EDIT: Reply collision w/Keeper -- but we're pulling in the same direction, so here it is anyway. :0)
I have a 97 k1500 with 5.7 with maybe 220k on the truck ran fine then sat for about year then wouldn't start throws a p1345 code sounds like a intake valve is stuck open when cranking so I pulled a valve cover off and was cycling the motor and it started it valves look to be fine won't start with all plug wires hooked up but unplug #3 and starts right up I checked the plug wire to make sure it wasn't grounding out not it has new cap rotor cam sensor and I'm kind of at a loss on what to look for next any advice would help I'm a diesel mechanic and forgot about ignition systems years ago
WAG, if it is not a defective new cap, it has a blown head gasket between 3&5 or a stuck valve in #3. Obviously #3 has a problem, diagnostics should start there. A bad cap could be causing #3 to spark at random times, similarly a blown head gasket between 3 and 5 could ignite #5 during the intake/compression stroke.
Hello Jrivers0688,
That is a real specific failure footprint that you have described. Guess what? Since you are driving
a '96+ Vortec 5.7 with the 'crab cap', we've identified a weakness particular to this design.
It seems that the center conductor (where all 8 sparks are delivered to the spinning rotor underneath
burns through the plastic insulator to the spark plug pathway routed closest to it.
Guess what? That's the #3 cylinder path! And if the spark intended for a different cylinder
jumps through and fires the #3 cylinder while the intake valve is still open, then boom the
charge lights up, and sneezes through the open valve and throttle body.
Please remove your cap, and see if it has any discoloration similar to the one below:
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NOTE: This cap was removed because after sitting for awhile the truck it was on also would not start. (!)
And here's a Bird's Eye view of the #3 cylinder spark routing from above.
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Especially if pulling #3 spark plug wire solves the no-start problem (as you said) ...but
pulling the spark plug wires on other cylinders doesn't make the same improvement, then
as crazy as it sounds your 'new' cap is obviously causing the sparks intended for the rotor
to take the path of least resistance to the #3 cylinder. And again, if the mistimed spark
occurs while the intake valve is open you are going to hear about it via the throttle body.
Give it a close look, and if you find anything, please take a pic & post it here.
Happy Hunting. If it will run on 7, we should be able to get it to run on all 8.