Got a '94 BC 400 with STC dropped in my lap running like crap, pulled the valve covers and all three of the STC internal manifolds had at least one tube "blown out" of the injector adaptor. When you start the engine cold it pumps about 100 psi at 1000 rpm for 7-8 minutes and drops to normal as the oil warms. It runs great when I pry the tubes back in but of course they're sprung now and wont stay in on a cold start with a ham footed driver. I know there is a high pressure relief in the pump, but haven't been in one for years, reman pump or try to fix it? This is the pump with the sensing line from the block.
I think because of the age I would replace with a re-man pump. But I would check the STC control box too-see if there is any oil in the fuel line from the control box. With that kind of pressure I would be skeptical about the control box condition. Lucky you. Truck Shop
Already done, and checked the STC shift points with hot oil. right on specs. Was there an update for stronger manifold tubes?
That I can't answer. Truck Shop
I'll be checking with Cummins, Got a trailer replumb/rewire/brake job going right now, and Thursday is the eye fixing so I'm probably out of the shop til Tuesday or so.
I seem to recall a bulletin regarding STC manifold on L10/M11 to enlarge the bleed off hole to .030 from original. Don't remember the reason. Hope this helps even if it's a different animal.
Your engine should have come from the factory with a viscosity sensor installed. The viscosity sensor is a steel block with orifices in it that caused the oil pressure at cold start to be 70 to 90 psi until the oil started to warm up. This was supposed to clean up some of the heavy smoke at cold start and it did help. The internal manifolds may have just given out from old age.
Had a chance to look through the manual today and found no mention of a viscosity sensor. Whereabouts would this be located?
Can you pull the relief valve from the outside like on the older Cummins engines ? Pull it out , wipe it off & install it back & see what happens .
I thank the STC's were a different deal. About 40 PSI tops.
Yes. Make sure the plunger and bore are not skuffed up and maybe replace the spring. Pump is not worn out it it makes to much pressure.
As we always promote safety on HEF ….. Be careful about knocking that 855 up . At RZ's age he don't need anymore surprises .
Nope, the high pressure relief on these is internal and takes a few special tools to remove and reset the spring retainer properly, Its just as easy to throw a reman pump on there and be done with it.
Yeah, 40-50 psi with the DFC pump.
They were supposed th have 15 to 20 psi at idle and 40 to 45 psi at high idle. The viscosity sensor was located on a bracket that was located between the oil pump and the block. Two of the oil pan bolts held it in place.
Here's a pic of the new internal manifold tubes, they appear to be considerably more substantial than the originals.
By golly he's just-a take'n pictures and a post'n em there Maw, by golly you betcha there Maw, yup that's a what he's a do'in. Good for You RZ. Truck Shop
I have absorbed way too much 2 stroke Detroit DNA to breed a Cummins.
It's gettin' easier,
Its the viscosity sensor. Of the 3 stc engines I've had and 2 I still run the viscosity sensor has been replaced on 2 of them. Sometimes lots of brakeclean and air can bring things around. Check the oil pump gears, trash gets into the sensor and its ****. Then pull the spring and plunger out of the oil pump and get new ones.
This has been a back burner project, found the sensor and tried the cleaning trick... No Bueno. Said "what the he!! and got a new one, end of issue. The pressed in screens seem to prevent proper cleaning with out destroying the thing. Now a cold start hits 75 PSI and drops to 60 immediately, Runs 43 psi on the raod with hot oil and idles at 15-18 PSI hot. Now I gotta fix a bunch of electric gremlins in this thing. Typical broken wires and bad grounds on a 1990 model with years of crappy maintenance.
Well at least the finish line is in sight.
Not yet... they want to fix the A/C too, lots of missing components and brackets. This will be interesting. I do have 'til mid September.
A/C completed just in time for fall. Now that's irony.
Yep, but that's still hot here, and that's when they want to use the truck for harvest.