What happens if you remove the air intake and drizzle fuel into the throttlebody while cranking? I once used this technique to back a truck with a bad pump into the shop. If the truck fires, you've got some fueling issue somewhere.
If this is a 96+ L31 Vortec 350 the fuel pressure will be over 62-66psi at WOT. These stock pumps will dead head at 100psi. The OEM fuel pressure regulator is located inside the intake plenum therefore is always exposed to manifold vacuum while running
Pull a plug, ground it an see the spark. These engines run 0.060" plug clearances, if the spark is lazy and orangey at all, just wait til it has to fire at 9.4:1 the pressure during the compression stroke. You want a nice bright white/blue spark, these OEM coils are quite good. Same coil is used in the LT1/LT4 engines and that engine redlines at 6400rpm. The 96-98 truck blackbox VCM's have the 6000rpm hardlimit. The rpm coding simply stops at 6000rpm. These CSFI(Centralport Sequential Fuel Injection) was the last distributer based ignition system to be used on production vehicles. The medium duty Vortec L21/LP4 GEN-VI 454 being the first GM bigblock engine to employ Electronic Throttle Control(ETC) and Coil Near Plug(CNP) ignition. Now each cylinder has its own coil. Each coil now only has to fire once for every 8 ignition events.
I've seen coils go out slowly. Throw in a new one, they arent expensive.
96 and 97 were models years of the GMT-400 truck lineup that had yet to use any sort of VATS(Vehicle Anti Theft System).
If the system recognizes an unauthorized ignition attempt, the VATS will disable the fuel injectors for 30 minutes. The GMT's got VATS for MY1998.
With the way you are describing the behaviour, you gotta be off by a tooth. I would go to the extremes of where you are now (loosen hold down and "clock" the distributor and see how it changes what you have now.
Also another low buck test for these trucks to test the fuel system. If you leave the key in the ignition turned to run, then on your back and grab a hold of the crank pulley and turn the engine over. Just go slow and let the compression bleed off. Eventually you'll hear the fuel pump prime itself by running for 2 seconds. IIRC you can get the pump to cycle twice for every single crank rotation.
I seem to remember saying that something plastic was broken? If it was there is the CranKshaft Position(CKP) sensor is housed in that one use only front timing cover.
peace
Hog
If this is a 96+ L31 Vortec 350 the fuel pressure will be over 62-66psi at WOT. These stock pumps will dead head at 100psi. The OEM fuel pressure regulator is located inside the intake plenum therefore is always exposed to manifold vacuum while running
Pull a plug, ground it an see the spark. These engines run 0.060" plug clearances, if the spark is lazy and orangey at all, just wait til it has to fire at 9.4:1 the pressure during the compression stroke. You want a nice bright white/blue spark, these OEM coils are quite good. Same coil is used in the LT1/LT4 engines and that engine redlines at 6400rpm. The 96-98 truck blackbox VCM's have the 6000rpm hardlimit. The rpm coding simply stops at 6000rpm. These CSFI(Centralport Sequential Fuel Injection) was the last distributer based ignition system to be used on production vehicles. The medium duty Vortec L21/LP4 GEN-VI 454 being the first GM bigblock engine to employ Electronic Throttle Control(ETC) and Coil Near Plug(CNP) ignition. Now each cylinder has its own coil. Each coil now only has to fire once for every 8 ignition events.
I've seen coils go out slowly. Throw in a new one, they arent expensive.
96 and 97 were models years of the GMT-400 truck lineup that had yet to use any sort of VATS(Vehicle Anti Theft System).
If the system recognizes an unauthorized ignition attempt, the VATS will disable the fuel injectors for 30 minutes. The GMT's got VATS for MY1998.
With the way you are describing the behaviour, you gotta be off by a tooth. I would go to the extremes of where you are now (loosen hold down and "clock" the distributor and see how it changes what you have now.
Also another low buck test for these trucks to test the fuel system. If you leave the key in the ignition turned to run, then on your back and grab a hold of the crank pulley and turn the engine over. Just go slow and let the compression bleed off. Eventually you'll hear the fuel pump prime itself by running for 2 seconds. IIRC you can get the pump to cycle twice for every single crank rotation.
I seem to remember saying that something plastic was broken? If it was there is the CranKshaft Position(CKP) sensor is housed in that one use only front timing cover.
peace
Hog