Does C4 really need new engine?

[dave241283]

Hello, I’ve been having intermittent trouble with my 2018 C4 Picasso - sometimes judders when I put my foot down to suddenly accelerate to the point engine light appears and it goes into limp mode. This can be reset by turning ignition on and off.

Took to local mechanic who ran diagnostics and changed wet belt (apparently common fault in C4s) as well as spark plugs and coil pack.

Problem has persisted so I took car to Citroen dealership who ran diagnostics and a compression test.

Their diagnosis revealed ‘combustion misfires and sparks before rumble faults’. Cylinder leakage test revealed cylinder 3 is faulty. They say the solution is a new engine, which will cost more than the car is worth!

Is a new engine necessary for a faulty cylinder?!

[wurlycorner]

Hi
If you have a cylinder with excessive leak down, it means there is a mechanical fault in that cylinder, which is allowing the combustion gases to escape from the cylinder when they shouldn't. It's good that they did a leak down test, because that is a fairly conclusive result that there is a mechanical problem with the engine. Out of interest, did they give you a 'percentage leakdown' figure for each cylinder on the report?

The cause of excessive leak-down could be many things, e.g. worn/broken piston rings, worn cylinder bores, holed/cracked piston, bent valve, worn valve seats, cracked/broken valve, incorrect valve clearances, timing set incorrectly etc. and depending on what the cause is, depends on whether you need a replacement engine or it can be repaired in situ.

Any fault with the piston/piston rings/cylinder bore means the engine would need to be removed from the vehicle and completely disassembled to repair (meaning you're into a full overhaul, which economically might not be cheaper than buying a replacement engine).
Problems with the valves could likely be repaired by leaving the engine in the vehicle and doing only a partial repair by just removing the cylinder head.

Based on the information you've given there though, it's impossible to know what the cause of the leak-down is.
Checking the timing is set correctly can be checked by a mechanic removing the timing covers and checking everything lines up to spec (marks on the pulleys and position of the cams etc).
Checking for what internal fault there is, could be confirmed by a mechanic removing a spark plug and placing a borescope camera inside the cylinder.
The above checks would enable a better decision to be made on what kind of repair is required.

A Citroen dealer is most likely only ever going to recommend a replacement engine rather than doing a partial repair in situ though, since they want simple jobs that carry zero risk for them, rather than a longer/more complex job that carries some risk of bad diagnosis/repair by their technicians (plus they earn more money replacing an engine than doing a repair!).

If a replacement engine is needed, there are options on either 'new' engine, reconditioned engine, or another alternative (that would be the cheapest) is to fit a 'used' engine.
A Citroen dealer would never fit a used engine (and would only fit a reconditioned engine supplied by Citroen) but an independent garage might be ok doing so - or there are specialists who do offer that service. This carries some risk because you don't know for sure the condition of the used engine, but most places will give something like a 3 month warranty.

Hope that helps a bit?

[xantia_v6]

You could employ an independent mechanic to remove your engine, and for an extra couple of hours labour, dismantle it and look for an obvious fault with the pistons and bores.

You also have the option of fitting a second hand engine.

[Stickyfinger]

A "rough & ready" way to check if is valves or piston rings/bore is to do a simple compression test, time the leak down of the pressure.

Add some thick oil (90 ?, not much is needed) into the cylinder and repeat....if the leak down test takes longer it is a good bet it is ring/bore rather than the valve.

[dave241283]

Thanks for all the suggestions!