FC 559 Video 4- Low pressure side troubleshooting 

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It is under the number three that is farthest to the right in the slide or the green colored number 3. That big nut that the yellow line points too is unscrewed and the check valve screws inside of the housing the nut came out of. The check valve looks like a short 12 ga shotgun shell and is made of stainless steel. The new x15 engines are much different when it comes to this area right here. I will have to photo and do an updated video on them.

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If you are referring to the orificed dump line installed at the fuel filter housing (port 4) that dumps fuel into a bucket- No. You could, it wont affect the injector return diagnostics. The dump line is just to make sure we measure maximum suction side restriction. We achieve that by forcing a high flow rate from tank to inlet side of the suction gear pump.

@@ENGINESHOPJOE Thankyou for clarifying

I am having an issue with a cm2350. The decay rate is excessive on it. Drops from 28097 to 540 psi in a minute. It passes injector return flow test 150ml in 30 seconds, it passes the relief valve test, and on the fuel pump head return flow I get 400 ml in one minute. So that seems to be good. Cant figure out why it's not passing the leakage test. Any ideas? Thanks for your help and you are awesome at explaining your videos

@@jamesrobinette3038 First let me say we have many units in our fleet that fail the decay rate and others will hold pressure for hours at a time. Here is the kicker neither unit may be logging FC559 -low fuel pressure. Last i Knew the ecm had to see over about 1500 psi below commanded for about 30 seconds before it would log. So decay rate alone is not a show stopper. So I don't know how many miles/hours are on the injectors or pump head. Take my advice at your own risk here ok. I would loosen , oil and retorque the injector connector nuts to torque - keep in mine if your torque wrench is off 4 foot lbs that is huge in maintaining that seal connector to injector. If the injectors still flowed at 150ish i would run the automated injector PERFORMANCE TEST. If they all pass all check points I would replace the pump head. If you are not logging faults decay doesnt seem to be an issue until you get fuel filter restriction over max limits. Tell your friends to subscribe to help me out. Thanks

It is logging 559 faults, currently driver is complaining about truck loosing power climbing hills, then coming out of it when not climbing. Also logged three filter restriction codes. 2434 code I believe.

I am assuming you have a common rail isx. If yes then check the rail dump valve and see if it is hot. If it goes bad it gets so hot you cant touch it. It should be hot as the rail or sensor if working properly. It could also be a problem with your fuel actuator - it is electrical and could be the cause. I dont know what faults you have etc. Last make sure you dont have a fuel line collasping when the hot fuel makes it soft. The restriction can get very high then go down when the fuel is cold. use a restriction gauge to verify

@@ENGINESHOPJOE yes code 0559 and common rail isx. I will check those items. Installed new accuator because of wiring. I am leaning towards a hose. Rail pressure goes negative if it stalsl from no fuel pressure. Rail pressure stays if its shutdown with key.

Thanks for your reply.

Let us know what the problem was. If you have it someone else will too.. Some problems follow chassis make too. I try to put up things we run into daily because that is the real world. Your welcome. Truckers keep America strong

@@ENGINESHOPJOE ended up that the tube to injector #3 was bad at the injector. Engine would get to 175 degrees then fuel return from head would increase to 300 ml at 15 seconds. Back to normal at lower temp. Capped off each injector 1 by 1 and found it.