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Must the fuel pressure be no less than 25lbs when measured at the top of the filter???
Must the fuel pressure hold its full pressure when the vehicle is shut off????
Thanks
Thank you for the reply. It seems I can't get any better than 20lbs at idle. Never checked at throttle. Installed new fuel line, lift pump, filter, pre heater filter, and the elbow between the heater and pump. Doubled checked all connections and used WD40 to spray connections to see if the pressure would pick up, but didn't.
When shut off the pressure drops to nothing in about 15 seconds. Replaced all the O-rings or gaskets at the filter housing connections. Now drops off to 10psi in about 2min. I'll keep digging in...........😭😭😭😭. Thks again...
Ok, you need to determine if it is the pump or the overflow valve causing you your issue. Betting it is the overflow valve since you have changed your pump, unless you happened to get the low pressure piston pump........ What you need to do is restrict the return line to the tank a pair of vice grips squeezing the hose while running will do. You should see an immediate spike up near 60 when the fuel return is restricted. See the attached picture to show the return line.
Thks, Patdaily.... I just came in from working on it and seen I had mail. I got her started, but took a while. She had 20lbs at idle, then she lost 1 to 2 while being throttled. I pulled the line off the tank and stuck it in a 5gallon can. Primed her. She fired and ran great, with a crisp response. Then the pressure dropped and fuel poured out from the tank. I hooked the line back up and she would not fire off. When she did, she shut down quickly. So, I thought either the vent for the tank or the Overflow valve or the IP is building up too much pressure. I was NOT sure if a pump can do that?? But I thought I'll try a overflow valve first. So thanks for the response!!!! I greatly appreciate it!!!! I will pinch the line tomorrow and check pressure. Thks again. It's nice of you to help me, this is my first diesel and it's all new... Thks
Thks thisguy65 for the test. I hope I don't disappoint you...
If 60 or more= Overflow valve
If no spike= Overflow valve working and IP is bad
So, did I pass????
From Joe G's fuel system writeup: "If there is low fuel pressure that is caused by a weak or defective overflow valve it is easy to check. While the engine is running have someone watch the fuel pressure gauge. Clamp the rubber return line closed with some pliers. If the low pressure is caused by this valve the pressure read by the pressure gauge will increase very quickly. Do not hold the return line closed very long to prevent damage to the fuel system."
You have low fuel pressure, you suspect the overflow valve is opening at too low a pressure. But it could be the lift pump isn't providing enough pressure. If you get a spike when you pinch off the return line, you know the lift pump is providing enough pressure, so you confirm the overflow valve is weak. If you don't get a spike, you have to keep working on the supply side (lift pump, air leaks, restrictions, etc.).
Nothing in this test would implicate the IP itself.
Thks, Req Field. I greatly appreciate your response. I ordered the Overflow valve yesterday morning. I completely eliminated the preheat circuit, and went from tank to the lift pump. Same results. Being the lift pump was just out of the box, and the line from the pump to the filter was off and clear and new O-rings installed and the same for the line from filter to IP. ... So, all being done and your advise that the IP is not to be considered, which I heard all kinds of reasons why it was that, even by a diesel shop, which I felt was never a problem with, I feel confident the valve is the problem. I didn't get the chance yet to pinch off the return line, but I shall when time permits. So, Thank you and all very much for the help in trying to assist me making this problem as easy as possible. Thank you again......
If the pressure goes up to or past 60psi what does this tell you?
If the pressure does not spike what does this tell you?
Pressure jumps right up your overflow valve is not building pressure, if it does not jump up, something is not allowing the lift pump to produce enough to build pressure, could be pump, blocked line, etc....... but something downstream of the overflow valve is not working to specification.
Thank you Patdaily. All help is greatly appreciated. I already pulled the overflow valve out. Waiting on the new one. Should be here today or tomorrow. Let ya know how it turns out... Thanks again.....
06-14-2017, 06:46 PM
