LTFT increased over 10% after oil change (new E85 user)
 

I was driving to Chick Fil A today and peered over at my OFT and noticed that LTFT was around 8%. Later noticed it over 10% on idle. I had normal fuel trims on my first full tank of E85 two weeks ago. I filled in my second full tank of E85 yesterday (and took it easy, under 3k, for first two miles) and performed an oil change this morning. So those two have been the only varying factors.

Here is my log: http://datazap.me/u/tracerit/new-ene...og=0&data=8-10

No exhaust leaks ??
Stock intake ??

If stock intake and no leaks, you may have just got some high ethanol content E85, that tune will have low trims with about E70-E75.

Try giving it a bit more time, say another 10 minutes or so driving, if still high positive trims see below

since the trims are mainly positive, ie ecu is adding fuel to correct lean condition it appears you have E85 that probably close to E85, if you add 3 or 4 litres (is that about a gallon ??) of petrol to a full tank of E85, will dilute the E level and will cause it to run richer and positive fuel trims will come down a bit.

Intake I'm using the stock airbox with aftermarket filter and a Perrin inlet hose. Is that generally considered "stock" whereas CAI are "non stock"?

I don't believe there are any exhaust leaks, I've driven with no issues the last 1.5 years without modifying my exhaust setup in anyway. That will change when my OFH comes in though :P

Ah, I do recall adding 2oz of Lucas Ethanol Fuel COnditioner after filling up my second full tank of E85 yesterday.

Will try to add a gallon of gas tomorrow and see how the trims react. Thanks!

I had the same thing happen the last couple weeks. I switched back to 98 and found the same problem even with the stock tune. We found that the overpipe to frontpipe flange was poor/damaged and leaking. While addressing that, we also found that the stock header cat had completely disintegrated. I hadn't changed anything on the car in over 6 months so that isn't always a reason.

Since fixing the exhaust leak in the frontpipe, my trims have gone back to +/- 5%.

i hope it's nothing mechanical. but i will check those parts later next week. Are these leaks easy to identify for a novice with just four jackstands?

here's an updated datalog from an hour ago. thte first four minutes are a drive to the gas station to f ill up 1 gallon of 91octane, then a few miles drive to Carls Jr and Mcdonalds.

http://datazap.me/u/tracerit/1gal-91gas?log=0&data=1

If you have the car up on stands and its safe, you could have another person give the car a few rev's while you're under the car and inspecting the various joints.

Do you have any WOT Pulls? I think this would help in determining if there was a problem or not.

This may sound silly but does WOT mean pedal to the floor or just max RPM? I"m only asking because I'd rather not floor it in say 3rd gear tonight since it just rained and i'm still a little sissy after losing control a month ago on a wet on ramp :/

It means the throttle valve is fully open

No worries :)

WOT = Wide Open Throttle. Pedal to the floor.

Basically what you want to log is a 2nd or 3rd gear pull from about 2k RPM - Redline (7450 I think). The shorter your log the easier it is to analyze, you don't want to do a WOT pull then keep logging 5 minutes afterwards.

http://datazap.me/u/tracerit/wot?log=0&data=1-2-10

just two very close WOTs tonight. Road was too wet so I figured I'd try another time.

On your WOT pull your AFR & fuel trims look good. I'd suggest doing a better pull tomorrow at 2k RPM, then pedal to the floor. You really only need to log from 2k rpm to redline, then pretty much stop logging. It looks like you didnt go WOT until about ~4k RPM.

It also looks like your fuel trims settled a bit below 10%.

Pretty much no FLKC or Knock Corr. as expected on E85, which is good. Everything looks to be in order.

http://datazap.me/u/tracerit/wot-2nd...0&data=1-2-7-8

WOT twice in 2nd gear then 3rd gear. LTFT looks better now. Is the FLKC at +7000rpm a concern? It's -0.65 which is eerily close to -0.7 which steve99 mentioned should be investigated.

looks good now. that little bit of minor knock is not rearly a concern just pull 0.35 to 0.7 out of the timing around the load\rpm it occurrs if your rearly kean

Here's another log I pulled after driving a bit more. LTFT seems to be idling higher at +6.25, but still .78 on WOT which is stil what I want right? Still +/-8% however which is still acceptable... I'm getting the feeling I should start measuring my ethanol content when filling up :P

http://datazap.me/u/tracerit/chick-f...&zoom=730-1832

Your ltft is always going to vary a bit on E85 without a fexfuel tune and sensor, its how the ecu copes with varing ethanol content as long as your less than 10% should be fine.
around idle will vary on petrol and e85 due large changes in intake air temps in traffic..

(topic kick)

I have the same problem, LTFT is high on idle (between 8 and 10), I use Belgian 98 ron fuel. The problem started after the car got back from the shop after maintenance.

Monday the car got his maintenance at an official dealer, they replaced the airfilter, the pollenfilter and installed the OEM oilcooler using the throttle body install method.
Wednesday I started the car and had a backfire in the exhaust, first time the car did that in the 2 years I owned it.
So I connect my OFT and noticed my LTFT and STFT where complete out of wack, I checked that all of the intake piping was connected properly, listin and smelling for exhaust leaks. So for nothing was wrong. Drove around a little bit, hoping that it would settle down back to normal values, but it didn't help.

I reflashed the tune with a new modified one, after that when driving around my LTFT was back to normalish values, except at idle. As soon I'm at idle the LTFT goes up to the 8 a 10%, while before the maintenance it was around 0 a 2%.

I also checked my dashcam vids and noticed they took a "test" drive without checking anything so I call it just a joyride. Dude was driving hard with a cold engine, speeding over rough terrain. I'm lowered on KWv3 coil-overs.

So has anyone got an idea why it changed? Nothing is changed, except the maintence.
Does it hurt the engine with a high LTFT at idle?

My carspecs:
- Modified intake snorkel, original airfilter and box
- OpenFlash Header with Milltek primaire resonated exhaust (no cats)
- used this flash (link)

- Datazap

you can get varying LTFT at idle due to large changes in intake air temps.

also for different fuels like 10% ethanol fuels to 0% ethanol fuel will alter fuel trims.

if you are sure their is no intake leak (the dealer would have removed intake tube to fit oil cooler) hopefully the crankcase breather pipe is secure at both ends and also sound tube.

the ltft away from idle is ok and at end of log its 7%. large ltft at idle only will not cause big issue, maybe slight hesitation. Its big trims at higher rpm and load than can be problem especially if afr and commanded afr large difference.

Thanks for the info steve99, the fuel inside the tank was the same as before the maintance, didn't fill up. IAT were around the same is before. I did a new run, all look normal except the LTFT at idle. Though it's dropped to around 5 - 7%. But I will check the crankcase breather tube, the intake piping and the exhaust for any leaks to be sure.
I still wonder why the car backfired, hopefully it's the first and last time it did it.

Thanks again :respekt:

thanks

the dealer guys may also have reset ecu (battery terminal removal) when fitting oil cooler, so trims may have been reset .