A bent rod is a hell of a lot more likely than anything else when you are pushing the power past safe limits
LB7: Rough Idle with White Smoke (Injector or Cracked Piston)
- Thread starter Sandracer799
- Start date
A bent rod is a hell of a lot more likely than anything else when you are pushing the power past safe limits
yeah for sure. seems if your at the limit though wouldn't more then one rod bend unless that particular cylinder was the healthiest and making the most cylinder pressure? or the injector in one particualr cylinder was somehow injecting a small amout more fuel and makeing more cylinder pressure? this is a good thread.
To the op. Do a compression test. That will most likely tell you were your problem lies either bent rod or cracked piston.
Generally they all get shortened at different rates. In my case they were all short but the #2 was extra short and lettibg the piston slap the crank.
To the OP, do a leakdown test on all of the cylinders. Judging by the blowby you have a crackes piston but the leakdown test will tell you which piston(s) is/are or isnt/arent cracked. 350-450psi iirc is kind of the area for a stock LB7 but more important than anything is the difference between cylinders. Anything more than 50psi difference means theres an issue.
A shortened rod will just show low pressure but will hold pressure. A leaking cup or valve will slowly pressurize then leak down. The cracked piston will act the same as thoae two but probably at a more sramatic rate.
Good luck.
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My compression was as follows iirc
1.-300
2.-330
3.-310
4.-250 (more like 240ish)
5.-300
6.-260ish
7.-300
8.-320
the truck runs awesome still just white smoke at idle bad and starts like ass when cold. also gm says they need be within 10% so no more then 30psi apart in my case
350-400 is the norm but i have delipped pistons and lbz rods that i thought id never bend :roflmao: i bent my lb7 rods now these ones :thumb: so with delipped pistons i think 300-330 is normal
8 cylinder probably has a hole in the piston. Maybe pull that glowplug and see if its got a bunch of oil on it. I bet its a piston by the symptoms.
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I pulled the glow plug and it had no oil on it. The truck does not knock. It just has blow by, a miss, and of course smoke. Part of me is beginning to think that it may be a broken injector hold down.
Opinions??