Hi Guys,

After a lift pump failure and the installation of a new Fass DDRP pump I began having hot start issues. The problem was discussed in this thread:

https://www.dieseltruckresource.com/....html?t=249141

It was suggested that I tie the pump to the Run Only circuit in the cabin fusebox. The fuses suggested was fuse 2 or 10.

I cut the connector that feeds 12 volts to the pump rather than cutting the connector to the Fass and voiding the warranty. I then taped the two electrical leads from the previous 12 volt supply so they could not touch.

I wired the side of the plug that feeds the red wire on the Fass Pump to an ADD A Fuse connector the other wire to ground. I then plugged into the cabin fuse box on 2. The truck started and died.

I moved it to another fuse that had power all the time so I could bleed the truck and get it started again. The pump was running but the truck could not be started by bleeding as I normally would.
I finally disconnected the lift pump line at the filter and there is no fuel when the lift pump is running.
I am showing a 1/4 tank of fuel, I guess it is possible that I have a faulty fuel tank sending unit and that the tank is empty, but thats a stretch.
The pump was working before this rewire. in the current state of wire, you can hear it run when it is turned on.
Is it possible I have the wrong power lead connected on the Fass pump and it is running backwards? I really figured that the red wire would be hot and that was the lead that should go to the fusebox.
Could it be that the pump picked this exact time to die?

I also checked codes and I have a p1693 code,

Any ideas for me?

Thnaks.....gary

 

I added 4 gallons of fuel and it did not change the situation. Still no fuel from lift pump....gary

 

anyone?

 

If the pump still does not pump fuel, then it must be bad (my guess) Not sure on the wiring if you hooked it backwards or not, but if you remove the out line from the pump, with the pump running you should be able to use your thumb and feel if its sucking or blowing.or do the same on the inlet line. On one truck I needed to pressurise the fuel tank (rag and airhose in the filler neck) to get the stock pump to pick up the fuel. but that truck had a failing LP

still it should pick up the fuel....I bet the pump is faulty

 

I'm to the point where I am ready to hook it back up to stock wiring and see if the pump runs again.

I will do this tomorrow and repost...thanks...gary

 

I would take it back to the start and test the pump by just giving it 12V and making sure it pumps fuel. Then I would hook it up to the truck to make sure it is primed and starts up. Then, I would re-wire it with a relay and Run only circuit.

 

With the diameter of the wires paul, I didn't think I would need a relay. What is the purpose of the relay?

thanks...gary

 

The purpose of the relay is to isolate the original LP circuit. The aftermarket pump (my Walbro) pulls more amps than the original LP, and the LP circuit come directly from the ECM. I did not want to damage the ECM control circuit.
I used 14 gauge wire I think to power the pump and 16 gauge for the relay; the latter is not important as it is short and carries very little current.

 

I went back to the original wires and still have no fuel at fuel filter.

The pump hums but nothing comes out of the fitting.

Should I start checking the fuel supply from tank?

 

Well, I have confirmed that the pump is now running backwards. I put a clear line on the outlet of the pump and sucked till I saw fuel to end any prime problems I may be having, cranked the starter and had suction on the outlet side.
I went to the gas tank and listened and could hear bubbling in the tank.

Could I somehow have reversed polarity on the motor? I checked the wiring and it is correct.....gary

 

No idea! I have never seen that before. I'd call the pump manufacturer.

 

Could they have marked the pump body backwards?

 

I spoke to a guy at FASS and although he could not explain the reversing of the polarity, he told me to just switch the wires..I will do it tomorrow...gary

 

The motor used in the DDRP must be run with the green lead to the power supply or it will run backwards.

I originally thought I had somehow reversed the polarity on this motor. polarity reversal can be done to certain styles of AC motors by touching positive lead to negative side of power then grounding other wire on case.

But no, they are just running the motor backwards in this application.

I finally swapped the wires and hooked green to fuse 7 via an "add a circuit" and it works great!