Safe Rail Pressures

[Hellsteed]

I am studying the performance tune of another programmer I have and am astounded at the tuning... at 1,300rpm the air density commanded fuel pressure is ~20,000 and from 1,400rpm on the commanded pressure is 33,000! I ran this tune daily for a long time and didn't have any issues.

I'd like to know what y'all think is a good safe max in rail pressure? The above is from a 100hp tune (dyno'd). I've heard anywhere from 20,000psi to 26,000psi.

 

[IdahoRob]

Have you compared to stock? Stock is showing 18500+/-psi at 1400rpm at 55mm3. 33,000 is not achievable, so someone just maxed the table out. Log it, never will get anywhere near that.

Fuel system is designed to handle 26k and more.

I think the Cummins fprv will pop after 160mpa on most of the trucks, some have held more. If you have a plug, might want to watch the psi. Dmax Bosch common rails see way more than that without issues.

 

[mq105]

Look at D0784 under fuel pressure, parameters. That limits the max commanded RP regardless of what is in the tables. I'd say it's 160-165MPa.

 

[Hellsteed]

Have you compared to stock? Stock is showing 18500+/-psi at 1400rpm at 55mm3. 33,000 is not achievable, so someone just maxed the table out. Log it, never will get anywhere near that.

Fuel system is designed to handle 26k and more.

I think the Cummins fprv will pop after 160mpa on most of the trucks, some have held more. If you have a plug, might want to watch the psi. Dmax Bosch common rails see way more than that without issues.

Ok that makes more sense... sure the system can handle it but what kind of pressure can it handle sustained on a daily driven basis?

Look at D0784 under fuel pressure, parameters. That limits the max commanded RP regardless of what is in the tables. I'd say it's 160-165MPa.

Yes the stock limit is 160MPa but it's software limit is 250Mpa. I think I'll up mine to 190 and see how things go.

 

[IdahoRob]

Software and mechanical limits don't always agree.

Lets say your wife says don't spend more than 1,000 dollars tonight at the ***** bar, but your wallet only has 100.00 in it. You have a much bigger limit than your wallet can obtain. Just because you went out the door with big plans, mechanically you can only reach so far.

 

[Hellsteed]

I'd rather aim lower than what the hardware can handle since I don't feel like paying for another motor :doh:

I'm still learning the software and am doing it little by little.

 

[mq105]

What is the limit set in table D0784 on the programmer's tune you were studying? Also, what are the values in table B7511, low pressure limiter?

...
Yes the stock limit is 160MPa but it's software limit is 250Mpa. I think I'll up mine to 190 and see how things go.

 

[Hellsteed]

What is the limit set in table D0784 on the programmer's tune you were studying? Also, what are the values in table B7511, low pressure limiter?

B7511 is set to 126 across the board, D0784 is 160 max commanded which is strange unless they forgot to change that value/didn't want to and dump fuel into the motor.

I edited my tune and changed the max commanded pressure to 190 as well as a few other things were changed and the truck is running great so far, I just need to troubleshoot why I got the MAP out of range code this morning... I have a few ideas.

 

[mq105]

That 160 limit has kept your pressure at or below 23200psi even though the tables have values much higher. What that box tuner does is increase the pressure sooner.
The low pressure limiter pulls back volume under low a pressure condition to allow the pressure to climb back to the commanded value. Those limiters have helped keep your hard parts undamaged. 190 MPa is 27557 psi. That's quite high, especially for a DD.
What is your injection pump situation? Without a big modded single or duals, you won't be able to make/sustain 27k+ psi, and your volume will be cut to 126mm3 (limiter value).
I think a good amount of logging is in order.

 

[Hellsteed]

I'm currently running stock with the exception of an intake, elbow and exhaust. I logged a good bit this morning and my pressure never exceeded about 24,000 even at wide open. I do plan to keep logging the current settings for a week or so.

What would you suggest is a good pressure range for a DD?

 

[mq105]

Rob is a much better source than I am for that kind of info. In my opinion, though, 160 MPa is plenty in a stock, DD truck.
I think you need to log so you can see what commanded RP and actual RP are, and also what the volume and timing are. This way, you'll know if you're reaching the limits of your hardware.
For example, let's say at WOT your RP gauge stays at 24k psi. You may think that your CP3 can meet demand. However, the ECM, via programming, may be cutting volume in order to keep RP up. You need to be able to see several parameters to get the entire story.