LBZ loud knock

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Teamvi

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Oct 26, 2011
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I have an LBZ with a very loud knock, almost sounds like it is a knock and backfire through the air filter. It throws a code p0303 and I think that's about it. It has a bad injector balance rate of +12 on injector 3 all the other injectors I believe are in spec.
Any ideas what it might be? changed injector #3 but had no change, Do you have to reprogram anything after you change an injector on a lbz or???
Thanks.
Any Ideas are much appricieted also any checks I can do
 
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Dallas S

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Bent push rod

Knocking that seems to come from intake can be signs of valve train issues. I'm sure if you YouTube broken rocker or bent pushrod power stoke you will find many examples.

Excessive crank case pressure?
 
Bonestock

Bonestock

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Aug 9, 2010
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Broken or cracked piston? Or hell maybe another Lbz injector failure? Have you used a stethoscope on it? Can you kill the cylinders one @ a time to narrow your problem child down? If you habe a scan tool or efi v2 use your dvt tool to isolate noise by killing cylinders 1 @ a time.
 
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Teamvi

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I have killed one injector at a time on all cylinders and haven't found any that made it better, some made it worse and some stayed the same
 
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Teamvi

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I don't have a bunch of pressure blowing threw the oil fill cap. if it had a bad pushrod how could I tell? would it run if the crank was bad?
 
JoshH

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Dallas S said:
Bent push rod

Knocking that seems to come from intake can be signs of valve train issues. I'm sure if you YouTube broken rocker or bent pushrod power stoke you will find many examples.

Excessive crank case pressure?
Click to expand...
Exactly my thought as well. Definitely sounds like a valvetrain issue.
 
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Teamvi

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Should I be able to hear where the knock is coming from with a long screw driver? Putting my ear up to it and so on for each cylinder? If pushrod was messed up what's the easiest way to find out?
 
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Teamvi

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wouldn't it start hard if it was valvetrain issues like a pushrod? truck starts easy just has a major knock
 
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bmc1025

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At some point you are going to have to start taking things apart to figure out what's going on. I would pull all the glow plugs out and go buy a diesel compression tester from Harbor Freight. I think they are less than 50.00, much cheaper than throwing another injector at it.

Pull all the plastic clips out of the fender wells and take out the fender wells. Then take out all the glow plugs, the hardest one is by the steering shaft. Then use the adapter that fits and have someone crank for about 3 seconds each, while you watch the gauge. If a cylinder takes longer to come up to pressure or has considerably less pressure than the others, you have narrowed it down.

Once you narrow it down take the corresponding valve cover off and look for excessive play on the rocker and push rod, you may have to roll the motor over some to get the piston near TDC on the compression stroke. I use a ratchet on the alternator nut to roll the engine over, you may have to pop off the plastic cap.

If you find excessive play loosen up the adjusters, you may have to take them off the rocker completely, and pull out the push rods. If they are bent, replace them. If they are not bent you will have to dig deeper.
 
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Porno Joe

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bmc1025 said:
At some point you are going to have to start taking things apart to figure out what's going on. I would pull all the glow plugs out and go buy a diesel compression tester from Harbor Freight. I think they are less than 50.00, much cheaper than throwing another injector at it.

Pull all the plastic clips out of the fender wells and take out the fender wells. Then take out all the glow plugs, the hardest one is by the steering shaft. Then use the adapter that fits and have someone crank for about 3 seconds each, while you watch the gauge. If a cylinder takes longer to come up to pressure or has considerably less pressure than the others, you have narrowed it down.

Once you narrow it down take the corresponding valve cover off and look for excessive play on the rocker and push rod, you may have to roll the motor over some to get the piston near TDC on the compression stroke. I use a ratchet on the alternator nut to roll the engine over, you may have to pop off the plastic cap.

If you find excessive play loosen up the adjusters, you may have to take them off the rocker completely, and pull out the push rods. If they are bent, replace them. If they are not bent you will have to dig deeper.
Click to expand...


he said in his very first post he has a cylinder 3 misfire code and a balance rate of 12 on cylinder 3. I think we can make a pretty good guess its cylinder 3.

I'd be pulling the valve cover
 
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Teamvi

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What did it do when you broke The crank? Did it start easy? How did you find out the crank was broke
 
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Teamvi

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if I did bend a pushrod? do you think I might have also bent or broke a valve or hurt a piston? Would a compression check tell if I did?
 
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