So I decided to do a little experiment over the past days, and I'm now sitting with a perplexing question about how and why my LTFTs (at idle) have gone up from the +3 range, to the +15 range. Here's the rundown.

8/1: I decide to remove the off-the-shelf tune that I'm running with my Cobb AP, and put the ECU to stock configuration. At the same time, I stop running 85 octane, and start using 91. Things seem to run fine, AFR's are good, KR seems to improve slightly, car is obscenely slow now, but the lack of zip, I realize has come at the expense of the "detune". Either way, it's late at night, so I don't get much data logging done.

8/2: A monitoring day, and I see a noticable difference in KR%, right off the bat. Although I never really got dangerous KR on 85 gas, when it did happen (~10 to 20 times during 30 minutes of driving), it came to the tune of 3 to 5 degrees normally. I would see the ocassional 6 and 7* on days where the temperature was in the 90's, and at WOT. However, on the 91 octane, I got virtually no KR (3 total occurances total in 21 minutes of hard driving) and those three instances were 0.35* (twice) and 1.05* one time. I can say confidently, that 91 octane has virtually eliminated KR in my engine, under stock ECU settting, and on a rather hot day, to boot. The car is still missing its anger since I'm still w/out tune, but still runs very well, and pulls okay. I must give credit again to the 91 octane for allowing my ECU to advance timing a bit, and squeeze a bit more pep.

8/3: I decide to finally have MAC install my new, 1-step-colder, NGKs. Long story short; an entire day is used, because my shipment of 4 plugs came with one dud, and thus I had to wait for NAPA to get one, and MAC had to wrench on the car twice. Either way, the new plugs are in, and all is well. KR is still very much reduced, with it never being more than 1.75 degrees.

However... My LTFTs at idle are now sitting at +15 (??)

What's the deal here? Does it take a couple of days for this to settle into a more reasonable range? I'm still on a stock ECU configuration, but I found this a little concerning, and I don't want to put my off-the-shelf map back on the car, until these figures get more into spec.

Thanks in advance for the thoughts.

What are you STFT's at idle?

Do you have an aftermarket intake?

chickenwafer wrote:What are you STFT's at idle?

Do you have an aftermarket intake?

I'll look now, hold please.... And yes, I have a Mazdaspeed CAI, mated to a Vibrant turbo inlet pipe.

Well basically whats going on is the car thinks there's more air coming in and is adding more fuel to compensate. Honestly I think you have a vacuum leak, this will cause the exact issue you're having. Check the vacuum lines to the BOV, as well as the pcv system.

Basically nothing wrong w/ the tune, or because the gas you're using or the plugs, just something didn't get plugged back in right vacuum wise or there's a hole in a line.

At idle, my short terms are averaging around -8. It's volatile at idle though, bouncing all over from -15'ish to -3ish.

It's kind of all over the map, but averaging -8

one other thing to try...reset the ECU by pulling the battery and waiting for 5-10 minutes with it disconnected. Hook it back up, start the car and see where your fuel trims are at. If they're still ****ed, vacuum leak.

tbot wrote:Well basically whats going on is the car thinks there's more air coming in and is adding more fuel to compensate. Honestly I think you have a vacuum leak, this will cause the exact issue you're having. Check the vacuum lines to the BOV, as well as the pcv system.

Basically nothing wrong w/ the tune, or because the gas you're using or the plugs, just something didn't get plugged back in right vacuum wise or there's a hole in a line.

I'll check all of the lines to/from the BOV. I don't know what a PCV system is though. (?)

Will most vacuum leaks not throw a CEL at some point though? I'm surprised I haven't seen one light up yet.

No they won't thro a CEL unfortunately. You could also call up MAC and ask them if they had to disconnect anything. Check your intake too, there's a couple things that attach to it, aka pcv system (hose comes from the valve cover) as well as the bleed off from the turbo, those would cause issues like this too.

Wait, you were running 85 octane? Why? Educate me!

^^don't ask!!!! Please for the love of god don't bring this debate back up!!!!

~Barn~ wrote:So I decided to do a little experiment over the past days, and I'm now sitting with a perplexing question about how and why my LTFTs (at idle) have gone up from the +3 range, to the +15 range. Here's the rundown.

8/1: I decide to remove the off-the-shelf tune that I'm running with my Cobb AP, and put the ECU to stock configuration. At the same time, I stop running 85 octane, and start using 91. Things seem to run fine, AFR's are good, KR seems to improve slightly, car is obscenely slow now, but the lack of zip, I realize has come at the expense of the "detune". Either way, it's late at night, so I don't get much data logging done.

8/2: A monitoring day, and I see a noticable difference in KR%, right off the bat. Although I never really got dangerous KR on 85 gas, when it did happen (~10 to 20 times during 60 minutes of driving), it came to the tune of 3 to 5 degrees normally. I would see the ocassional 6 and 7* on days where the temperature was in the 90's, and at WOT. However, on the 91 octane, I got virtually no KR (3 total occurances total in 21 minutes of hard driving) and those three instances were 0.35* (twice) and 1.05* one time. I can say confidently, that 91 octane has virtually eliminated KR in my engine, under stock ECU settting, and on a rather hot day, to boot. The car is still missing its anger since I'm still w/out tune, but still runs very well, and pulls okay. I must give credit again to the 91 octane for allowing my ECU to advance timing a bit, and squeeze a bit more pep.

8/3: I decide to finally have MAC install my new, 1-step-colder, NGKs. Long story short; an entire day is used, because my shipment of 4 plugs came with one dud, and thus I had to wait for NAPA to get one, and MAC had to wrench on the car twice. Either way, the new plugs are in, and all is well. KR is still very much reduced, with it never being more than 1.75 degrees.

However... My LTFTs at idle are now sitting at +15 (??)

What's the deal here? Does it take a couple of days for this to settle into a more reasonable range? I'm still on a stock ECU configuration, but I found this a little concerning, and I don't want to put my off-the-shelf map back on the car, until these figures get more into spec.

Thanks in advance for the thoughts.

I hope you didn't pay him to put plugs in ur car...thats very easy to do urself!

Stealth01 wrote:Wait, you were running 85 octane? Why? Educate me!

tbot wrote:^^don't ask!!!! Please for the love of god don't bring this debate back up!!!!

Yeah... A discussion worth having, but maybe this thread isn't the best place for it. I'll chat you up about it, over a beer sometime!

rmeeker13 wrote:I hope you didn't pay him to put plugs in ur car...thats very easy to do urself!

I did actually. Half-hour of labor (read: 45 bucks). But then again, if it weren't for them doing it, I would have never been able to find out the misfire that was being caused by the dud plug. He went from bank to bank with it, watching the misfire happen in each cylinder, he tried it on.

So yeah... I guess it is a noob-move on my part, but in the end, well worth the money. It's would have been a disaster if I tried to do it myself.

Wait so you were getting 6-7 degrees of KR at WOT while using 85 octane and you didn't think that was a problem?? I thought you were using 85 because you weren't seeing any KR.

But yea, I just had a problem with my fuel trims skyrocketing and it ended up being a vacuum leak.

Stealth01 wrote:Wait, you were running 85 octane? Why? Educate me!

tbot wrote:^^don't ask!!!! Please for the love of god don't bring this debate back up!!!!

~Barn~ wrote:

Yeah... A discussion worth having, but maybe this thread isn't the best place for it. I'll chat you up about it, over a beer sometime!

An octane discussion should be very, very short.

Fact: And engine will run THE BEST on the LOWEST octane it can SAFELY burn. That is indisputable. This is why putting race gas in a car not tuned for it will actually make you LOOSE power.

The only "debate" that could come into play would be what is the lowest octane a given engine can safely burn. If you're picking up excessive knock on a given octane, then it's not safe.

IMO, if you pick up excessive AUDIBLE knock, the octane is too low.