Duramax Diesels Forum Truck of the Week
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Old 07-09-2012, 09:03 AM
turbo_bu turbo_bu is offline
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Default LB7 Injector balance rate questions

I know - I own an LB7 so I shouldn't be too shocked with injector issues. Well, recently I finally got around to checking injector balance rates on my LB7. 2004 LB7 with 64k miles on it that I bought new. At around ~4k miles, I put on a Caterpillar 1R0749 fuel filter on the frame rail (before GM filter). Several years ago, I started throwing in 2 cycle oil to help out with lubricity. During the winter I usually don't add the 2 cycle stuff since the diesel anti-gel additives claim to have something in there for lubricity.

Anyway, here's my issue:

Balance rates

Neutral Drive
Cyl # mm^3 mm^3
-------------------------------
BALRCYL1 = -1.7 -3.0
BALRCYL2 = -0.1 0.6
BALRCYL3 = -1.7 -4.0
BALRCYL4 = 1.5 2.3
BALRCYL5 = -2.6 -3.0
BALRCYL6 = -0.2 0.1
BALRCYL7 = 3.8 5.6
BALRCYL8 = 0.7 0.9

It looks like cylinder 7 is on the way out. It is showing a + (positive) which I believes means that the ECM is having to injector more fuel to compensate. Does this mean that the injector is leaking? Pretty sure the next step would be to do the return test. Although some others have mentioned just pulling out the glow plugs and cranking it over (not sure exactly if I should be seeing lots of fuel or not fuel with a leaking injector).

I am really kicking myself since I have been meaning to do this check for a while, but never got around to it. Anyone have a guess on how long it "could last"?

The truck starts, runs and drives fine. No smoke or hazing. As a sanity check, I went ahead and threw in some 2 cycle with my latest fill up (don't think I had the previous couple of fill ups). And I am driving it for a while to see how much the balance rates change.

One last quick question, are the "new style" Bosch injectors only available at GM? They still like $250 each? Trying to decide if I should just replace one bank .... do them all .... or just try to find an LLY top end and do an LB7 to LLY swap.

Thanks,
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Old 07-09-2012, 09:13 AM
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how many miles are on it now and have they ever been replaced before?
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Old 07-09-2012, 09:31 AM
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Injectors from GM are about $350 each. I'm pretty sure Merchant's injectors are the 'new design' as well, so you'd probably be better off buying from them unless you've got a connection at a dealer. Is it making oil or is your fuel mileage down any?
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Old 07-09-2012, 09:43 AM
turbo_bu turbo_bu is offline
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Truck has 64,000 miles on it. Original injectors that have never been replaced. So far, it is not making oil and my mileage is somewhat close .... within 1 MPG of where it usually is.

BTW - how do you tell that injectors are the "new style"? Belive that I have read that you have to see the serial #??? Or is there an "date code" that you can check?
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Old 07-09-2012, 09:54 AM
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well you definitly dont have the "new style" if your have never been replaced. there is a thread somewhere in here that tells you what numbers to look for on the side of the injector to make sure they are the 09 and up ones. Either way, make sure you buy Bosch reman only injectors.

I would DEFINITLY replace all 8. it wont be long down the road before another injector from the other bank starts goin as well.

there is no set "how long will this injector last" as many variables dictate that. At this point though, i would definitly be lookin for injectors and saving pennys. On my truck, i had 65k on my injectors and had Guy at Socal Diesel test them all before going back into my new motor. all but 3 were no good and my balance rates were no higher than 2.5 on a couple. i could have kept runnin them but it wouldnt have been long before they really went bad and i really didnt wanna have to go back into the truck to replace them.
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02 2500HD CC/LB dmax/alli "The Limo"

BIG THANKS TO: Mike L, Steve, Trent, Guy, Dan, Ruben, Josh H, Scott, and everyone else who has put a hand in to help me.

best time to date: 12.39

motor died/bent rods = 3/11/11
back from the dead 7:04pm 4/9/2012

driving a turboed Samurai now
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Old 07-09-2012, 09:58 AM
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I think the only way to tell is the serial# on the injector. I'm kinda in the same boat as you, the numbers are off and I've got a haze at times, but its not making oil and the fuel mileage is staying consistent, so I'm just gonna keep going until I have to do something with them
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Old 07-09-2012, 10:18 AM
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If your not smoking makeing oil or running like garbage you might try the injector cleaning process it works for some.
Its only like around 18 for the cleaner from GM and a couple 3 or 4 ft sections of hose and a half gallon of diesel and a couple hours of your time watching the truck run.
I did it and it smoothed my idel and acceleration but did not do much for my rates but my rates are all within spec anyway but some have claimed good results on balance rate improvements.
I agree with the rest though if you can aford it do all 8 it does not look or sound to be a fun process.
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Old 07-09-2012, 06:35 PM
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Thanks for the input guys ... guess I am in the wait and see category. That and start looking for a LLY to swap heads / injectors ... or a complete LBZ ... or something else to swap with.

Does anyone whose had them on the way out had any luck with troubleshooting using the pull the glow plugs test???? I have only read one other post where someone was doing this, but still am not sure exactly how bad it has to be to see anything or what I am looking for. Wondering if this only works for really bad injectors.
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Old 07-09-2012, 07:54 PM
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There's nothing wrong with lb7s every one is quick to bad mouth them. all the rest have injectors go bad also maybe not as often but i think 65k miles is good and their are lots that have gotten 100k+ out of lb7 injectors. Save yourself the headache and just replace all of them and they will last another 65k+.
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Old 07-09-2012, 09:09 PM
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The price of the injectors hurts me more than replacing them imop.
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02 2500HD CC/LB dmax/alli "The Limo"

BIG THANKS TO: Mike L, Steve, Trent, Guy, Dan, Ruben, Josh H, Scott, and everyone else who has put a hand in to help me.

best time to date: 12.39

motor died/bent rods = 3/11/11
back from the dead 7:04pm 4/9/2012

driving a turboed Samurai now
Tailgate Crew Member #4
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Old 07-09-2012, 09:47 PM
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x2.
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Old 07-10-2012, 09:04 PM
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Atleast we can buy two new ones for the price of one of the other model trucks
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