My nephew has a 1987 Bronco II that has a problem that is driving us nuts. My dad and I fixed the Bronco up for him when he turned 16, and it was in great shape. He drove it for a while then the lifters started knocking and it started fouling spark plugs. The oil was extremely thin and had a distinct gasoline smell. Since the engine had nearly 200,000 miles we figured that it was just worn out so we replaced it with a 2.9 out of a later model Ranger that had less than 50,000 miles. The new engine ran like a top for a while, but shortly after the second oil change the lifters started clicking again. Just like the original engine, the oil was thin and smelled like gas. I did a compression check and found 60 psi on the number 1 cylinder. We pulled the engine and replaced it with another
2.9. I pulled the heads on the 2.9 we took out and found the number 1 piston was burnt. All the other cyinders looked great. Less than a month after putting the latest engine in it is doing the same thing. This time the number 4 cylinder has low compression and is fouling the plugs. That makes three engines that have burnt pistons in this Bronco in less than 6 months. Each of the new engines was in perfect running condition
when we installed it. I would suspect the injectors if we used the same injectors on each engine, but we used the injectors that were on the engines when we bought them so it was a different set each time. My next thought was that maybe a bad wire was not letting one injector get the proper signal causing that cylinder to run lean enough to burn the piston, but it has been a different cylinder each time we have burnt a piston. Does anyone have any ideas as to what could be causing this? Any help will be appreciated.

 

Backwoods, take a look at the air flow sensor that is between the air filter and the throttle body. This was probably retained on the engine swaps, and is the only thing I can think of that would cause a lean condition on all the engines.