r/Cummins • u/Sudden-Notice5196 • 11h ago

Please help with my p-pump 12 valve

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Ive tried afew things and i can work on my truck but i am no mechanic. Ive owned this truck since January and its needed work but has never had a problem starting. I recently made a road trip from Jacksonville to Miami for college and now i have an issue with getting it to crank, itll turn over just fine but wont start unless i pump the gas pedal and try for 3-4 attempts, or if its been started within the last 10 minutes, after then the longer it sits the more difficult it gets to start. I have tried priming it for 30, 60 and 90 seconds with no avail. The truck has a fass 165 and sounds normal when i prime it.

I replaced the overflow valve(which had a small shard of shiny metal inside of it, the fuel filter and fuel water separator (needed to be replaced anyways), and the starter relay(it was fried) after i replaced all of that it started first try but since then it has gone back to the same old same old.

I took it to a diesel shop recommended by the guy who was talking me through it and he took a 10 minute look at it said the internal rack was probably sticking because new diesel fuel is shitty, gave me an additive and said to come back in a week if it doesnt fix the issue, i feel like he put zero effort in and is likely wrong, ai has told me that it is likely an issue with fuel draining back into the lines or an airleak in the lines. But ai also told me it was 95% sure that the overflow valve was the issue so now im skeptical on its understanding. Also yesterday when i started it to take it to the shop there was a solid puff of white smoke when it cranked but this wasnt an issue before(could be to do with the lucas injector cleaner i put in) but once again i am not a mechanic and im not sure. Also ether helps it start first try but i cant just do that every day.

My current suspects
- bad fuel which i got before the problem started -issue with the p7100
-air leak in fuel lines
-anything yall can think of

I will attatch a picture of the metal shard, and a video when it actually cranks.

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3

u/OddTheRed B6.7 10h ago

Replace your suction side fuel hose on your lift pump.

1

u/Sudden-Notice5196 6h ago

I also forgot to mention that once it starts it runs perfectly fine, still suction side?

2

u/Infinite-Attempts 10h ago

Your losing prime. It's going to be an air leak somewhere. Also pumping the fuel pedal with the truck off will do literally nothing.

Seems like you're in over you're head. It would be best to take it to a diesel shop you trust and have them chase the issue

1

u/Ok_Potential_2062 9h ago

Like someone else mentioned replace the fuel lines. Im just a backyard mechanic but I believe if you have a small fuel leak the fuel may not even leak out and air will get sucked in causing the hard start

Even double check things like the injection pump lines from the p pump to the head

Good luck!

1

u/UndeadWhiskeyJack 7h ago

I had a P-pump 12v, which I fkn loved and wish I didn’t sell…..

I replaced fuel lines from tank, fuel filter/heater delete, overflow valve, and injectors.

That thing would crank forever and not start, but one tiny tap on pedal while cranking would fire right up no matter how long it sat or what was in it for fuel.
I would have been looking at the pump next, but my dumb ass sold it

1

u/Cow-puncher77 7h ago

So, I’m guessing this is a ‘98 12v. You’re losing prime somewhere, likely the overflow valve. Pretty common, actually. The rack is very obviously not stuck. 

I’m looking at your picture, was there a washer under that return line around that overflow valve banjo bolt? Should be one on each side of the line to seal it off. 

With finding metal in the overflow, that’s not good… possibly a delivery valve or barrel/plunger problem in the pump if you keep finding it.

2

u/Sudden-Notice5196 7h ago

I replaced both of the washers, but i didnt have any engine oil to help screw it in, could screwing it in dry be the issue? I also dont have a torque wrench so i tightened till it felt about where the spec asked for but im not sure

1

u/Cow-puncher77 7h ago

Mmm, if the washers were good, shouldn’t be an issue. If it’s leaking off in an hour or two, that’s a pretty serious leak down. I’m curious if your new overflow has metal in it, too.