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Low rail pressure

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03 5.9 California truck

fuel problem

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A friend has an 03 that runs poorly. Checked rail pressure. Around 4000 at idle, but with the FCA unplugged it still idles at less than 10,000. I was expecting 18-20,000lbs. Checked relief, swapped out the rail pressure sensor, no change. He has an Edge, but all tests were performed with it totally removed. Did a cyl kill test, and found 2 weak injectors. Could a high return flow cause low rail pressure at idle? Also cranks for about a 5 count before firing. One of the symptoms is poor power and MIL after a long, hard pull with his 5vr. Thanks, Jeff.
 
Yep, sounds like it is time for injectors. A high return flow will mess with a lot of things and create a CEL.
 
It's possible that it could be that some lines are loose under the valve cover. My "real" mechanic discovered this while chasing down a low rail issue a few weeks ago on my 07.5. He changed the Cp3 out with another used one and didn't get the gain that he was expecting and when he went to do the line block test, he noticed that they were loose and as he tightened each one up, the rail pressure got higher and higher. Turns out that the dealership that did my head gasket last spring didn't torque the nut!!! Man I am getting so sick of poor workmanship! Would be nice if you issue turns out to be a cheap fix. Just one thing to check. This made the truck run better than it ever has. I may have described this wrong, but whatever it was it was allowing too much return flow.
 
I am tuning for a guy with the same symptoms, and same parts replaced. His new injectors are in the mail now. He talked with Todd at T&C and the conclusion was very high return flow.
 
4000 psi at idle for 03/04,s is from my observation, normal, they tend to run lower idle pressure than the later HPCR's.
Mpaulson, loose torque on the cross tube locknuts will definitely cause high fuel return rate, and is a very common problem with these trucks.
 
Here is the stock rail pressure table. Idle should be around 5,000. There are things that effect this, coolant, IAT, etc.. but that's close.

Rail Pressure.jpg


Rail Pressure.jpg
 
What he said. A good rail pressure on the 03-04 truck should be around 5k psi when warm to operating temp. If it is not, something is causing it to be high\low.
 
I'm still a little puzzled about the fact that unplugging the FCA didn't cause a rattle or any roughness, and didn't give max rail pressure.
 
Thanks guys. I guess I was on the right track, but I wanted other opinions and this is the best place to go for them. I don't like wasting other people's money if I can avoid it.
 
4000 psi at idle for 03/04,s is from my observation, normal, they tend to run lower idle pressure than the later HPCR's.
Mpaulson, loose torque on the cross tube locknuts will definitely cause high fuel return rate, and is a very common problem with these trucks.

Here is the stock rail pressure table. Idle should be around 5,000. There are things that effect this, coolant, IAT, etc.. but that's close.

View attachment 88547

What he said. A good rail pressure on the 03-04 truck should be around 5k psi when warm to operating temp. If it is not, something is causing it to be high\low.
I'm basing what I stated from my observation of my Dipricol RP gauge on my 03...you want to beat me down with facts..take aim :-laf:-laf.

Where's the chart for the 04.5+ years, does their rp not run higher than the 03/04's throughout their rpm's? That was kinda my point, but I missed the mark...my gauge usually reads 7k idle at start up, when warm it reads 4+ to 5k, is that more suitable for you two forum policeman :D ???

I'll try to be more accurate in the future, lest I am looking to be fed upon...Geeesh!

Jess
 
Here you go. Oo_Oo.

pressure.jpg



My Pricol RP gauge was never as accurate as I thought it should have been, had to unplug/plug it in often while driving to reset it. I even replaced it a few times under warranty, they all did it.

pressure.jpg
 
I'm basing what I stated from my observation of my Dipricol RP gauge on my 03...you want to beat me down with facts..take aim :-laf:-laf.

Therein lies the problem, the gauge and calibration to the factory sensor. I don't think any of the gauges read exactly correct based on the factory set points. Some seem closer than others but not perfectly accurate.

A couple hundred psi deviation is probably nothing to worry about, a 1000 psi is either a guage issue or a mechanical issue. All you can really do is look at commanded vs actual with a scan tool and HOPE the sensor is good.
 
How do I read the charts, I believe the top row to be RPM, the left side..TPS?, requested/commanded pressure? Sure seems to be a heck of a difference in ramp up pressure between the two, can I assume this was to meet emissions with the later CR's?

With your new pistons, do you tend to run with the 03/04 pressures, or did you keep closer to the original pressures your ecm was programmed with? I can see where UDC is a very useful and fun tool, I am certain my truck is sold so I am not going to play with it now, wouldn't be fair to the new owner if something went south. However it must be rewarding, being able to make and see changes, then make adjustments to fine tune, Sorry I missed out on that!

Jess
 
Left is approximate engine load.

I run in between the two. There are places I run more than both, but generally I am lower than 04.5-07 and higher than 03-04.
 
??? Another reason I have not plugged my dongle into my PC :confused: .

The ECM is trying to meet a certain fueling demand, or load. 100% load is 140mm3 of fuel per main injection event. Once the ECM determines how much fuel it needs, based on throttle position, rpms, boost, etc it looks to the rail pressure table for desired pressure. So if you where WOT at 2000 rpms, on you 03 with stock tuning) it would want 15954 psi. 50% throttle would be approx 70mm3 or 50% load.

Clear as mud? That's the cliffs notes, there are other factors but the concept is the same.
 
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