Do you have access to a scan tool? You will need that to diagnose the p0108. I do not believe that the map sensor code is the reason for your no start issue. The ecm should be putting the map sensor voltage into a preset parameter that works so the vehicle will still function. I would check for fuel pressure and spark on the nostart issue. The p0300 has to do likely with your valve guides in the heads. Here is some info on that. I hope this helps! Let me know if I can assist you any further!

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

Condition/Concern:

The vehicle may exhibit a SES Light due to a P0300 and misfire. If the misfire is related to the information below, it will typically happen while cruising uphill, pulling a trailer or on hard acceleration and then stop misfiring shortly after returning to an idle. Typically, cylinders 3,4,5 or 6 will be the ones to experience this.

Recommendation/Instructions:

If the P0300 SI diagnostics did not isolate a concern, the following may help:

Remove the valve cover, valve springs and valve seals on the effected cylinder or cylinders. A small wire tie or rubber bands can be placed in the valve stem keeper groove to prevent the valve from falling into the cylinder. Rotate the valve while moving it up and down in the guide to see if it binds. If a binding valve is found, remove both cylinder heads and use either of the following methods to increase the stem to guide clearance:

Reassemble the cylinder heads using new valve seals.

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Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

Models:

(96 - 02 Chevrolet Astro) and (96 - 02 GMC Safari) and (96 - 00 Old Body Style Chevrolet Suburban) and (96 - 00 Old Body Style Chevrolet Tahoe) and (96 - 02 Chevrolet Express) and (96 - 00 GMC Yukon) and (96 - 00 Chevrolet Old Body Style C/K Truck) and (96 - 00 GMC Old Body Style C/K Truck) and (96 -02 GMC Savana) and (96 - 99 P32 Cab and Chassis) and (96 - 02 Chevrolet S-10) and (99 - 02 Chevrolet Silverado with 4.3L V-6 Engines (96 - 02 GMC Sonoma) and (96 - 02 GMC Sierra with 4.3L V-6 Engines)