Pontiac Firebird Formula 1991 V8 5.0 TBI. Both injectors no spraying. New VATS key, New ignition switch. Im getting spark, and the Fuel fump is fine. Plenty of fuel pressure, and NO computer codes. WHAT COULD IT BE?????

 

Have you checked the INJ1 and INJ2 fuses? Is there 12V at the injector pod? If you have voltage at the injectors, try grounding the ECM side of the harness intermittently to see if the injectors spray.

What is the fuel pressure? Injectors won't operate well with less than 8-9 PSI fuel pressure.

It is possible that the ECM is not operating the injectors for several reasons, including VATS, an open circuit between the injectors and the ECM, poor ECM grounding, open (failed) injector operating coils, and several other more obscure reasons.

 

Paul,

It's customary to continue a discussion in the originating thread, rahter than start another one. That's probably why the other thread you posted was closed.

As for your findings, the INJ1 and INJ2 fuses power the injectors from the ignition circuits. If you can meter voltage at the injector pod, the power circuits are fine. There are no other fuses (other than fusible links) between the ignition switch, injectors, and the battery.

The injector coils are the solenoid coils in the inectors that operate the pintle, allowing fuel delivery through the injector. There are two connection on each injector, and with power off and the connector unplugged you should be able to test the resistance of the injector solenoid coils. Expect to read about 1.2-1.5 ohms.

The ignition control module in the distributor is a transistor switching module that gets a signal from the pickup coil and reluctor under the distributor rotor. The module switches ignition coil primary power accordingly. It also sends a signal to the ECM (known as a distributor reference pulse) so that the ECM can determine when to operate the injectors. Make sure all the connections at the distributor are clean and secure.

What is possibly more of a problem is your fuel pressure. The specification is for operating pressure between 11-13 PSIG. Usually, TBI injectors will stop delivering fuel when pressure falls below 8-9 PSIG. That seems to be right where you are at, and could be your problem. There can be many reasons for low fuel pressure, including a clogged fuel filter, low fuel level, a failing fuel pressure regulator, low voltage to the pump from bad connections or a weak battery, or a pump that is failing. Get your fuel pressure up to at least 10-11 PSIG and see if you get fuel delivery through the injectors.

Another way to determine if the problem is with fuel pressure or injector control is to plug in an injector solenoid test light, commonly called a 'noid light. It will flash when the engine is cranked if the ECM is trying to operate the injectors. If you get power pulses at the injectors and no fuel, you've eliminated the ECM and wiring as a possibility. If you don't have a 'noid light, you can perform the same test with a digital meter with a peak-hold feature or an oscilloscope.