Long Term Fuel Trims off after PRL Cobra Install?

davemarco · Jun 26, 2018

Hi all. Installed my PRL Cobra CAI with Street MAF last night and after a 30 minute drive today, I noticed that my Long Term Fuel Trims had increased from 0% (on my stock airbox) to -3% (on my PRL CAI). My AFR also now rapidly fluctuates at idle between 14.7 and 15.3 (it was a constant 14.7 at idle on my stock airbox). Did anyone else notice this behavior with theirs?

l15b7allturbo · Jun 26, 2018

its normal

davemarco · Jul 2, 2018

francomakou said:
its normal

Thanks. I installed my PRL FMIC this past weekend, and noticed that my LTFT's have slipped even further into the negatives - currently sitting at -7% LTFT. I could've sworn that I read somewhere that the FMIC does not require a tune, though I know that for pretty much any other car, you won't see any improvements from an upgraded FMIC without a retune.

airickmatthews · Dec 20, 2018

davemarco said:
Thanks. I installed my PRL FMIC this past weekend, and noticed that my LTFT's have slipped even further into the negatives - currently sitting at -7% LTFT. I could've sworn that I read somewhere that the FMIC does not require a tune, though I know that for pretty much any other car, you won't see any improvements from an upgraded FMIC without a retune.

Been searching through threads about ltft. During highway cruises, it’s gotten as low as -10%. Should this be a concern? I have a 3 hour drive to take on Christmas Day, was hoping everything will be fine.

davemarco · Dec 20, 2018

You'll be fine. That number represents the car correcting things for you so that everything will run smoothly. Long run, you should do a once over on your setup to make sure that everything is hooked up properly, but if it's only hitting -10 with LTFT and STFT added together, you'll be fine. Larger numbers could be indicative of an underlying issue, but unless you're seeing massively negative or positive trims, there's nothing to worry about.

I fixed the above posted issue by realizing that my FMIC piping was on backwards and not fitting 100% flush. You could have a minor leak like I did, or you could just have a car that trends towards a -10. It could also be your tune.

airickmatthews · Dec 20, 2018

davemarco said:
You'll be fine. That number represents the car correcting things for you so that everything will run smoothly. Long run, you should do a once over on your setup to make sure that everything is hooked up properly, but if it's only hitting -10 with LTFT and STFT added together, you'll be fine. Larger numbers could be indicative of an underlying issue, but unless you're seeing massively negative or positive trims, there's nothing to worry about.

I fixed the above posted issue by realizing that my FMIC piping was on backwards and not fitting 100% flush. You could have a minor leak like I did, or you could just have a car that trends towards a -10. It could also be your tune.

Short term will spurt down to -25% at some points, I just let off the throttle a little and it goes closer to zero. I’m in the process of breaking in my clutch before doing a tune with Derrick.

davemarco · Dec 20, 2018

You're probably fine. I believe that the real test is at idle. Let the car idle for a few minutes and see where the trims settle.

airickmatthews · Dec 20, 2018

davemarco said:
You're probably fine. I believe that the real test is at idle. Let the car idle for a few minutes and see where the trims settle.

Alright. I’ll check into that tomorrow. Thanks!

airickmatthews · Dec 21, 2018

Alright, just let my car sit at idle in the garage for a few minutes and looks like it rested at -4% ltft and 0% stft. Both seem normal and reasonable. But out in “the Wild” is when I gets to be going rich. My assumption is from the race MAF and maybe the 27won turbo? Since ktuner doesn’t have an actual basemap for the turbo, I just been babying it until the clutch break in.

davemarco · Dec 21, 2018

airickmatthews said:
Alright, just let my car sit at idle in the garage for a few minutes and looks like it rested at -4% ltft and 0% stft. Both seem normal and reasonable. But out in “the Wild” is when I gets to be going rich. My assumption is from the race MAF and maybe the 27won turbo? Since ktuner doesn’t have an actual basemap for the turbo, I just been babying it until the clutch break in.

Are you at least using a race MAF tune for the stock turbo? Using the Race MAF without a proper tune will cause problems.

airickmatthews · Dec 21, 2018

davemarco said:
Are you at least using a race MAF tune for the stock turbo? Using the Race MAF without a proper tune will cause problems.

Yea I have the race function enabled. I waited till ktuner had the update before installing it.

MGZ · Jun 25, 2019

Hate to necro this thread, but seemed like an appropriate subject for my question –

Been loving the TSP stage 1 for the last few months, it's been a lot of fun and the powerband is really nice! I've been running my intake(PRL, as thread implies) as a short ram for the last couple months and all my fuel trims have been pretty well behaved, mostly around +/-3%.

As it's been getting hotter in the summer months, I've installed an intercooler(also PRL) and recently converted the intake to the cold air set up. Intercooler seemed to keep my fuel trims around the same, but since converting the intake setup, my LTFT seem to be going up at idle (usually around 7~10%). It'll lower once I start driving and it gets better after the car's warmed up, getting as low as 0% if I'm cruising for a bit on the highway. But it's definitely not as consistent once i'm back to street driving or idling so I'm trying to figure out if this is indicating a leak somewhere. I'm thinking it can't be anything too serious since it seemed to be fine with the short ram configuration, but I'm wondering if someone can take a look at some datalogs or explain why this might be happening?

Any help would be appreciated, thanks!

Myx · Jun 25, 2019

I just read this thread, went down to my car and took a snapshot of the fuel trims. This is with my own personal SRI (With cold air feeding it), PRL Race maf and a TSP Stage 1 Beta tune. This is no recently uploaded tune. It's been a few weeks now with a lot of driving in between. Disregard the 113F. It's a false reading in my Torque Pro App. Haven't been able to get IATs working in Torque Pro yet.

Honda Civic 10th gen Long Term Fuel Trims off after PRL Cobra Install? Fuel Trims

D-RobIMW · Jun 26, 2019

MGZ said:
Hate to necro this thread, but seemed like an appropriate subject for my question –

Been loving the TSP stage 1 for the last few months, it's been a lot of fun and the powerband is really nice! I've been running my intake(PRL, as thread implies) as a short ram for the last couple months and all my fuel trims have been pretty well behaved, mostly around +/-3%.

As it's been getting hotter in the summer months, I've installed an intercooler(also PRL) and recently converted the intake to the cold air set up. Intercooler seemed to keep my fuel trims around the same, but since converting the intake setup, my LTFT seem to be going up at idle (usually around 7~10%). It'll lower once I start driving and it gets better after the car's warmed up, getting as low as 0% if I'm cruising for a bit on the highway. But it's definitely not as consistent once i'm back to street driving or idling so I'm trying to figure out if this is indicating a leak somewhere. I'm thinking it can't be anything too serious since it seemed to be fine with the short ram configuration, but I'm wondering if someone can take a look at some datalogs or explain why this might be happening?

Any help would be appreciated, thanks!

You're right in line with factory behavior, actually.

MGZ · Jun 27, 2019

D-RobIMW said:
You're right in line with factory behavior, actually.

Thanks for chiming in @D-RobIMW. Good to know this is expected. Fuel trims have calmed down a bit over the last few days, back down to 0~4%, so I'm feeling better about things even tho I'll see STFT hit some crazy numbers sometimes.

Car's pulling great with the tune, CAI and intercooler! No complaints there, intake temps have been as low as 5 over ambient!

Long Term Fuel Trims off after PRL Cobra Install?

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