2008 Renault Laguna misfire

[Izzye]

My other half has a 2008 Renault Laguna estate with an LPG conversion which recently had an engine replacement due to a warped block. Unfortunately due to the first engine arriving damaged a second one was sent which was the same engine but out of a different Renault (mechanic wasn't sure which one) so the manifold and coils were changed for the ones on the original engine as it wouldn't fire on the new ones, but other than that it's a new engine.

Having got the car back it seemed fine, he pootled around in it for a bit, went up to see the LPG man about getting the kit reinstalled and never made it there, instead the car ended up back in the garage within 350 miles running on 3 cylinders. The mechanic changed all of the ignition coils and spark plugs for new ones, did a bit of investigation and found it wasn't firing on cylinder 3, no fuel was going in to it. So he changed the injectors around and it's still an issue on 3 rather than with the coil, apparently the sparks still spark but there's just no fuel getting into the cylinder.

Has anyone experienced anything similar? Because the car's been in the garage pretty much permanently since September and I'm not too impressed with being a taxi.

[E-bmw]

Assuming there is fuel at the fuel rail & the injector swapped was known good (sounds like both are true from your post) then all that leaves is the wiring loom to the injector from the ECU or the ECU itself.

Better bet of the two would probably be the wiring/plugs etc between the ECU & injector.

[Izzye]

He was very much hoping for a wiring fault, unfortunately it seems to be the ECU so that's being sent off for diagnosis. I think the poor mechanic will be very happy to see the back of this car!

[GreenV8S]

Izzye said:

coils were changed for the ones on the original engine as it wouldn't fire on the new ones

I wonder whether those coils could have damaged the ECU. A consistent total failure like this will hopefully be easy to diagnose and fix.