The 89 thru 91 models came stock with the GM Rochester Multecs and the ohm readings should be in the range of 16 to 17 ohms. Anything less than 15 ohms should be considered suspect and all eight injectors should all be within about 1 ohm of each other. A reading of less than 15 ohms indicates the injector coil is starting to short out. The resistance should be checked when the engine is cold and when hot. I learned this the hard way on my 89 model. I hope this is helpful to you!
Dirty Fuel Injector Symptoms
Fuel pressures are : 36 psi for 1985, 43.5 psi for 86-91
Turn key to ‘on’ but do not crank. Do you hear the pump run and the relays click on and off? This test is best to do with a fuel pressure guage attached. Note that reading. If fuel pressure is 35psi or greater, that’s good. If not, you have a fuel pump/relay problem.
Next, crank the engine for a few seconds. Pull the plug of choice. Is it wet with fuel? If no, you have a fuel delivery problem at the injectors. They are not firing. If they are wet, you have an ignition problem. Start by making sure that all harnesses are properly attached to the distributor.
If a Noid light or ohmmeter is not available a stethoscope or a piece of rubber hose can be used to listen if the injector click. Place the stethoscope or rubber hose against the injector and listen at the other end to hear if the injector clicks.
A quick test of pulsing injectors is the use of a tool called a noid light. Although not accurate for proper pulse width it will tell you if they are pulsing. NAPA and most tool companies sell them. you just remove the wire from the injector and plug in the noid light .If it blinks while cranking…..its pulsing
Remove the spark plug wire or disconnect the coil pack or remove the coil pack that goes to that cylinder.Start the engine. It should sound the same.
Remove the spark plug. If the spark plug is dry, then the injector does not deliver fuel to that cylinder. If the spark plug is wet and smells like gasoline, then the injector on that cylinder is not your problem.