no start LB7 please help

T

turbogmc

POWER JUNKIE
Joined
Dec 17, 2008
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189
Rebuilt motor just installed but will not fire. Motor is all stock besides arp head studs and lbz inj pump (I know this will need to be changed in the tune but it should still start).

Heres what we know and have tested:
-Makes desired rail PSI while cranking (6000+ PSI)
-No codes in any of the 12 modules on truck
-Tried another known good ficm with no luck
-Has 400+ psi compression
-Tried multiple stock tunes
-Injectors were bought from reputable injection shop and were cleaned, tested on stand
-Has rpm on scanner while cranking and tech 2 shows inj pw
-Drained all fuel and put in brand new fuel
-Checked ecm pins and engine harness pins
-Tested power at glowplugs with test light
-Checked CMP and CKP conectors for correct placement
-Checked all fuses on underhood fusebox and dash fusebox
-With glowplugs/intake heater disconnected it ran on a couple sprays of ether but wouldnt stay running
-Injectors all ohm out at 0.4-0.5 ohms
-switched out engine harness with no change

Any input would be greatly appreciated.
thanks in advance
Bret
 
We have checked for leaks and everything looks to be perfect. Now we have it tuned for the dsp 5, modded lbz pump, and the other mods. It was tuned by a reputable tuner and still no difference. Anybody else have any other ideas? Thanks, Bret
 
Not sure about FRP actual VS desired. But if i remember right, for the no start the book says to check FRP MPA while cranking, value needs to reach 10 for the truck to start.
 
1pieceatatime. said:
Not sure about FRP actual VS desired. But if i remember right, for the no start the book says to check FRP MPA while cranking, value needs to reach 10 for the truck to start.
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In the first post he says it hits 6000PSI while cranking, and it only needs 1450 to make the injectors pop. Since this happend after engine work, I would question if the correct cam or crank reluctors got put in it. Or if they are in correct alignment. Pull the glow plugs out and turn it over and see if there is any mist that would show it is injecting fuel or not. Also double check your connections at the FICM for nay pushed out or bent pins.
 
whenever we can get a spot in the shop again, we will check all cylinders for compression again to cover our bases. In hindsight, we only checked one cylinder which was at 400 psi cranking with a leaky fitting which we dont think was quite right. The new fitting will be here any day. Also, we swapped the crank postion sensor already and will try a different cam position sensor as soon as we get back in the shop. Thank you again for all the replies, sometimes another set of eyes mean all the difference.
 
Another thing to check is if your ignition 1 relay is working and if the fuse for it is good. Just had an LLY today that wouldn't run and it ended up being a shorted power wire to the FICM. It had popped the fuse for it which should have thrown an ignition 1 circuit code, but didn't.
 
The crank reluctor can be put on in the wrong orientation. I've seen it done before, everything tests good but will pulse injector at the wrong time.
 
Thank you for the ideas, we will check on them. On a side note, We double checked compression on all 8 cylinders and had 440-450 psi on all of them. Also bypassed factory filter head (since we already had an air dog and bled fuel lines and no change. Still stumped. Any help appreciated, Bret
 
How long have you been cranking it? When we changed injectors on an lb7 it took almost 45 minutes to prime everything with fuel. Not a complete motor swap but if everything is dry you might not have fuel. Maybe I'm missing something here though. This is a couple weeks old but I'm curious as to what it was.
 
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The truck is still at the shop . We have been kind of burned out on it because nothing we are trying is working. Is there any way or any sort of tester we can rig up to tell if the injectors are actually getting and spraying fuel? Thanks, Bret
 
Make sure u have the crank position sensor and cam sensor plugged into the correct ones. I can't remember on an lb7 if other plugs will fit in them or not. Cummins u can lol
 
If it reads RPMs tho they should be plugged in correctly. Simple stuff like ignition fuses have been checked?
 
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