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rebuilt lq4 wont start

Old Oct 15, 2012 | 10:20 PM
  #21  
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Originally Posted by 2005 Silverado
Comp xr281hr, ls7 lifters, 7.350 comp pushrods. I took the best care of the crank I could. I'm trying to tune it myself.
Is it a stock 6.0 tune that you modified the injector tables on or is the old 4.8 tune???
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Old Oct 15, 2012 | 10:36 PM
  #22  
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From: NM
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Stock 6.0 with marine 8.1 injector data.
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Old Oct 15, 2012 | 10:42 PM
  #23  
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Was the stock 6.0 tune from the same year truck???
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Old Oct 15, 2012 | 10:45 PM
  #24  
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Does it have the right cam sprocket? Some were 1x, 4x and so on. Could be reading cam position all wrong or sumething. Also isnt the crank rotation vs cam rotation like 2:1 or sumething. U can set the timing 180 degrees off. Make sure piston #1 up top when the cranks dot is lined with the cams. I did it once on my old v8 s10.

Last edited by RS/SS 4.8; Oct 15, 2012 at 10:50 PM.
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Old Oct 16, 2012 | 09:05 PM
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Originally Posted by 1FastBrick
Was the stock 6.0 tune from the same year truck???
The tune is the same os as the original tune in the truck. By original I mean when it was a v6 5 speed. It wont start on the old 4.8 tune either. So I think its time to pull the intake and canker it and see if it is sucking and blowing in the right holes.
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Old Oct 16, 2012 | 09:09 PM
  #26  
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From: JunkYard
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Originally Posted by 2005 Silverado
The tune is the same os as the original tune in the truck. By original I mean when it was a v6 5 speed. It wont start on the old 4.8 tune either. So I think its time to pull the intake and canker it and see if it is sucking and blowing in the right holes.
Sounds good!!! One last thing what color is your crank sensor???
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Old Oct 16, 2012 | 09:38 PM
  #27  
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From: JunkYard
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Originally Posted by RS/SS 4.8
Does it have the right cam sprocket? Some were 1x, 4x and so on. Could be reading cam position all wrong or sumething. Also isnt the crank rotation vs cam rotation like 2:1 or sumething. U can set the timing 180 degrees off. Make sure piston #1 up top when the cranks dot is lined with the cams. I did it once on my old v8 s10.
You seem to be mistaken. The cam sprocket all have the same teeth. It wouldn't matter if it was LS1 or LS2 style.

On an LQ4 generation 3 LS motor the cam sensor reads off the back of the cam. This is something that can not be changed. It is manufactured into the camshaft.

On the crank they had 24x teeth wheel on the Gen 3 and 58X teeth wheel on the Gen 4 motors.

The crank spins 2 full revolutions to every 1 full rotation of the camshaft. If you lined the cam sprocket up at dot to dot. Or in other words Cam dot at 6 o'clock and crank at 12 o'clock At 1 revolution of the crank the cam and crank would both be facing up at the 12 o'clock position.

Unless you spin the crank trigger wheel on the crank, It is physically impossible to have the timing out 180* on one of these motors. This is not a Distributor engine.


Hope that helps clear things up.
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Old Oct 16, 2012 | 11:13 PM
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Originally Posted by 1FastBrick
Sounds good!!! One last thing what color is your crank sensor???
Black
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Old Oct 17, 2012 | 12:43 AM
  #29  
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Originally Posted by 2005 Silverado
Black
Good !!! Sounds like you have the right one.
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Old Nov 2, 2012 | 07:53 PM
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Ok so its torn down again. Its firing 180 out. When the exhaust closes and the intake just open and the exhaust isn't quite closed it fires...or its firing in overlap instead of compression.

I just want it to run so I can sell it.

Also recap, the cam is installed right. Sensors work. I have fuel spark and compression its just not firing in the fight time. Tune is the old turbo 4.8 tune.
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