Rail pressure problem

duck_04

duck_04

resident quack
Joined
Oct 19, 2010
Messages
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My truck seems to be a little low on RP at cruising speeds. At interstate speeds(70+), my pressure is only reading 8-10k on the gauge.

The truck is an early 04 with an Evil Twin kit(2 stock cummins pumps), airdog 200 set at 20psi, and new injectors with Bosch Motorsports nozzles(100hp). I run smarty TNT for tuning, and an edge EZ for pressure. With the edge hooked up, my pressure is still low while cruising, but if I call on it my gauge will slap 26k instantly. With the edge unhooked and running just the smarty with RP on 4, it struggles to hit 20k at WOT.

With this pump kit, I run the RP sensor in the back of the top pump. Any ideas on what may be causing this? Heres a short video.

http://i868.photobucket.com/albums/ab247/Matthew_Wood/96c4e04f.mp4
 
Any particular reason your battery voltage is non existant??

I would suggest a scanner instead of gauge...to determine actual rail pressure.

If you have access to one.
 
Its been like that for over a year. I suspect its the TIPM, just havent had the extra cash to get a new one. It still charges, so I havent been overly concerned about it.

I'll try to get ahold of a scanner. Due to my work schedule and work load of shops with them, its kind of difficult to.
 
I know that the Early CR's DO run lower pressure than the current ones, but I dont have one at my disposal to test on...has your pressure always been like this or is this a new situation?
 
Kinda new. Seems like one day its fine and the next it isnt. Its kinda random.
 
Then I would look for a scanner...I have yet to find a rail pressure gauge that is 100% accurate all the time.
 
These 16 hour days make it hard for me to get anything done. I'll try to get a scanner put on it in a day or two.
 
Mine does the same thing, it's temp dependent. Seems like 40 degrees is where it starts to cut rp noticeably. I've been told its normal on 03-04's.
 
94ttss said:
Mine does the same thing, it's temp dependent. Seems like 40 degrees is where it starts to cut rp noticeably. I've been told its normal on 03-04's.
Click to expand...

I agree. Mine does it as well.
 
I was just coming into this section of the forum to post a similar question.

I've noticed over the past month or so that my RP seems down as well. Cruising at 65-70 it's about 7-8k. FP is holding steady at 9-10psi.

Why does temp cut the pressure down so much?
 
I am also curious why cooler temps would have a direct effect on pressure.
 
There might be a temp vs rail pressure multiplier table within the ECM that essentially pulls pressure based on IAT.
 
2007 5.9 said:
There might be a temp vs rail pressure multiplier table within the ECM that essentially pulls pressure based on IAT.
Click to expand...

Thats a good point, it very well may be.

I just don't remember it dropping so low like this last winter. Then again I hardly ever drive it during winter, I may have just over looked it.

I even adjusted my Smarty to add pressure, thinking it would up my RP some but no dice there.

Just curious here, if I were to run a CP3 "Bag Of Parts" would that keep RP bumped up at all times some?
 
If it is a ECM table that regulates pressure based on temp...then nothing short of fooling the ECM with a pressure box can increase pressure above ECM desired.
 
Nate-03 D said:
Thats a good point, it very well may be.

I just don't remember it dropping so low like this last winter. Then again I hardly ever drive it during winter, I may have just over looked it.

I even adjusted my Smarty to add pressure, thinking it would up my RP some but no dice there.

Just curious here, if I were to run a CP3 "Bag Of Parts" would that keep RP bumped up at all times some?
Click to expand...

I doubt it because I was having the same problem after I put my new pump on and its 120% over. But I increased rp to 3 and I decreased timing from 4 to 3 and that fixed the proroblem. I'm not really sure y that fixed the problem because I'm running a dual feedline without a relief valve but if I peg it now I can't get it to 30000 before I let off.
 
No matter what IP you have or pump mods it will only deliver whats being commanded at a certain RPM/load. Ill have to look for a multiplier when i get home. I dont believe there is a direct acting table but may very well be an indirect table.
 
There isint a multiplier table for the Can trucks...so far.

Maybe one that hasn't been found...I'll ask Ross to check the code on the 06+ ECM to see if it exists.
 
It is definately IAT that regulates it. I had my grid heater hooked to a push button and if I cruise on level ground steady throttle in sub 40 degree weather and hold the button I can watch the rp rise as IAT increases. Let off the button and it falls again.
 
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