1991 Pontiac Firebird: Solving TPI Nightmares

Day Six: Swap The Regulator

The fuel regulator diaphragm had been eaten through and wouldn't hold vacuum, so the pressure was going sky high and causing a rich condition. It was supposed to be from 34-47 psi max. After the fix, we drove it for some gas and idled around the deserted warehouse district near the shop. The car powerslides great. Donuts are easy too.

Day Seven: Why Bother?

Finally, we were ready to have fun and install our pile of mods, including SLP's headers, after-cat, and some other TPI goodies. So we got to the shop and fired up the car, but then the idle became rough and the engine stalled. Bummer. No engine light, and no codes in the computer. At this point we began to hallucinate and checked the TPS. Smith had delivered the scanner, so we plugged it in to the ALDL and took some readings. With the key on and the throttle closed the TPS read less than 2.5 volts, so it wasn't jammed open. With the engine off, we slowly floored the throttle and watched the TPS reading progress to 5 volts at WOT. Rats. TPS was fine.

Day Eight: No Trigger Finger

With a fresh brain we went through the diagnosis. Fuel pressure? Check. Codes showing on the scan tool? Nope. TPS working? Check. RPM indicated while cranking? Ruh-roh! Neither the tach nor the scanner was giving us an RPM reading while the engine cranked. That meant one of two things: The distributor module was toast or the ECM wasn't functioning properly. Actually, they are both related. The ignition module sends a reference pulse to the ECM while the engine is cranking and to the coils to throw some sparks. We pulled the No. 1 plug and grounded it then cranked the engine. Big blue sparks. We also pulled the four-wire connector off the distributor and touched the purple and white (rpm reference) wire with a test light connected to 12-volts. The scanner didn't read rpm. We were close to the problem. The last thing to do was check continuity to the ECM from the purple and white wire to the distributor. We peeled open the harness by the A/C accumulator (that's where the EST is, remember?) and spiked a continuity tester there. The wire was good from the ECM to the distributor. Our flow chart ended with the statement, "Faulty ECM."

Day Nine: Tire Smoke

The new computer cost us 100 bones plus another $75 for the core. We plugged it in and the car fired right up and ran smoothly so we went out for some test laps. It's good, but the gas gauge is still broken, the radio doesn't work, and a lot of that worthless '91 GM water-based paint flaked off the hood and roof when Freiburger washed it. That just means there's more work to come. Stay tuned! END