My tune drifted lean...Why?

[StealthyStu]

I have an AEM EMS with speed density and I do lots of the tuning now myself. I had it tuned pretty well in the middle of May. Since then though, the car has started to drift lean. It was very noticeable at idle. The first sign was the car killing itself after going from engine breaking (deep vacuum) into neutral. I thought that may have been something to do with my IAC. I was pretty busy finishing up school so I didn't have time to figure it out then. Over the next month or two, the car started having a harder and harder time starting. I've never had a great start tune, but it would sometimes take 4-5 times to start now instead of 2 tries at most. Then, more recently, I noticed that my idle drifted from 15 afr to 17 and leaner.

I thought the air temp correction table was the problem, but I had to adjust it about 15% to get my car back to a good afr!

I retuned my car and added 15% across the board for fuel. My car started better, didn't kill itself after engine breaking, and had better afr for idle, but my WOT pulls went from 11.5 afr down to 10.

What would cause my car's tune to drift in vacuum but not under load? I'm running speed density, so if I have a vacuum leak it would have to be at my throttle body or after. Is there something else that it could be?

[Badandy247]

A vacuum leak is most likely especially since you're only noticing a lean condition at idle and you went rich under throttle when you added fuel to compensate. Good luck with it, hope it's a simple fix.

[i3igpete]

he is running speed density, so any vacuum leaks are already accounted for by the manifold pressure sensor.

can you post up your air temp correction table?

[Badandy247]

Pete, what do you think about the possibility of an injector O-ring leak? Would the MAP sensor be able to comp for that? I was also thinking about the FPR but if that were malfunctioning he would be rich at idle correct?

[StealthyStu]

3203

This is my current setting for air temp correction. I tried to get it back to what I had it at originally. When I messed with it last time I pulled the temp from 60-176 up to about +15%. My IAT reading is about 104 degrees now, so that change would be a difference of about 20%

[StealthyStu]

Also, in regards to an o-ring leak at the injector, I have yet to smell any fuel in my engine bay, though I have been meaning to replace the o-rings because they are beginning to crack. I should also mention that my fp drops to about 10 psi after a minute or two of killing the engine. I probably have a leak at an o-ring somewhere, but if it's able to hold even 10 psi I would think it's a fairly small leak. Let me know if you think otherwise though

[StealthyStu]

Any thoughts?

[Badandy247]

What have you done troubleshooting wise since we last threw out ideas?

[StealthyStu]

Hi Badandy247,

Unfortunately busy doesn't even begin to describe me right now. I haven't had any time to spend in my car with a laptop. To be honest though, I don't know where to start. My guess is that something mechanical must be going for my tune to drift, and at that, I want to say it's fuel related, but with the right fp at the rail and no smell of fuel in my engine bay, maybe it's not. I've turned off individual injectors to see if 1 may not be spraying but they all caused the engine to bog when turned off. All of that makes me think it's not fuel. Having speed density makes it tough for me to believe that there is air somewhere that is unaccounted for. And that leads me to where I feel I am now. Stuck :/

[niterydr]

Simple question. Do you have 02 feedback on? What are you settings? How old are your 02 sensors? I've seen vehicles with an incorrectly setup 02 correction (wide range) have an wideband 02 sensor fail and pull the vehicle lean.

[StealthyStu]

I hadn't thought about that! I'll try to figure out if the wideband works or not. It's been in the cars for ~4 years and my tune has o2 feedback turned on. Unfortunately I probably won't be able to get to that until next week. I'll post an update when I do get to it. Thanks!

[i3igpete]

what is your load point to disable o2?

[niterydr]

what is your load point to disable o2?

Great point. He could also just turn off o2 feedback, reset the tune to where it was, and see how it reads as a quick test.

[J. Fast]

So my tune drifted lean this week. Haven't touched it in months. I opened up the cal at Errons house on his laptop and what do I find, the decel table was zero'd out. Opened up the original cal (the last saved one on my laptop I uploaded) when I got home and the decel table was on there. Hrmmm, wierd little bug in the EMS, just got a mind of it's own on Thursday or Friday day and deleted my decel table. I fixed it in about 5 mins, but WTF? Anyone have their EMS do some witchcraft like that?

[i3igpete]

i've heard of something like this before in the past, but i think it was related to the firmware change not carrying all the tables over correctly.

[J. Fast]

Hrmm, very strange, it's never done that. I'm still running 1.19 and have been for years. Just started behaving strange last wednesday. I asked Erron if I could borrow his laptop when I stopped by on Saturday because I got stuck in traffic for two hours and the engine wasn't behaving like it normally should. Idle started hunting, decel sounded a little throaty and was popping, and when I would pop out of gear into neutral on decel the Tac needle would crash to 300-500 rpm, dim the headlights, and hunt to recover.

Sure as shit when I pulled up the decel graph it was zero out. As a matter of fact all the decel features were missing? Checked on it yesterday before our meet and everything was there? I'll be watching this from now on. I've put nearly 10K miles on it since July so I'm used to a certain type of behavior. From being in the drivers seat so often I immediately recognized a changed and knew something was up right away.

I've never had to reload a cal. I could disconnect the battery for months and come back and crank the car and it would fire with the same cal. This was strange to me.

[zba857]

update?

[vr4tune]

I had a recent experience causing my tune to change around on me. Some days it was fine and other days it wouldn't idle. The culprit was the map sensor. Put in new map sensor and had to retune for it. Perfect ever since.