Looking at the ecu codes the one that was fitted was from a 4.0 and the other one that I tried is 3.9 I must admit the 3.9 did smell a little less fumey but not had the chance to take it out on the road to test it properly. Compression seems ok but not perfect, lowest 155psi and highest 170. I’m just gathering the kit to do a leak down test this weekend to determine if I need to bite the bullet and pull it apart!