2350 Fueling Issues

[CANNONBALL]

First and foremost a big thank you to Unilevers for getting my tune straightened out. A big name tuner who has done 5 trucks for me in the past had really lost their marbles on this one but that’s for another story time.

One day started jumping a couple 100 rpms when at an idle. High idle or low idle didn’t matter. Then it quit for a month or so. Now it does that and more.
1. Some days it will idle perfect at 700 next time you stop it won’t go down past 850. You can bump the high idle up on it then turn it off. Still at 850. Couple stops later back down to 700 couple stops later it’s back at 850.
2. Surges at idle similar to a motor sucking air run rough spit sputter and then go back to running right. Doesn’t do it all the time just when it feels like it.
3. Low rpms below 1500 or so trying just to runs 30 mph/ 50 km/h it will buck and spit. Try to run off or try to go lower. Won’t hole constant rpm
4. Sometimes when rolling thru the gears you can mash it to the floor won’t even try to build any power. Hold it a second or 2 and it’ll take off like normal.
5. Seems the longer you let it idle or more stop lights you take it too the worse it gets.

Here is what I’ve checked.
1. Ran a high fuel pressure leak down test a few times. It’ll get up to 29,000 psi or so kill the key and before the motor turns off it looses the ecm connection. But it’ll be down to 14,000 or so by the time it dies. Reestablish the connection and it’ll be at 150 psi.
2. Turned the relief valve banjo bolt out 2 turns as Mr. hag had instructed in a previous post. Started truck it idles at 14,000 psi. No fuel leaked out
3. No fuel is leaking anywhere that I can see. Bumped all the lines with a wrench all seemed tight.

I’m leaning towards an injector but here I would be throwing parts at it.


Truck runs fine. Pulls fine. No smoke when it acts up or any color.
Changed the fuel filters last oil change 4000 miles or so ago. It didn’t change anything.
NO FUEL ANYWHERE ITS NOT SUPPOSED TO BE.

My dad has a pop tester and 9000 plus fittingS from over the years in a box. Would it be worth my time to try to pressure each one to 4000 and see what holds or just pull them and get them checked.



Truck has 265k miles and 7000 hours.

Any direction to look?

[Rawze]

an injector leaking into a cylinder will make it idle higher than normal. Look in Insite and you will see your commanded fuel go to 0 when it does this.

[CANNONBALL]

thanks for the tip. I’ll hook it up first thing in the morning.

[Unilevers]

you've found the issue already, just didn't realize it but not the cause.

When you do the leak down and it loses connection and reconnects and is at 150 psi - that is 30,000PSI in less than 10 seconds. You have a large leak in the high pressure system, find it. From what you describe its a injector leaking into the return probably. Start capping injectors and running the leak down again until you find it.

Uni

[snailexpress]

(01-06-2019 )Unilevers Wrote:  you've found the issue already, just didn't realize it but not the cause.

When you do the leak down and it loses connection and reconnects and is at 150 psi - that is 30,000PSI in less than 10 seconds. You have a large leak in the high pressure system, find it. From what you describe its a injector leaking into the return probably. Start capping injectors and running the leak down again until you find it.

Uni

Not to hijack the tread, my question is the fuel pump head could be a cause to fuel rail pressure drop?
Like a bad valves or leak back ?

[Unilevers]

there are 2 check valves that can be the leak. They are easy to test when you take the head off cover the output with your finger and press down on the plunger - it should spring back at you if you let off it. If it doesn't the check valve is toast.

yes it can be a leak

[CANNONBALL]

the magical cap! My pops was telling me about that the other day and we got distracted by shooting pigs and drinking beer. Thank you.

[CANNONBALL]

Pulled the pump head. Intake side bounces up and down. Cover the output with my finger and the plunger sticks down, does not come back up.

[snailexpress]

Please pictures if you find something. I'm just waiting for better weather to go this way.