My 89 iroc 305 tpi only has 10 pounds of fuel pressure when running at a idle. when you cycle the ignition to the on position the fuel pump runs for about 5 seconds and stops as it should . My question is does the fuel pump run until its hits a given pressure or does it have a specified time to run until it shuts off. That is when the key is on and the engine is not running.

 

The pump runs till itis turned off by the ECM. If the engine does not start spinning within 3-5 seconds the pump is turned off. The pump runs at constant pressure, the pressure to the injectors is controlled by the pressure regulator. The pressure reg is controlled by engine vacuum, the lower the vacuum the higher the pressure. The pressure you measured at idle looks to be too low,
Test #1, fuel pump:
Turn the key on & off several times to prime the fuel system, the pressure should be around 40 PSI +-5 and holding, or dropping very slowly when the key is off. If pressure is low, the pump could be bad, clogged fuel filter, clogged fuel line. If the pressure drops quickly, the pump could be bad, regulator could be bad, injector leaking, or plain fuel leak.

Test #2. fuel reg:
Start the engine & let it idle, the pressure should be about 10 PSI less than in the first test. Too high or too low shows a bad regulator.

Test #3, load test
Drive in high gear at steady 50-60 MPH, pressure should be between 30-40 PSI
Go to WOT, pressure should increase to about 40-45 PSI

 

I did cycle the key to prime the pump 10psi is all I coud get out of it . does the 89 tpi have a cold start injector because I have to prime it to make it run. From what I understand the cold strart injector requires more pressure to fire. W henthe motor warms up it will start on its own. I can't do the lat test because the motor will not accelerate I guess due to low psi. I bought the car in its present cond. (not running) so I have been trying to diagnose my prolems thanks for the info. also the car sat for a long time and the fuel gauge sats on full at all times maybe there is alot of corrosion around the sending unit and the pump.

 

I'm in a similar world..... PSI should be about 42psi and hold, or drain slowly. The 1989 has the cold start delete. The PROM has it programed into the startup to add fuel to compenstate during cold start conditions

Check filter, and also, check http://www.chevythunder.com

lot of great TPI info.

 

I don't think I ever saw a multi port injection run with only 10 PSI. Are you sure your gauge is correct?