Health Check on fuel system - Chevy and GMC Duramax Diesel Forum
01-04.5 LB7 Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #1 of 7 (permalink) Old 10-01-2019, 09:31 AM Thread Starter
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Health Check on fuel system

Okay folks so I’m still learning daily on my LB7 so please forgive me if I don’t use all correct terminology! Recently I noticed that on light acceleration if the truck is making under 5psi I can hear a faint clatter / knock and also does it if I go WOT and let off (for literally 1 second) I immediately assumed I had an injector letting go although I have no haze at all and the truck runs really strong/well. So I checked balance rates and from what I can tell everything seems to be perfect but I would love to get a second opinion. After checking I’m wondering if what I’m hearing is possibly valve lash out of adjustment? The truck has roughly 300k on it and I know the injectors we’re done at a dealer @ 220k prior to me purchasing it.
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post #2 of 7 (permalink) Old 10-01-2019, 09:43 AM Thread Starter
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I didn’t realize the pictures would become so distorted so I will list the values here.

Main Inj. timing = -3.0
Inj 1 Command = .31ms
Inj 2 Command = .32ms
Inj 3 Command = .40ms
Inj 4 Command = .43ms
Inj 5 Command = .35ms
Inj 6 Command = .38ms
Inj 7 Command = .29ms
Inj 8 Command = .29ms


Balance Rates

Inj 1 = -1.3
Inj 2 = -1.0
Inj 3 = 1.5
Inj 4 = 3.0
Inj 5 = 0.4
Inj 6 = 1.4
Inj 7 = -2.0
Inj 8 = -2.0
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post #3 of 7 (permalink) Old 10-01-2019, 10:42 AM
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Some thoughts...

Regarding just the valve lash part of your question, I believe I have read here GMC did not specify a recheck period on valve adjustment (someone help me out here) but I can say when I did my injectors at around 155k last year all the valves were extremely loose. Don’t recall the spec I used for adjustment, but believe it was somewhat tighter than the factory number (10 thou?, help, again) and the engine ran much more quietly (as if putting LB7 and quiet in the same sentence makes sense).

Getting to the valve adjustments is a pia, and since many engines endure with noisy valves, I would be reluctant to go in just for that reason, since, well, keep reading.

While your numbers look excellent (notice my firm grasp of the obvious) casual observation of the experience of others here seems to point to around 75k being a nominal life expectancy for VCO injectors.

Obviously YMMV.

Cracked injector bodies are a failure mode from years ago and seldom experienced these days (fuel in oil) and the most common symptom of impending doom (as you are aware) is the dreaded “haze at idle”, as dripping fuel from fouled injector nozzles that don’t shut off properly begins to carbonize on the tip, disrupting the spray pattern and excess drops of unatomized diesel don’t combust and head out the exhaust.

Interestingly, other than a loss of mpg, LB7 Duramax with failing VCO’s run strong, until the owner becomes too embarrassed by the white clouds at stop signs to keep driving. And not to forget the possibility of a stuck open injector that will definitely ruin your day...

Looking down the road to the inevitable, folks are reporting good results with the improved design of SAC injectors, as used in all subsequent Duramax, and have sourced OEM fuel delivery models that won’t require special tuning (although to further complicate matters, some owners have installed somewhat oversized SAC’s w/o engine management mods and reported good results).

Depending upon your situation, this may be a good time to begin considering unloading the truck (I know, like most of us, you luv it!) or at least start a fund for injector replacement. DIY seems to run about $2500, with replacement by the Big Kids approaching $5,000.

Hate to be Catastrophizing, but thems pretty much the facts, as I see them.

Notice I have craftily avoided answering your original question, but maybe this bump will encourage others to weigh in.

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post #4 of 7 (permalink) Old 10-01-2019, 03:57 PM Thread Starter
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I am not making oil nor hazing which is why I was really hopeful it wasn’t injectors. The price doesn’t scare me and I will be DIYing it. I’ve had the valve covers off twice now and it’s really not that bad of a job as long as I stay organized! I’m not afraid to spend a weekend tackling the valve adjustment.
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post #5 of 7 (permalink) Old 10-01-2019, 04:00 PM Thread Starter
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Is this small amount of clatter normal for an LB7? I’ve know they’re noisy and maybe it did it before but I just now noticed it? It will make 3-4 ticks in park if I mash the throttle and one more tick when it comes to idle... no tick at idle.
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post #6 of 7 (permalink) Old 10-02-2019, 07:26 AM
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Quote:
Originally Posted by Pommier921 View Post
Is this small amount of clatter normal for an LB7? I’ve know they’re noisy and maybe it did it before but I just now noticed it? It will make 3-4 ticks in park if I mash the throttle and one more tick when it comes to idle... no tick at idle.
Sounds like an injector that is sticking to be making the clatter sound.

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Phone: 920-361-7700


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LB7 Injector Install Instructions
post #7 of 7 (permalink) Old 10-02-2019, 02:48 PM
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I pretty much always agree with Brent at Lincoln but you need to make sure its not regular old LB7 noise . Mines much louder then all my friends newer Duramax's and I've come to accept it . I have the new SAC style injectors and I love them especially with the tunes (thanks Brent) and have had my valves adjusted and its still noisy . I think its a little of the nature of the beast .
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