M923A2 loosing fuel prime overnight

[djhenley]

I've been not dealing with this issue for a few years! When primed fires up faster than a UFO, but let set overnight... maybe 24 hrs and it looses prime.
removed tank, cleaned it with industrial steam cleaner, dried it out, removed pick up tube and it had hole at support few inches from bottom of tank, had it brazed. replaced old canister with dual filter bracket / filters, replaced all fuel lines to lift pump, new lift pump, changed injectors with reportedly rebuilt injectors, new relief valve.. outlet of injector pump ? bypass, over the past 2 maybe 5 yrs. today said I will find problem, pulled tank off again pressurized line from lift pump including lift pump all the way including pickup tube. After blowing all the fuel out could hold finger over end of pickup tube and raise to 25 psi with all this under water in a drum saw no bubbles! thought i had not checked suction tube well enough, when i go to crank it after setting, say 2 day will not attempt to fire... should it run and pull filters empty? I even put a cut off valve thinking that would help and open it just before trying to crank.. no good HELP
Cummins 8.3L

 

[Jbulach]

How old are your batteries, and what is your idle RPM at operating temperature?

 

[74M35A2]

Watch out for smart people.

 

[WillWagner]

Rubber lines or the selector valve. Plumb a line to a bucket and see if it still loses prime.

 

[74M35A2]

The engine draws fuel off the top of the filters, this is so any water settles to the bottom and is not utilized. So, it only takes a whif of air and it loses prime.

You have changed a lot of stuff. New doesn't always mean good. There is more than one person here who also could not find leaks using pressure, but would leak under vacuum. One was a fitting connection, and another were the flexible suction lines from tank to pump.

In order to find it, you may need to do as Will advises. Start with a new hose from the lift pump into a jug of clean fuel alone, see how that does. If OK, then start moving that back while introducing more components into the system.

Also as Jb said, make sure your fuel cut solenoid is not closing during cranking. This is a very deceptive thing. As battery voltage drops, its ability to pull and hold open diminishes, even though engine cranking seems normal. This is more pronounced with aged batteries that are unable to meet and hold their CCA label rating anymore.

 

[WillWagner]

Also as Jb said, make sure your fuel cut solenoid is not closing during cranking. This is a very deceptive thing. As battery voltage drops, its ability to pull and hold open diminishes, even though engine cranking seems normal. This is more pronounced with aged batteries that are unable to meet and hold their CCA label rating anymore.

Poor connections at the 3 pin and high resistance grounds in the pull/hold in circuit cause this also. And as stated above, if an engine has been cranked with weak batteries, the coils in the FSOV get damaged. Somewhere here I posted a chart with he different types of FSOVs and their resistance values. Easy enough to check.

 

[Jbulach]

Watch out for smart people.

Yeh, your one of the only ones that ever take the bait, sometimes you just have to start with the hard questions... Did you reboot your computer... Does it have fuel in it... Did you test your batteries...

Doubt we’ll ever learn anymore about his real problem if he’s likely still battling the same problem that he let a thread go dead on four years ago, and still hasn’t replaced the right part(s).

 

[djhenley]

Mounted lift pump back on, connected another new fuel line to 5 gal bucket of clean fuel. Primed thru lift pump, then connected to head connection, primed thru injector pump and injectors. engine cranked easily. Shutdown and restarted few times, allowed to run without problems. All other filters and lines are now bypassed. I do have a solar battery charger to one set of batteries , not two. It always cranks over great.
Will let set till late Sunday or sometime Monday.
Is the transducer on top of the lift pump required for the cranking/run circuit?
And does anyone remember who makes the new fuel line in the tank with jic connection replacing the flare fitting?

 

[djhenley]

No on computer reboot
does have fuel
batteries OK
tires OK
Not sure if computer reboot is real or ?

 

[WillWagner]

Yes, the "transducer" is the fuel shut off valve, FSOV. It needs to pull in at crank and hols in when the engine is running. When the ignition is shut off, the FSOV releases and the shut off lever on the pump moves the rack to the zero delivery port in the pump.The FSOV will not cause prime to be lost, but if it isn't being pulled in the proper amt, the rack in the pump could still be at zero delivery. When you have the no start issue and it finally does start, does it run and idle correctly, no white smoke, just starts and idles fine?

 

[WillWagner]

Check these out....

 

[djhenley]

Yes, the "transducer" is the fuel shut off valve, FSOV. It needs to pull in at crank and hols in when the engine is running. When the ignition is shut off, the FSOV releases and the shut off lever on the pump moves the rack to the zero delivery port in the pump.The FSOV will not cause prime to be lost, but if it isn't being pulled in the proper amt, the rack in the pump could still be at zero delivery. When you have the no start issue and it finally does start, does it run and idle correctly, no white smoke, just starts and idles fine?

No I'm not talking about the FSOV , I mean the transducer located on the lift pump, like a pressure switch?

 

[74M35A2]

The transducer atop the lift pump is for the diagnostic tool only. It is a known leak point over time. Best to remove and discard, cap port.

”Cranks easily” is the worst way to quantify battery health. That is what causes people to keep using batteries more than 5 years old, and the voltage drops during cranking, fuel cut solenoid extends during, yet starter speed is unaffected. This unique situation is specific to 8.3’s here.

Key point is to tie back, or have somebody watch to make sure FSOV is not extending during cranking, when doing any a2 fuel diagnostics.

 

[TedCat]

I make the new pickup tubes. I have one set available and more in the process right now.

 

[74M35A2]

Ted, you are terrible at marketing.

Ted’s tubes are full stainless including the top male JIC fitting, and available as plug-and-play, custom length, or extra long (cut to fit). Available for suction and/or return sides. TIG welded construction. Look like they belong on the space shuttle. I’ll update this with a pic when I am back at my desk.

 

[djhenley]

ooh.... does the return side go down to the bottom of the tank like the suction?, not sure if i've ever removed it.

 

[djhenley]

How do I contact you for purchase. Jeff 770-654-8689

 

[djhenley]

Would a pressure gauge be of any use in place of the transducer on the lift pump, thanks for the other info as well.
If the FSOV is tied back is that the only engine shut off other than the emergency kill?

 

[djhenley]

Just pulled the return fitting out, and found a rotten rubber braided line running to the bottom of the tank, if it can suck air back from this line i'm sure this one was leaking. Wow

 

[74M35A2]

Try not to do 17 single sentence posts in a row.

Yes, return lines typically go the bottom of tank as well. It is advisable if the entire fuel system is air-free, including the return line. This keeps it full of fuel, all the way back to the injection pump. It is also quieter this way (no dripping or splashing sounds), does not aerate the fuel in the tank, etc......

Yes, the FSOV and mechanical stop cable pull the same thing on the 8.3L, this is the only fuel cut lever.

No advantage to having a gauge on the lift pump, and they are actually not advised to have there for normal daily driving, as they can vibrate, crack internally or crack off, and you'll be stuck on the side of the road. Use direct mount gauges for short term diagnostics only. If you do want a fuel pressure low side gauge, do it remotely, and even then it is not recommended to place it in the cab unless using an isolator device if mechanical, or use an electric gauge. With diesel maybe it is a little more safe, but if gasoline then this is always a big no-no.

Tank straws (dip tubes) from TedCat:



Fitting and tube are stainless, TIG is as well and tested to be liguid tight. Tube is thick wall and rated past 5000psi. I heard they are wanting to do-away with plastic ones, so you may as well make the change ahead of the curve.