? about tuning

[boostless]

I'm new to MS and was reading through the manuals wondering if you actually have to do the calculations to figure the time open (PWM?) for the injectors? I was reading the manual and couldn't understand if this is something you tell MS what size/how many injectors your running and it calculates it for you or you have to do the calculations and put it in yourself. I apologize for the ? but couldn't find it elsewhere and want to know what I'm getting into before I jump in.

[Zmanco]

MS calculate PW based on the setup criteria you give it (# and size of injectors, size of engine, etc) along with MAT (manifold air temp), MAP (manifold absolute pressure), and VE table. It's the VE table that you use to tune.

 

You might want to reread the section in the manual where it discusses the ideal gas law and how MS uses it to calculate the PW.

[BLOZ UP]

It's based on the brand/model of injectors. High-impedance injectors are generally a little slower to open fully. You can guess (ie use the times mentioned in the megamanual), and if it's wrong you can just tune it out. However, the more accurate you are with the opening time, the easier it is to tune. Especially at idle with large injectors.

[Zmanco]

I think I misunderstood your question and blozup got it right. Injector opening time has to be measured. You can tune around it if you're not close, but you may see strange patterns in the VE table. If you use a time that's too short, you'll see the VE rising as MAP goes down - which isn't how the physics actually works. That's a clue that you need to extend the opening time a little.

[boostless]

Zmanco, I think you were on the right track with your first post. So you adjust your fuel off your WBO2 sensor right? I.E. if it's running lean you would have the injectors open for a longer period of time and vice versa if it's rich?

[Zmanco]

So you adjust your fuel off your WBO2 sensor right? I.E. if it's running lean you would have the injectors open for a longer period of time and vice versa if it's rich?

I think you're missing the bigger picture: based on the engine constants and variables such as MAT and MAP and target AFR, MS can calculate how much fuel is required for a given combustion cycle assuming the cylinder is filled to atmospheric pressure. However, an engine is an imperfect air pump so will usually not fill the cylinder with 100% of the air it could hold (to keep this simple I'm ignoring forced induction and only discussing NA). At part throttle it's less efficient than WOT. That's where the VE table comes in. Think of it as a scaling factor that tells MS that at a particular MAP and rpm that the engine can only "pull in" so much air. The VE table is the main thing you tune.

 

In a perfect world, once tuned, the VE table would result in the exhaust hitting the target AFR all the time. In the real world there are other factors that affect the combustion process that MS cannot control. With a wideband O2 sensor, MS looks at measured AFR, compares it to the target AFR, and adjusts the PW to get closer. Depending on which version of MS you run, there are different algorithms it follows. The O2 correction is useful for making small corrections, but it is NOT a substitute for a properly tuned engine. Hence it's important to tune the engine (mostly with the VE tables) to get pretty close and only rely on the O2 correction for small errors.

 

One more thing: in terms of how you would tune a new MS install, it's easiest if you can find someone with a similar engine build and use their tables as a start. From there go drive while datalogging, and then use MegaLogViewer (MLV). MLV will look at the datalogs, compare them to the target AFRs, and make changes to the VE table. Before accepting them you need to review them and make sure they follow the rules of common sense. If they don't, that's usually a clue something else isn't set right.

 

All of this is discussed in more detail on the MS site and I really encourage you to spend a few days there reading. MS can seem overwhelming at first, but as you begin to understand the theory and get used to the new vocabulary, it actually becomes rather simple. But you can't spend too much time reading! This isn't one of those types of projects where you study a little, then jump in and do the install, and then figure the rest out by trial and error. That approach usually ends in frustration.

[Zmanco]

FYI, here's a thread I started shortly after I finished my original install:

 

http://forums.hybridz.org/showthread.php?t=122277

 

Each version of MS is its own world and switching from one to another can cause you to start to over with tuning. So it's most efficient if you can start with the one that best fits your needs. I'm a huge fan of MS 2/Extra, but if you're doing fuel-only, and not using it to control idle, MS 2 works well too.

[BLOZ UP]

Ohhh, I see what he's asking now.

 

Yes, MS calculates how long to hold the injectors open from the injector size (actually req_fuel, but it's calculated from injector size), engine size, number of injectors, number of cylinders. Then, It also factors in what RPM and load % you are at. As well as Warmup enrichment, etc., etc., etc.

[boostless]

Thanks guys, I have a better understanding of how it works and will definantly be looking to get MS