Hi all, long time reader first post,

My 91 3L pickup was in the shop the other night for fuel loss issue which ended up being the fpr. But in the process it started running terribly. Something in my fuel system was my first guess but no luck both rails fuel pressure was now in spec and did not drop off when engine was shut down. Spark was the next guess, wires were a little spotty and were testing intermittently so I replaced them with no change. It was at this time I started pulling plug wires off while it was running trying to isolate cylinders. I was able to pull 4 wires of with no change in idle sound! The entirety of bank 1 the passenger side was not working. It was at this time that I tested for compression and all the passenger side was below 40 psi. This was very strange to me as when I purchased the truck 2000km ago I tested the compression when I changed the spark plugs and it was 125-150 on all cylinders. I'm currently pulling my valve covers and then my timing covers off to inspect and hopefully find the issue. Curious if anyone has any ideas? Would like to get this back on the road asap as its my daily.

 

I’m gonna guess the cam isn’t spinning and all the valves are open to some degree which is causing the low compression.

 

I assumer we're talking about a 3.0 liter 3VZ-E correct? There's also a 3L Diesel engine so have to clarify

If it is the 3vz I'd say there is a chance that you may have popped a head gasket. Unless the camshaft broke in half, its probably not related to that as the only other thing that can make it not spin is a busted timing belt, but that would cause the other camshaft to not turn as well, which would lose all compression.