LB7 Low rail pressure and other problems

[catman3126]

I got a 02 LB7 in for tuning and edge insight and after I put tunes in it I drove it and it would only build around 12K rail pressure so I flashed it back to stock to make sure that it wasn't anything with my tune and the same thing. 12 K I checked the cp3 and found it was returning fuel more then it should as I have done this test before and replaced CP3s and cured the problem. I get it put back together today and now it builds 17K but still will not hit 23K I also changed out the rail relief and no change. so I check the oil and had no reason to check it before and its up to the round weight about 6 inches above the full mark. so it must be leaking also under the vale cover. I guess the best way to tell is remove the valve covers and clean the lines, install and run it and see if I can see where the fuel is leaking? cant think of much else to do. one other thing the guy asked me if I would change his fuel filter so after I saw the rail pressure was that low I changed the fuel filter to make sure that wasn't causing an issue and found that the last time it had been changed the rubber top hat looking seal had been left behind and the gm filter would not screw on but the Napa filter that was on there would screw on just fine and I'm wondering if that would allow unfiltered fuel into the system being that the center seal on the Napa filter and the seal that was left behind had gotten doubled up. SO I gues the next step is too pull the valve covers and clean the lines install them and run it and look for leaks? anyone run into this or similar?

 

[Muff]

What we did to diagnose a lose of rail pressure was pull both upper valve covers, start the truck and command max rail with EFI or you could pull the regulator plug. Found #3 injector was cracked and was blowing fuel out under high rail pressure but not at idle. Good luck hope you get it figured out!

 

[DIESELMAFIAPER.LB7]

Sounds like bad injectors or leak from return lines tear it apart and out the hard lines back on and fire it up with covers off.. be ready for a damn mess if you haven't done it before

 

[onebaddmaxxx]

return side has nothing at all to do with fuel pressure. Unless its returning TOO MUCH FUEL only would it effect it. the truck doesn't care how it gets returned or what route it takes. I would use efi live and watch balance rates and command rate (mm3) and use a general consensus with the command rates and look for one high. Like if the engine is idling and you have 7 injectors at 38-40mm3 command, and the last one is at 55mm3, then likely i would cap off the higher commanded injector and go ahead and command rail psi at idle and see if it cured it.

Sounds like a body might have cracked.

 

[catman3126]

Ive had an 02' that came in with really low rail pressure, it would drop down to 4k when WOT and fall on it's face. So to say that return fuel has nothing to do with rail pressure I don't completely agree with. A new cp3 and it's still running great a year later. Even at idle commanded it would make 10k but once a demand for rail and higher pulse width and it just wouldn't keep up. It hasn't overfilled the crankcase yet, I will check the return for the injectors tomorrow but my experience with that issue is that they start hard. I had one a few weeks ago that would maintain rail pressure on a 2k pulse tune but would almost not start start when cranking. So on this one is it possible I have a small leak and a returning a little too much fuel issue? Idk kinda a head scratcher because if there was much of an internal leak the crank case would be full of fuel before too long and if it is returning a large amount of fuel shouldn't I have a hard start issue also?

 

[catman3126]

In the last picture I was commanding 160MPA and had the engine revved up to 3K and that's the highest I have seen the rail since I have had this truck at the shop.

 

[onebaddmaxxx]

Return does have something to do with frp, bit I'm saying if a return line on the injector/head is loose.....nothing is gonna be effected. That's why I said the truck doesn't care where the fuel goes from the return line. If one was leaking it would fill your base, but, not effect rail.

From my judgment, they look fine

Stupid question but have u changed the fuel filters ?

 

[S Phinney]

If you are dropping rail there can only be a few issues. Simplest of them would be a supply issue. Restrictions in tank or collapsed line etc... Secondly the pump being faulty via low pressure not sucking fuel or high pressure not pressuring fuel or pump returning fuel. Third the pressurized fuel is bleeding off into the return side via injector return or FRP blow off malfunctioning. Injector could be damaged and leaking the crankcase under high pressure as well. My bet is that it will be an injector causing the problem.

 

[zf>allison]

If you are dropping rail there can only be a few issues. Simplest of them would be a supply issue. Restrictions in tank or collapsed line etc... Secondly the pump being faulty via low pressure not sucking fuel or high pressure not pressuring fuel or pump returning fuel. Third the pressurized fuel is bleeding off into the return side via injector return or FRP blow off malfunctioning. Injector could be damaged and leaking the crankcase under high pressure as well. My bet is that it will be an injector causing the problem.

He could also be experiencing more than one of these problems. I could see how that might get confusing.

 

[catman3126]

Return does have something to do with frp, bit I'm saying if a return line on the injector/head is loose.....nothing is gonna be effected. That's why I said the truck doesn't care where the fuel goes from the return line. If one was leaking it would fill your base, but, not effect rail.

From my judgment, they look fine

Stupid question but have u changed the fuel filters ?

Yes the filter is new I've been a diesel mech for 15+ years and this is always the first thing I check when a low power or low pressure issue comes up. Did you read the part in my first post about the seal getting left behind on the old filter and it didn't come out of the napa filter that was on there and the New delco filter wouldn't screw on because the seal had been left there.

I agree with your statement that the truck doesn't care where the fuel goes what I'm saying is if the injectors were returning a high enough rate of fuel to cause a low rail pressure issue then it should have a hard start issue especially when hot. also If I had a leak big enough to cause this low rail pressure issue the crankcase should be over flowing by now? to me the balance rates look fair and the pulse width isn't out of spec either.

 

[catman3126]

Cracked injector. the new pump making more pressure must have made the leak worse. it started shooting fuel out the dipstick today and I could smell it when Idling today. I didn't drive it enough yesterday to overflow the crankcase yesterday. he said it was giving of that diesel smell at Christmas when he drove it last. and he only lives a couple miles from the shop so apparently it was slightly leaking before hand.