Dreaded lb7 fuel leak.i can't find it

[Floridaedd]

Hello. I'm new to the forum my name is Edd.ive been reading the forum for a few days and finally had to ask for help.
My truck is a 2001 2500HD. It has 150k fuel injectors were replaced at 120k not warrantied.Missed it by 30 days. Fuel pump was replaced at 130 as was the fuel pressure regulator.
The other day I was on a 10 hour drive highway speeds 75mph. About half way through my trip my fuel level got low. Most likely the lowest I've ever run it.
About an hour after filling it up I started smelling Deisel which was reminiscent of my pressure regulator failure. I was able to physically watch my fuel gauge drop and knew I was leaking pretty good..I stopped for gas and to check it out. As suspected it was just streaming fuel.
I checked the oil and there was no fuel in the oil so I knew injectors were good. Now had there of been fuel in the oil I would have had it towed but decided to fill up and shoot for home about an hour away. Before I left the gas station I cracked the bleeder screw and pumped the fuel primer a few times. Don't know why I did it but had to try something.
The engine was running fine. Started fine and didn't smoke. There was no check engine message light ect.
Back on the highway the fuel gauge was holding steady for about 60 miles than it seemed to start dropping but not as fast as before.
I made it home and it was leaking but not like it was when I stopped for gas.
The next day I put in a new fuel filter thinking that may have boosted pressure if I sucked up trash when my fuel got so low earlier during my trip. The filter that was on there had about 1500 miles on it.
I started the truck and let it run for about 30 minutes after that I held the Rpms at 1500 for a few minutes. No leaks.
I drove less than a 1/8th of a mile and it was leaking again. The least amount it has leaked yet but still leaking.
So after studying many posts on this forum I tore into the motor. I should note I'm more than mechanically inclined but have never worked on my duramax.
So I have the ac compressor removed. Thermostat housing removed. Wire harness disconnected air intake tube removed.
I found a ton of insulation where a mouse had made a nice home in my engine valley. I checked all wires and nothing chewed. That was my first thought.There is what appears to be wetness from fuel in the bottom of the valley. My driver side valve cover has wetness from Deisel on what I would call the inside valley but is dry near the rear of the engine so it's not running down there.
I can not figure out where it is leaking. My only thought is the pump but I just don't know. Could it go out so quick since last being replaced?
Today is the last day I have to diagnose it ,wife says it's going to the shop tomorrow. If I can diagnose it I will attempt to repair it myself.
Went and looked at a new truck but not for 63k.
I'm sorry for the long post but was not sure how much of the circumstances were important and appreciate anyone who took the time to read it all.
Thanks Edd

[DmaxMaverick]

Welcome aboard, Edd!

Where, exactly, are you seeing the leaking fuel? How much fuel is leaking over what period of time? If it's a high pressure side leak, you may not see the source, as it can leak a lot and stream away from the source, leaving the source appearing dry. A high pressure leak will often leak more/less according to demand pressure, meaning the leak at idle can be significantly less (or not leak), and more under higher load. A low pressure side leak will generally leak with little change in volume at any RPM/load.

(Assuming OEM, no fuel system "upgrades")
The fuel system from the tank to the HP (High Pressure) fuel pump is 100% suction. The truck has no fuel lift pump to pressurize the system prior to the HP fuel pump. This leaves the lines from the tank to the HP fuel pump (including the filter assy) out of the diagnosis, IF the truck starts and runs fine with no filter priming help. The HP pump is not self-priming, and will fail to pump fuel once prime is lost. A high volume leak on the HP side will very likely cause any of several fuel pressure loss DTC's, and the SES lamp. If you have a large HP leak, large enough you can see a high volume, and especially if you can notice it on the fuel level gage, it should set a code and the SES lamp.

The fuel return circuit, on the other hand, can leak a large volume of fuel, and the PCM won't complain, as the circuit is open and (should be) unrestricted to the tank. A blocked fuel return line can cause leaks, as it is designed for relatively very low pressure. The 01/02 models are less sensitive to fuel pressure variations than later models, so much depends on the volume of fuel loss and the source.

Any of the codes (commonly P0087, P0093, P0193) associated with HP fuel will remain, once set, until cleared or 40 consecutive warm-up cycles w/o a failure. If you haven't/don't see the SES lamp, a large volume HP fuel leak is unlikely.

[Kennedy]

Mav did a great job of laying it out.

CP3's can leak in the valley. If so replace it. We've been doing more new than reman these days. The return plugging can happen, but it will typically leak internally. Had a customer friend with truck in on a fuel in oil complaint. OK 8 injectors simple done right? wrong. OK replace CP3 now we're done right? wrong. Turned out to be a plugged return orifice in the tank. Too much PSI apparently leaks in the CP3 and dumps to crankcase. I sure would have thought the Bosch would have incorporated a weep hole like a water pump on an ATV etc but no...

[Floridaedd]

Thank you for the replays. I definitely have more knowledge now than I did two days ago. From what I'm understanding the issue is most likely in the return line. Could I assume the pump and fuel pressure control are ok? I ended up taking the truck in yesterday as it's our only transportation and I could only play with it so long. I just could not find where it is leaking. I haven't heard back yet as to what they found. Told me to leave it apart before I took it in. Now they have to put it togather to run it to try to find the leak. More $$$.
It is totally stock and I've owned it since new.
Until I found this great forum I had no idea what kind of performance modes were being done to these trucks. I'm impressed. I'm an old school hot rod guy which is why I like the turbo Deisel but am amazed at what you guys are doing.
I will definitely visit the forum more and will post the findings of the shop hopping it may help someone else.
Thank you Edd

[More Power]

... I stopped for gas and to check it out. As suspected it was just streaming fuel....

To narrow it down a little, where did the leak appear to be the worst.

[Floridaedd]

It's hard to say exactly. I couldn't see In The valley because of the insulation. When I removed the water neck coolant got the valley wet. I did take some of the insulation a see if it would burn from having Deisel on it and it did some what. The insulation was dry except for the bottom inch of material. I pulled a piece of fabric looking material left by the mouse from the top side of the valve cover which I referred to as a valley and it burned immediately being soaked with fuel. How ever the "wet" looking area in the valley of the valve cover did not extend all of the way to the rearmost of the valve cover.
Sorry to sound so vague I should have taken a pic but didn't.
Thank you Edd

[johndoeLB7]

New to forum so thanks for having me.So as my title states im lost. I just replaced my cp3 pump on my 02 Dmax. cranks up great and runs GREAT! it fixed all the troubles i was having with long starts and no power. But much like Floridaedd i have a leak that i just CAN NOT FIND! Ive replaced all hoses twice and currently just 5 mins ago pulled the thing back out to check for any visible leaks and i got nothing, even hooked my air compressor to it to make it leak still nothing. As with Floridaedd it does not leak when idling only when im driving. PLEASE HELP! and sorry for misspelled words or any other screw ups im not very savy with these computers.

[johndoeLB7]

floridaedd what turned out to be your leak

[More Power]

Power-wash the engine valley area to remove most of the crud, let it completely dry, then dust the valley area with dry baby powder. Drive a few miles, then take a good look for any wetness in the valley area. You should be able to narrow down the area of the engine where the wetness is worst... then focus on that area till it leads you to the leak. Jim

[frank.williams741]

Mav did a great job of laying it out.

CP3's can leak in the valley. If so replace it. We've been doing more new than reman these days. The return plugging can happen, but it will typically leak internally. Had a customer friend with truck in on a fuel in oil complaint. OK 8 injectors simple done right? wrong. OK replace CP3 now we're done right? wrong. Turned out to be a plugged return orifice in the tank. Too much PSI apparently leaks in the CP3 and dumps to crankcase. I sure would have thought the Bosch would have incorporated a weep hole like a water pump on an ATV etc but no...

What is the plugged return orifice in the tank? I am working on my father-in-laws 03 Duramax with fuel in oil issue. Replaced all injectors, just replaced cp3 pump and same issue. It has put roughly 2 quarts in less than 50 miles. Also it has a slight hazy smoke at idle. Other than the fuel in oil issue it is a great running truck. He bought it used a few months ago with 107k miles and didn’t catch this issue. I want to see if the return orifice you refer to could be the culprit before we tear back into the motor. Thanks!

[Kennedy]

What is the plugged return orifice in the tank? I am working on my father-in-laws 03 Duramax with fuel in oil issue. Replaced all injectors, just replaced cp3 pump and same issue. It has put roughly 2 quarts in less than 50 miles. Also it has a slight hazy smoke at idle. Other than the fuel in oil issue it is a great running truck. He bought it used a few months ago with 107k miles and didn’t catch this issue. I want to see if the return orifice you refer to could be the culprit before we tear back into the motor. Thanks!


My first question is where did the pump and injectors come from? Haze at idle points towards injectors.

The plugged return line scenario is exceptionally rare. There should be nothing in the system large enough to block it. You can try blowing back through the return line and see if it blows bubbles in the tank. Just be sure to keep psi low.

[spongebob]

More Power ,

that’s how I would find a oil leak in my airplane..