The Vortec 4.8L and 5.3L engines used in 1999–2007 Silverado and Sierra trucks use a Central Sequential Fuel Injection (CSFI) system commonly called the “spider” injector. It’s a single unit that feeds all 8 cylinders through individual poppet nozzles — and when it fails, it usually does so slowly and destructively.
WHAT THE SPIDER DOES
- One central injector body connects to 8 nozzles via fuel tubes
- Each nozzle injects fuel directly into the intake port
- The system relies on fuel pressure regulation from an internal FPIM (Fuel Pressure Injector Module)
SYMPTOMS OF FAILURE
- Rough idle that gets worse over time
- Long crank times — especially after sitting overnight
- Rich running at idle, lean at WOT
- Fuel smell from the intake
- Fouled spark plugs
- Hard start when hot
- Codes P0300 (random misfire) and P0171/P0174 (lean bank 1/2)
FAILURE MODES
- Poppet nozzles stick open — fuel floods cylinders causing rough idle and fouled plugs
- Fuel pressure regulator fails — hard start and fuel pressure loss
- Internal spider tube leaks — fuel drips onto intake floor
FIX
- Replace the entire spider assembly — replacing individual nozzles doesn’t work
- Use an AC Delco or Delphi replacement — avoid cheap unbranded units
- Always replace the intake gaskets when pulling the intake
- Check fuel pressure before and after: should be 58–64 psi at key-on