[Cat-tech]

Actually, that is not entirely accurate. (not trying to step on toes, just providing more informed info).

(this answer is copy-pasted from the guy who runs his own isx forum after showing this post to him ) ...

Even if all the combustion request tables are set to zero, there is still pulse cycles active, as the integrated fueling control manager (the manager that has the final say to what happens in the cylinders, does injector trim offsets, etc.) has settings in it that have minimum pulse quantity and width settings, even if the combustion manager is requesting zero fuel or offset on a particular cycle. This applies to all engine modes, not just one of them.

As far as the original question about egr/oxygen burning, -- some,.. but no, not really. depends on engine mode how much extra above the minimum safety range might be added or not. - First pulse cycles are not just simply there to burn off oxygen to make  / simulate egr. It is used heavily to control combustion rate (detonation rate) and also take up slack between the piston and the crank (smooth the engine operation and reduce excess wear due to higher than normal vibration because the detonation that is happening is very violent otherwise, and hard to control).

Most of the red engines, common rail, (when studying the programming carefully) also use the third injection cycle as the main firing pulse. A lot of ppl do not take this into consideration when screwing with them.

Also, I think a lot of ppl doing tuning do not also know, like in the 2350 for example, it shows 4 main cycles.. well, there are usually 10 pulses, sometimes 11 pulses (+trim offsets) (depends on injector size and program) of the injector to make each of these cycles happen. I.E..> there are 4 -cycles x  11-pulses  each. leading up to as many as 44 pulses of a single injector, as the cylinder rolls over tdc. -- The injector does not stay open, but rather simply oscillates. The design dictates that if you applied a steady (non-pulesd) voltage to the injector that was continuous, the injector would simply only one-shot the cylinder, then no more fuel would come out. It is a safety feature of the injector so the engine does not go into runaway if the circuit fails,.. so the injector has to be pulsed at high frequencies for the fuel to keep flowing through each of the 4 cycles.

no one should ever just look at part of the programming and make an assumption to what might be happening (or not) .. always put some test equipment on it and see what the final result actually is too.

If anyone is curious, they can simply put an oscilloscope on an injector and see all this for themselves, do tests, etc. - A person can easily see these 4 main cycles, when they happen, their spread, and see all the 10 (or 11) pulses happening within each if these main mentioned cycles if they have a zoom feature on their scope (I have this test equipment and actually did all this a few years back when researching the injection cycles on the 2250 and 2350). - This happens even if the engine is in a certain (chi4) mode, like mentioned above.

So .. adding injection offsets, and/or fueling offsets  to the combustion oulse cycle tables simply adds more to the minimums, and sometimes this can be good, but sometimes it can be bad too. --Too smoothed out = a bit of fuel loss like mentioned, but also equates to higher carbon and soot buildup on pistins and rings 4 enines that that use a lot of pto, and eventual carbon packing, even if it is de-mandated. - There needs to be at least some minimal measure of 'play or lash' in the system for oil allowance, and to keep it clean. too 'sloppy' tho and head wears too fast, or wrist pins sufer.

Can the pulse cycles be turned off so that fuel is put in a single 'all-put-into-one' (40 to 44 continuous oscillating pulse) stream? -- Sure, by editing the injection strategies themselves, but you had best bet it will beat the wrist pin bushings up after a few months too. Most of the detonation rate control is lost and either you beat up on the wrist pins badly, or if you retard it, or alter fuel-air-ratio enough to reduce it, then you have already crossed over the threshold that beats up on the liners up because piston wants to bang against the side-wall of the cylinder (exhaust side, leads to fretting liners). Detonation just cannot be controlled properly on these high compression engines with trying to single-shot it.. it just is not going to happen, they are not designed that way at all. - Seen guys do crazy crap like that plenty, even seen some very smart people who know all this back end stuff try to achieve it too,.. even on low hp engines its not good for em. its not pretty. just don't even think about going there. The minimums in the fueling controller are there as a fallback protection to the engine, and should not be removed or narrowed.

I have seen a couple people successfully alter injection strategies around to improve them (without removing pulse cycles). Mainly it is only done to de-couple that load-based garbage, or to narrow the injection timing advance range because theres no more egr gas. some slight gains can be had there, but it is a very delicate matter, and a lot of things have to happen for it to work without something suffering, like completely different injection and other tables to go along with it.

in the end, no matter what tho, just a little bit Too good, Too efficient, and/or too clean ..=> all lead to someone loosing their engine prematurely over it, and re-building more often far outweighs in costs, the little bit they think they might have gained.

(just as a generalized perspective view here)...
So .... a 4 pulse cycles in the simplest terms ==

Place that bag of sand gently onto the top of the piston and apply a little force to take up all the slop so we don't hammer on the wrist pins or crank bearings(first cycle), Pre-combust the chamber so that fast-spraying, very atomized mist of fuel cannot build up / sweat onto the piston surfaces and cylinder walls (second cycle), Now we can finally push with a LOT of force to get the piston moving downward (happens after TDC, is also the main pulse) but not too sharply, so that the piston does not drag against the exhaust side of the cylinder, it wanting to deflect hard in the opposite direction of the connecting rod, and finally follow through with a residual bit of force to ensure everything stays tight, the rest of the oxygen, heat, etc. is used up, and to keep it happening / burning / the energy stretched out (fourth cycle) through to about 160-degrees of the stroke to complete the combustion cycle and get as much as possible out if it as we can. The whole purpose of the fourth cycle, if a person really thinks about it, is only necessary because we are limited (because the piston is still mostly at the top of the stroke) on how much 'uumph' we can initially make in that third cycle. The fourth cycle makes up for this limitation and gives uswhat we had to back off of and the rest of what we want without all the side-loading and axtra wall friction.

The first and second cycles are very important too. On that first cycle, Some could argue that, so what, it has a little slop at the start of combustion if we eliminate it, we don't need to quiet the components, they are big and clunky.. I used to think this way a long time ago myself.. (many years ago). I did not see the point and used to argue with others about it burning up oxygen too fast, thought like everyone else that it was only for egr. - boy was I wrong. - because I never ever considered the simple fact that high pressure rail, atomized fuel, and high compression ratio combined with almost horizontal spray angles was so incredibly violent in that chamber, and it absolutely has to have some kind of serious dulling effect for it to work even half-way right. -- That is the part that I did not understand for a long time. -- So... I know exactly where some people's logic comes from, and how all this stuff can make someone's head spin out of control .. all this stuff is NOT any kind of ho-jo fancy-talk bullarky, but all of it is real, and needs to be understood well, to really get a solid hold on how this stuff works.

As far as the second cycle goes, I had no idea (again, a long time ago when I was learnign too) that fuel could actually sweat onto the cylinder walls and piston top (it is called fuel impingement), and for the longest, I did not know that if you don;t pre-heat that cylinder close to the final operating temp, that this will happen on these high-pressure systems. this is a bigger and bigger problem as these engines get higher and higher combustion ratio's designed into them, and the fual rail pressures go up and up, and the injectors tip openings get smaller and smaller.

-- I.E>. Eliminate one of these cycles, or screw with it in the wong ways, then there can be problems real fast. The problems will show up right away sometimes, or not for a while, depends on how bad these cycles has been damaged by altering either that egr gas flow and not compensating for it, or by trying to improve things incorrectly because someone thinks that they can beat the many years of this development technology by simply eliminating or altering these cycles heavily.

Where does the 4 main cycles idea come from? As far as I've seen every 2350 file I looked at has 2 pilot, 2 post, and one main injection cycle. And from studying the file and datalogging, it appears to mainly use those for warmup, regen, or in idle/low fueling regions............