Xantia MK2 engine replacement

[Cotter]

Hi,

is there need to change ecu, if i replace 1.8 16V-engine to 2.0 16V?

[citroenxm]

If the 1.8 and 2.o use the SAME ECU for the engine management then NO. If you had to change ECU then you would have to get it coded to the car body computer so the ignition key would unlock it.

Im not an expert on the 1.8 and 2.0 petrol engines but that the face of it.

I swapped a HDi 2.0 engine for another one, and it was perfectly fine, as they used the same ECUs

[xantia_v6]

The ECU software, as well as the hardware needs to match the engine. You can't necessarily tell from the part number of the ECU which version of software was installed, and it is probably a one-time operation, so an ECU programmed for one engine type can't (with standard tools) be re-programmed for a different engine type.

A 2.0 will probably run with a 1.8 ECU, but the fuelling and ignition timing may not be optimal.

If you can, you should get hold of the engine ECU, BSI and keys that match the new engine.

[citroenxm]

ah i thought as much it may be more complex... bloody petrol engines!!!

[xantia_v6]

The fundamental problem is that for an ECU driven by a MAP (rather than MAF) sensor, the fueling is calculated using a software map that is largely based on the volumetric efficiency of the engine at each speed and throttle opening. I imagine that the VE curves of the 1.8 and 2.0 are somewhat different. The closed-loop lambda control mitigates this somewhat under steady state conditions, but is not perfect. Likewise the knock sensor mitigates timing issues, but I suspect it just retards the entire programmed map, rather than correcting the map for the engine characteristics.