Fuel pump woes...

[35Remmy]

Hey fellas...88 Ranger, originally 2.9L, now 5.0 CARBED.
If i turn key to ON, fuel pump will prime system and carb to the 6.5psi needed for the carb (i am using a Holley pressure regulator as this system, as you know, also has the high pressure pump.
Problem is system wont maintain pressure. As engine runs the pressure gradually bleeds down on fuel pressure gauge until engine shuts off.
I dont think the high pressure pump is running after engine starts??? I tried feeling the pump for life while she was running but cam is so lopey all i feel is vibration from the engine.
What would you do at this point. Thanks for your time guys.

 

[Dirtman]

Are you using the original fuel pump setup? If so how do you have it wired up? The stock pump runs for 3 seconds then shuts off and requires the crank sensor to turn it back on once the engine is running...

 

[35Remmy]

So this 302 needs a crank sensor to operate the fuel pump properly? Or is there a way to wire the pump differently? It is currently wired as the stock 2.9L setup but am using a Holley fuel pressure regulator to bring the high pressure line down to a carb friendly 6.5PSI.

 

[Dirtman]

So this 302 needs a crank sensor to operate the fuel pump properly? Or is there a way to wire the pump differently? It is currently wired as the stock 2.9L setup but am using a Holley fuel pressure regulator to bring the high pressure line down to a carb friendly 6.5PSI.

So you still have it wired through the original 2.9 ECU?

Fuel pump command on comes from the ECU, key in run position or start position the ECU commands the pump on for 3 seconds to prime the system then shuts it off UNTIL the crank sensor reads above 400rpm (meaning engine is running). This is a safety feature so the pumps don't run if the engine stalls. With no crank sensor the ECU never sees the engine as running so you're just getting fuel until the 35psi in the system before your 6.5 psi regulator bleeds off and the engines dies.

You don't need to add a crank sensor, you need to remove the factory ECU and all that nonsense and run the pumps independently either via key on relay or a toggle switch so they are no longer dependent on the ECU for on/off function.

 

[35Remmy]

I really appreciate the enlightenment!! I didnt realize this would get so interesting....wont removing the factory ECU (i switched mine for a manual transmission ECU as im running a C4 and was told this is what i needed to do...no one ever gave me a heads up about the fuel pumps!) cause other problems? This guy hates electrical. Thanks again man

 

[Dirtman]

A C4 has no computer controls so dunno who told you that you need an ECU for it, and even if it did a factory auto ECU from a 2.9 is made for a A4LD not a C4...

 

[35Remmy]

I was told it needed it since the A4LD was computer controlled and the C4 is not. ???? I believe this was from James Duffs site

 

[Dirtman]

Im confused here. You have a carbed 5.0 so no fuel injection, no computer controlled transmission, what exactly are you using the ECU for? There's nothing else for an ECU to do. Think we need more details on your setup and what exactly you have, and have done.

 

[Shran]

If you leave the ECU and the associated wiring intact, you could jumper the ECU test connector so that the fuel pump runs all the time with the key on. Otherwise you will need to rewire your fuel pump relay so that an Ignition Hot wire triggers it instead of the computer. Most people wire all that from scratch, I am surprised to hear of someone trying to use the factory wiring for a setup like this although it could be made to work.

I also think that you could remove the high pressure pump completely and run a carbed engine off of just the low pressure in tank pump...should easily supply enough fuel, that is how 85/86/87 F250/350 trucks with the 460 were set up, electric lift pump in the tank and a carburetor.

 

[35Remmy]

Dirtman and Shran, thanks....how would i go about jumping the test connector so i have the pump running with the key on?

 

[35Remmy]

"...Otherwise you will need to rewire your fuel pump relay so that an Ignition Hot wire triggers it instead of the computer". Doesnt this seem like the more practical solution if keeping stock wires intact?

 

[35Remmy]

Ok, i figured out how to ground the OBD1 test port at the fuel pump slot and keep high pump energized with key on...