That sure does alleviate some of my worries. But knowing how "dumb" the ECU is stock once it gets introduced to FI makes me want to discover why that is.

I am assuming the ECU isn't able to recognize the capacity of the larger injector and therfore doesn't adjust the pulse accordingly? It would make sense...because in that scenario more fuel would be introduced (same pulse timing on a small injector vs. large...that obvious) but it would not be able to make full use of the 315cc's on tap.

What I don't understand though is, why would it use the previous closed loop setting when it turns into open loop with larger injectors when it wouldn't do that with stock injectors. I would think it's more logical for the ECU to open the large injectors to whatever the max was on the stock injectors. But my thinking might be way off...

I also realize that this is where something like a Megasquirt shines, and while I would love to implement something like that...it is a long learning curve and I am afraid of the downtime it would cause. It would be nice if someone came up with a preset file of base settings for it...hey, I can hope

 

FWIW the 312's (Mark's old injectors) I installed ran 25% too rich at idle with the global fuel trim at 0 and I threw a CEL (too rich) driving around with it at 0. Had to go to -2 to get it right. Oh, and mine would idle for a minute, then die with the global at 0.

I got a chance to experience all this because I was waiting for my friend (with his Scan Tool) to come over and help me.

 

Oh that's bad... were you able to keep the truck running if you gave it a little gas?

 

This thread is really good reading! Hope you get things figured out with the engine Mark, and definitely x2 with the get-what-you-pay-for mentality.

I just thought I'd mention that a logging system is a useful thing for quick tuning (in theory at least) because for open-loop running (or modified closed-loop, as in O2 signal conditioners) you can do some logging of RPM-MAP-AFR readings (assuming you have a compatible wideband setup, for a 3-D plot), and then adjust your fuel map based on any anomalous AFR readings. I don't have a logger, but it would seem that in theory at least you could go drive around and log a broad a spectrum of engine conditions (perhaps even 2-3 runs averaged) and then crunch the data on your computer, adjust the fuel map as needed, and you're off!

And Mark, I'm definitely interested in helping out with a S/C FAQ. I'm a bit new to the scene, but I'd love to help make a really useful document for all of the information that gets dumped in this forum (and others). Let me and Marko know...

My 0.02 for now.

 

Well, remember that the ECU is designed to set 14.7:1 ("Stoich") in closed loop, and it does that by sniffing the A/FR from the O2 sensor and then messing with injector timing until it gets there. Now add that it's also looking at the TPS and MAF to figure out if you're trying to get more power, and if so it'll run things rich in anticipation of more air coming in.

Now, the ECU doesn't really know that you have 240cc injectors in there, it just knows that it has a gap this ]----------[ long in which it could possibly hold the injectors open. So, right now, lets say that it's running the 240's at a 40% duty cycle for a certain TP/MAF/O2 reading in order to hit Stoich.

Now you drop in injectors that have the ability to flow 25% more fuel _at a 100% duty cycle_. I underline that 'cause the "25%" may not be linear for the next example...

So, the first thing that will happen is that when you get to the spot where the ECU used to know "40% duty cycle", you'll be running rich. The ECU will go "oh, umm, okay" and then will be stoopid and guess WAY low and probably set the duty cycle to something like 20%. That'll be lean, so it'll go to 35, then 25, then it may settle on 33. This is what causes the wide swing of an A/FR narrow band.

Anyway, the ECU will eventually find the new Stoich point.

SIDE NOTE: This is why you should reset the ECU any time you do something that will modify fuel or air flow. It'll make the process of finding Stoich a LOT quicker.


It does do that with the stock injectors. Kinda' see above - the ECU's been tweaking itself all along, and with everything else being equal, then it's pure math to figure out how much fuel it takes to mix with a given amount of air to hit Stoich. So, when the ECU readjusts to my example 33% number above, then that's what it knows. Again, it doesn't know anything about your injector size, only how long it has to leave the injector open to get to Stoich.

There's no AI in there that says "oh, for the last 5 years, I've been running at 40%, now I find that I'm running at 33% for this map position, so that must mean that the injectors are 7% larger".


Oh, the MS is a WHOLE 'nudder can of worms. There are plenty of upsides, but yeah, it's a curve.

 

Really? Wow... I guess I do remember you saying that. With my SMT5 issues in loosing it's memory for a while I'd often have to run without it in the loop, which lead me to say what I told Marko.

Hmmm...


(brian... hang in there for your PM!)