[Whistlindmaxx]

Ok, so I’ve got a 03 LB7 duramax, with 402,000 miles. it has a kinda rough idle, like it’s missing on a cylinder, with a constant power surge. when you give it some gas, either in park, or going down the road, it clears up and runs great, but it black smokes like crazy. I’m talking about cars behind me pulling out of the way if you get into it. It’s got plenty of power. Could it be an injector?

 

[duramaxsky]

Try a cylinder test. It will tell you if there is a bad cylinder. Then you can go from there.

 

[Flyguyphil709]

check your balance and return rates on injectors, could be badly set valve lash aswell.

 

[DMAXfirefighter]

Does it have a fuel knock to it at all, either idle or when you get into it and it blows smoke? Definitely check the balance rates and see if you have one that is way off, and the cylinder cutout test would probably help narrow it down too

 

[Whistlindmaxx]

It does have a fuel knock at idle, which seems to disappear when driving, but then it just smokes. I wish I had a programmer so I could check it out, I guess I’ll have to find one

 

[DMAXfirefighter]

If it has a fuel knock at idle- does it smoke sitting there idling? Kinda sounds to me like you have one sticking open not closing all the way.

 

[duramaxsky]

If you replace your injectors get the SAC replacements from LDS. Don't let them talk you into the 45% overs. I did and wish I had not. But they will last longer as the tips are like the newer ones. And if one dose go bad you can just change one. But with the stock ones just change them all. If one is bad the rest will soon follow. The standard rebuilts don't last long. Just get the SACs. Trust me on this. I did mine at a little over 100'000 miles. One side 30,000 later. The sacs 10,000 later. They have 170,000 on them and work fine. It's too much work on an LB7 to keep doing them. Get the good ones and you won't have to do it again for a long time if ever.

 

[Whistlindmaxx]

When it’s idling it does smoke a little, just a light grey haze.

 

[77cruiser]

If you replace your injectors get the SAC replacements from LDS. Don't let them talk you into the 45% overs. I did and wish I had not. But they will last longer as the tips are like the newer ones. And if one dose go bad you can just change one. But with the stock ones just change them all. If one is bad the rest will soon follow. The standard rebuilts don't last long. Just get the SACs. Trust me on this. I did mine at a little over 100'000 miles. One side 30,000 later. The sacs 10,000 later. They have 170,000 on them and work fine. It's too much work on an LB7 to keep doing them. Get the good ones and you won't have to do it again for a long time if ever.

Why didn't you like the 45's?

 

[duramaxsky]

Why didn't you like the 45's?

You can't make it not smoke. They are just too big. Ihave a lot of mods including a bigger turbo but at part to full throttle it smokes for a few seconds and then clears up. I don't have big tunes either. They are trans safe tunes even though I do have a Mike L built trans. But I don't want more smoke. The fuel mileage also went way down with them.

 

[DMAXfirefighter]

Is it tuned for 45% injectors? Because if its not tuned for oversized injectors, yeah its gonna smoke...

 

[duramaxsky]

Is it tuned for 45% injectors? Because if its not tuned for oversized injectors, yeah its gonna smoke...

Yes it is. They have tried to clean it up. I even put a bigger turbo on it to try and clean it up. The intercooler and tubing, air horn and exhaust are already larger. They are just too big for the truck to run clean. Unless you want to make power that breaks things they are a bad idea. You can make enough power to break things with stock injectors. So if you're not building a race truck they are a mistake. I bought a new Silverado 1500 with a 6.2 for a daily driver so my LB7 is just for hauling big loads and some RV towing trips now. I never want to do that horrible job of replacing the injectors again. But if it was still my daily driver I would. I would get the new SAC injectors that don't have a core charge and retune for stock size. I am only keeping it because I would never buy a diesel with emissions garbage. So my new truck is a 1500. It pulls most things I need to pull. But it won't haul a heavy load in the bed. The Duramax will and still tow more behind it. I figured it would be cheaper to keep the old truck around for those needs than buy a 2500 gasser and pay for gas it uses every day. I hate the smoke enough I may break down and change the injectors 1 more time.

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[DMAXfirefighter]

Dang, and they can't get it cleaned up? Thats kinda strange. Is it only until it spools or is it even after it spools?

 

[duramaxsky]

Only till it spools. I am told the fuel doesn't atomize like it should at the low flow rate with the bigger holes. Not enough pressure or flow. It's just annoying to leave a big trail of grey smoke every time I accelerate a little quickly. Once it builds boost and RPMs it clears up. The LB7 just doesn't do well with more than 25% overs from what I have been able to find out. The 45% are for making big power and that will smoke no matter what. Stock is plenty for me. At the time SAC replacements were new for stock size. They said they didn't have any experience with them but the 45% had been around for a while and they were reliable. I wish I had gone with my gut and got stock size.

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[DMAXfirefighter]

I get what you're saying, but its not necessarily an LB7 think with bigger injectors- its kind of a diesel thing all the way around. The old Cummings engines were the same way too- high fuel low air low atomization. And I'm well into what you are saying too, my LB7 is running 60% injectors and until this year was running a 63mm stock appearing charger. But anyway, we kinda highjacked op's thread here lol

@Whistlindmaxx its sounding more and more like you have a sticking injector. I would look into getting them changed before it sticks wide open and melts down the engine