Cx 25 GTI Turbo white smoke and hitching

[Hadmund]

I recently bought a 1985 Citroén Cx 25 GTI Turbo and I've been having some problems with.

It blows quite a lot of white smoke no matter if the engine is warm or cold. It stops if drive the car for about 10 minutes, but if I just let it idle up to temp it still smokes. This leads me to believe that it's just the catalytic converter that's getting rid of the smoke.
The engine doesn't seem to be consuming any noticeable amount of oil either as I couldn't notice a difference on the dipstick after 500km of driving.

Video of the smoke:


Now what's annoying me more is the "hitching" or "stuttering that the engine does when engine braking or during the transition from pressing the accelerator and letting go.
When this hitching happens the stop light and coolant warnings flash on. But usually there are no warning lights on.

I've tried swapping out the "big blue" relay and changing both engine knock sensors but it didn't seem to make a difference. The air flow sensors flap moves freely and I haven't been able to find any false air getting into the system either.
The engine also idles completely fine which also makes me think it's not false air.

I'm completely new to working on CXs and even though I've read quite a bit now I'm still not very confident on how the ignition timing or fuel delivery system works.

Thanks in advance.
-Odin

[aerodynamica]

Hello, I'm not sure if it is just me but that amount of white smoke - or steam doesn't look excessive for an engine that was not heated fully. If it was burning oil the smoke would be darker and more blue. If it was blue smoke at start up and low idle then likely would have been valve stem oil seals. If it is blue haze when the revs are raised and held then more likely worn piston oil ring. This would also make the spark plugs all dark and glazed.

White excess steam with a 'sweet' smell might be coolant getting in to the combustion as a result of a failing cylinder head gasket but there would be other symptoms such as misfire and/ or coolant boiling and vanishing. Also the cooling pipes/tank/etc would pressurise. Also white smoke caused by cylinder head gasket failure would hugely increase when you raise the revs and could be quite obvious (like 5x more white than in your video).

I had a similar 'hitching' as you describe in my old XM SEi turbo. I changed everything as well except one thing: the fuel pump in the petrol tank. I never did verify if the fuel pressure was correct on that car. Do you know that the fuel pressure is right? And if the electric pump is working properly?

Sorry, your question was months go and perhaps you already have fixed this. It would be good to learn what you found.

The CX Turbo 1 has flywheel sensors and a conventional distributor as well as an alloy plenum intake. The Turbo 2 has one flywheel sensor, a coil pack and later, a plastic intake plenum (this can get a crack that draws air). But faults with these aspects tend to see the engine stall and not do the hitching.