P0172 on Chevrolet: How to Diagnose & Fix

NHTSA lists the 2000 Impala in this recall when it left the factory with the 3800 V6 (L36) and one of the suspect Delphi fuel pressure regulators. Those regulators leak far more often than they should. On the Impala the leaked fuel does not simply drip away — it is drawn into the intake manifold through a vacuum line. Should the engine be cranked and fail to start, the fuel sitting in the manifold can be lit by a mistimed spark and backfire. NHTSA's stated consequence is a ruptured intake manifold, which can in turn displace a fuel line and pull an injector out of its bore, leaking fuel with a possibility of fire. Owner notification went out in phased mailings beginning June 30, 2004, with a second phase on September 30, 2004. Across every model in the campaign, 910,873 vehicles were involved.

The 4.3L Vortec V6 used a Central Port Injection system (CPI 1992-1995, CSFI 1996-2002) with a central injector body and six plastic poppet lines — the "spider" — mounted inside the intake manifold. The plastic lines and nut-kit connections crack and leak raw fuel into the plenum, while deposit buildup sticks the poppet valves open or closed, mis-fueling individual cylinders. The result is hard hot starts, persistent misfires, fuel-pressure leak-down, and a rich/fuel-smell condition; GM addressed sticking poppets in TSB 00-06-04-003B by back-servicing the CSFI unit with a redesigned MFI assembly.

The 4.3L Vortec uses a Central Sequential Fuel Injection (CSFI, often called the "spider") assembly buried under the upper intake plenum, with individual nylon poppet lines feeding each cylinder. The poppet valves and the integrated fuel pressure regulator crack, stick, or leak with age and heat, dumping raw fuel into the plenum. This is one of the single most common driveability failures on the 1995-1999 S-series Blazer and is extensively documented across enthusiast forums and repair sites.

Only the 2000 model year Monte Carlo is named in this NHTSA campaign, and only cars carrying the 3800 V6 (L36) together with one of the affected Delphi fuel pressure regulators. The defect is a leaking regulator, occurring at a much higher rate than normal. Leaked fuel travels through a vacuum line into the intake manifold, where it sits. The danger is confined to a specific sequence: the engine is cranked, it fails to start, and a mistimed spark ignites that fuel. The resulting backfire can rupture the intake manifold. NHTSA describes the follow-on damage as a displaced fuel line that pulls an injector out of place, leaking fuel and creating a fire risk. GM notified owners in two phases starting June 30 and September 30 of 2004. The campaign as a whole covered 910,873 vehicles across all included models.

The direct-injection fuel injectors on the 1.5L turbo can leak - internally past a cracked injector body/tip (dumping raw fuel into the cylinder and causing a misfire) or externally past worn upper O-rings (fuel smell, weeping at the rail). This is distinct from the covered high-pressure fuel-pump and in-tank fuel-pump-module failures. GM issued a Customer Satisfaction Program for a fuel-injector leak on some 2025 Equinox that directs dealers to replace all four injectors and the fuel feed pipe.

GMT400-era Vortec V8s use a Central Sequential Fuel Injection (CSFI) 'spider' assembly with poppet-valve nozzles inside the intake. The poppet valves clog with carbon or the nozzle seats fail, so they leak/dribble fuel instead of atomizing. This causes hard starting, misfires, rough idle, hesitation, poor fuel economy, and often a raw-gasoline smell; failing poppets can dump fuel into a cylinder. A very high-demand repair for high-mileage 1996-2000 Suburbans.

The 1996-2000 5.7L Vortec (L31) uses a Central Sequential Fuel Injection (CSFI) 'spider' assembly: one central housing feeds six nylon poppet spray nozzles via tubes. The poppet valves gum up with carbon and either stick open (raw fuel dumps, rich condition, hard hot/cold starting, fuel smell) or the plastic tubes crack/leak causing a lean misfire. This is one of the defining driveability failures of the GMT400 Tahoe. GM issued bulletin 87-65-07 and later covered many trucks under an extended emissions warranty for the poppet nozzles.

The 5.7L, 5.0L and 4.3L Vortec engines used a Central Sequential Fuel Injection (CSFI) "spider" assembly with nylon fuel tubes ending in spring-loaded poppet nozzles inside the intake. The poppets clog with carbon or leak/stick open, causing raw fuel intrusion, hard starting/flooding, and misfires. GM acknowledged the problem with special coverage 99066F on 1996-2003 CSFI systems (emissions-related, extending injector warranty to 10 years/200,000 miles for cleaning or replacement).

The 1996+ 4.3L Vortec V6 uses a Central Sequential Fuel Injection (CSFI) 'spider' assembly under the upper intake plenum: a central injector body with flexible nylon tubes feeding poppet-valve nozzles at each intake port. Residual fuel bakes into varnish on the ball-to-seat face, so the poppets clog and, more importantly, lose their ability to seal, leaking fuel into the intake and opening at the wrong pressure. This is one of the most-documented S-10 4.3L driveability faults. GM issued warranty extension 99066F (to 10yr/200k mi) covering the poppet spray nozzles on 1996-2003 CSFI systems, confirming its prevalence.