Another lb7 issue

[JeremyK]

I recently bought a bone stock 2002 lb7 with 200k. Shortly after my purchase it felt low on power and started smoking at an idle so naturally I assumed injectors and found a set of Bosch remans and swapped them. I didn't buy new pressure lines and just used compressed air and solvent to clean them. I put it back together and started out in the road and it had a bad knock. The next day it smoked white at an idle and the knock was worse I took it to a friend who had a scan tool and we found #7 was out of range. This time I got diesel in the oil. I was able to get another injector on warranty. When I disassembled to get the injector I found crud blocking the inlet. I put the new one in and started down the road and there is still a slight knock I'm low on midrange power but no smoke and no diesel in the oil. The also is significantly more blow by than before the initial tear down. I've looked at a bunch of forums and can't quite find one that matches my problems. Any help would be appreciated. U really don't want to pull the valve cover again

[More Power]

The defective #7 injector may have resulted in damage to a piston, which is likely causing the increase in blow-by and producing the knock you’re hearing. A cylinder compression test will help you determine whether that is indeed the case.

I recently had the injectors replaced in my 2001 GMC. I chose a reliable local shop with experienced techs to do the work. Changing the injectors is a complicated process with significant consequences for a misstep, and may be a bit of a stretch for a first-timer. Hiring a pro shop is expensive (currently about $3k for an LB7/LLY), but it helps limit the risk.

So... Get that compression test out of the way. Compare the cylinder compression of #7 (rear passenger side cylinder) to a few other cylinders to determine whether it is low. If you find a bad piston, you can hone the cylinder and replace just that piston and ring set. At the same time, I would take the cylinder head to a shop with Duramax cylinder head experience to put a fresh surface on the head deck and reseat the injector cups. Good luck.

[JeremyK]

I've considered that.the other thing I'm thinking is that the pressure lines were inadequately cleaned so another injector has some crud in it. But a compression test is definitely on the list of things to do before tearing into it

[Kennedy]

The fact that you went from smoking to knocking without any real use tells me that the injectors are suspect. My first suspicion is the quality of the "reman" injectors. Second issue is reuse of the original lines. The lines sluffed off the junk that was blocking the inlet. They should not be reused and cannot be cleaned properly. When we do injectors we use the genuine GM lines.

Line corrosion: http://www.kennedydiesel.com/docs/Duramax%20LB7%20Injector%20Line%20Corrosion.pdf