740 & 760 Fuel System Strangeness
Greetings all. Needing some guidance to those who may have experienced this in the past.
1988 740 Turbo Estate with Auto.
A short while ago it started to not pick up revs ie: no throttle response. then it just died and wouldn't start again. Usual Checks :
- Fuel Pump Fuses - OK
- Fuel Relay replaced with new one - Same symptoms
- Replaced In tank Pump as it was the original one
- Tested fuel delivery from In Tank to Main in Line external pump-Check
- Tested Fuel output from the filter-Check
- Swapped out the Fuel pressure Regulator-same symptoms
- Then decided to remove the return line from the Fuel pressure regulator - Ah-Ha
So, It started and ran fine(with the line disconnected). Then I cleared the return line with air pressure (disconnected at both ends)
When I applied air pressure to the return line input that runs into the tank , I noticed that the air would simply displace the fuel and return it back out the 'in door' as it were.
So, I am guessing the vent is blocked as it seems to be not allowing the fuel to return to the tank. Or, it may be something in the fuel sender/pump assembly blocked?
Any ideas or prior experience with this problem?
All commentary is appreciated!