Timing and Metering Valves

[TerryB]

I started my working career working on Big Cam Cummins along with a few Small Cam engines, learned and done everything on these engines. About the time engines started becoming more electronic controlled, my path sort of veered away from Cummins and more to International, Detroit and Cat. So I didn't really get to know the electronics of a Cummins engine. Now, as the owner of a CM570 I'm trying to learn the electronics. One area is the timing and metering valves and how they do what they do. The timing valves, how do they control timing? My thoughts: The injectors are mechanically controlled, the camshaft is timed to the crankshaft. How can the actuators affect timing?(this is when I try to compare this engine to a Big Cam engine and it's timing. I know, can't do that). I'm thinking the timing actuator controls the exact time the fuel is fed to the injector, depending on the position the injector is at that split second, determines the timing. The injector could be already half way to being bottomed out before fuel is supplied to that injector, or maybe almost bottomed out if the timing is more retarded. Would that be correct? I'm not asking what position the injector rocker would be at any particular time, I'm asking if that's how timing is controlled? On the metering valve, this seems to be a little easier to understand. More fuel=more power. The metering valve controls the quantity of fuel supplied to the injector. How is this achieved? As far as I understand, the metering valve does not control fuel pressure going to the injector.(I could be wrong on that) Is the metering of fuel controlled by the length of time the metering valve is held open? The longer the valve is open, the more fuel goes to a particular injector. Sorry of being long winded, just trying to get a better understanding of how this engine operates.

[Nostalgic]

Here's how the 570 IFSM works:





And while 870/871 is shown, this shows how the actuators and injectors work in the same manner as the 570 (just that the IFSM on the 570 is unique in the way the pump and internal plumbing operates and it uses a different style of metering and timing actuators).

[Nostalgic]

Also, I will NEVER fail to be impressed in how fast everything happens. @2100 RPM each cylinder is firing off 35 (or is it 17 1/2?) times a second. All that magical signal/opening and closing of the actuators, fuel flowing into the head, into the injector timing valve and metering valve, compressing, spraying combusting, exhausting, etc. is happening however many times inside of a second.

[TerryB]

(11-28-2022 )Nostalgic Wrote:  Also, I will NEVER fail to be impressed in how fast everything happens. @2100 RPM each cylinder is firing off 35 (or is it 17 1/2?) times a second. All that magical signal/opening and closing of the actuators, fuel flowing into the head, into the injector timing valve and metering valve, compressing, spraying combusting, exhausting, etc. is happening however many times inside of a second.

Nostalgic, thanks for this information! Makes alot more sense now, kind of how I thought it worked, but not really!

[Rawze]

basically ...

The metering actuator loads the injector up with the quantity of fuel to be put into the cylinder BEFORE each compression stroke.

The timing actuator is used to change the length of an internal piston inside the injector that causes the fuel to be put in earlier or later... and the injector is pre-loaded with this setting as well.

BOTH of those things happen when the cylinder is NOT firing yet.. when there is plenty of time to do such things, long before the cylinder fires.

When the overhead cam finally does come around on a compression stroke, the injector is crushed downwards, pushing the fuel that is already waiting in the injector, at the offset of "when" that was set by that hydraulic timing piston inside the injector.

Therefore, the injector is pre-loaded with its timing offset + quantity of fuel and waits there for the mechanical system eventually rotate around and take over.

==============
system pressures...

The fuel pressure only needs to be about 250-300 psi in the rest of the fuel system because the overhead cam itself crushes the fuel inside the injector directly... making all the actual extreme high pressures at the injector tip. The actual injected fuel pressure on a CM871 is about 28,000 - 32,000 psi as it goes into the cylinder, produced by the crushing action of the overhead cam as it pushes it down. Actual pressure does vary tough depending on rpm and other things. This is why the older ISX engines did not need a (40,000 psi) high pressure fuel pump like the newer models do.

[TerryB]

Yeah there's a lot going on here. My CM570 has a rough idle when cold, and every now and again when warm. But not at any other speed other than idle. It's runs rough, stutters, misses or whatever else you want to call it. It's easy to believe it could be any one of these components causing the problem. No warning lights, haven't had Insite hooked up yet.

[Rawze]

(11-30-2022 )TerryB Wrote:  Yeah there's a lot going on here. My CM570 has a rough idle when cold, and every now and again when warm. But not at any other speed other than idle. It's runs rough, stutters, misses or whatever else you want to call it. It's easy to believe it could be any one of these components causing the problem. No warning lights, haven't had Insite hooked up yet.

rough idle...

Could be a leaky injector, that is the most common cause. Could also just be the valves in the allowing some compression loss when its cold too.

Check for leaky injector and don't give it any excuses to be rough.. and then go from there.

[TerryB]

When you say leaky injector do you mean it's not sealing off tight and letting compression back in? Or fuel leaking by internally in the injector allowing the timing to be incorrect? I know how to test for compression leaking back with the hose in the cup looking for air, I'm not sure how to test an injector for timing to see if the liquid cylinder is holding tight.

[Rawze]

(11-30-2022 )TerryB Wrote:  When you say leaky injector do you mean it's not sealing off tight and letting compression back in? Or fuel leaking by internally in the injector allowing the timing to be incorrect? I know how to test for compression leaking back with the hose in the cup looking for air, I'm not sure how to test an injector for timing to see if the liquid cylinder is holding tight.

A leaky injector will back-feed a tiny bit of the cylinder pressures, backwards into the fuel system, throwing off everything intermittently. It can become bad enough to eventually cause solenoid damage too.

The test is simple. I have videos on how to check for leaky injectors + how to identify which one it is ...

ref: http://rawze.com/forums/showthread.php?t...8#pid67948