Fuel pressure not holding issues.

[SpeednV6]

It all started as I was driving. The car had 1/2 a tank of gas and I started loosing fuel pressure fast. The car didn't want to start and when it did, the pressure wasn't holding. I do have an adj. reg.
Anyhow, I changed my fuel pump(307), put back a set of good injectors(stock), chip, ecm, and adj. reg. I put on a Bosh 0-280-160-237.
I changed regulators because I applied vacuum to the old unit and it didn't hold. The new unit helped.
I changed fuel pumps because the fuel wasn't going up with boost. The new unit helped.
I changed injectors and no difference.
All the plugs (Cr42's @.35) are dry.
I continued to pinch hoses like the manual says and same result.
Now, I put the car to the "on" position and the fuel pressure shoots up to 45psi and immediately drops. All hoses are new and voltage is 14 at the pump.
I'm out of ideas...Please help.

 

[TWISTER]

I had the same problem a few years ago and kicked myself in the head for a few days and pulled the tank again and found the rubber hose that came with the Walbro 340 M I had installed awhile back had split. It let the gas run back in the tank and didnt hold pressure, Just a thought for you.

 

[SpeednV6]

I repulled the fuel pump, inspected it, and the hose was in excellent condition. I tested the hose with a vaccum pump and it held up. How can I check the pump check valve? I don't have any leaks so how can I loose pressure almost immediately?

 

[TurboBuRick]

Pinch the feed hose as soon as preasure builds. If it still drops,try pinching return line.
If feed line pinch does the trick its the pump check valve.
If return line pinch does it then its the regulator.
If you pinch both and fuel preasure still drops its a injector. .
My car does the same thing but does not seem to effect anything. Checkvalve in my pump is not working. Mabye it does not start as quick, thats about it.

Good Luck!