Speed Density on Evo ECU

[scheides]

Wow, reports are already coming in that setting this to 255 solves the jitter problem! Can't wait to try it out :)

[Matt D.]

Is there any reason that I should not do this to my car as soon as possible? Based on everything you've said it seems like it would cure my drivability issues and cold start idle.

[scheides]

For me to do this safely I have a wideband and have been logging logging logging my car under all driving conditions and openly accepting the fact that ultimately I could do more harm than good during this process. without a wideband, a trip to the dyno is really really necessary to get this done, and I'm sure it'd be more time than a standard tune although it isn't much more work than dialing in injectors and standard maf scaling it does take some time.

The other thing to remember is that if your volumetric efficiency (VE) changes at all, you need to brush up your fueling. If you put a few parts on and make a bit more power, you'll be running lean, as this whole system is built around specific scaling for the engine's current VE.

I'd say its worth having a wideband in the car (they're cheap now) and owning a logging cable so you could plug it in and verify all is well now and again, but I would say if shane is willing to do a tune on it I'd be willing to help anyone get converted and make sure everything's ready to rock.

Parts list:
-IAT sensor
-uprated MAP sensor, JDM/EvoX 3.3 bar or the Omni 4 bar
-wideband (LC-1 or similar)
-tactrix cable

Once I make sure all is dandy with my car I'm willing to let people check it out for themselves, I think it is absolutely worth the effort.

[scheides]

mrfred's MAF airflow reset tweak works! At cruise, at any speed (specifically 1800-2800rpm) the car drives SMOOTH AS SILK! I will be logging over the next few days to verify nothing else is changed but I'm confident that this was something that only affected airflow levels at cruise.

I'm now fully sold on speed density. This has completely transformed the car into a new level of smooth on all things that previously set the car apart from your average car that already has a smooth idle, steady cruise, and keeps everything that makes it an evo :D

[jrohner]

I'll have to give it a try again then. I'm also going to give ceddy's 98-99 DSM speed density a try (ordered an openport 2.0 cable the other day), which is based on the same thing.

[scheides]

Check back here this week, there's a change that mrfred gave us to try that might actually work better to accomplish the above issue w/o affecting some of the accel enrichment stuff (which the original hack may or may not have affected, but better safe than sorry). I'll post my findings :)

[scheides]

http://forums.evolutionm.net/7753333-post44.html

fix#2:

<table name="Scaling Factor for Transition Load" category="Speed Density Programming" address="1630" type="1D" level="1" scaling="uint16"/>

Put fix#1 back to 205 (or leave it stock if you haven't done it yet) and set fix#2 to 0.

fix#1 was SOOO SMOOTH it left my car feeling like a caddie! I was initially so impressed, I was blinded by the fact that what this fix did was actually make the car lethargic under 160load. It's too bad, because it was so nice :D Fix#2 brings back quick response and leaves the car nice and smooth, probably the best solution for 99% of everyone that would want to try this and not touch any other tables.

Here's an excerpt from mrfred about what the two fixes do:

You are welcome to use either fix if you are not having any driveability issues. Here's a rundown of the situation:

For uncompensated loads of < 70, the FPW calculation subroutine wants to use the following formula to scale the base fuel pulse contribution to the total fuel pulse:

BFPW scalar = (MasterLoadW +/- C*DeltaMasterLoadW)/2048

where "+" is used when the load is increasing the "-" is used when the load is decreasing. The "W" means the values are scaled by the fuel pulse width warmup up compensation table, aka MAFMULTWARMUP.

When uncompensated load is >= 70, then the code wants to use this formula for the base fuel pulse scalar:

BFPW scalar = MasterLoadW/2048

For reasons that aren't clear to me yet but are surely in the details of how the master load is calculated in low load conditions, a car in MAF control seems to do ok with this scenario, but a car with the SD patch does not like the DeltaMasterLoadW contribution.

Here is what the first fix does:

1) It forces the code to use MasterLoadW/2048 at all times for the base fuel pulse width scalar.

2) It changes the method for calculating the min load change needed to induce a SyncLoadAccel contribution to the total fuel pulse width. Compared to the factory setup, at low loads, the min load change required is increased, and at high loads, the min load change required is decreased. Thus the car may have a little more hesitation during load change at low loads (below 160 load), and may be a little richer during load change at high loads (above 160 load).

The second fix just forces the use of MasterLoadW/2048 at all times.

Without knowing how much SyncLoadAccel contributes to the total fuel pulse width, the second fix seems the safer route to go. However, if you are happy with AFRs during load transitions when using the first fix, then its ok to use.

What ultimately may be the best solution could be the use of the second fix in combination with access to the tables that control the min load change required to induce a SyncLoadAccel enrichment contribution. These min load change values for SyncLoadAccel contributions may be causing the jittery response that you feel with the second fix. I plan to post those tables in my advanced fuel control options thread later this week.

I'm going to run on fix#2 for a few days, see how I like it, and go from there. Might try a combo of the two or maybe dig deeper, but for your basic bang/buck speed density setup, fix#2 (Scaling Factor for Transition Load=0) is IMHO the way to go.

[rose0529]

Got to drive this car last night with the #2 fix on it. Felt very good! I had ridden with scheides just before the speed density set-up and this is a vast improvement. It had a rock solid idle and cruising seemed nice.

[jrohner]

Looks like I gotta order another GM 3-bar MAP sensor (robbed it off my 2G for my Holset-powered 1G that's running speed density) so I can give my SD rom another try with this change.

[scheides]

Do it, you will like it :) I ordered a new filter to delete my MAF today from perrin. It has a 3.125" inlet and is 95%+ the surface area of the old one but will bolt straight to the existing 3" intake pipe already on the car. I've had the MAF unplugged for a week or so now, no need for it anymore :)

http://scheides.com/misc/pics/evo/speeddensity/perrin-filter-3.125-vs-4.5.jpg