Funny Rail Pressure Issue??

[RMalone]

My truck is modded as in sig. except for V. A. 3. 1 (pressure), mild injectors and walbro 392 kit from Glacier.



Before my troubles started the truck was running like a raped ape. At WOT with V. A. on high, TST on 1/1 would give me 40psi boost, egt under 1200 deg, and 26-27,000psi on the rail. When cruising @70mph the truck would run about 22-23000psi on rail and go to 26-27Kpsi when throttled. All in all a wonderfull experience.



After my troubles started the truck cruises @70mph with 17-18kpsi on the rail and falls to 12-13kpsi when throttled, obviously this drops my power and egt skyrockets. The above setting will now generate close to 1400deg egt at WOT, boost still hits 40lbs no problem but the truck doesn't have anywhere near the "get up and go" it had before. Even accelerating with traffic will get me to 1,200deg egt. At this point rail pressure never makes it above 21k and I believe that is just a spike the guage is recording but not displaying, the guage never seems to read much above 19k but the memory will show up to 21k. When the fuel control actuator is unplugged the truck will idle at about 12k rail pressure but wont go above 20k and runs like hell (no power, poor throttle response).



So far:

1. the fuel control actuator has been replaced twice (once by me once by the dealer), no change.



2. the cp3 was replaced twice (once before the problem started and once after the problem started), no change.



3. one injector was replaced and all crossover tubes replaced, no change.



4. the rail pressure valve has been both replaced and capped, no change.



5. Each box has been removed one at a time and both together, each box change makes some difference but the truck still doesn't hold rail pressure, even boxless. Rail pressure is a little higher at light throttle with the pressure box and the timeing from TST helps egt a little.



So what do ya think??? my next plan is to reflash the ECM (pretty cheap) the truck doesn't throw any codes other than 336 which is has always thrown with any timeing box. After that I think I will try stock injector nozzels. Come on guys help me NOT spend my money.

 

[Tomeygun]

OPPS. I thought I was going to point out the pressure relief valve, but you said that was replaced...



Have you ever tested it?



EDIT - and one more thing, what was the turning point of the bad performance? was it all at once of more graduale (sp)?

 

[Lightman]

Check your injector return flow you could have a bad injector or two, also check your injector feed tubs could be leaking by passing fuel back to the tank.

use the link below for instructions on injector return flow test



http://www.cumminsforum.com/forum/showthread.php?t=5764

 

[RMalone]

Tomey I have even capped the rail with out results, the problem started all at once while going from Michigan to Montana, I noticed while passing on the interstate that egt was higher than usual when I checked the rail pressure it was running about 19k instead of the normal 23k.



The return flow on the injectors was checked and one injector replaced, all 6 cross tubes were replaced also. Supposedly (dealer did the job I do believe him he is a friend of a friend) the truck would hit 26k with the FCA disconnected but the rail wouldn't maintain pressure when the FCA was hooked up and a load put on the motor. I unhooked the FCA myself this afternoon and the truck wouldn't even hit 20k. After I shut down and reconnected the FCA the truck is giving me more pressure than before, not like before my trouble started but it will hold 18k at wot VA box only. Temps under moderate throttle are somewhat better also. Go figure!!

 

[AK RAM]

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On edit: Never mind. Re-read your post and you already covered it. Odd problem to say the least.

 

[Tomeygun]

Tomey I have even capped the rail with out results, the problem started all at once while going from Michigan to Montana, I noticed while passing on the interstate that egt was higher than usual when I checked the rail pressure it was running about 19k instead of the normal 23k.



The return flow on the injectors was checked and one injector replaced, all 6 cross tubes were replaced also. Supposedly (dealer did the job I do believe him he is a friend of a friend) the truck would hit 26k with the FCA disconnected but the rail wouldn't maintain pressure when the FCA was hooked up and a load put on the motor. I unhooked the FCA myself this afternoon and the truck wouldn't even hit 20k. After I shut down and reconnected the FCA the truck is giving me more pressure than before, not like before my trouble started but it will hold 18k at wot VA box only. Temps under moderate throttle are somewhat better also. Go figure!!

Maybe a bad rail pressure sensor? Like it is reading too low - thus the CP3 is loofing around??

 

[RMalone]

Tomey that is an excellent suggestion, any idea how much that baby runs??



Another thought I had was maybe a bad signal to the FCA causing it to dump fuel back to the tank. I imagine that would be an ecm issue??

 

[Tomeygun]

Tomey that is an excellent suggestion, any idea how much that baby runs??



Another thought I had was maybe a bad signal to the FCA causing it to dump fuel back to the tank. I imagine that would be an ecm issue??

The sonsor is not servicable that I know of. The rail assembly that includes the sonsor is about $500 - But I see them on ebay all the time for under $100 and thats with the relief valve too...

 

[Lightman]

Maybe a bad rail pressure sensor? Like it is reading too low - thus the CP3 is loofing around??

If the sensor was reading low the ECM would be telling the CP3 to put out more fuel not less and pressure would be higher, also where does the spa gauge get its signal from? Does it have its own sending unit or does it use the factory unit? The pressure sending unit can be replaced with out buying the rail I have one setting on my desk D/C Part #05093112AA

 

[RMalone]

The SPA reads from the factory transducer. As I think about the problem (and I have been doing so way too much) I doubt the factory pressure transducer is the problem. I agree a low reading would lead to an increase in rail pressure not a drop. Pressure boxes are essentially doing the same thing.



I "think" the problem lies in the FCA/cp3/signal into the latter or the injector nozzels. Cruising in 3rd gear at 2000rpm I am seeing 18-20kpsi on the rail. When the throttle is tipped in rail pressure falls. When the trottle is released rail pressure "catches up". The dealer checked my SPA against the DRB and said it was damn close.



One other item that bears mention is this: Highest rail pressure is seen first thing in the morning when fuel and air temp are the lowest. The rail seems to hold more pressure, longer at low temps. High air temps seem to limit max rail psi and cause the rail to lose pressure faster when accelerating.



EGT does reflect these observed changes in rail pressure. Much higher egts in the heat of the afternoon.



Sorry for all the long posts, It's just that I am at my wits end with this truck!! And thanks for the help guys.

 

[sag2]

You should probably run the return flow tests. I looked at the link given and it is a little confusing. Here is a little clarification.

Once you install the 9012 in the back of the filter housing it separates the return into the pump and head return. The fitting from the 9012 is the pump return, and should be 1000 ml or less in one minute at idle. The hose going back to the tank is the return from the head only with the 9012 in place. Measure the flow from that line at the bottom of the filter housing and that is the one that should be less than 180 ml in one minute. You might have a leak that is only showing up at high pressure/temps, so be sure the engine is at operating temp before you check the results.

 

[RMalone]

Thanks Sag, I may well be getting the tools to do a return test myself. I will say for every problem I have with this truck I learn 10times more than when everything goes smooth. I seem to meet more good people also. Thanks for the help gentlemen!!

 

[Diesel Power]

if all is well in the fuel system, i would say it is ecm or sensor related, your apps could also have a drastic effect on the way your truck runs, along with camshaft sensor and air intake temp sensor--they can fail with out codes and within there range. let us know how it comes out

 

[RMalone]

I would think ecm or sensor also but the sucker wont make pressure with the FCA unplugged. I am going tommorrow to have the ecm reflashed, I don't have high hopes but it's worth a try.

 

[Diesel Power]

I would think ecm or sensor also but the sucker wont make pressure with the FCA unplugged. I am going tommorrow to have the ecm reflashed, I don't have high hopes but it's worth a try.

an unplugged fca should throw a high rail psi code if it does then you good --it's electronic, make sure your at idle only dont drive it.

 

[RMalone]

It throws a code but it only gives about 12k at idle and 20 when throttled with FCA unplugged

 

[Diesel Power]

It throws a code but it only gives about 12k at idle and 20 when throttled with FCA unplugged

thats a problem for sure, its sounds like the correct command is not there---maybe a ecm

 

[RMalone]

Dieselpower would it still be the ECM, I thought unplugging the FCA removed ECM control from the cp3?



Get this, I took the truck to the dealer this morning and was told that their diesel tech just started working on diesels and does not know how to flash the ecm. :-laf



Oh yeah and he said the service manager wasn't real comfortable touching the truck since it was modified. They made the appointment knowing full well ALL of my mods, I think they got scared at least they never saw my vin #. Since I am going to pay for the flash the next dealer isn't going to know about the mods, other than the velcro on the fuze box and that big ol sps66 hanging off the exahuast manifold, any bets on whether or not they notice??

 

[Diesel Power]

Dieselpower would it still be the ECM, I thought unplugging the FCA removed ECM control from the cp3?



Get this, I took the truck to the dealer this morning and was told that their diesel tech just started working on diesels and does not know how to flash the ecm. :-laf



Oh yeah and he said the service manager wasn't real comfortable touching the truck since it was modified. They made the appointment knowing full well ALL of my mods, I think they got scared at least they never saw my vin #. Since I am going to pay for the flash the next dealer isn't going to know about the mods, other than the velcro on the fuze box and that big ol sps66 hanging off the exahuast manifold, any bets on whether or not they notice??

you still have rail pressure controll at the sensor on the rail --it still communicates, that would be a good place to start!!! Oo.

 

[tlgdiesel]

you still have rail pressure controll at the sensor on the rail --it still communicates, that would be a good place to start!!! Oo.

When you unplug the FCA the pump go's full bore no control from the ECM

If you go over pressure it will set a code because of the rail pressure sensor

which the ECM still reads and will pop the over pressure valve if it go's high enough. Oo.