rail pressure not keeping up

[TCluff]

pulled rail pressure down to 9000 psi at bully dog, but still had 11 psi at the inlet of the cp3, or at least that is what the dipricol said, i can only run the tst twins on 3x3 or i start to loose rail pressure quickly, only made 430s on 7x7, is my cp3 goin south or do i need a 150 gph fass, the pusher pump i run is only 100gph... . industrial injection tested my rail pressure after a very weak and hot run, boost was at 63psi in 6th gear

 

[lmills]

wow was 430 the best run you made? Or did you have better ones?

 

[Hawkeye 04]

Sounds like your pressure relief valve is pretty much shot. If it has too much pressure for too long, it will weaken and lose the factory setting and not allow the rail to build the pressure that it needs to throw out the hp you want.

 

[lmills]

yeh, sure sounds that way. what was it, 400 for a new relief valve mentioned in the other thread? and you can't buy just the valve.

 

[mattymac]

there was a fuel rail on Ebay not to long ago that was mentioned on this board and I think someone here bought it for pretty cheap.

 

[Jeff_K]

Look up AK RAM, I believe he may have a spare fuel rail with sensors & relief valve.

 

[AK RAM]

Look up AK RAM, I believe he may have a spare fuel rail with sensors & relief valve.

I do and I can sell you just the valve if you want for a fraction of a new one, but you should test yours first to make sure it is bad. No sense in wasting cash and it is very easy to test.



Two options:



The easiest way to test it is to get some time with a tech from your dealer with his/her DRBIII. The test can be done in about 30 minutes, so approximately $50 in labor is all it should cost you. What you would be looking for is a relief valve that is stuck open or has been popped a few too many times and not seating correctly anymore. If that is the case, you should be able to do a very mild acceleration run that doesn't tax the rail very much and actual pressure won't be able to keep up with commanded pressure due to the relief valve bleeding off fuel all the time. Unplug your Ramifier, turn the TST off, and go for a ride and they can display commanded pressure versus actual pressure. On stock power, your truck should see aprox. 23,400 psi in rail pressure (don’t quote me on that number, the tech will know or can look it up). Do a run on stock power and see if that pressure can be maintained. If the valve is stuck open for some reason, commanded rail pressure will be XXXXXX, but actual rail pressure won’t be anywhere near that number. On stock power, your truck should be able to maintain 23,400 psi all day long at WOT.



or



There is a special fitting that you screw into the top of the valve, attach a piece of 1/4" hose to it, crank the truck, disconnect the rail pressure sensor plug forcing rail pressure to go to max , and measure the amount of fuel passing through the valve in a measuring cup. The first time this is done, I would aim the hose out across the yard somewhere just in case the valve is passing LOTS of fuel. You should see X amount of fuel in X seconds of run time (there will always be a little). If you get more than that, the valve is bad. I have the special fitting that I can let you borrow if you want to try it or you can buy one from Miller Specialty Tools. You would have to look up the specs for this test (allowed fuel flow) in a service manual or get them from your dealer…I don’t have them handy.

 

[TCluff]

i replaced the relief valve about a month ago and i quit running the ts unless i pull or dyno, the rail pressure is normal untill you run it over 3x3 tst only at 18000 psi, any more and the faster it falls, is it possible i may have air or cavitation bubbles in the fuel that a fass would get out... by the way the relief is 420 after tax at cummins, and around 500 at the dealer

 

[JStieger]

Just remembering a thread you posted a while back about high EGT with even an EZ (??) IIRC so I'm just thinking out loud here...



Would FUBARED injectors cause low rail pressure? Or if the injector solenoid is bad (sticking open - even ever so slightly) when the TST calls for more duration on the higher settings? But then that would show up on oil analyses or torched pistons or codes? I'm just thinking about the retarded cam timing on these 3rd gens for emissions purposes that keep EGT a bit higher anyway so any extra duration from a bad injector or two would make the EGT worse than what the TST can compensate for with injection timing.



Might be worth the trip to SLC to Industrial Injection to have them go through your injectors and (maybe pick up a few goodies!)... they seemed pretty straight-up when talking to them at Bully Dog this past weekend.

 

[TCluff]

they were pretty straight forward and very helpful at bully dog, i think the high egt is from retarded injection timing caused from low rail pressure and possibly an injector issue, i think the injection timing starts to retard from not having enough rail pressure to spray the fuel exactly on time, 9000psi would have a slower spray then 23,200 psi, also at the bully dog pulls, it took forever to spool the turbos, even while just pouring mad smoke, i think the smoke is the fuel still trying to burn in the exhaust pipe, hence causing it to have a very high drive pressure, like 63psi of drive at 55 pounds of boost, maybe what i am trying to say is i dont have the fuel, it just looks like i do because it is burning in the exhaust from way retarded injection timing.....

 

[ChrisKringle]

I do and I can sell you just the valve if you want for a fraction of a new one, but you should test yours first to make sure it is bad. No sense in wasting cash and it is very easy to test.



Two options:



The easiest way to test it is to get some time with a tech from your dealer with his/her DRBIII. The test can be done in about 30 minutes, so approximately $50 in labor is all it should cost you. What you would be looking for is a relief valve that is stuck open or has been popped a few too many times and not seating correctly anymore. If that is the case, you should be able to do a very mild acceleration run that doesn't tax the rail very much and actual pressure won't be able to keep up with commanded pressure due to the relief valve bleeding off fuel all the time. Unplug your Ramifier, turn the TST off, and go for a ride and they can display commanded pressure versus actual pressure. On stock power, your truck should see aprox. 23,400 psi in rail pressure (don’t quote me on that number, the tech will know or can look it up). Do a run on stock power and see if that pressure can be maintained. If the valve is stuck open for some reason, commanded rail pressure will be XXXXXX, but actual rail pressure won’t be anywhere near that number. On stock power, your truck should be able to maintain 23,400 psi all day long at WOT.



or



There is a special fitting that you screw into the top of the valve, attach a piece of 1/4" hose to it, crank the truck, disconnect the rail pressure sensor plug forcing rail pressure to go to max , and measure the amount of fuel passing through the valve in a measuring cup. The first time this is done, I would aim the hose out across the yard somewhere just in case the valve is passing LOTS of fuel. You should see X amount of fuel in X seconds of run time (there will always be a little). If you get more than that, the valve is bad. I have the special fitting that I can let you borrow if you want to try it or you can buy one from Miller Specialty Tools. You would have to look up the specs for this test (allowed fuel flow) in a service manual or get them from your dealer…I don’t have them handy.

I'm having my relief valve tested wednesday at the dealer. I think the 130 hp Bddl with a 80hp pressure box did it. Truck just seems low on power, is that the problem?



How much for a new one?

 

[dieselpilot1969]

Is the relief valve a dealer only part? What is cost?

 

[lmills]

low power is a sure sign of a bad relief valve.

 

[Hawkeye 04]

I'm having my relief valve tested wednesday at the dealer. I think the 130 hp Bddl with a 80hp pressure box did it. Truck just seems low on power, is that the problem?



How much for a new one?

That's what happened to mine. BDDL stacked with EZ for too long... .

Low on power and a "fish-bite" kind of surge... I'll see what happens this week after it's replaced.

 

[TCluff]

I'm having my relief valve tested wednesday at the dealer. I think the 130 hp Bddl with a 80hp pressure box did it. Truck just seems low on power, is that the problem?



How much for a new one?

they are 420 after tax from the cummins dealer and about 100 more from daimler chrysler, have it checked before you buy one, i already made that mistake, but now i have a spare... .

 

[Devan Manis]

63-55 drive pressure to boost

63-55 drive pressure to boost isn't high in fact is that not pretty efficient? its about a 1. 14:1 is still a good ratio correct? also you could be right about the low rail pressure and retarded injection timing at 9,000 psi the fuel wouldn't be atomized as well as if it were at say 23,000psi. Unburned fuel does show up as black smoke but i don't think its still trying to burn while its in the exhaust... however don't quote me on that. some one correct me if im wrong.

 

[JStieger]

i replaced the relief valve about a month ago and i quit running the ts unless i pull or dyno, the rail pressure is normal untill you run it over 3x3 tst only at 18000 psi, any more and the faster it falls

After reading the above I have some other thoughts in no particular order:



1) If this happens WITHOUT a pressure box, but with a new and seemingly perfectly functioning relief valve then I guess the worst case scenario is a failing CP3. It just can't keep up to the duration demands from the aggressive TST twins program. Just to sidetrack a bit, I remember reading on here last year about guys running the TST with injectors and the fuel rail was being run "dry" on the higher settings and HP was lost since the stock CP3 could not keep up. Now in your case the fuel rail is being run "dry" because the CP3 might be going out? And perhaps a combination of bad injector(s)? But heck I would really think that a bad injector would show up obviously in oil analyses. Also, wouldn't a bad CP3 put out some codes?



2) I get the same minimum fuel pressure @ 10-11 psi as you feeding my CP3 with whatever boxes I ran or even with these DD3 injectors and DD pressure box and did ~500 HP at BullyDog. I just have the Holley Blue @ 110 gph that replaced my lift pump. So I think your fuel supply is good!



3) Your friend was telling me that he had a bad CP3 (leaking fuel everywhere!) that he had replaced a while back. Aside from this, did he notice any drop in performance? Maybe you should wait til he's on day's off and "borrow" his CP3 for a test :-laf



4) I never thought about the reduced fuel pressure = retarded injection timing. Learn something new every day!



How hard are the CP3 to change out? Dealer only item? Cost? Say if a diesel shop (NOT Dale White!!) had a test loaner unit to try out?



Anyhow, hope this helps...

 

[scotty1]

I have been chasing a stumble for weeks now with a dealer helping out with the parts.

Initially the stumble would occur at 70 mph cruising... I would get the stumble and fuel pressure at that speed would go from 10-12 UP to 15 and I would have no pedal... I could not speed up but could feel a slow down when off the pedal. Changed the fuel filter and checked the Essex pump and all was good there. Left for Denver, stumbled whether I ran stock power or not.

Changed the fuel filter again in Denver, stumble was getting worse.

Pulled an Injector pump Comm code there.

Put my stock lift pump back on to trouble shoot... it was worse then the Essex, so the Essex went back on.

Had the stumble all the way back to Canada... every stumble would give me about 10-15 seconds of higher pressure and then another stumble and all returned to normal. Took it to the dealer and they replaced the pop off and pulled an ECM code now. They did a tsb on the ecm and I left. Next day it stumbled for 200 miles and on the way back it started dropping fuel pressure.

Gradually I lost pressure from 15 at idle down to 7. Moderate acceleration would net 0 pressure and a stumble and then eventualy it stalled a few times.



So back to the dealer where they found my injector lines where are all off torque spec and they felt that would solve the problem, nope.

They tested the injectors and all were fine.

Then they changed out the Essex with a new Holley Blue I had... same pressures... then they changed EVERYTHING out to the in tank pump DC has.

Same pressure... 7 but it did not drop as fast... but I can get the stumble. Probably improved it a bit by it being a pusher pump now. It should be 10 psi at idle though.

Then the tech felt it was the fuel filter and told the service mgr it was fixed... went and picked it up on Fri... of course the tech is gone. :-laf

Same problem.



I am taking it in tomorrow to diagnose the relief valve in the CP3 since it was the first code I had.



I had the Essex pump checked and its fine. The new Holley however was a dud. The most fuel flow out of all these pumps was 380 ML from the Essex.



I think its the CP3.



Scotty

 

[JStieger]

Scotty-



After reading all that - holy crap! Makes one want to swap a 12-valve in...



Not to change subjects, but what's an Essex pump? Overlooking your truck problems do you feel a need now for a pusher pump after your dealer swapped in the in-tank pump? I thought Holley finally overcame all of their dead-out-of-the-box pumps? I hope so because I have a brand new spare Holley under my back seat.

 

[scotty1]

Scotty-



After reading all that - holy crap! Makes one want to swap a 12-valve in...



Not to change subjects, but what's an Essex pump? Overlooking your truck problems do you feel a need now for a pusher pump after your dealer swapped in the in-tank pump? I thought Holley finally overcame all of their dead-out-of-the-box pumps? I hope so because I have a brand new spare Holley under my back seat.

Essex makes fuel pumps for many different companies and for some of the military in the USA. I have been testing a 160 gph pump for nearly 5 months now. I cannot comment on whether I need a different pump or an additional one with the in-tank yet as there is an issue that needs to be resolved with this stumble and loss of pressure with ALL the pumps.



7 psi at idle with the in-tank is what I was getting with the Essex and the stock pump on the back of the filter housing whereas I had 15 at idle with the Essex and 10 with the stock pump on the filter housing. The stock pump would go from 7 to 0 in seconds and the Essex would take longer... probably because of its ability to provide more fuel... a stronger pump. Since the in-tank pump from Dodge is only netting 7 psi as well, this is whats telling me something is relieving the pressure and dumping fuel back to the tank.



The tech mentioned that there was fuel flowing back in the return line but did not measure the flow.



Since the pop off valve in the CR is good and was replaced anyway and all the pumps are doing the same thing, it does mean something else is not right.



The Holley did produce 7 psi but hit 0 as fast or faster then the stock pump on the filter housing. It may be fine but it sure fell on its face fast while I am dealing with this issue. My old Holley I had on before the Essex ran well with 12 psi at idle... I have not yet tried it again.



I can tape up two valves per cylinder to get a 12 valve I guess. :-laf



Scotty