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Old fuel addy #5320254 01/11/20 09:49 PM
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Mad_Hatter Offline OP
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Ok, riddle me this...

Both my LTFT's on B1 and B2 have historically been around +4~6%, sometimes as high as 8, at idle since I've been over 150k miles on the clock. Just today i plug in my obd2 and i see them sitting at 11 and 12. They do drop to or close to zero under load. Now initially I'm beginning to think vacuum leak..but a quick check (wiggle) of the hoses i can get to doesn't reveal anything (no drop in %, it's fairly static). So dunno..i guess i gotta take a more in depth look-see tomorrow but here's my question below..

2 things are different in the last few weeks from months past...a) i stopped and filled up at a non top tier, mom and pop station because well, I had too. I found myself in bfe around the backside of Mt st. Helen's recently needing gas and didn't want to chance running out. And b) i used up an old, opened bottle of fuel ST motor cleaner I used on my OPE this last summer. I thought the bottle was tightly closed but when I dumped it into the tank i noticed there was a yellowish color to the fluid (i think it's supposed to be clear) and plastic pour spout. I dumped it in anyways ignoring better judgement but now I'm wondering if there was gum or varnish forming?? Is this possible? Or is it possible the unknown quality of the fuel i picked up, either one is clogging an injector, pump, filter or something in the fuel delivery.. because nothing under the hood has changed and all my hoses appear to be in good shape/fairly young in their service.

I just don't wanna start pulling crap off if i can avoid it (TB has to come off just to check the pcv and brake booster systems/hoses) if there's a chance i just inadvertently introduced something into the fuel system and maybe it's nothing a good strong cleaner can't resolve... thoughts?

(not one but both banks simultaneously jumped to double digits lean %, no CEL or pending..so maybe a fuel clog/restriction??)

Last edited by Mad_Hatter; 01/11/20 09:51 PM.
Re: Old fuel addy [Re: Mad_Hatter] #5320280 01/11/20 10:22 PM
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tiger862 Offline
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I would run something like Techron in tank with TopTier fuel then check.


Tiger862
2018 Grand Caravan
Re: Old fuel addy [Re: tiger862] #5320344 01/11/20 11:18 PM
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Mad_Hatter Offline OP
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Originally Posted by tiger862
I would run something like Techron in tank with TopTier fuel then check.

Have you seen or heard of bad fuel or bad additives doing this? My limited experience with high LTFT's has been cause by vacuum leaks.

That's kinda what I'm leaning towards. I've got about 12gls to burn through, then I was thinking of running some Techron concentrate or B12 with some Shell or Chevron gas or maybe even the 76 i USUALLY go to. Really irks me that i didn't plan my trip ahead better and had to fill up at a backwoods station. Who knows, maybe it's not that. It's just such a PITA troubleshooting a vacuum leak on this car, as half of what you would check involves removing pretty much the entire intake just to get to the pcv hose, back half of the egr hose, brake booster hose and you can't properly check the plenum (back side) because of how tight it is up against the firewall.. sounds stupid but you pretty much have to take the plenum off to confirm a vacuum leak with the plenum gasket but then it's off so if course it's a leak duh! But at minimum everything to the intake plenum has to come off to do a half way decent job of checking for a leak. Thing is, is i haven't monkeyed around under the hood lately so I'll be a bit surprised if it's a VL but i guess ya never know when/where one can develop. Not exactly what i wanted to be doing with snow forecast to start Monday and no covered area to work. (I have a garage but it's full of crap)

Last edited by Mad_Hatter; 01/11/20 11:26 PM.
Re: Old fuel addy [Re: Mad_Hatter] #5320346 01/11/20 11:24 PM
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OilReport99 Offline
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Originally Posted by Mad_Hatter
Originally Posted by tiger862
I would run something like Techron in tank with TopTier fuel then check.

That's kinda what I'm leaning towards. I've got about 12gls to burn through, then I was thinking of running some Techron concentrate or B12. It's such a PITA troubleshooting a vacuum leak on this car, as half of what you would check involves removing pretty much the entire intake just to get to the pcv hose, back half of the egr hose, brake booster hose and you can't properly check the plenum (back side) because of how tight it is up against the firewall.. sounds stupid but you pretty much have to take the plenum off to confirm a vacuum leak with the plenum gasket. But at minimum everything to the intake plenum has to come off to do a half way decent job of checking for a leak. Thing is, is i haven't monkeyed around under the hood lately so I'll be a bit surprised if it's a VL but i guess ya never know when/where one can develop. Not exactly what i wanted to be doing with snow forecast to start Monday and no covered area to work. (I have a garage but it's full of crap)


Mine is fuller of crap!

Try Redline SI-1

Re: Old fuel addy [Re: OilReport99] #5320350 01/11/20 11:29 PM
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Mad_Hatter Offline OP
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Originally Posted by OilReport99

Mine is fuller of crap!

Try Redline SI-1

😂..i keep saying, "this spring I'm gonna clean things out".. been saying that for years now. I could prolly make a killing having a garage sale if i weren't so lazy.😂

I'll look into the Redline... I've always used Techron but maybe this is a good opportunity to try out the Redline. 👍

Re: Old fuel addy [Re: Mad_Hatter] #5320384 01/12/20 01:09 AM
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LvR Offline
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Originally Posted by Mad_Hatter
Ok, riddle me this...

Both my LTFT's on B1 and B2 have historically been around +4~6%, sometimes as high as 8, at idle since I've been over 150k miles on the clock. Just today i plug in my obd2 and i see them sitting at 11 and 12. They do drop to or close to zero under load. Now initially I'm beginning to think vacuum leak..but a quick check (wiggle) of the hoses i can get to doesn't reveal anything (no drop in %, it's fairly static). So dunno..i guess i gotta take a more in depth look-see tomorrow but here's my question below..

2 things are different in the last few weeks from months past...a) i stopped and filled up at a non top tier, mom and pop station because well, I had too. I found myself in bfe around the backside of Mt st. Helen's recently needing gas and didn't want to chance running out. And b) i used up an old, opened bottle of fuel ST motor cleaner I used on my OPE this last summer. I thought the bottle was tightly closed but when I dumped it into the tank i noticed there was a yellowish color to the fluid (i think it's supposed to be clear) and plastic pour spout. I dumped it in anyways ignoring better judgement but now I'm wondering if there was gum or varnish forming?? Is this possible? Or is it possible the unknown quality of the fuel i picked up, either one is clogging an injector, pump, filter or something in the fuel delivery.. because nothing under the hood has changed and all my hoses appear to be in good shape/fairly young in their service.

I just don't wanna start pulling crap off if i can avoid it (TB has to come off just to check the pcv and brake booster systems/hoses) if there's a chance i just inadvertently introduced something into the fuel system and maybe it's nothing a good strong cleaner can't resolve... thoughts?

(not one but both banks simultaneously jumped to double digits lean %, no CEL or pending..so maybe a fuel clog/restriction??)

I dont know if you meant to say STFT there .................. wiggling on stuff on the intake will not immediately show a change in compensation values - you need to be looking at STFT while wiggling - LTFT will only adapt on a sustained trend change reflected on the STFT.

Your description of the actions leading to the jump in LTFT (if indeed it was directly as a result of that and not a trend that developed recently as result of something else changing anyway) will have me drive and empty the tank - fill with known fresh fuel and see if you get a "return to historically normal" LTFT after a few 10s of miles driving both cold and hot

Re: Old fuel addy [Re: LvR] #5320388 01/12/20 01:35 AM
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Originally Posted by LvR
I dont know if you meant to say STFT there .................. wiggling on stuff on the intake will not immediately show a change in compensation values - you need to be looking at STFT while wiggling - LTFT will only adapt on a sustained trend change reflected on the STFT.

Your description of the actions leading to the jump in LTFT (if indeed it was directly as a result of that and not a trend that developed recently as result of something else changing anyway) will have me drive and empty the tank - fill with known fresh fuel and see if you get a "return to historically normal" LTFT after a few 10s of miles driving both cold and hot

You're right..i overlooked that fact (wasn't thinking straight). Well, i need to do a proper look at each hose if it turns out to not be the fuel.

I'm actually pretty regular about using my obd2 but for whatever reason i became lazy the last several months but I can say i last looked at FT's maybe October/November and they were where they normally are.. nothing unusual. The O2's right now seem to be behaving fine, switching like they should so I'm doubtful it's a lazy/dirty sensor...so that leaves what, fuel and vacuum. When i did the spark plugs a couple years ago everything had to come off so i took that opportunity to inspect the hoses and all seemed good. No obvious cracks or abrasions at the typical wear points like at bends and connections..but who knows, right?

Re: Old fuel addy [Re: Mad_Hatter] #5320392 01/12/20 01:55 AM
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If STFT at idle and warm engine is varying around 0 by relatively small numbers I'd say the ECU is in control of the animal ............... you just need to define the animal - Id also check on coolant temp values - if its really running cooler (thermostat) or thinking its running cooler (sensor) then you are par for the course

Re: Old fuel addy [Re: Mad_Hatter] #5342889 02/06/20 06:01 PM
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UPDATE: LTFT's are back to normal lvls. It must have been some bad fuel. I've done nothing else but ran one tank with B12 and I'm on a 2nd for good measure... that Berryman's is good stuff! 👍

The LTFT1 & LTFT2 are in the upper right-hand corner. This is @ about 1600 rpms.


[Linked Image]

Last edited by Mad_Hatter; 02/06/20 06:02 PM.
Re: Old fuel addy [Re: Mad_Hatter] #5342926 02/06/20 06:50 PM
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On my Gen Coupe 2L Turbo my LTFT will 0 out after a 1/2 hour at highway speeds. Drive through town and they go way up. But then go back down in a few miles. I generally drive the same speeds all the time though, either 30 mph in town or 50 mph out in the boon docks.


2008 Hyundai Accent 1.6L 5 sp manual hatchback
2010 Hyundai Genesis Coupe Track 2L Turbo 6sp manual
Re: Old fuel addy [Re: Mad_Hatter] #5342975 02/06/20 07:32 PM
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Originally Posted by SHOZ
On my Gen Coupe 2L Turbo my LTFT will 0 out after a 1/2 hour at highway speeds. Drive through town and they go way up. But then go back down in a few miles. I generally drive the same speeds all the time though, either 30 mph in town or 50 mph out in the boon docks.

This was in town too..Sometimes it hits zero (closer to zero) while at freeway speeds but I've got nearly 200k miles on this engine, so I'm fine with it being a little on the lean side and better a little lean than rich. Plus my total trim values are relatively low, so I'm not concerned there's a problem being masked by the LTFT values. I'm just glad I've got them down from the double digits they were a few weeks ago... just goes to show what "bad" fuel can do to your system.

Last edited by Mad_Hatter; 02/06/20 07:34 PM.
Re: Old fuel addy [Re: Mad_Hatter] #5343139 02/06/20 10:47 PM
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LvR Offline
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Originally Posted by Mad_Hatter
..........................so I'm fine with it being a little on the lean side and better a little lean than rich. Plus my total trim values are relatively low, so I'm not concerned there's a problem being masked by the LTFT values. I'm just glad I've got them down from the double digits they were a few weeks ago... just goes to show what "bad" fuel can do to your system.
LTFT is an indication of the current mechanical status of the engine, also of the current state of tune and quality of recent maintenance ....................... its basically telling you how close the engine is running to the factory fuel map - its not telling you if its running rich or lean at all. The factory fuel map is always attempting to get the engine to run at 14.7 A/F ............. and if the engine is running at 14.7 then its not running rich or lean and the ECU is in good control of the fuel map

Re: Old fuel addy [Re: LvR] #5343267 02/07/20 01:55 AM
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Originally Posted by LvR
Originally Posted by Mad_Hatter
..........................so I'm fine with it being a little on the lean side and better a little lean than rich. Plus my total trim values are relatively low, so I'm not concerned there's a problem being masked by the LTFT values. I'm just glad I've got them down from the double digits they were a few weeks ago... just goes to show what "bad" fuel can do to your system.
LTFT is an indication of the current mechanical status of the engine, also of the current state of tune and quality of recent maintenance ....................... its basically telling you how close the engine is running to the factory fuel map - its not telling you if its running rich or lean at all. The factory fuel map is always attempting to get the engine to run at 14.7 A/F ............. and if the engine is running at 14.7 then its not running rich or lean and the ECU is in good control of the fuel map

Ok, that's not my understanding at all. (what am I missing?)...I understand the fuel map/learning part but my understanding is a positive FT meant the ECU has been making fuel corrections based upon what it has perceived as a "lean" condition (unmetered O2 or not enough of the commanded fuel) over time. But that's over time, and STFT is what it's doing in the "now" which could very well be a negative or positive.

Fwiw, my "total fuel trims" (LTFT+STFT) is still pretty low, below 6% positive I think the highest I've seen it. So that, to my understanding, tells me I'm still running a bit "lean" but not horribly lean as the ECU is still able to control the F/A mix within tolerance. I purposely didn't disco the battery (to reset the fuel map) because I wanted to run the cleaner through the system on the same learned correction and thus far it seems to be working... the trims have come way down. 2.3 and 1.6 is much better than where it was.

Re: Old fuel addy [Re: Mad_Hatter] #5346006 02/10/20 10:47 AM
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Originally Posted by Mad_Hatter
UPDATE: LTFT's are back to normal lvls. It must have been some bad fuel. I've done nothing else but ran one tank with B12 and I'm on a 2nd for good measure... that Berryman's is good stuff! 👍

The LTFT1 & LTFT2 are in the upper right-hand corner. This is @ about 1600 rpms.


[Linked Image]


Did you reset the vehicle's computer by erasing DTC or disconnecting battery?

If you did, it may take a few drive cycles before it MAY act up again. If it does not, Congrats!

Re: Old fuel addy [Re: Mad_Hatter] #5346219 02/10/20 02:27 PM
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Nope. Didn't touch a thing and no DTC to clear since you won't typically get one until you're above 20%.

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