Fuel Rail Pressure Affected By Temperature

[JohnnieBishop]

When the temp is 45 or below rail pressure will not get any higher than 12,000 PSI but when the engine starts to warm up the CP3 will rise consistently and after it does the pump will pump whatever you want it too. Fuel pressure is a consistent 18 PSI. The CP3 is an Industrial Injection Reman 85% over. Any help will be greatly appreciated. Thanks.

 

[cerberusiam]

Cold engine, cold fuel, and high pressures are a recipe for problems. Could just be the fuel system protecting itself, a problem with the rail pressure sensor, an FCA problem, or a problem with the CP-3 since it is an aftermarket. Try unpugging the FCA when at a cold and see if the RP will then max out at whatever your year of truck is.

Any other mods that could contribute? Specs on truck?

 

[JohnnieBishop]

The truck is an 03 5.9 changed the fca, no change, changed the rail sensor as well, no change, and when it is above say 50 outside it will run whatever pressure you want it to. Give it WOT and it will hold a constant 25,000 PSI. What else do you need to know?

 

[cerberusiam]

When it is cold and you unplug the FCA will the rial pressure max out at 20k psi? That will tell you if it is being limited by the software or it is a mechanical problem.

The only other thing I can think of that would cause it to be low cold would injector cross over tubes. As they warm they seal better. Have changed out injectors? Chnaged cross over tubes?

You might have to get it on a scanner that can read actual rail pressure vs demanded to see if there is a discrepency.

 

[JohnnieBishop]

Have changed both injector and cross over tubes both. The injectors are Industrial Injection 125 HP and the cross over tubes are the superseded ones from Mopar which actually come out of a 6.7L and are much larger than stock. I don't think it is gonna get cold like that here any time soon now since I'm in SC.

 

[JJPage]

Is it standard practice to use 6.7 cross tubes on a 5.9 ? And if they are larger than the 5.9's, that means more volume has to be made available before max pressure is achieved...kind of like TC's enlarged rails, makes me wonder what affects that could cause. I have not heard of this practice, but I am way behind on any of the current mods being performed.

As far as holding a constant 25k at WOT, mine does that too, but at any temp, that's peculiar that yours will not go above 12k@45*. Maybe TC will have some insight on this, since he has done extensive research and mods on the rails. Jess

 

[JohnnieBishop]

Yea the cross over tubes that you buy from the dealership now are correct and come from a 6.7L. The stock cross over tubes are .072 and the ones you buy now are .116 in diameter. They may not look right when you get them but they fit fine no problem.

 

[cerberusiam]

That is your problem, the 6.7 cross over tubes are not seating correctly until the engine warms up. Not a good idea using the newer tubes with an older injector, pretty sure bevels are slightly different between old style and new style injector which makes it hard ot get a seal on on the injector. You might go back and re-TQ all of them to 42 ft\lbs and see it that helps.

My guess is you got II reman injectors with the larger tips? Probably older style injector and are problematic with the new style tubes.

 

[JohnnieBishop]

The only problem is you can't buy the older style connector tubes any more, and the connector tubes are torqued to 37 ft. lb. which is factory spec. I'm going to go back and make sure the connector tubes are seated correctly with the injectors like it says from the factory and see if that helps. I do work at a dealership and the diesel tech says that I need to do that before I do anything else. Also the other day he replaced all 6 connector tubes and 2 injectors in a customers truck, which was a 2005 5.9L, and the truck ran fine no problems.

 

[cerberusiam]

Incorrrect, the 5.9 injector tubes are available almost everywhere that carries Bosch parts. Bosch stills makes and reccomends the 5.9 tubes with 5.9 injectors. Cummins superceded the number becasue they do not build 5.9 engines anymore.

The 6.7 tubes are known quantity in causing rail pressure issues, not seating corectly, etc. Use the 5.9 tubes with the 5.9 injectors or you run the risk of issues. The 6.7 tubes gain you nothing anyway, no reason to roll the dice.

The factory spec on tube TQ has changed 42 ft\lbs years ago. The 37 was an old spec that has been superceded. If you try to TQ the 6.7 style tubes to 37 you will not get a good seal for exactly the reasons I explained, they do NOT fit the older injectoprs correctly and they need more crush to work correctly.

The differences between running ok and running correctly are myriad. Yours runs ok but you see RP problems that should not be there. Did you do the exact same troubleshooting on the other vehicle? Were the injectors the same as you used and everything installed the same? You can't make a fair comparison until the answer is yes to all of those questions.

By all means, re-TQ the cross over tubes and take them to 42 ft\lbs, a lot easier and cheaper than replacing them. If that doesn't help then you have an answer. Good luck with it.

 

[JStieger]

The factory spec on tube TQ has changed 42 ft\lbs years ago. The 37 was an old spec that has been superceded. If you try to TQ the 6.7 style tubes to 37 you will not get a good seal for exactly the reasons I explained, they do NOT fit the older injectoprs correctly and they need more crush to work correctly.

Not doubting you... I have not been able to find any proof of this new torque spec anywhere online, but have only seen 37 consistently in 6.7 service manuals that I could find. In what year did this spec change? Can you post an updated service bulletin?

I'm fighting rail pressure issues now that are pointing to a faulty FCA (or two :-laf). P0088 code and my lower CP3's FCA sporadically doesn't cycle / click when keyed off. At the same time I recently installed new injectors with the only change being 6.7 tubes. My searches on the various enthusiast forums in the past week found people have posted torque specs 37, 41, 42, and 44 with 37 being the only one backed up. I used 37. The rail pressure issues started a month after the injector install hence my reluctance to totally tie the issue to the tubes.

When the temp is 45 or below rail pressure will not get any higher than 12,000 PSI but when the engine starts to warm up the CP3 will rise consistently and after it does the pump will pump whatever you want it too. Fuel pressure is a consistent 18 PSI. The CP3 is an Industrial Injection Reman 85% over. Any help will be greatly appreciated. Thanks.

I have a 2003 and I see the same when the temps are similar, but as soon as the IAT start increasing I can achieve the max RP at WOT. At cruise I'll see +/- 3000 psi between cold and hot IAT. It's annoying when troubleshooting problems at around these temperatures. It's even more annoying that this happens with "custom" UDC programming.

 

[cerberusiam]

The 42 TQ spec came out of Cummins service division. Whether this is codified TSB or just a service rec from their experience I am not clear on. That rec along with using loctite on the cross over tube hold down and light oil on the injector line threads are frequently not officially sanctioned but used to solve problems in the field. There are frequent discrpepencies between the official published specs and what is actually used by the people in the field. Use the info as you will.

 

[JJPage]

The rail pressure issues started a month after the injector install hence my reluctance to totally tie the issue to the tubes.

I would be reluctant to blame the tubes but only if they still are torqued properly, whether that's 37 or 42 lbs. From watching your post's over the years, I am certain you did your own injector install. I had to re-torque mine after a relatively short period of time, like 2500 miles, after I allowed a diesel shop in Spokane install new tips in the month of January(had no garage to do myself).

I would quickly check the torque on the cross tube lock nuts, just to eliminate that possibility. Still trying to understand, is the practice of using 6.7 cross tubes on a 5.9 an excepted practice today? Jess

 

[cerberusiam]

Still trying to understand, is the practice of using 6.7 cross tubes on a 5.9 an excepted practice today? Jess

Only if you listen to Dodge and want the potential for issues. There are differences between the tubes that can and will throw a monkey wrench into the sealing and rail pressure. Where the source of the issue is depends a lot on an individual truck and how it is setup so there are no concrete rules. The tubes work for a lot of people, don't work for others. The question comes down to why use them when Bosch still makes and recommends the 5.9 tubes.

 

[AH64ID]

What are you running for tuning?

 

[TCDiesel]

Yep..I don't recommend 6.7 tubes in the 5.9. The 6.7 tubes in 5.9 are NOT forgiving...You need absolute perfect matting surface or they will leak, Re-TQ tubes to 42, if that does not resolve the Problem You will need to send the pump out to be check, Here's why if the pump is good the injectors will need to be replace,the LV may also be to culprit. I would replace the LV 1st, they all leak after time and miles.

 

[JStieger]

I would be reluctant to blame the tubes but only if they still are torqued properly, whether that's 37 or 42 lbs. From watching your post's over the years, I am certain you did your own injector install. I had to re-torque mine after a relatively short period of time, like 2500 miles, after I allowed a diesel shop in Spokane install new tips in the month of January(had no garage to do myself).

I would quickly check the torque on the cross tube lock nuts, just to eliminate that possibility. Still trying to understand, is the practice of using 6.7 cross tubes on a 5.9 an excepted practice today? Jess

To follow up...

Retorqued 6.7 tubes to 42 ft-lbs - same issues
Installed old 5.9 tubes at 37 ft-lbs - same issues
Swapped around FCA's - same issues
Swapped rail pressure sensor - same issues
Bypassed second CP3 and dual cp3 controller - no issues
Replaced dual CP3 controller = problem solved
Conclusion: 6.7 tubes work with 5.9 injectors @ 37 ft-lbs connector tube torque

 

[JJPage]

Thanks for the update. Always the unexpected....what kind of dual CP3 controller?

 

[JStieger]

Thanks for the update. Always the unexpected....what kind of dual CP3 controller?

It was a Relentless Diesel controller. I put 80,000 miles on it. I replaced with an ATS controller.