Rail pressure fluctuates

[Pokey81]

Ok this is my first post so hold your breath last eve i went to the neighbors which is only 1/2 mile away and i noticed a strange noise at idle, my rail pressure would go from around 5k to 15k without doing anything,my truck is a 06 and is stock other than ATS manifold and K&N filter

 

[steved]

Maybe a fuel control actuator?

 

[cerberusiam]

Rattle a little bit more than normal did it?



Could be fuel supply, could be the CP-3, could be a RP sensor. More likely though its the FCA.



Do you run additives? If , not a mixture of Power Service and 2 stroke oil with about 10 ozs in every tank will provide extra lube to the FCA and other prts effected by dry diesel.

 

[Pokey81]

As for the rattle yes thats the noise i was hearing, my low pressure was around 10 psi when this happened and it dropped very little if any, would my gauge show an increase in psi if the RP sensor is bad ? I haven't bin running any additives, do you think by adding some now i could save the FCA if thats the problem or is it to late

 

[Mobius1]

Mine would do the same thing w/o the rattle turned out being the fca

 

[cerberusiam]

As for the rattle yes thats the noise i was hearing, my low pressure was around 10 psi when this happened and it dropped very little if any, would my gauge show an increase in psi if the RP sensor is bad ? I haven't bin running any additives, do you think by adding some now i could save the FCA if thats the problem or is it to late

It should idle around 6k psi, more than than that it has a problem.



RP sensors can go bad but the FCA more often.



You might be able to get the FCA freed up with heavy doses of lube and additive, or not. The FCA is a picky critter on operations so an additive all the time is a good idea and sometimes will return them to normal operation.



Mix 96 ozs of Power Service with a quart of 2 stroke or 10wt non-detergent oil. A normal dose per 20-25 gals of fuel would be 8-10 ozs. I would double that and drive it for a while as long as there are no other symptoms.



Every 3rd mix I use a quart of Marvel Mystery Oil for cleaning capabilities then back to 2 stroke or 10 wt oil. So far 185k with no fuel system issues.

 

[Pokey81]

Thanks for the info everyone, ill try the lube and if it doesn't free it up ill replace the FCA

 

[TCDiesel]

Just replace the FCA..... No miracle lube will repair it... Let us know how its goes when you add the lube trying to find out... . and it stalls in the middle of some intersections.

 

[JJPage]

I have 4, brand new, slightly used FCA's, whichever one I place on my truck, it behaves differently,what gives???



Everytime someone has an idle problem, or rail pressure instability,..... someone says, replace your FCA... , It will change the behavior of your truck, mask the problem.



Something else is most likely causing the FCA to mis-behave.....

 

[TCDiesel]

The FCA Valve and chamber is tight and the spring the suppresses the valve will weekend causing instability. . When we mod the FCA not only to we open the valve we make a much strong/larger spring. . in addition we bore the chamber to allow more movement. . if done correctly this will add 25% more top end fuel. . if done in-correctly it will start hard and surge and hang... high idle pressure knock ETC. . Most FCAs I see modded only add about 10-15%. We have 12v FCA tester they are $60. 00.