Data log, how rich is too rich?
 

I finally got my PLX Kiwi2 in the mail, I fixed my vacuum leak and wanted to get a data log to ensure that everything was good. Far as I can see it looks good, but its pretty rich on the top end. I wasn't sure how much timing I should be seeing in the power band, or if running 11.0 was richer than normal. A pdf of my run is attached.

AFR's look "normal" for the OEM tune. What is concerning is seeing the +9 on the LTFT through the band. I personally would reset your trims and let the trims build fresh after fixing your leak. (disconnect battery, hit brake pedal within 30 seconds)

Paimon, I reset the fuel trims after fixing the leak which was about a week ago. Does a high long term fuel trim mean that the ecu is still seeing too much air and is trying to adjust? Aka, I still have a vacuum leak somewhere?

edit, I reloaded the pdf with the AFRs on the same page as everything else

A high positive ltft could be an indicator of a leak, but I would also take a look at your maf. Make sure it isn't dirty (dirt or oil).

Where was your original leak? Is your intake OEM?

my leak was in the aux runner section of the intake manifold, the two layers of plastic had warped/pull apart enough for cleaner to leak through (and air). Post was here :

https://www.rx8club.com/series-ii-te...-253766/page2/

My intake is stock, I have an Afe dryflow panel filter. The intake tube did have some oil in it, I took the tube/airbox assembly apart and cleaned everything with MAF cleaner. I was surprised at the oil, when I changed the filter the first time (3months ago) the tube was bone dry. This time there was a small amount that dripped down into the airbox. I was planning on getting a catch can setup, just havent yet. I doubt (hope) that the MAF isn't dirty after a week...

This thread is very timely for me. I have been watching my fuel trims recently, and am also seeing a consistently high (9-10 range) LTFT. I've reset the trims twice over the last 2 weeks and both times it eventually went back to ~10; the first time it took 3 days to go back, the second time it went back within a day (same driving route).

I had some oil in my (stock) intake which I cleaned up and replaced the air filter over a year ago (most likely my fault for over filling the oil when I first got the car). Since then I've cleaned the MAF and periodically pull the air box out to make sure I'm not getting oil in there (just checked again last week and it continues to remain dry). This confirms my suspicions that I should clean the MAF again, and start looking for a possible leak.

Any chance that the perennial P0420 from the cat-less midpipe is involved in this? Unfortunately I didn't start monitoring the fuel trims until after I had already changed over from the stock cat to the midpipe, however, +10 seems (to my uneducated eye) to be more than I would expect from a post-cat O2 sensor.

P0420 shouldn't cause this. I ran catless and continue to run catless without any abnormal LTFT (even before i tuned).

I would double check all sources of leaks
- if you have oem intake, make sure the accordion tube isn't cracked
- make sure your maf is properly cleaned and sealed (it never hurts to put some dielectric grease on the maf housing to make sure that the maf is properly sealed in its seat
- make sure that your vfad line didn't become disconnected (behind the TB)


If I remember correctly, O2 sensors typically fail lean, so a positive fuel trim could also point in that direction, but I have yet to hear of an S2 having issues with its o2 sensors (maybe someone else can chime in).

Could you get some idle logs? I'd be interested to see your idle trims against the maf voltage and maf g/s

I am catless as well but I haven't had a P0420 code in weeks. When I cleaned my accordion I looked for cracks, wasn't any. It was nice and flexible still. The 02 sensor occured to me, but if it was failing and reading lean wouldn't I be seeing lean on the AFR? I had the data log set to read exactly what the sensor was seeing, no calculations involved. I'll do a idling log tomorrow, see what comes up.

Assuming that my faint memory recallign someone saying o2 sensors fail lean (meaning dont take this at 100% truth), yes your AFRs would show leaner than actual ... but that is where your trims would start to pile up to help bring that afr back to stoich.

I'm seeing air flow rate through the MAF at 4.2-4.4 grams/second at idle (fully warmed). My ultragauge won't let me view MAF voltage.

Interestingly, I cleared the P0420 and the LTFT went up ~15. When the code comes back I'll see if clearing it again causes the same change. If it turns out to be a consistent thing then I'll put the cat back on and see where that takes me. In the mean time I'll continue to route around for any possible leaks.

4.4 is really low. you have a vacuum leak somewhere. 5g/s is the average you should be seeing from our cars.

Posted From RX8Club.com Android App

Looks like my leak may have been at the MAf itself. The two screws that hold it in were just free spinning, allowing the sensor itself to be wiggled easily. No idea how it got like that, since it wasn't like that the last time I took it out for cleaning, and nothing I did could get them to tighten up. Couldn't find any other leaks.

At idle my LTFT sits right at 7, so not too high. My idle G/S is around 4.6 at ~825 rpm. Could still be a small leak somewhere, there was a spot on the main plenum that I thought about filling as well...... I'll have to take another look at it. The car feels a lot better though, nothing like before. Engine sounds a lot nicer too lol. I've attached a idle log with everything warmed up.

Positive fuel trims (your persistant STFT has just transfered to LTFT at this point) and under ~5.0-5.5 g/s of airflow means you have a vacuum leak. When I had a UIM to LIM gasket pinched that caused a leak, it was 4.5g/s and +6% STFT.

The engine is still consuming the same amount of air, but not all of it is going past the MAF, so the O2 sensor sees air for 5.5g/s and is fueling for 4.5g/s, which is lean, so the ECU adds fuel to compensate.

Thanks for your input RIWWP, I'll dive back into my manifold and fill those other spots that were questionable. I looked at all the gaskets and they all looked/felt good (they should with only 40k). Don't know how I got such a bum manifold, how do people hold any boost with all these seal issues?

Any luck on locating your leak? I have been trying everything I can think of to locate my vacuum leak (while the MAF itself was leaking some, it didn't get me up to 5+ grams/second), but so far it continues to evade me. My leak appears to worsen when the engine gets hot (sitting in stop and go traffic correlates with a reduction in the MAF's grams/second reading), so I'm starting to think it's possibly a gasket or other metallic piece with a low specific heat capacity. Really, I just need to take the entire manifold apart to try and find the leak. :icon_no2:

No updates on the leak, I have sourced a another manifold that I am going to put on and see if that changes anything. I went back and sealed a few more seams, no change like before. The only symptom I have now is the lower MAF reading and the LTFT, it drives great. In fact my last tank of gas I averaged 18.6mpg, and that was mostly "spirited" back road driving. It's been so long since it was 100%, I don't know that I would know how its supposed to feel like lol.

When you do take your manifold off, spray cleaner inside and tilt it around and see if you can get any to leak out. You might be surprised like me.