Fuel Trims while at the drag strip doing a data log

[rtcat600man]

Originally Posted by TriGun

Fuel trims info means nothing when the car enters Power Enrichment mode. Only a wide band O2 sensor data at PE is dependable. Maybe the mV readings of the narrow band sensor could give an indication but again is not dependable.

Correct. The debate about the fuel trims was weather the RX breather was creating issues with the fuel trims. So I posted what mine looked like so as to continue this debate.

Someday I might add a wide band O2, but for now, the computer is doing it's job.

[AKA-22]

sub

[pgustavson]

Originally Posted by rtcat600man

Correct. The debate about the fuel trims was weather the RX breather was creating issues with the fuel trims. So I posted what mine looked like so as to continue this debate.

Someday I might add a wide band O2, but for now, the computer is doing it's job.

+1 I own a wideband O2 sensor, and plan to install it when I do my exhaust and when I finish my custom gauge pod design.

I think I may know why I have such high positive LTFTs during cruising - I had forgotten that I did the Tracy-recommended "drill mod" of the dirty-side PCV orifice. That probably increased the amount of un-metered air entering the system. I still must say that I never noticed any issues at idle even though I effectively had a vacuum leak...

Anyway, I was able to restore my OEM clean-sided by modifying my Vararam intake, so I now am back to a closed-loop PCV set up. After I get some miles on it, I'll do another data-log. Hopefully the LTFTs will drop and stabilize.

[rtcat600man]

Originally Posted by pgustavson

+1 I own a wideband O2 sensor, and plan to install it when I do my exhaust and when I finish my custom gauge pod design.

I think I may know why I have such high positive LTFTs during cruising - I had forgotten that I did the Tracy-recommended "drill mod" of the dirty-side PCV orifice. That probably increased the amount of un-metered air entering the system. I still must say that I never noticed any issues at idle even though I effectively had a vacuum leak...

Anyway, I was able to restore my OEM clean-sided by modifying my Vararam intake, so I now am back to a closed-loop PCV set up. After I get some miles on it, I'll do another data-log. Hopefully the LTFTs will drop and stabilize.

IMHO I do not think this is the cause. I too did the opening of the holes, and do not see anything strange with my numbers.

[pgustavson]

So maybe I have a leak somewhere else...

[rtcat600man]

Originally Posted by pgustavson

So maybe I have a leak somewhere else...

Have you done a data log and asked Vince to take a look? I am going to guess it will show up as everything is fine. But worth the time and effort to make sure.

Other thing that comes to mind, CAREFULLY check the intake manifold bolts for proper torque, I know they loosen up over time after the re-install.

Lastly check all the connections for the Vararam.

[pgustavson]

The log I posted was sent to Trifecta, and yes, I got a "Looks good" response.

Yes, the first thing I thought about was the IM bolts. I re-torqued them about a week after the ported IM/isolator install almost a year ago. I haven't checked them since - I'll try to make some time this week to do so again.

Thanks.

[Jason@JacFab]

Great info guys... I will keep an eye on this thread...

I had some issues early on with the RX breather/can on my previous 2010 SS, and in the end, I ended up running without the breather, and utilizing the OE clean side hard line. I currently have the catch can installed on my 13 LFX car, but not the breather.

[pgustavson]

I have just realized that there could be another reason for my f-ed up LTFTs above. About two or three months ago, I found that I pulled the boneheaded move of leaving my catch can drain valve open. So it's entirely possible that the data-log above was done with the valve open. Talk about maybe ruining my experiment here...

I'm still going to check the bolts, however...

[rtcat600man]

Originally Posted by pgustavson

I have just realized that there could be another reason for my f-ed up LTFTs above. About two or three months ago, I found that I pulled the boneheaded move of leaving my catch can drain valve open. So it's entirely possible that the data-log above was done with the valve open. Talk about maybe ruining my experiment here...

I'm still going to check the bolts, however...

That will do it for sure. That is a vacuum leak. Run another set of data logs with it closed and see what happens. Nothing to it. Good Luck and be sure to let us know what happens.

[911medic]

All right, here's a few charts of my fuel trims.

The first two graphs are the stock intake setup on 87 octane gas. This is a 74 second snapshot with a WOT acceleration period on a freeway onramp. This was from last April. Temps were in the low 30's (F).

Graph #1: LTFTs are the red and blue lines. STFTs are the green and yellow lines. The purple line is AFR-commanded. The WOT period was where the two yellow lines have their highest peaks (right before the STFTs go flat):

Graph #2: The same run, but this one shows the STFTs (same colors, green/yellow), the MAF rate (blue line, makes it easy to see the WOT section), as well as Knock Retard (red line) and AFR-commanded (purple line):


Graph #3: The very next day. Same stretch of road, same temperatures, same WOT section, etc. The only difference is, I filled up with 91 octane the previous evening. Otherwise, this graph has the same parameters as graph #1 above:

Graph #4: Again, same run as #3. Identical situation as graph #2, except with 91 octane:


OK, let me see if I have any data from the brief period I ran the RX breather...

BRB

[911medic]

OK, this data was taken on May 10, so about a month after the last data set. It was a bit warmer here at that time; around 41 (F). I'm not sure what effect (if any) that would have on the results.

Same freeway entrance ramp, same 74 second time period, same WOT section in the middle. 87 octane gas again. Difference this time is that the RX breather and RX catch can were installed.

Graph #1: Same as graphs 1 and 3 in my previous post:



Graph #2: Same as graphs 2 and 4 in my previous post:



So, to my relatively untrained eye, the immediately noticeable differences here are:

• My LTFTs are much higher. A lot of time over +10%, and certainly hovering around the +10% area, whereas without the breather LTFTs hovered in the 3-5% range on 87 octane, and in the 4-7% range on 91 octane.
• The STFTs aren't adjusting as abruptly. The sawtooth pattern is generally wider.
• The STFTs start out positive and then go negative after the WOT phase, once the car is up to highway speed (see the MAF rate after the WOT acceleration; it's higher than pre-WOT because I'm on the highway going 75+ MPH).
• There is consistently more KR, which appears to coincide with higher MAF rate.

I'm not sure how to interpret this data, and quite frankly I've had too much Jack Daniel's at this point to try.

I'll admit that three sample runs are not a good sample size. But again, Jack says, "Enough number crunching for tonight," and I'm taking his advice.

I welcome the thoughts and interpretation of the more knowledgeable.