnt fuel in the exhaust system plus rough running and awful fuel consumption. This could be a ‘load of ‘Old Bo**oc*s’ for the thp beacaue its what happens to some of the BMW motorbikes which essentially use the say pump/injection design.

[Tim451]

Thought I'd post an update on this. The car has been off the road since Christmas and almost 3 months ago it went into a local Citroen dealership. In that time it's had a new timing chain assembly, a new high pressure fuel pump (helped the issue but still didn't cure it) and then a complete timing rebuild. Apparently when the chain was done by another local dealer a year ago (now no longer a Citroen dealer) it hadn't been torqued up correctly which was allowing the timing to slip. They also queried me having to pay for that to be done as apparently Citroen UK are paying heavy contributions towards chain replacement and have acknowledged that it is an issue. The latest replacement was covered by Citroen. After replacing the chain again and replacing the HPFP the dealer noted that the vehicle would behave perfectly until revved, at which point the timing would slip again prompting a full head strip and complete timing rebuild. Thankfully I received a call this morning to inform me that it is finally running perfectly and now has a valid MOT. Finally after around £2000 in repairs during just over 2 years of ownership I should have a fully working vehicle again. I'm hoping to attend some meets and shows once it's back with me and can commence with a few performance modifications once finances allow. Many thanks to all who have provided suggestions and advice.