400 CUMMINS BIG CAM 4 - TheDieselGarage.com
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post #1 of 12 (permalink) Old 12-27-2011, 10:31 PM Thread Starter
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400 CUMMINS BIG CAM 4

I have a 88 peterbuilt with 400 cummins cpl 833 how do i know if it has stc and can you adjust stc ?
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post #2 of 12 (permalink) Old 12-27-2011, 10:35 PM
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I have a 88 peterbuilt with 400 cummins cpl 833 how do i know if it has stc and can you adjust stc ?
Three connected oil lines going to the center of the rocker boxes. And the adjustment is only to make it function.
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post #3 of 12 (permalink) Old 12-27-2011, 11:19 PM
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A cpl 833 is stc engine
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post #4 of 12 (permalink) Old 12-28-2011, 12:59 AM Thread Starter
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my engine has about 5000 miles on a complete in frame overhaul with rebuilt injectors i had my pump rebuilt set at 10% over stock the engine still smokes gray and mises when cold and does not pull like i think it should i am the 2nd ower have all the repairs records that have been done on it. can the stc not work right and cause this?
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post #5 of 12 (permalink) Old 12-28-2011, 01:16 AM Thread Starter
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i do not understand how the stc works can someone explain this to me? what does the block with the lines running to it that is below the pump do? my pump man says i should have 66# of fuel presure idling i don't i have very little presure about 6# thats all i had before i took the pump off for rebuild.
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post #6 of 12 (permalink) Old 12-28-2011, 08:08 AM
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i do not understand how the stc works can someone explain this to me? what does the block with the lines running to it that is below the pump do? my pump man says i should have 66# of fuel presure idling i don't i have very little presure about 6# thats all i had before i took the pump off for rebuild.
I think he means it should have 66 psi of oil prssure to set the stc in advance mode.If not then the injectors may be in retard mode and this will cause a smoke problem. The oil line to the oil manifold that goes into the top of the rockers for the STC tappets needs a tee fitting put in line and the oil pressure checked their. f not enough takie it to some one that works cummins and ask for help. Another thing is does the idle oil prssure on the engine stay up good?If not remove the pressure releif valve on the bottom of the oil pump and pull the plunger and spring out and clean it and see if that helps. This is a coomon problem of something hanging the plunger and sticking the plunger causing low oil pressure.
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post #7 of 12 (permalink) Old 12-28-2011, 11:19 AM
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I think he means it should have 66 psi of oil prssure to set the stc in advance mode.If not then the injectors may be in retard mode and this will cause a smoke problem. The oil line to the oil manifold that goes into the top of the rockers for the STC tappets needs a tee fitting put in line and the oil pressure checked their. f not enough takie it to some one that works cummins and ask for help. Another thing is does the idle oil prssure on the engine stay up good?If not remove the pressure releif valve on the bottom of the oil pump and pull the plunger and spring out and clean it and see if that helps. This is a coomon problem of something hanging the plunger and sticking the plunger causing low oil pressure.
I put a couple washers behind the spring also. Adds about 10psi at 1500, 4 at idle. Helps a bit sometimes.
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post #8 of 12 (permalink) Old 12-28-2011, 01:32 PM
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The block below the pump is the STC Valve. At Higher fuel pressures it retards timing and advances timing at low fuel pressures. I could be wrong but at max power your fuel pressure should be over 200psi. A 400 should make ~ 21psi of boost. Add a dual line kit to make it a 425hp. Too high of fuel pressure can bend push rods. On initial start up the truck should smoke run rough until oil pressure makes it to the timing advance and then the injectors. It should then run clean.

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post #9 of 12 (permalink) Old 12-29-2011, 02:46 AM Thread Starter
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thanks every one for the info its been very helpfull. How does the stc make the timing change?
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post #10 of 12 (permalink) Old 12-29-2011, 06:12 AM
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thanks every one for the info its been very helpfull. How does the stc make the timing change?
Thru the tappets in the hi priced injectors.
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