Smoking Cummins 855 | Page 2 | TruckersReport.com Trucking Forum

So here’s what I’ve learned in the last 5 months, right or wrong let me know this may be incorrect, much of it came from the WWW; I’m working on a Cummins 855 NTC 444 CPL. Factory rating of 444hp at rpm, the 444 was given a compression 14:1 ratio instead of the 17:1 ratio of its predecessors so the Turbo could pack more air in it. The STC is a system to adavance the injection timing to reduce smoke at idle and low to no loads, this is controlled by the pump outlet pressure. The PT fuel system works by adjusting the fuel pressure from the dampened gear pump pressure, unreturned pressure from the governor and boost (or ATC) valve. All this feeds a set of injectors that exchange pressure for volume in injection tip just before injection. Injection pressure (atomization) is created by the force of the cam shaft on the injector train. After injection fuel it’s circulated through the tip to cool the injector. The STC system advances the injection timing by adding engine into the Injector which makes it push on the injector stem sooner. The engine oil pump has 2 regulators one of which is controlled by the oil viscosity valve , so that it adds fuel pressure for the STC system help with cold start smoking. ... that may be it..

The 444 was in production from the first BC4 until the end of big cam truck production, many different variations and CPL numbers.

To the OP, how did you time it and did you reuse the old timing key to ensure you got it close to spec?

Thing about a PT system is that a miss comes from injectors, you need to get the truck to someone that knows how to set the overhead, you need a tool to hold the STC tappet up when you set IBC, and OBC torque settings change depending on the engine.

It is also not the correct way to do things, he pushes retarded timing because he wants people pulling these engines down to rpm he also pushed changing the gear pump as well, none of this is needs if a big cam is being driven right and never pulled below rpm.

He would have everyone cranking fuel pressure when a simple injector change to an increased flow injector will take stress off of the cam and make more useable power.

You can test that STC valve with regulated air, you should be able to make it shift timing.

Do you know 855 engines? I do not except for what I've read.