High LTFT Both Banks Idle/Under Load

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WarrenBoostit

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Hey everyone,

Came back from a week and a half away staying with my grandpa during hospice, and had left my car in a temperature controlled garage. Started up sounding a bit colder than expected, and down the road a bit after a pull, received a blinking CEL for a short period before it disappeared. Code was Misfire on Cyl 4, it was 4 am so I couldn't do much more than clear it.

This morning started the car, Long Term Fuel Trim on both banks read 1.24. Since the misfire reset the OAR, I threw it in sport and did low rpm 5-6th gear pulls to bring the KR to -3.00 or higher (to initiate OAR adjustment), bringing it all the way back up to -0.96 OAR, and still seeing KR values that dash across -3 even at that OAR ( I was running about 27% E bc MN winter gas). After that, I figured it was worth a few WOT's to see if I could clear any gunk that may be in the injectors, and after that, idle LTFT in both banks read 1.14, but still read around 1.22 under load.

To me, without looking at deeper logs, I feel that bad injectors can be ruled out, as I'm seeing near identical LTFT on both banks. It seems like the lean condition must be occurring behind that. I also think I can rule out a VAC leak, as the LTFT increases with load. I've heard about the fuel pump or pump driver module behind the passenger seat going bad, though I know O2 sensors like to go as well, however I am uneducated on if O2 sensors can impact both banks, or just one (I'm semi-certain it's the latter).

Does anyone have any hunches on which rabbit hole I should start going down? Also, if you have any recommendations on other diagnostics I should pay attention to, please let me know!


Black 2018 SHO Non-PP 60K Miles | GH e30/AO Tune | PPE Catted Downpipes | DG2 Trans Mount | M-12405-35T plugs at .026 | 170 Tstat | 3 bar | H&R Springs | XDI-35 | Badges removed | Chrome delete | Fuel-it Bluetooth ethanol analyzer | GH IC | EPP Gen2 CAI | Noisemaker delete | MSD coils | Ceramic coating | Window Tint | EPP Hot Pipes | Black AR924 w/ General GMAX AS 05 255/45r20 | MRT axle back w/black tips
 
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ridered74

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My car had trims like that when I bought it, then still had same trims when I sold it 55k miles later.

Pretty sure I remember at least two people saying that they fixed theirs by replacing the fuel pressure sensor that is under the intake manifold in the fuel rail.
 

WarrenBoostit

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I would be inclined to ignore it or chalk it up to winter conditions, but the misfire really concerns me.
 

ridered74

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I would be inclined to ignore it or chalk it up to winter conditions, but the misfire really concerns me.
Could be two separate issues. For misfire I'd start with checking plugs, and I'd swap plug and coils between 4 and 5. That way if the misfire comes back, either you narrow it down to two things or you've completely eliminated two things as the cause of misfire.
 

WarrenBoostit

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Could be two separate issues. For misfire I'd start with checking plugs, and I'd swap plug and coils between 4 and 5. That way if the misfire comes back, either you narrow it down to two things or you've completely eliminated two things as the cause of misfire.
Probably the right course of action. Any idea why trims would be higher after sitting for a while? That fuel pressure sensor looks a bit tough to get to, so I'm hoping it's that. I also will probably swap the pump module behind the passenger seat, as that's easy enough.
 

ridered74

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Probably the right course of action. Any idea why trims would be higher after sitting for a while? That fuel pressure sensor looks a bit tough to get to, so I'm hoping it's that. I also will probably swap the pump module behind the passenger seat, as that's easy enough.

Maybe the injectors got gunked up from sitting? I dunno but now that I think about it mine had sat at dealer for over 2 months before I bought it. I had it tuned within a couple days of buying it, but I don't know if the trims were off for previous owner.

I think replacing the module is a good idea since it is cheap and they are prone to failure. Throw the old one in the glovebox for down the road just in case.
 

WarrenBoostit

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Any recommendation of fuel additives I could maybe use if it's a gunk problem? Although the car runs ethanol heavy I'd tend to think at 60k the buildup wouldn't be too bad, I've heard use seafoam, but simultaneously watched a Scotty Kilmer where he says seafoam is meant for two stroke engines, and to use Gumout Multisystem Tune-Up. Would I have to revert to a stock tune to use it? And if so would I have to throw a 2bar MAP back on?
I'm going to replace the module today, I'll update on if that improves numbers. My feeling is that it won't make them move more than 2-3% but I'm willing to be surprised. I have some memory of the car having trims around 1.04-1.07 when I bought it.
 

ridered74

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Any recommendation of fuel additives I could maybe use if it's a gunk problem? Although the car runs ethanol heavy I'd tend to think at 60k the buildup wouldn't be too bad, I've heard use seafoam, but simultaneously watched a Scotty Kilmer where he says seafoam is meant for two stroke engines, and to use Gumout Multisystem Tune-Up. Would I have to revert to a stock tune to use it? And if so would I have to throw a 2bar MAP back on?
I'm going to replace the module today, I'll update on if that improves numbers. My feeling is that it won't make them move more than 2-3% but I'm willing to be surprised. I have some memory of the car having trims around 1.04-1.07 when I bought it.

Seafoam type products generally aren't recommended on these unless you do it early in the motor's life and then do it consistently every so often. After 30-40k miles you run the risk of it knocking a larger chunk of carbon buildup free and that chunk clogging an injector.


A little lucas fuel injector cleaner in the tank a couple times won't hurt tho.
 

WarrenBoostit

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Module Replacement lowered numbers about 2-3% as expected. Top end still looking ugly, going to try some form of injector cleaner before moving on to replacing the rail pressure sensor.
 

WarrenBoostit

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Numbers have gone to around 10% now after half a tank of fuel cleaner. Another thing I had not considered was the fact that both cold temps (it's currently 33 here) and ethanol (running about 30-35%) are two things that would increase LTFT. So maybe these numbers aren't so scary.

Edit so I don't bump: Trims sitting around 1.04-1.07 now. It was 100% the ethanol content.
 
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