I have low rail pressure on reading at 200psi on my programmer. I have replaced all 6 injectors then found out the motor needing rebuilding. Found bad piston rings. pulled engine ringed it and installed all new gaskets. Reinstalled the engine into the truck. Found that I only had 200 psi. Had the injector pump rebuilt and now it will get up to 600psi during cranking. When I stop cranking I have noticed that the rail pressure immediately drops to zero and does not maintain 600psi. It will run on straight ether but I stopped because I didn't want to ruin anything and it still would not run on fuel. Everything is stock except Edge with Attitude programmer. Need help! I've dumped $3000+ and still not running good or at all!!

 

The RP should drop to zero when you stop cranking. Unplug your fca and see what happens

 

Ok so that is normal good. I tried unhooking my fca and still no start. Next thing I guess is get a rail cap to block off injectors and see if it starts then

 

did your RP change at all during cranking with it unplugged? it also could be your PRV letting fuel through back to the tank.

 

Honestly didnt pay attention to rpm while cranking. To rule out that PRV can I just take the banjo bolt out of it and stick a regular threaded bolt into it to block it off so there is no return?

 

Sorry thought I read rpm but no the rail RP was the same both unplugged and plugged in highest it would get after 5-10 seconds of cranking was 600psi

 

Ok found out some news. I unhooked the return line quick connect under the fuel filter housing and with key on (not starting or cranking) found the fuel to run out of the return line with the fuel pump running. It was a lot of fuel too. Tried to block off the fuel return lines with bolts and was able to get the RP to 900psi. I took the banjo bolts out of the return lines and I put regular bolts in there to stop the flow but they were leaking a little diesel out of them though but still the RP increased. So which part would I be looking to replace because of too much return flow?

 

i am having a very similar problem just insalled new engine and injectors, truck ran when i brought it in. now i can only build 89 psi of rail pressure. i have tried all the test on it like blocking of rail to test inj. so i could isolate but no change. unplugged fca and no changed still the most pressure at rail is 89 psi any help with this would be greatly apricciated

 

I found the problem with mine I capped off the injectors and found 2 that were bad. They had high injector return flow. For yours Fopar, I would be looking at where your fuel is going. Unhook your return line quick connect under the fuel filter bowl. See if key on if the fuel runs out of the return line. Like a steady heavy flow. That would mean something is wrong. Then try cranking and watching to see if it flows. That would also mean bad. Spec says less than 70ml of fuel to come out of there while cranking. I had wayyyy more than 70ml. After that simple check I would be looking at your high pressure fuel pump specifically the cascade overflow valve in it, the fuel pressure relief valve, or the banjo bolt return valve in the back of the head. To rule out some of those out take a regular bolt stick it in place of the banjo bolts. The bolt in the back of the head is a 19mm and the thread pitch is M14x1.5mm fine thread. that would rule that bolt out. If still same result. Then I would take that same bolt out of the back of the head and put it in the pressure relief valve. If still same result I would say all you have left is your high pressure fuel pump.

 

This is straight from the service manual. It describes fuel delivery.


Fuel enters the system from the electric fuel transfer (lift) pump, which is located inside of the fuel tank and attached to the fuel tank module (the fuel transfer pump is no longer attached to the engine). Fuel is forced through the fuel filter element and then enters the Fuel Pump/Gear Pump, which is attached to the rear of the fuel injection pump.The Fuel Pump/Gear Pump is a low-pressure pump and produce pressures ranging from 551.5 kpa (80 psi) to 1241 kpa (180) psi . Fuel then enters the fuel injection pump. Low pressure fuel is then supplied to the FCA (Fuel Control Actuator).

The FCA is an electronically controlled solenoid valve. The ECM controls the amount of fuel that enters the highpressure pumping chambers by opening and closing the FCA based on a demanded fuel pressure. The FPS (Fuel Pressure Sensor) on the fuel rail monitors the actual fuel pressure and provides it as an input to the ECM. When the actuator is opened, the maximum amount of fuel is being supplied to the fuel injection pump. Any fuel that does not enter the injection pump is directed to the overflow valve. The overflow valve regulates how much excess fuel is used for lubrication of the pump and how much is returned to the tank through the drain manifold. Fuel entering the injection pump is pressurized to between 300-1600 bar (4351-23,206 psi) by three radial pumping chambers. The pressurized fuel is then supplied to the fuel rail.