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1991 Pontiac Firebird - Third Generation

Third-Gen TPI Cars Are Cheap! Our $1,500 '91 Formula Proves It, But First We'll Show You How to Overcome

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Day Four: StrandedWe got a two-day pass to get the car smogged and reregistered (which really meant we were going drag racing) then made a few blasts near the shop and headed for the freeway. We made it about 15 miles before the car began to lose power. Uh oh. We shifted down and increased the revs but we knew we were in trouble and looked for a place to stall. We found a closed off-ramp and pulled to the side just as the car died. It would crank but not run. Fortunately, California has a state-funded fleet of tow trucks that roam the freeways looking for chicks in white Firebirds with high-heels and flat tires. They stopped for us and dragged the 'Bird off the road

Day Five: Rich. but in a bad wayBack at the shop we checked the timing to make sure that the chain hadn't fragged or the distributor gear hadn't given up. To check the timing on these cars you must first disconnect the EST (electronic spark timing). It does what the vacuum advance and centrifugal weights do in a regular distributor, but it uses math in the ECM to make the timing adjustments. The base timing checked out at 6 degrees and seemed to be OK. Fresh tune-up, good timing, and the motor wasn't blown up. The only thing left was fuel.

The cool thing about Tuned Port cars is the fuel rail is pretty easy to diagnose. The fuel is pumped from an in-tank electric through a fuel-pressure regulator that bleeds to a return line to control pressure. There is a port on the passenger side where a fuel-pressure tester can be added directly to the system. Our pressure-gauge needle was buried past 50 psi. Oops.

Day Six: Swap The RegulatorThe 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 FingerWith 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."

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