my 1993 K3500 crew cab 6.5L with a 4L80E automatic transmission will sometimes start and idle really rough... seems to be getting too much fuel, but then once it warms up I can floor it under load - like up a hill and it makes a weird "ticking/clacking" noise (really quick clacking and not very long) - not much but after making this noise will puff a cloud of blue - fuel i'm thinking... and then is running great... higher miler - 347000 km's - approx. 216000 miles... only happens 1 out of 5 starts and once it's running, usually no problem. any ideas? i'm leaning toward an injector...

fuel pressure> probably oil pressure switch bad

i agree with Diesel Pro, ops switch, lift pump, or lift pump relay. had a similar problem and it ended up being the ops switch. $50 from the gm dealer. its located behind the drivers side head, i would start with that.

Use a genuine gm or ac delco ops.None of the others will last much more than a week. Check for fuel pressure at the Tee valve[next to thermostat] while idleing.