P0303

2003 Tacoma 3RZ-FE 2.7L motor 290,000 miles

Low compression #3 cylinder causing error code. All exhaust valve clearances low and one of the #3 cylinder exhaust valves with no clearance at all. I'm hoping this valve not closing is the only cause of low compression (I know, wishful thinking that valve is probably burnt) If I replace that shim to obtain proper clearance and compression returns to normal, problem solved. I would then set all valve clearances to spec and be good to go. If compression remains low after clearance adjust, then time for head removal/valve work and I would not bother with remaining adjustments at this point.

In order to simplify troubleshooting could I;
a) After removing shim from bucket, remove tool holding down bucket so lifter returns to normal position without shim in bucket (will now have excessive clearance)?
b) Crank engine briefly (spark plugs removed of course) to check compression (then I don't have to mic existing shim and obtain a replacement, especially if compression remains low)?

 

My proposed last 2 steps would probably be a bad idea since cam lobe would scrape on bucket edges, ouch$$!
Looks like I will need to put in proper shim prior to cranking. First time at doing this so learning as I go along.

 

Low exhaust valve clearances can also cause burnt valves. Hopefully thats not the case.