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Thread: need help with 1.4 turbo negative fuel trim mystery

  1. #1
    Tuner in Training
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    May 2019
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    need help with 1.4 turbo negative fuel trim mystery

    hey guys, I'm going to reach out here and see if anyone has experience with an issue I've been having with my '12 1.4 turbo. I keep getting large negative fuel trims, some days hovering around -5 and some days reaching -1. On top of that the car keeps pulling timing like crazy which im guessing is tied into what's causing the fueling issue. Ive thrown tons of money at this since seemingly pulling fuel is only caused by a few things. Now I don't know where else to go, first the pressure disc in the cam cover blew for the 4th time and I came across the "cruzekit" fix of which I did and I also pulled the charge tubes out down to removing the intercooler to clean all the oil out that was everywhere. The negative fuel trims were present prior to that but none of the KR that is very easily prevalent while driving now even when not really loading the car up. it will create a bobble feeling. I found that the cats were bad so I switched too the zzp downpipes and intermediate pipe. That didn't sort anything out so I changed the upstream O2 sensor bc it looked lazy, bt no change so I did new plugs and a new maf just moving along down the list of potentials. I changed out the pcv line from the manifold to the turbo a long with the MAF wondering if oil was maybe the culprit. I pulled the injectors today and pressurized the system and none leaked. I did a resistance test and all 4 injectors were the same at 13.3. I even capped off the evaporations tube to check that as well with no change. If the fuel pressure sensor is accurate on the car then it is getting the requested fuel pressure. According to my boost logs its showing im getting commanded boost, if those are accurate. Ive never ran a boost leak test because of that reading. I do a lot of tuning on LS cars and this thing has just been baffling me.It has the trifecta tune on it currently and Im going back and forth with them bc the ECM won't allow me to put the car back to stock as of yet so I can then tune it with HP. Ill include some logs that may point some things out or maybe get directed to what parameters to watch that im not? Thanks in advance for any knowledge.
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  2. #2
    Tuner in Training
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    -5 or -1 trims is not lots by any means...that is actually good if its LTFT because when it goes into PE it will be a bit richer rather than leaner if it was +1 or+5. If my LTFT's were -5 I would leave it alone and call it a day. As for your other issues I cant see your tune to look over as I am on my phone...
    2010 /2SS/Shorty headers/ Magnaflow axle back/LSA Conversion/ 2 bar OS running MAF

  3. #3
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    Yea I'm just reaching at straws at this point. I don't know what else to monitor or even look at. The trims are just the only thing sticking out. Especially when they start reaching over -10. I don't think it's the coil bc it doesn't act up more under load plus I replaced it around 20k miles back. I don't like just throwing money at a problem but I'm baffled now. I don't think anything is banging around under the hood. I'd like to get trifectas tune out bc I don't like their PE delay or how lean they make WOT. I appreciate your input.

  4. #4
    Tuner in Training
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    If you do switch to hp tuners i would gladly share my tune with you. It runs strong and makes the car fun to drive. I been running this tune for 20k and no probs on 91 octane.
    2010 /2SS/Shorty headers/ Magnaflow axle back/LSA Conversion/ 2 bar OS running MAF

  5. #5
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    That's awesome! I'd gladly take it as well! I've been reading up on how to actually tune our cars right and they seem be challenging from the looks of it. I'm over the trifecta tune tho. I know it could run a lot better. I'm sure theirs is just generalized and left with a large window of error.

  6. #6
    I have some experience with Trifecta, overall I'd say it was a very good experience. Any problems we had were all self induced like not knowing what MAP sensor I was actually using, and things like that.

    If you are blowing the pressure disc your PCV system is messed up and letting boost into the crankcase. That needs to be fixed first. Doing a boost leak test will check that for you. Under boost pressure the dipstick tube will blow oil and pressure out with stick removed. It will also keep turbo oil from draining back into the oil pan and blow oil out the seals on the turbo and you will oil everywhere. IF, you already fixed the PCV problem there will not be pressure in the crankcase. I would recommend logging with the Trifecta cable and sending the log back to Trifecta, after you've fixed the PCV. I say that because I just went through the damn PCV problem and wasted a lot of my time. Just trying to help.

  7. #7
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    I appreciate your help and I feel your pain lol I did the pcv V1 bypass kit from cruzekits bc it was the 3rd or 4th time it happened so I knew something had to be wrong. I wasn't expecting what the culprit actually was after I started researching it. there was oil everywhere in the charge pipes and in the intercooler. I cleaned all that out hoping to fix the issue but it did not. lol I had to send some .tpl files to trifecta bc their software isn't giving me access to the ecm. I've even downloaded their driver 4 different times....... I changed the knock sensor yesterday but it made no change. im out of my knowledge at this point bc there isn't anywhere it can be picking up extra fuel from the rapid change in trims. the only reason why I keep hanging on to trims being part the issue is this car trimmed perfect with no kr a month prior. might just be a coincidence. but that's sent me down the road with the bypass, new downpipes and the sensor changes. but with the downpipe alone it should be adding fuel in my experience? it will reach -18% at times and performance aside it has me concerned its washing the cylinder walls down.