Trouble starting, need help!

[jsutterby]

I'm kind of stumped here. My truck has been a daily driver since I have had it, about 15 months now, and has always started right up. About 2 weeks ago, I haven't needed it as much so it sat 4 or 5 days and then when I went to start it, it just cranked over and over and wouldn't fire. Finally, I got under the hood and pumped the manual fuel pump 15 or 20 times and then it started. It has done this since then several times, even with a 24 hr or less wait. If I drive it and then shut it off, then start again shortly, I don't have a problem.



What do I need to look at?? I have not done anything to the fuel system since I have owned it other than change filter last fall. Thanks for any help.

 

[B.G. Smith]

Starting

I have read of this problem on the 12 valves on this forum before. The usual cause is a leak in the fuel return line I believe causing the pump to lose prime. There are other causes and I'm sure someone with 12 valve experience will add some knowledge to this thread. bg

 

[Alaskaskiff]

Yes, more than likely the return line. You need about 18" of 5/16 line for the return and the same amount of 3/8 for the supply. If you are there for one, might as well do both. You may see fuel dripping down the lines under the truck, but you may not. The line gets porous over time.



Make sure you replace it with diesel rated fuel line (gasser line will rot out fast). Marine rated for diesel (with a CG rating) is thicker and will last longer, since it needs to work reliably in a bilge next to a hot engine.



If the lines don't fix it, you need to check the overflow valve on the forward passenger side of the P7100 pump. The spring may have compressed with age, or one of the seals may be leaking. They are cheapest from Piers, but if you need it fast any Cummins dealer has them.



If that doesn't cure it, there is a check valve in the lift pump that could be getting tired. Pump is not rebuildable. $140 from Cummins.



Good Luck

 

[KPerkins]

These pumps have a pressure relief valve where the return line exits the pump. There is a little spring inside it and if it breaks it will cause the pump to loose pressure when stopped and cause hard starting.

 

[Missouri Mule]

jsutterby,



If the return fuel line is leaking tell tale signs of leakage will be on top of starter and some moisture (wet area ) on head next to hose. If your lucky you will see it actually leaking but it mite be only sucking air mostly right now.





A fuel pressure test can be performed to tell if return(overflow) valve or transfer(lift) pump is acting up.

 

[jsutterby]

You guys hit it right on the nose, it was the fuel return line. I finally got a good look at it and it was cracked in many places, fuel was really seeping out of it. It had evidently been replaced before as they had used 3/8" line and I replaced with 5/16" as directed above for the return. Not a difficult job, just very hard to get to, luckily I have long arms and I went ahead and changed the fuel filter while there, that gives you a lot more room. This should take care of that problem.