Spiking rail pressure at start up

[BMeier]

Sometimes when I start my pickup the engine would hammer and the rail pressure will be running up to 26k-27k psi and log a high rail pressure input code, but smooth out after a couple seconds and be back down to 5500 psi. This has happened quite a few times, more so at cold start up, 10-40 deg F. I tried a new FCA, it worked for a while now this morning when it was 20 deg F, right when it started the engine hammered for a second and smoothened out after logging a high rail pressure input code. I am starting to wonder if the CP3 pump is the problem. I am also worried about damaging the rail pressure relief because of the high pressure at start up. It only does it at the initial start up and never bothers once running. I have been running a 2 micron fuel filter ever since new and have had two stock lift pumps fail, but now have a FASS DDRP pump installed and the problem still occurs.

Anyone have some ideas I can try?

Thanks.

 

[JJPage]

I would double check the wiring and plug to the FCA, it is behaving as if it is losing contact momentarily. Maybe just buy a new connector/FCA harness?



Why just on start up... .



I doubt you will hurt the Rail relief valve with a slight bounce to 26k for a moment, but that is what will happen if you unplug the fca while the engine is running, That's why I was thinking bad connection.

 

[BMeier]

I checked the connector and found no problems. I wiggled the wire while it was running and could not get it to act up. Of course I haven't been able to get it to act up again for the last 3 days. I think I have a ghost Unless for some reason the ecm is not sending the signal right away. I think I am gonna make a break out harness and check the pwm signal at start up and see if it acts up again.

 

[Joseph Donnelly]

Do you have a pressure box/program on the truck?

 

[BMeier]

I have a Banks 6 gun in, but I had unplugged it and the problem still happen with the programmer out.

 

[AH64ID]

Seems like the FCA is sticking wide open after the start. .

What year? How many mile? Which 2um filter?

 

[BMeier]

I did try a FCA thinking that was the problem also, but the problem still occured. My truck is an '03 with 86,000 miles on it. I am running a 1R-0751 cat fuel filter.

Sorry, I cant figure out how to put my pickup description with my posts.

 

[AH64ID]

Go to User Control Panel under Discussion Forums at the top, then Edit Signature on the left side of the screen.

 

[BMeier]

Thanks, I got it figured out.

 

[TCDiesel]

One concern is the Fass Pressure ,on factory CP3 excessive pressure (feed) will over come some springs and valves in the CP3. it generally takes time for this to develop. any pressure past 15 psi on factory parts will cause premature wear. The CP3 only concern is volume at 5 psi with 30gph Minimum the unit could live its entire life at this pressure and volume. Add pressure for some gain (HP) volume at adequate pressure is the sweet spot.

 

[BMeier]

I did have this problem with the stock lift pump before I put the FASS pump on. I was concered about the pump pressure though, it runs at 17-18 psi. Is there a way to back off the pressure or put some kind of bypass in?

 

[TCDiesel]

Yes, Fass has a low pressure spring,or check with II.

 

[JJPage]

One concern is the Fass Pressure ,on factory CP3 excessive pressure (feed) will over come some springs and valves in the CP3. it generally takes time for this to develop. any pressure past 15 psi on factory parts will cause premature wear. The CP3 only concern is volume at 5 psi with 30gph Minimum the unit could live its entire life at this pressure and volume. Add pressure for some gain (HP) volume at adequate pressure is the sweet spot.

BBRam on Cummins Forum is claiming 60psi to his CP3? At 30psi, I blew the lid off the factory fuel filter housing... .



How much pressure before you overcome the cascade valve? This really is a volume vs pressure balance... yes

 

[cerberusiam]

How much pressure before you overcome the cascade valve? This really is a volume vs pressure balance... yes

Factory COV fully opens at 75 psi and just routes excess fuel back to the tank. Typical performance upgrade is up the case pressure to 120-125 psi to flow more fuel. That along with a higher volume gear pump is the typicla bag-of-parts upgrade.



The gera pump is going to flow only so much fuel no matter the pressure to the front end of it. When you run out flow internally rail pressure will drop even its at 60 psi at the inlet.



You run 60 psi to the CP3 inlet if you bypass the OE cannister and it won't hurt a thing internally to the CP3. Case pressure will still be 75 psi. There are really no springs to effect with front loaded pressure.



From the OP's description its probably the internal pump pieces that control fuel to the high pressure cylinders. The usual result when they go bad or stick is the pump blows the plugs out of it and dumps fuel everywhere.



If everything else has been replaced then its probably time for a new CP3.

 

[TCDiesel]

If You have excessive pressure to the Inlet with Lack of Proper volume it will overcome factory springs. Case In point I presently have a customer with up/down Rpms when cold when in gear,He has our Stage 3 Wild pump, the COV and FCA are modded for that pump,I mistakenly install a factory COV witch caused the problem,But when he lower the pressure it was fine, So after I felt stupid and sent the correct COV it was fine. with so many different pump mods out their its very important to pick the correct builder. If I may point out the most significant ingredient to CP3s is volume,Volume must equal the Pump, what ever its modded too.

 

[cerberusiam]

If You have excessive pressure to the Inlet with Lack of Proper volume it will overcome factory springs.

I am not buying that. In essence what your saying is pressure to the gear rotor pump is going to over pressure the case and wear on the springs cuz thats the only place there are any springs.



Now, you didn't specify what pressure caused the problem and what supposedly solved the problem. For argument sakes let say it was 30 psi. Knowing the stock COV is going to maintain pressure at 75 psi it does not compute the case pressure is going to be more than 75 psi.



The other things that is wrong here is you WILL have more volume with more pressure. Its a given. Lowering the pressure will lower the volume. How much is dependent on line size.



On a highly modded pump swapping out a key piece like the COV is going to introduce some weird behaviour. The FCA is modded to expect higher pressures and flow so when its not there it is over compensating trying to maintain correct flow without it. Lower the input flow and the FCA probably just flips wide open to maintain demanded rail pressure.



What you describe tracks pretty well with observed behaviour when volume to the high pressure circuits is borderline. The stock COV was bypassing too much fuel and bouncing the case pressure the FCA needed. Lower the volume, the case pressure stabilizes and the FCA doesn't have to correct as much.

 

[TCDiesel]

Cerberusiam I rarely if ever Quote from your replies, and I am not going to debate on the Forum,I received a memo from Bosch about HPCR ( I can't remember who forward it to Me) on direct pressure it broke down all the CR pumps. Excessive inlet pressure will over come internal component's and will cause failure. Answer this question what purpose does excessive pressure serve..... Here's my answer... . so the popular pump companies can promote their high pressure pumps (lift Pumps). Maybe if they would have invested some resources into developing new products they would not... . sheep off the precipice. How many sensors to measure pressure on the Dodge 5. 9. CR 1. Why did Cummins,Bosch,Dodge or some feel it was not necessary to measure the lift pressure?What happens to the CP3 when volume is not adequate? what pressure is adequate?The CP3 is one of the most simplest pumps and at the same time is one of the most robust designed ever,if adequate fuel and maintenance the internal component's should last 1000s of hrs and 500k plus regardless how you mod it within its original characteristics .

 

[cerberusiam]

Twest, why NOT debate the subject in the foums? Isn't that what they are for?



Isn't this the perfect venue and perfect thread to debate these ideas, mods, etc? Why not lay it out there and state your findings and facts as a support for your opinions? Obviously, if you don't want to reveal what would be proprietary info on how your rmodding the pumps thats fine, but, its easy enough to discuss at least the supply pressure and its potential pros\cons without getting into other areas.



Like I said, where and exactly how can excess pressure influence internal parts thru a gear rotor pump? The parts breakdowns and diagrams I have seen to date do not show this. If you have something please post it up and help me understand where the reasoning for this is coming from. I want to know, and am sure a lot of others want to know, if they are systematically destroying their CP3 by running X pressure to the inlet.



You say you have a memo from Bosch stating excess pressure will wear internal parts, what exactly prompted this memo and where is the technical justification for it? Thnink about if for a minute, this is from the same company that STILL cannot acknowledge the VP-44 was a less than robust design. Bosch is a large company and by nature self serving, just because they say something doesn't mean I will automatically believe it. Especially when it flies in the face of observed phenomena.



I am NOT knocking your opinions but you have made some statements that run contrary to experience. I would like a little more info on where they are coming from before I change my mind about such a critical area. Not looking for a flame war just a good healthy discussion of possibilities.





Fair enough?

 

[cerberusiam]

Answer this question what purpose does excessive pressure serve..... Here's my answer... . so the popular pump companies can promote their high pressure pumps (lift Pumps).

You yourself run and promote a multiple pump setup that, correct me if I am wrong, is running more than the stock pressures, correct? You know the answer as well as I do, pressure equates to volume. Volume has been the problem from day 1 on the CR engines and since we don't have an easy way to measure volume we use pressure to do that. Simple fact is if the gauge reads 30 psi we know we have adequate volume for most needs.



The second reason why is to stop cavitation on the gear rotor pump and beating the wear plates and end of the IP crankshaft up. Adequate pressure stops the inherent bounce on the gears when the supply pressure is inadequate or bouncing.

Why did Cummins,Bosch,Dodge or some feel it was not necessary to measure the lift pressure?

Might as well ask why no pyro, to boost gauge, etc. The dirty little secret is too much info will casue them more problems. Period. Compare the cost of the light duty trucks to the medium and heavy duty and what you really get in a lot of cases and thats apparent. Bosch developed the system, Cummins installed it because there are really no other options for emissions, and Dodge just bought the package and did their minimal engineering provisioning for cost purposes.

What happens to the CP3 when volume is not adequate? what pressure is adequate?

Those are the $64 questions, eh? Its pretty obvious what happens when volume is inadequate to the CP3. The supply question has multiple parameters and it is not a hard a nd fast rule. Each person needs to assess that from their build to answer it correctly.

 

[TCDiesel]

Cavitation. . Should never be a problem with a negative feed Pump. Pressure and Volume are totally unrelated in Fluid mechanics. Your answer are correct,although common. .