85 Celica GTS Fuel Pressure Problem

[Denis]

I am looking for some ideas about a fuel pressure problem I have with my 1985 Celica Convertible. The fuel pressure decreases from normal operating pressure to less than 5psi during approximately 1-2 minutes and after several minutes of vehicle running. I have followed shop manual tests including "Check fuel pump operation" and "Check fuel pressure"; shorted the fuel pump check connector and verified there is 33-38 psi (normal) fuel pressure requirement. At idle when short is removed the pressure operates between 27psi and 31psi (normal). These tests were conducted for at least 20 minutes continuous. This confirms the fuel pump (new), fuel filter (new), and pressure regulator (new) operates correctly. ALso verified that when fuel pressure drops during operation the voltage at the fuel pump remains between 12 and 13 volts. Since the short bypasses the air flow meter and the ecu, on chance, I replaced the air flow meter and ecu with spare components. There was no change in the symptoms. This did not correct the problem. Still, when I start the vehicle with normal operation, (fuel pump check connector short removed), the fuel pressure drops after several minutes of operation under normal running condition. and the engine stops running. Sure could use some help here with this one ... Thanks

[stepho]

Three things I can think that might be the problem.

1.
Possibly their is dirt or water in the tank.
Water would also show up in the fuel filter.
Dirt could be floating in the fuel tank.
When you turn on the engine it is gradually sucked up to the in-tank filter sock.
After a few mintues it would completely block off the fuel flow.
When you turn the key off, it floats away again.
Check the condition of the in-tank filter sock.
You get to this by removing the screws around the thin pipes going into the tank through a 4" plate and pulling it out carefully (sparks are very bad).

2.
There is a one way vent valve near the fuel filler (not sure of exact position on an '85).
If this is block then a vacumn gradually forms in the tank.
When it starts going slow again, open the fuel cap and see what happens.
If it comes good, then it is the vent valve.
If nothing changes (ie still goes bad) then it is not the vent valve.

3.
Tired motor.
If it overheats then it can't pull as strong.

- Stepho

[Denis]

Thanks for your thoughts Stepho,

The engine is a brand new rebuilt. The fuel tank has been drained. If there is a dirt strainer clogging problem, my guess is that dirt would clog the strainer no matter if it is operating normal condition or if operating under test (fuel pump check connector shorted). The strainer and the fuel pump have been replaced.

Interesting thought about the vent valve. It will try your suggestion.

What do you think about the fuel dampner? Although this would have caused a failure when the fuel pump check connector is shorted, I think.

[stepho]

Sorry, I'm all out of ideas.
- Stepho

[Pineapple]

Sounds like ECU cutting fuel after warm up. Check ICV if you have one and other cold start related items.
Also check fuel pressure regulator. BTW what engine is it? 3S-FE? 3S-GE?

[Denis]

Pineapple;

I replaced the ECU with a spare. Also replaced the Pressure regulator. Not sure what the ICU is?. THis is a 22RE engine. The voltage at the fuel pump remains constant whilem the pressure drops.

Guess I need to check the current draw on the pump when the pressure drops.

Thanks for your thoughts

[Pineapple]

ICV, Idle Control Valve. Its below the throttle body if you got one. Could some valve got open and release fuel pressure in fuel line after engine warm up. Don't know much about the 22R.