LB7 bad knock???

[Yellow Jacket]

I have a customer truck that has a pretty bad knock and white smoke on startup... Balance rate on #3 is 10.xx when cold and settles down to a 6.xx warm, and number 6 is a -4.xx... When I do a injector cutout test it doesn't go away.

Any suggestions.

 

[blk smoke lb7]

Injector is stuck open i would imagine.Pull all your inj fuses or the fuse for the ficm pull the glow plugs out and have a guy on each side of the motor and someone to crank it over,your hung injector will stillshoot out fuel if its hung open.

 

[Tony Burkhard]

Injector is stuck open i would imagine.Pull all your inj fuses or the fuse for the ficm pull the glow plugs out and have a guy on each side of the motor and someone to crank it over,your hung injector will stillshoot out fuel if its hung open.

X2

 

[Yellow Jacket]

It doesn't appear to be spitting fuel out of any cylinder, I have all glow plugs out, FICM disconnected, and fuel regulator unplugged... It's running 15,000+ rail pressure cranking and nothing spitting out.

There is definitely fuel in oil, its overfull and if I drip some on a paper towel it has the darker inner oil spot and a outter lighter line of fuel...

 

[bluecollar]

Piston? Just an idea my brothes lly did the same thing..

 

[RENODMAX]

What are you using to cut injectors out? If its EFILive the injector number on the DVT tool correlates to firing order not cylinder number.

 

[Yellow Jacket]

I have had a lly with a cracked piston, the blowby gave it away. I had a c4500 that had a rough idle and slight miss and pitch would change when #6 injector shut off; it was 80 psi less compression on #6 than the rest... Had a piston melted to the first ring and a ever so slightly bent exhaust valve. Also had another lly that knocked similar and smoked black at idle and a cylinder cutout test stopped the knock when I shut off #4 injector, replaced it all good.

I hate to convince this guy to put all 8 injectors in and charge him $3000 and it doesn't fix it... Never even had a semi act like this when I worked 4 freightliner... His truck only shows 118,000 miles and the valvecovers have definitely been off. Not sure on any more of the truck's history...

I don't have a compression checker of my own yet... I'm thinking that's the next step??

 

[x MadMAX DIESEL]

What are you using to cut injectors out? If its EFILive the injector number on the DVT tool correlates to firing order not cylinder number.

Thought that was just the lly. And IIRC its not the firing order either, like some people thought it may have been.

 

[Yellow Jacket]

What are you using to cut injectors out? If its EFILive the injector number on the DVT tool correlates to firing order not cylinder number.

I use both, the lly I had a problem with, EFI showed #6 bad... I replaced it, and it didn't fix it. Used Tech 2 and it was actually #4 I had to replace... And #4 isn't #6 in the firing order.

 

[RENODMAX]

Thought that was just the lly. And IIRC its not the firing order either, like some people thought it may have been.

The EFILive programming is the same for all of the trucks concerning the DVT tool, and they use the GM programming.

 

[RENODMAX]

I use both, the lly I had a problem with, EFI showed #6 bad... I replaced it, and it didn't fix it. Used Tech 2 and it was actually #4 I had to replace... And #4 isn't #6 in the firing order.

Youre saying it showed a bad #6 on the DVT or on the balance rate? Interesting as it would'nt correlate with anything.

 

[Yellow Jacket]

Youre saying it showed a bad #6 on the DVT or on the balance rate? Interesting as it would'nt correlate with anything.

#6 in the DVT stopped the knock, but it was #4 that was bad. On that truck the balance rates were very erratic and all over the place... Balance rates didn't help or point to #4 at all.

 

[Yellow Jacket]

Ttt

 

[RENODMAX]

#6 in the DVT stopped the knock, but it was #4 that was bad. On that truck the balance rates were very erratic and all over the place... Balance rates didn't help or point to #4 at all.

Ive actually seen this on two LLYs here in town. Acts like a bad FPR and the balance rates are erratic just as you stated. Turning the injectors off with DVT pointed to bad injector. Injector swapped out and all is well. Did you do a return test?

 

[Yellow Jacket]

#3 hole has 250 psi compression and other 7 are around 350 psi...

 

[MACKIN]

#3 hole has 250 psi compression and other 7 are around 350 psi...

Well IF the compression check was done correctly and your guage is good then you found your answer to balance rates being all over the place trying to smooth out the idle on a dead cylinder or "hole" as you put it.

Sounds like you lost a piston unfortunately.

 

[Yellow Jacket]

Well IF the compression check was done correctly and your guage is good then you found your answer to balance rates being all over the place trying to smooth out the idle on a dead cylinder or "hole" as you put it.

Sounds like you lost a piston unfortunately.

Yeah, gonna pull the engine and pull the heads to see if the bore is salvagable... Its a customer truck, so unfortunately for him! Either way it doesn't matter to me!

 

[MACKIN]

Maybe I missed it but what are the specs on the truck? Year,mileage,any modifications as in power adders?

 

[LReiff]

So the DVT cylinder correspondence is still up in the air? My 02 LB7 just lost a cylinder. It's smoking white and puffing out the oil fill so I'm sure it lost a piston. On the DVT it show cyl 7 balance rate to be maxed. Which cylinder is #7? Right rear or 3rd back on the left?

 

[curt]

#7 is passenger side firewall! passenger side is 1,3,5,7 front to back!