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Offline longball

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Lb7 fuel issue
« on: January 02, 2021, 10:35:36 PM »
Back in the summer I bought a 2004 LB7 from a coworker. 192k miles now and had new injectors fall of 2018 at roughly 185k miles (reputable, local, diesel shop). When I bought it there was a barely noticeable surge at idle. Fast forward to the morning following the first sub freezing night of the year and I had some white smoke on startup that lasted until I took off. No smoke after its warm or at stoplights like my other LB7 when the injectors went out. Throughout that first cold snap the surge got worse and it started surging while coasting to a stop. I ran a dose of HotShot secret though it with my usual XDP additive then changed the fuel filter and the symptoms went away. Today when changing oil I drained more than 2.5 gallons out of it. I having trouble understanding how it made enough oil to be obvious when draining it but I haven't had any white smoke for over a week now. Does it sound to y'all like a fpr problem or are the new injectors taking a dump? Trying to prepare myself before I have a chance to get the balance rates checked.

« Last Edit: January 02, 2021, 10:37:26 PM by longball »

Offline TexasRedNeck

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Re: Lb7 fuel issue
« Reply #1 on: January 03, 2021, 08:31:14 AM »
I don’t think FPR would cause it to make oil.

Usually it’s the injector body cracking or a line leaking


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Offline longball

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Lb7 fuel issue
« Reply #2 on: January 04, 2021, 01:58:16 PM »


Cant read return rates on this device and these readings were near operating temp.

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« Last Edit: January 04, 2021, 03:56:55 PM by longball »

Offline longball

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Lb7 fuel issue
« Reply #3 on: January 05, 2021, 12:41:35 PM »
After doing som reading I believe Tex is correct and there is an injector body cracked. It makes sense that a problem like that wouldn’t show up on balance rates. I’m wondering if it will show on return rates?


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« Last Edit: January 05, 2021, 12:42:47 PM by longball »

Offline KensAuto

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Re: Lb7 fuel issue
« Reply #4 on: January 06, 2021, 09:39:44 AM »
I'm going with a line connection at the injector, but only if you're 1000% sure it's making oil.
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Offline longball

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Re: Lb7 fuel issue
« Reply #5 on: January 06, 2021, 01:27:25 PM »
I’m sure. When I pulled the plug it was under pressure. Made a hug mess in the floor. I drained my 16qt catch pan before I started and and it was full after i drained everything out of the truck. Poured the contents of the catch pan in a 5 gallon bucket and it filled it to roughly 5” from the top.

Is there a way for a shop to diagnose which side of the motor it’s on or do they just have a 50/50 chance of guessing correctly?


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Offline KensAuto

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Re: Lb7 fuel issue
« Reply #6 on: January 06, 2021, 04:53:10 PM »
Lets say it's a cracked housing or bad copper return line washer. Either way I would want to look at both sides. If it's a washer, they all should be done.

6 or 7 years ago I had one in here for that issue. Another shop replaced injectors. It was burning coolant AND making fuel. They had reused the return washers, and used silicone to "glue" one of the cups in.

I don't work on that many dmaxes, but seems like I sure end up with the crappy ones.
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Offline longball

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Re: Lb7 fuel issue
« Reply #7 on: February 22, 2021, 02:23:24 PM »
I had a shop tear into the truck and reseal all of the lines. I’ve put maybe 1,500 miles on it since. I can’t be sure but the oil level does seem to be creeping up slightly. I’ll keep an eye on it and see what happens. It also still has a slight surge at idle and when on a long, steady grade, I can feel it surge a little. After the shop worked on it it did stop smoking at startup, and starts quickly (as it always has). The shop owner did say that if they have to tear into it again he’ll do the labor for free, which I feel is pretty good of him.


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Offline JR

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Re: Lb7 fuel issue
« Reply #8 on: February 24, 2021, 01:13:04 AM »
Do you have a lift pump? That could be the surge.

Unless it make lots of oil, is it worth the trouble? At least the shop is standing behind the work and the LB7 injectors are way easier to work on.
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Offline TexasRedNeck

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Re: Lb7 fuel issue
« Reply #9 on: February 24, 2021, 07:00:02 AM »
You might look at the voltage meter.  My alternator was fluctuating between 14-16 volts and that was causing some surging in sync with the voltage surge but I noticed it mostly at idle.  Replaced the alternator and surge was gone.


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Offline longball

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Re: Lb7 fuel issue
« Reply #10 on: February 24, 2021, 08:48:14 AM »
Do you have a lift pump? That could be the surge.

Unless it make lots of oil, is it worth the trouble? At least the shop is standing behind the work and the LB7 injectors are way easier to work on.
No lift pump. I don’t think any amount of fuel in the oil would be good and since he offered the labor I’ll try to get it fixed. That, and the surging is one of those things that will drive me bat Schiff crazy.


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Offline JR

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Re: Lb7 fuel issue
« Reply #11 on: February 24, 2021, 02:03:35 PM »
Lift could help with the surging and keep the CP3 happy.
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Offline longball

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Lb7 fuel issue
« Reply #12 on: February 24, 2021, 07:07:44 PM »
You might look at the voltage meter.  My alternator was fluctuating between 14-16 volts and that was causing some surging in sync with the voltage surge but I noticed it mostly at idle.  Replaced the alternator and surge was gone.


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The voltage on the dash holds steady. Out of curiosity I unplugged the alternator and started it. The surge seemed to lessen with it unplugged. I’ll have it tested and check the idlers and tensioner.


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Offline JR

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Re: Lb7 fuel issue
« Reply #13 on: February 24, 2021, 10:18:47 PM »
It won't get to a smooth voltage output till you get a few minutes of RPM on the alt. That might be part of the idle surge.
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Offline longball

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Re: Lb7 fuel issue
« Reply #14 on: February 24, 2021, 10:40:28 PM »
It won't get to a smooth voltage output till you get a few minutes of RPM on the alt. That might be part of the idle surge.
Can you say that again but as if you’re talking to a 8 year old child? I don’t know much about anything, but I know even less about electricity.


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Offline JR

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Re: Lb7 fuel issue
« Reply #15 on: February 24, 2021, 11:14:17 PM »
No biggie, these trucks now are common high pressure rail injection. The injectors get the signal via electricity. An alternator will not fully start to charge putting out the voltage and amps required (about 14v) until the motor has run a little, usually over 1000rpm for a few moments, it will not do that right at startup.

Our injectors use multiple pulses to make these engines run smooth. Sure the CP3 is giving you mechanical high pressure, but the injectors control the pulses (multiple pulses make the engine run smoother/quieter) but it requires full voltage which may not occur until the truck runs a little.

The CP3 sucks fuel from the tank which may not be solid (air bubbles) when first started. Using a lift pump helps with this and prolongs the CP3 life and can make the engine run smoother as it doesn't have to work as hard since it is just making pressure not sucking too. If you have little bubbles or air in the system the lift can help big with those too. Note, ALL diesel truck now have lift pumps from the factory, they are learning. CP3 also has an electronic pressure Reg and a relief valve that can mess up too. I just replaced both my relief valve and lift pump. Valve was soft (mechanical) and the lift had stopped working. I have 210000mi on the truck now and I run Wally 2 stroke oil in the fuel (1/2oz per gal) or biofuel sometimes. I also run a 10mic filter at the lift pump and a 2mic filter in the stock location. Just had the tranny built too (to 700hp) and rarely push it hard, but have my moments.

Now Ken or Sean (or anyone else) may know more than me but think this is very close to how it all works. Remember I am just a old retired cop who reads a lot.
« Last Edit: February 25, 2021, 10:11:17 PM by JR »
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Offline KensAuto

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Re: Lb7 fuel issue
« Reply #16 on: February 25, 2021, 07:58:05 PM »
Pretty dang smart for an old guy.^^^
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