Won't run
 

2005 GMC Jimmy 4.3 4x4 230k. I let it sit for about a month then went to start it one day and the starter went. Ordered a new one and put it on a few weeks later. Went to start and just cranks over. Have blue spark coming out of the coil, confirmed engine was still in timing. Rpm gauge doesn't work on the dash but does when I hook my scanner up, resistance in plug wires is good and the cap and rotor are newer. Getting fuel, just don't know how much pressure. Seems to want to start after the first crank where it will back fire for a. Good. 10 seconds. Won't kick off brake clean. Does get spark to the plugs but doesn't seem very strong. Truck ran very well before it was parked and starting to get frustrated.

Could be any number of things

Failing ECU, Failing Ignition coil, Bad CPS, Low Pressure or jammed regulator.

Start with a pressure and leakdown test and go from there. check for vacuum leaks while your at it.