SOI?

[907DAVE]

Ok, so I know this is gonna sound kinda dumb.

Is there a magic number for max SOI?

Like a rule of thumb, dont exceed XX degrees at XXXX ICP at X.X PW at XXXX RPM.:doh: I realize this has been the mystery for tuners for quite a while, and probably varies greatly for different injector combo's and I'm sure no one wants to say. I have seen a few SOI maps that are extremely different and I am trying to establish some boundaries to play within.

Can you tell from engine noise when you have gone to far or is it not so obvious?


Thank you for being patient with me.

[F-127]

I can't help you too much, just maybe help point you in the right direction. Check out the forum for Analytune (http://forum.gopowerhungry.com/forumdisplay.php?f=97). The idea of Analytune from what I read is to make sure that your SOI, ICP, and PW are within safe parameters. My guess this will be to help make sure your small tweaks don't add up to a big change which could cause some problems.

[cleatus12r]

Oh boy.

This is going to sound real bad of me, but as far as the "magic number" goes, it is ALL dependent on so many things.

EOT plays a HUGE role in start of injection.
The SOI map is simply based on Mass Fuel Desired vs. Engine speed................

There's a map for an adder based on those but for low boost...............

There's a delay map that factors in the electrical/mechanical delay inherent in the injectors....................

The injection control pressure has an effect on the actual start of combustion........

Physical combustion chamber temperature has the same effect...............

Boost pressure (dynamic compression) has a similar effect on speed of flame travel......

Backpressure seems to have an effect as well...............

There are far too many variables to put a "magic number" in for any particular engine. Every engine is going to be different for a maximum or "sweet spot".

As for the ability to tell how much is too much; a trained ear can hear it but you probably don't want to hear it very long before fixing it. It sounds terrible...like marbles in a barrel at extremes.

Good luck.

[907DAVE]

Wow...boost and backpressure were two things I would have never even considered. I did not think there would be an easy answer to this, just trying to be cautious.

Is there any way to see the TOTAL commanded SOI, without the use of a labscope?

[cleatus12r]

Supposedly, the datastream will give you an actual "calculated" SOI. However, comparing that with a lab scope MAY show some discrepancies. I plan on trying it here in the near future.

[907DAVE]

I have never seen that PID before. Probably need the NGS or IDS to see it.

[cleatus12r]

I have seen it somewhere. Bill posted a link to an Excel spreadsheet datalog.....I'll see if I can find it.

[cleatus12r]

Here it is....

http://forum.gopowerhungry.com/showpost.php?p=18491&postcount=7

[907DAVE]

What was used to datalog? Looks like that truck had a decent HPOP on it tho:)

[cleatus12r]

Some program Bill has with a much faster sample rate than AE has....come to think of it, it's way faster than the Genisys too.

[907DAVE]

Some program Bill has with a much faster sample rate than AE has....come to think of it, it's way faster than the Genisys too.

Pretty neat to be able to datalog like that....... any ideas on what program that is?

[cleatus12r]

No sir.

I know AE will datalog as with most scan tools. However, I am still skeptical as to the accuracy of any data coming off of the OBD port.

[907DAVE]

No sir.

I know AE will datalog as with most scan tools. However, I am still skeptical as to the accuracy of any data coming off of the OBD port.

Agreed! I too am skeptical of most data that the scan tool shows. Great for getting an idea but 100% accurate, no way! I am curious what you find when using a scope to check thinks out.

[Power Hungry]

I am curious as to why you would be skeptical of anything coming from the data bus? I mean, with the exception of SOI which depends a LOT on the mechanical relationship between the crankshaft and the CPS, why would you assume that any of the data form the bus is invalid? You're seeing exactly what the PCM is seeing. The PCM doesn't fudge the numbers it sends you.

As for the SOI, I don't think there are ANY scantools that offer that parameter because it's not a PID.

The hardware and software that I use for datalogging are available for about $1200.00. Not practical for most folks. ;)

[cleatus12r]

I am curious as to why you would be skeptical of anything coming from the data bus? I mean, with the exception of SOI which depends a LOT on the mechanical relationship between the crankshaft and the CPS, why would you assume that any of the data form the bus is invalid? You're seeing exactly what the PCM is seeing. The PCM doesn't fudge the numbers it sends you.

As for the SOI, I don't think there are ANY scantools that offer that parameter because it's not a PID.



I guess I really don't have a valid reason for not trusting the data. I think it stems from a few different sources dating back almost a decade. I haven't datalogged or scanned a 7.3L for almost 6 months. I may have confused the scan tool timing data on a Duramax.

I apologize for causing a stink and possibly throwing out some bad information. :sigh:

[907DAVE]

You're seeing exactly what the PCM is seeing.

That is why I dont trust scan tool data 100%. There are alot of things that will affect what the PCM "sees" (volt drop, resistance, etc)and corrupt your PID's.

[Power Hungry]

Cody... don't worry about your post. It's not bad information as such, just a difference of opinion on how reliable you find the data bus to be. I certainly don't disagree with the theory of "garbage in, garbage out" but I would ask you to consider for a second that if the PCM can't produce consistently reliable data pertaining to the vehicle's operation, then what's the point of it in the first place. Granted there are mechanical aspects that the PCM might not be able to compensate for:


Timing gear/chain wear affecting the CPS output
Bad CPS
Worn injectors/weak solenoids
Weak IDM

However, the only thing that's going to tell you if those (or other) items are causing problems is a scope, a breakout box, and time.

Because I expect the PCM to generally work from reliable data, I tend to trust the data being provided via the OBDII port. After all, this is the same data that the PCM is using to generate all its outputs. Is it the end-all, be-all of tuning? Of course not. But it does provide valuable data in relation to changes on a specific vehicle and I can use it to determine just how much more or less aggressive certain files are in comparison to each other. In the grand scheme of things, is 2 or 3 degrees of SOI or .3 ms PW going to make all that much difference when there are tunes out there that more than DOUBLE the SOI or Injection PW? Probably not.

Like anything else, it's a tool that provides information. As I see it, the more info, the better. :2thumbs: