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1993 GMC C1500 Suburban Running Rich - OBD1 Code 32 (EGR Issue)

Model: 93 GMC C1500 Suburban Fault Code: C1500 Posted: 2016-04-10 05:53

My 1993 GMC C1500 Suburban with a 5.7L V8 and TBI fuel injection system is running rich. The vehicle shows OBD1 diagnostic code 32, which corresponds to the EGR (Exhaust Gas Recirculation) system fault. The truck initially runs poorly for about one minute after starting, then settles into a stable idle. However, the exhaust fumes are strong and noticeably choke anyone behind or near the vehicle. I've already replaced plugs, wires, distributor cap, rotor, MAP sensor, and rebuilt the throttle body with no improvement. I suspect the EGR system is malfunctioning — specifically, the EGR valve may be stuck open or not functioning properly. The EGR solenoid requires proper vacuum operation to function correctly. I've checked that the diaphragm can move freely when manually pushed, and the engine stutters under this condition. Additional checks include verifying the ECT (Engine Coolant Temperature) sensor input — a faulty reading could mimic a stuck-choke condition. I also recommend performing a KOEO (Key On, Engine Off) test to observe injector behavior: if injectors are spraying or dripping during this state, it may indicate wiring issues, such as a harness rubbing through the air cleaner and causing a ground fault. Also check for excessive blow-by fumes via PCV system. Avoid aftermarket parts like oiled air filters or 'miracle' magnets — AC Delco plugs are recommended over Bosch or generic brands. This issue may also be related to a stuck-open EGR valve, which can cause a rich fuel condition on speed-density (MAP) engines.

Related fault codes
C1500
Comments (4)
Anonymous 2016-04-10 09:42

Correct — this is a 5.7L V8 with TBI injection and two injectors mounted in a carburetor-style setup. Why do you say it's running rich? What symptoms are you observing? OBD1 code 32 indicates an EGR issue. Check the EGR valve — is it free to open or seized? Is there vacuum supply to the solenoid? Can manually pushing up on the EGR diaphragm cause the engine to stutter?

Anonymous 2016-04-10 12:42

Yes, it's a V8 with TBI. I've replaced plugs, wires, distributor cap, rotor, MAP sensor, and rebuilt the throttle body — none of these fixes resolved the issue. When starting, the engine runs poorly for about one minute before settling into idle. However, the exhaust fumes are extremely strong and can choke anyone behind or near the truck.

Anonymous 2016-04-10 13:32

Ensure the ECT (Engine Coolant Temperature) sensor is functioning correctly — incorrect input may simulate a stuck-choke condition. Perform a KOEO test to check if injectors are spraying or dripping, as this could indicate wiring faults. The wire harness running under the air filter has been known to rub through and cause grounding issues. Check the PCV system for excessive blow-by fumes. Avoid oiled air filters, miracle magnets, or low-quality plugs — stick with AC Delco. Always perform a KOEO (Key On, Engine Off) test for accurate diagnostics.

Anonymous 2016-04-10 14:37

A stuck-open EGR valve can cause a rich fuel condition on speed-density (MAP) engines, which may explain the running-rich symptoms observed in this vehicle.