Engine knock..

Can anyone shed any light on this? 2004 L322 4.4 with LPG... started misfiring, noticed it coming on slowly like when sat at lights (was like being rocked to sleep).. soon as the revs were up it was fine.. then came a rattle on number 7 ... it’s not there in park and once the engine is warmed up you can sit in park and rev right up.... no rattle.. soon as you put it in drive and under load the rattle is bad..... I’m thinking electrical and it’s not firing that cylinder so it’s detonating incorrectly causing the noise?.. has anyone come across this before?
(coil packs have been changed)
Thanks in advance!

What error codes do you get? A video of the noise would be good

kermit_rr said:

What error codes do you get? A video of the noise would be good

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Hi there.. multiple misfire is all the mechanic gave me .. we changed the coil packs and the codes went.. I do have ‘cat’ light/EML showing.. something just dawned on me that maybe a blocked cat and causing back pressure? Although on petrol less likely. I’ll see if I can get a video of it tomorrow.

Ask over in RR section this is for projects and builds not questions...

Shippers said:

Ask over in RR section this is for projects and builds not questions...

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My bad. Apologies!