Fuel pressure went to zero
01-03-2021, 12:58 PM
#46
Registered User
The ECM regulates the stock pump to about 50% duty cycle while cranking to avoid hard starts.
If you can access the plug easily just turn on the ignition, when fuel pressure is at 6psi unplug the FASS LP or it's relay whatever, try to start.
If the engine fires immediately you have found the culprit. Then you will need to install a relay like follows:
Wire the coil side of the relay so that it gets activated by the starter. (Small red wire to the starter to one end of the coil, other to ground)
Cut your fuel pump wire and route it through the relay, using the NC contact. This means that juice flows as long as the relay isn't triggered.
Nets you low pressure while cranking, and good pressure while running.
(Just as the ECM tries to do with the stock pump)
If you can access the plug easily just turn on the ignition, when fuel pressure is at 6psi unplug the FASS LP or it's relay whatever, try to start.
If the engine fires immediately you have found the culprit. Then you will need to install a relay like follows:
Wire the coil side of the relay so that it gets activated by the starter. (Small red wire to the starter to one end of the coil, other to ground)
Cut your fuel pump wire and route it through the relay, using the NC contact. This means that juice flows as long as the relay isn't triggered.
Nets you low pressure while cranking, and good pressure while running.
(Just as the ECM tries to do with the stock pump)
01-07-2021, 05:57 PM
#47
Registered User
Update: Rechecked all hose and banjo fittings, connections. Still hard cold start after sitting over night.
The ECM has been and is still working properly; 50% power supply to the lift pump at start after the small initial bump.
While cranking, fuel psi is at 8. After about 20 seconds of cranking it will finally start and fuel psi goes to 16psi.
Some how the fuel is draining back to the tank, or getting drawn/sucked back from the VP44.
I loosened the fuel tank cap so there is no pressure, temperatures are mild so there is no gel concern.
I read all the details about "hard start after FASS install" but am still at a loss.... but will keep reading.
Any ideas would be appreciated.
The ECM has been and is still working properly; 50% power supply to the lift pump at start after the small initial bump.
While cranking, fuel psi is at 8. After about 20 seconds of cranking it will finally start and fuel psi goes to 16psi.
Some how the fuel is draining back to the tank, or getting drawn/sucked back from the VP44.
I loosened the fuel tank cap so there is no pressure, temperatures are mild so there is no gel concern.
I read all the details about "hard start after FASS install" but am still at a loss.... but will keep reading.
Any ideas would be appreciated.
01-09-2021, 01:57 PM
#48
Registered User
OK, try to just bump the starter and have the LP run for the usual 30 seconds. Wait until FP has dropped to less than 5psi and repeat.
If the engine fires immediately at the next start attempt you get air in the lines while being parked.
Remember, the fuel pressure gauge reports air pressure in the line the same as fuel pressure.
If the engine fires immediately at the next start attempt you get air in the lines while being parked.
Remember, the fuel pressure gauge reports air pressure in the line the same as fuel pressure.
01-10-2021, 10:38 AM
#49
Registered User
UPDATE: I think I figured it out on the COLD HARD START PROBLEM
I used the blue 3/8 hose as supplied by FASS for the fuel line from the factor filter to the VP44. This hose was barely long enough. The factory banjo fittings were drilled out for improved flow and used.
When the VP44 bajo fitting/bolt is removed, the fuel will easily drain from it. In this case, If the banjo fitting/bolt is installed in a downward position, it will allow the fuel to drain back, if the fuel line is tight and straight back to the factory fuel filter housing, I think the fuel will then continue to drain out of the VP44 back to the filter housing, thus causing the cold hard start.
SOLUTION: I bought a new longer (16") 3/8 fuel hose line and installed it. The longer fuel hose loops up and down to the VP44 banjo bolt which is pointed upwards. So far after three cold starts, there has been no issues since I changed things.
Hopefully resolving the COLD HARD START PROBLEM. I'll provide updates if otherwise.
I used the blue 3/8 hose as supplied by FASS for the fuel line from the factor filter to the VP44. This hose was barely long enough. The factory banjo fittings were drilled out for improved flow and used.
When the VP44 bajo fitting/bolt is removed, the fuel will easily drain from it. In this case, If the banjo fitting/bolt is installed in a downward position, it will allow the fuel to drain back, if the fuel line is tight and straight back to the factory fuel filter housing, I think the fuel will then continue to drain out of the VP44 back to the filter housing, thus causing the cold hard start.
SOLUTION: I bought a new longer (16") 3/8 fuel hose line and installed it. The longer fuel hose loops up and down to the VP44 banjo bolt which is pointed upwards. So far after three cold starts, there has been no issues since I changed things.
Hopefully resolving the COLD HARD START PROBLEM. I'll provide updates if otherwise.
Last edited by high bid; 01-10-2021 at 10:39 AM. Reason: add text
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nothingbutdarts (01-10-2021)
01-10-2021, 04:12 PM
#50
Registered User
UPDATE: I think I figured it out on the COLD HARD START PROBLEM
I used the blue 3/8 hose as supplied by FASS for the fuel line from the factor filter to the VP44. This hose was barely long enough. The factory banjo fittings were drilled out for improved flow and used.
When the VP44 bajo fitting/bolt is removed, the fuel will easily drain from it. In this case, If the banjo fitting/bolt is installed in a downward position, it will allow the fuel to drain back, if the fuel line is tight and straight back to the factory fuel filter housing, I think the fuel will then continue to drain out of the VP44 back to the filter housing, thus causing the cold hard start.
SOLUTION: I bought a new longer (16") 3/8 fuel hose line and installed it. The longer fuel hose loops up and down to the VP44 banjo bolt which is pointed upwards. So far after three cold starts, there has been no issues since I changed things.
Hopefully resolving the COLD HARD START PROBLEM. I'll provide updates if otherwise.
I used the blue 3/8 hose as supplied by FASS for the fuel line from the factor filter to the VP44. This hose was barely long enough. The factory banjo fittings were drilled out for improved flow and used.
When the VP44 bajo fitting/bolt is removed, the fuel will easily drain from it. In this case, If the banjo fitting/bolt is installed in a downward position, it will allow the fuel to drain back, if the fuel line is tight and straight back to the factory fuel filter housing, I think the fuel will then continue to drain out of the VP44 back to the filter housing, thus causing the cold hard start.
SOLUTION: I bought a new longer (16") 3/8 fuel hose line and installed it. The longer fuel hose loops up and down to the VP44 banjo bolt which is pointed upwards. So far after three cold starts, there has been no issues since I changed things.
Hopefully resolving the COLD HARD START PROBLEM. I'll provide updates if otherwise.
I got rid of the banjo bolt on the VP44 inlet more than a decade ago, I have a straight aeroquip fitting drilled out to the ID of the inlet fitting cone. (And some braided 3/8" hose back to the fuel filter)
All the fuel pressure discussions are about keeping the VP44 supplied- so removing a lot of resistance at the critical point where fuel needs to get into the VP44 was a logical conclusion then.
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