4.0 is indeed an interference engine...

So my 2007 4.0 has been acting weird for years. Giving me intermittent CEL and misfire codes. Several years ago the harmonic balancer came apart and I replaced it with a auto parts store brand and never gave it much more thought. However, after chasing the fault codes and taking it to a shop, it has had multiple coil packs, plugs, wires, fuel filters, injectors and all kinds of sensors changed never actually fixing it. One day it just started running really really bad making a lot of clatter and died.
Compression test showed it had no compression so I figured it was a timing chain issue. Well it turns out that cheap balancer actually broke, split at the crank and must have been moving around causing the error codes. When it finally completely failed it had taken the lower sprocket with it. In doing so it took a few valves and pistons on the way out. Needless to say the 4.0 is now basically a boat anchor. It needs 6 pistons, a crank one head and all the valves in the other head, not to mention the timing set, gaskets, etc. It only had 97,000 on it and should have run a long time as well I as cared for it.
I am glad to finally understand the problem but t's going to be an expensive fix...





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Wow! My 2007 has a little over 126,000 so far. I was getting the CEL and mis fire codes. Funny thing, while in the shop getting the transmission fixed, my friend suggested replacing the foot pedal, since he suspected the position sensor on it was bad. So, he put a new pedal set up in, installed a new throttle body with new servo motor, and haven't has a single issue with it ever since.

I was also getting a random zero oil pressure light and warning. And the motor never stopped running when it happened. That also went away with the new parts.