Hey Guys-
Like a lot of you, I have been quite annoyed with the extremely inconsistent deceleration (and even acceleration in some cases) of my EVO X when my foot is off the throttle. The fact that mine is an MR makes it even worse because I can't push the clutch pedal to disengage the transmission. There are times when the car does it in 1st gear and I have to jam on the brakes to keep from hitting cars/people while I'm driving in parking lots. Then of course there are the times when I downshift and the engine misses high by about 1000 rpm (followed by a complete lack of deceleration)... that's fun. Oh and my favorite... when I'm driving agressively on a road with a slight decline... let off the throttle, heavy on the brakes, let off the brakes (foot off the gas) and the f^$%ing car wants to accelerate into the turn!!! It forces me to use the brakes in very dangerous situations which in my opinion is an epic fail on Mitsu's part. For a car that is meant more for the track than commuting, it's just stupid.
So anyway, done with my rant. About a month back I had a mysterious "service engine soon" light come on. Nothing out of the ordinary for a modified car so I kept driving. Shortly after I started to notice that the engine braking issue was gone. The car had consistent deceleration in all gears and all situations until about 3 days later when the light turned off. Hmmm... interesting.
A few weeks later the light came on again for about 3 days and just like magic the engine braking/deceleration was consistent again. The car drove normal besides that. Normal idle, normal power, normal SST shifting, etc.. So that got me thinking.
A couple days later I stopped by Road Race Engineering and let Mike know about what was happening. He ran the codes and found it was a cylinder 4 misfire that turned on the light. Sweet! So after a couple tests he had me unplug one injector for about 30 seconds (basically until the "service engine" light turned on) and now I have consistent engine braking again.
What I'm hoping of course is that someone out there can use this information to develop a patch to finally fix this BS. I'm also curious if others experience the same thing in their cars (both MR's and GSR's) if they unplug an injector. Is there any reason why I shouldn't be doing this to my car? Any and all feedback would be appreciated. I'm all ears. Reply, send a PM, send an email, stop by my house, call my cell... I'm ready to finally put this issue in the past!

 

You need a tune for the tranny. You didn't say if your car is stock, but I'm assuming not. Basically, you have increased airflow beyond the "expected" values. These "expected" values are very crucial for the tranny to function properly. Funny thing is, your misfire in cylinder #4 was reducing your VE, forcing your car back down to stock values. Not exactly optimal, as I'm sure you can surmise. Talk to an SST tuner.

 

Eric at SSP Texas (Kozmic27) has already tuned the transmission. AEM intake, full exhaust, IC + piping and an engine tune by RRE are the mods. Like I said before, the car feels the same with the light on or off.

 

These two statements contradict eachother.

I would ask Eric if he created new VE tables, or if he tweaked shifting characteristics.

I can't say for sure, but I'm throwing out an idea, gl!

 

I think what supergreen125 is saying is that he gets engine braking 100% of the time when the CEL is on... even when there is no misfire at all. Just the CEL, and presumably some special ECU "CEL handling" mode.


Yes, I get this random thing too. Wideband shows clearly when the ECU hasn't gone for fuel-cut, but is instead trailing a little bit of injector action to keep life exciting.

I agree, it's very annoying indeed - particularly down a long hill, when you want to keep it in a lower gear, throttle-off, instead of riding the brakes all the way down.


So, supergreen125, your cunning plan is for some internal ROM code tracing... starting from the relevant CEL, through the flag tripped to set it... and see what knock-on effects that has in the fuel management areas? With a plan of finally tracking down an OFF switch for the random "trailing fuelling" debacle? Correct?

Rich

 

Sorry... what I should have said is "the power feels the same with the light on or off." I have mentioned this issue to Eric but he didn't have any immediate feedback about VE tables. This is an issue that's been happening with my car since I drove it off the showroom floor.

 

OK, that changes things. Your first post made it sound like the problem went away when you had a CEL (misfiring cylinder) but returned as soon as the mis-fire was taken care.
So did the engine braking issue not get resolved?
But hearing this:
throws everything out the window. So this was NOT something that started one day, its been there since day one?

 

Are you talking about the Max Enrichment/Leaning tables that determine min/max afr values for off throttle driving.

 

YES!!!! That is exactly what I'm hoping for. I know nothing about tuning or ECU mods so I have my fingers crossed that one of the XML guys will see this and use the information to create a patch that fixes the issue.

 

I do a LOT of ROM/map switching - testing out my own stuff as well as things for razorlab's Ralliart base maps, and I must say that I've noticed this issue get better/worse at times. I'll try to pin down what it is I'm changing that might feed in to the off-throttle fuel cut (or lack thereof).

It's hard, as this has never been the focus of any of my testing. But now that I think about it, I reckon there might be a pattern...

I'll do some thinking!

Rich

 

Sorry, forgot to ask - are you on original factory ECU ROM image? No reflash? Or has your vehicle been tuned?

Rich

 

Isn't the Max Lean Oct Avg AFR vs Load responsible for that? My car seems to follow it exactly.

 

whats the DTC that makes the car run better?

 

^exactly!
all his statements contradict each other and it's very difficult to make heads or tails of what is being said....

 

A raised DTC may get the ECU switching to an "error" map... which might have lower values... which might cause a change in throttle-off fuelling.

So it's relevant.

Rich