Vortec 350 missing

[Alex V.]

And not found under hood after brief search... bummer.

Trying to fix a consistent misfire in a stock '97 K1500 on #5 cylinder. 182,000 miles, shows a hair over 180 PSI compression on that cylinder when the others in that bank are exactly 195. Plugs and wires were done recently, and the fouling on that plug was dusty, soft, white buildup - swapping in a new plug didn't do anything for it, even temporarily. I pulled the plenum off and performed the injector balance test via my Snap/on "brick" graphing scanner and a fuel pressure gauge - #5 behaves just like all the others. I cleaned the intake, externally cleaned the injectors, and replaced the distributor cap & rotor which were absolutely toast, but the miss is still there.

Initially the owner said it needed intake gaskets - that it was burning antifreeze on no.5. But by my troubleshooting and the fact that there are no coolant passages anywhere near #5's port from intake to head, I suspect the white buildup was just ash and such from that cylinder not firing at all, and lower compression was due to that cylinder being cool and having junk built up from no combustion taking place. The tip of that injector has a dark redish-brown tarnish while all the others were bright and clean - suspected the injector was bad as soon as I noticed that but it worked in the test so I'm puzzled. Is it likely the injector worked during the test but not under running conditions? The owner is open to replacing the injector spider assy. if need be but neither of us want to throw parts at it. Only code stored when I brought it in was 0300 Random misfire. Any help?