Mine would have trouble starting after sitting a few days, there is a check valve in the fuel pump tp keep the lines primed with fuel, when it goes bad it takes time to refill the system leading to longer crank times. I am not saying to replace the fuel pump but it is very sensitive to battery voltage to get the proper fuel pressure. The injectors will not squirt fuel at marginal fuel pressures. Sometimes the battery voltage gets low from cranking and the fuel pressure gets lower and it will not start, someone jumps it and the extra battery gets voltage up fuel pressure up and all of a sudden it starts. here is some stuff on the fuel pressure.
Central Sequential Fuel Injection (GM Trucks)
Central Sequential Fuel Injection (Central SFI) is used on 1996 and above light trucks to meet the increased emissions requirements. Central SFI is used on all 1996 truck engines except some carryover engines in G vans and P/G units over 8,500 pounds. This system is very similar to the previous CPI system used on the 4.3L V6 engine. The major difference is that in lieu of a single injector feeding all cylinders, the new design uses a single injector unit for each cylinder poppet nozzle. Each is then fired sequentially for precise fuel control.
Overall, system operation is very similar to the previous discussed CPI unit with fuel pressure being super critical. The fuel pressure specification is 60-66 psi KOEO. As mentioned, the fuel pressure is very critical for proper operation and may be somewhat misleading when a vehicle is close to specification. Close won’t work on these applications!
Fuel Flow Test at Different Fuel Pressures
Flow test is from left to right:
54 psi = 37 MILS
56 psi = 41 MILS
58 psi = 44 MILS
60 psi = 49 MILS
62 psi = 53 MILS
64 psi = 60 MILS
As shown above, for every second psi change in fuel pressure, the actual fuel delivered to that cylinder changes about 10%. As we have said in the past, fuel pressure is very critical. Our test unit (new OEM) is regulated to maintain 64 psi with some return beginning at 62 psi (KOEO). The poppet nozzle will begin to spray fuel at 48 psi (a poor stream at this pressure). Any pressure below 48-50 psi, this engine won’t even spray fuel at all.
As far as the bad mileage or fuel smell I will try to find some stuff on the fuel pressure regulator. To test fuel pressure there is a shrader valve " like a tire valve stem " back on the top of engine near distrubtor, a fuel pressure gage sscrews on to it to measure pressure.