Great tune to terrible tune overnight

[nicknorth11]

So yesterday I was tightening up some loose ends and finally got to a point where I could do an idle tune on my car. Surprisingly, it went very smoothly, and within 20 minutes everything seemed great. I forgot to log it, so I went out today to get one and, to my surprise, everything had changed. Now, the front 02 isn't cycling, the car won't go into closed loop, combinedft went from 0 to 5.3, etc.

So, was there a catalyst? Possibly the front 02 sensor? Or is this the result of something else? I'm sorry to say I don't have the log from yesterday, but I have a log from today's mess.

I'm not sure if this stuff directly correlates, but I'll provide it nevertheless.

The timing is increased by 2 to compensate for my mechanical base timing being 3. Also, my car is a 2.3L, so I tend to aim between 32-34 for airflowperrev.



So, my main question is what could cause the same tune to yield such different behaviors with no changes to the car?

 

[mitsu_matt]

Hey Nick, how do you know you had a great tune? Who did it? Also when was it done? way colder air temps then just two days ago.

 

[BrokenTsi]

Either your front o2 crapped out, or your tune wasn't as good as you though it was.

Your injector deadtime is pretty high. Try pulling it down some, you might see the front o2 start to cycle.

 

[nicknorth11]

Hey Nick, how do you know you had a great tune? Who did it? Also when was it done? way colder air temps then just two days ago.

I mean that the tune was making the car idle great and the parameters that should be in spec were. (ie. combinedft was at 0, front o2 was cycling, the car was in closed loop, isc position and airflowperrev were good, MAFRaw was good.) I did the tune two days ago and it was F'd up by yesterday.

Either your front o2 crapped out, or your tune wasn't as good as you though it was.

Your injector deadtime is pretty high. Try pulling it down some, you might see the front o2 start to cycle.

I doubt the 02 crapped out overnight, but it's possible. The tune may not have been perfect, and I was going to post a log asking for input on it, but it was a solid tune. As for the deadtime, it's been a while since I got that number, but I'm pretty sure it's appropriate for my injectors. I'll check that out, but I doubt that's the problem, as it didn't change from one day to the next.

 

[kthackst]

Something similar like this happened to me. It looks like you were trying to tune using your injectors. This is exactly what I was doing.

A buddy set me straight. Zero out all your injector stuff, sliders and put the Deadtimes down to 300 us.

Then use the MAF Comp to get your idle fuel trims right. Hold the car at idle for 10 sec, 1500 for 10 sec, 2000rpm for 10 secs and 2500rpms for 10 secs. Do MAF Comp and check fuel trims. Repeat until fuel trims are near zero. Add or subtract dead to raise or lower grams per rev. If you have to significantly change dead time do MAF Comp again.

Turn open loop settings all the way up go for a drive varying load, rpm and boost. After a good 20mins you should be able to do the MAF comp again this time it should do the higher Hz. After this return open loop settings to stock and go for a pull. Adjust MAF Comp up or down to get the wideband to match the Command table of AFRs.

I did all that it took about an hour and now my car runs great. If you tune via injectors the MAF cant pick up on changes in the density of the air when it gets cold. So if you tune via MAF it can pick up on the changes.

 

[nicknorth11]

Great information! Thanks!