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Discussion Starter · #1 ·
Hey guys so I have been having a knock while on the throttle sometimes its worse then others. Today I had the chance to hook it up to a CTS and take a look at the Inj. Balance Rates. Heres what I have found via pictures below. What are your guys opinions these injectors have been cleaned once before, or so that what previous owner had said. Truck has 200k on it doesn't have any blue or white smoke except for cold starts. Truck seems to run fine does have a slight idle issue but I believe thats the fuel pressure regulator.

I believe the top photo is in drive and bottom photo is in park.
 

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Have you ice picked the injector harness or ran some additive through a few tanks of fuel yet? Also inspect the wiring the runs by the alternator bracket & make sure no wires have rubbed through
 

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Injector #1 looks like it is leaking (and #5 possibly clogged/sticking), i would run the DIY cleaning, then replace #1 and retest the balance rates again.
 

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Discussion Starter · #5 ·
I doing the dyi cleaner tomorrow. I don't really want to just replace one injector since I'm sure it would be long before the rest start to fade out and need replacing.

If the cleaning doesn't seem to work. Where have you guys been buying injectors?
 

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Well you do have the advantage of having your injectors on the outside of the valve covers. So replacing one or two at a time may pay off. Ive seen people replace the one bad injector and not touch the others for years. I have also seen people replace the one they think is the problem, and end up replacing all 8 in the end because the next one failed later.

Keep us updated on the problem. And let me know if you need any injectors! We have OEM Bosch injectors in stock and ready to ship.
 

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Well you do have the advantage of having your injectors on the outside of the valve covers. So replacing one or two at a time may pay off. Ive seen people replace the one bad injector and not touch the others for years. I have also seen people replace the one they think is the problem, and end up replacing all 8 in the end because the next one failed later.

Keep us updated on the problem. And let me know if you need any injectors! We have OEM Bosch injectors in stock and ready to ship.
^^^^ This!

Since it is an LLY you can go ahead and change just one and see if that changes your issue at all or just do them all if you don't mind spending the money to do so. If you have alot of mileage on them then I would just do the set but under 150k then just do them one at a time because it may end up just one or two having an issue. Really hard to say until you start swapping or changing them though but definitely do the DIY cleaning first.

......and yes, LDS is definitely the best place to get reman'd injectors too.
 

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Discussion Starter · #8 ·
I did the DYI injector cleaner. I don't have a cts so I won't be able to see my balance rates till I get ahold of my buddy that has one. I still have a hammering noise which I have no idea what its from. Could it be injector 1? It does not happen all the time but most of the time it does.

Do you guys ever adjust valves on these trucks? Off topic but figured since I got your attention.
 

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The valves only need adjusting when the motor is torn apart for Head Gasket install or something.
 

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The hammering noise you're hearing could be pilot injection turning off in the upper RPM range and is completely normal. Read the below description and see if it's what you think is happening in those operating parameters.

The following info copied from link at bottom.

Diesel engine fuel injection systems that use a common rail system, as the Duramax™ diesel does, may or may not have what is referred to as pilot fuel injection at the lower engine speeds. Pilot fuel injection is defined as a pre-injection of a small quantity of fuel 5 to 20 crankshaft degrees before the main fuel injection. This pre-injection softens the main injection pressure rise and reduces combustion noise. At engine speeds above 2600 RPM, and a fuel quantity supply greater than 35 cu mm, it is necessary to eliminate pilot injection to meet emission requirements. When driving at or above these speeds, main injection combustion noise may be noticeable. It is normal and not harmful to the engine.

When traveling in 5th gear, the pilot injection to main injection transition is typically in the 136 km/h (85 mph) range, however it may also be heard under heavy acceleration and when pulling loads up a hill during shifts at or above 2600 RPM. Customers that install the fifth gear inhibit switch may encounter the fuel knocking of main fuel injection at speeds around 107 km/h (67 mph) in fourth gear between 2600 and 2700 RPM. This sound is considered normal and is to be expected.

Diesel Place : Chevrolet and GMC Diesel Truck Forums
 

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Discussion Starter · #11 ·
I usually hear it around 1700 rpm and its under normal acceleration. Could this be pilot injection still?
 

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I usually hear it around 1700 rpm and its under normal acceleration. Could this be pilot injection still?
Interesting. I figured off of your first post where you said it happened while in the throttle.

In that case there's a good chance it's injector related if not something else mechanical. A video would help also.
 

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interesting. I figured off of your first post where you said it happened while in the throttle.

In that case there's a good chance it's injector related if not something else mechanical. A video would help also.
x2^^^
 

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Discussion Starter · #14 · (Edited)
I am having trouble uploading the video I took. Its saying invalid file, anyone know how to fix that?

I still need to get hook up with a CTS again so I can check my balance rates.

The truck runs like a top and only time I see any blue smoke is if its on high idle during the winter warm ups. I figured it would throw a CEL if it was something mechanical.
 

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After watching that a few times it definatly sounds like an injector is stuck open or sticking

See what your balance rates look like.
 

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Discussion Starter · #17 ·
Hopefully this weekend and can get a look at them. I just want it to be quite in the cab again. Only noise I wanna hear is turbo.
 

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Discussion Starter · #18 ·
OK it took long enough but I finally hooked it up after the cleaning. The first picture is in park and the second one is in drive. what do you think?
 

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Those rates look awesome from where they were.
 

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If you have a android phone or tablet do a search on here for the Torque Pro app. Buy the full app ($5) get one of these
it will read most things the CTS will just not as fancy. I used it until I got the CTS2. That way you can check stuff whenever you want.
 
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