Can anyone help or suggest what's happening... My Idle Speeds dropped by 100rpm, a slight amount of brown smoke at idle also. Very strange induction noise from the air box. I've fitted a new lift pump, injectors and checked the EGR System (now blanked off). Checked all the inlet hoses and even tried running with the pipe of the turbo, but still no change!!! I'm now thinking a valve has gone, just don't understand why else I'd have the loud induction noise??? Has anyone else had this loud induction noise before ???? Help Help ...
Assuming the engine is running well enough, you should suspect that there is a BIG clearance at one (or more) valve-stem end. This should be sorted VERY soon, or some part of the valve-train will be hammered to bits.
The very small valve clearance (like NONE with hydraulic cam-followers) designed-in by engine-makers sets things up so that
1. the valve does settle fully down on the valve-seat to seal well
2. the valve is lifted off the seat very gently
3. the valve is lowered onto its seat very gently
4. there isn't too much SUCK (= noise) at the valve when it lifts, and more clearance DELAYS the valve-lift timing which creates more suck but it also advances valve-close timing which will also be noisier as the valve is slammed onto the seat.
With excess clearance, the cam will turn further than intended before contacting the cam-follower, and instead of the follower running smoothly up a nice gentle ramp, it will be hammered up suddenly by the wrong section of the cam profile. Only a small excess valve clearance can cause BIG problems, and one symptom (warning sign) is more intake noise.
One day the head may come off the valve .... then bye-bye piston, cylinder head, and Heaven knows what all else.
Fix it NOW!
CharlesY
