New to me 2008 997.1 Turbo, 51k miles, plugged in my torque app for fun (to watch IAT’s). IAT’s were consistently 10-20*F above ambient so all good there, but the LTFT show +6.7% and +9.8% on bank 1 and 2 respectively. Seems a little lean to me, wouldn’t you agree? What’s normal for our cars??

 

Good question, I was playing with my Torque app yesterday as well and have never really looked at those values and what might be "normal".

 

Any chance you can peek at them next time and let me know what you see? I’d greatly appreciate it!

 

I would imagine that if the trims were outside of their permissible range, they would set a system too lean fault. Depending on the ECU in a car they have a "normal operating range" for trims. On older Audi's for instance it was 0 - 5% max in either direction, vs now on the newer Audis anything within 10% is ok. Additionally if the car is tuned, it could change that range as well. For instance if you're approaching the limit of what the fuel system can handle but still within tolerance. The other possibility is that you may have a minuscule vacuum leak but the ECU is compensating for it, and not triggering a fault.

 

Motronic's adjustment range is +/- 25%. A decent tuner aims to less than 5% corrections.

 

Being that it can adjust +/-25%, is it normal that mine is adjusting 10%? I imagine it should be closer to 0.

What’s odd is that, I just went for a drive to watch it closely, and STFT seem to bounce -3/+3 the entire time, yet LTFT is around 10% at idle and light throttle, then drops 7% at wide throttle. I figure LTFT is average is of STFT’s, but doesn’t compute in my case...

 

Airbox (or lack thereof), exhaust, tune and even fuel type can all make a difference in LTFTs.

You may actually have a small vacuum leak that's allowing a slight lean condition at idle (hence higher LTFTs). It's less an issue/contributor at higher air flow levels hence why your trims as look better at higher RPM.

 

25% is the maximum range that the ECU can adjust for, you can be pegged out at 25% but that doesn't mean that thats within allowable normal operating range.

 

Do you have ethanol in your local gasoline? Long term should be close to 1.00 at all times ....

 

Local gas (NJ) is 10% ethanol from what I know, would that impact it?

As for 1.00, what is that in terms of percentage?

Car is 100% stock, and I only and exclusively fill it with Shell V-Power (93). What’s step one to chasing down a vacuum leak? Smoke test? Is there a common place check first?

 

1.00 is no deviation from expected, so 0% change in LTT.

FWIW my LTTs during a pull range from 1.01 to 1.04. (1% to 4%).

 

Does anyone else know what theirs are at idle and above 2,500 rpm/WOT? Just tried my 4Runner which shows about +7% too and I get gas for it at the same gas station as the Turbo.

 

I'd like to echo what was said above. A good tuner = 3-5% of accumulative Short-Term-Fuel-Trims and Long-Term-Fuel-Trims (STFT & LTFT) Yes, STFTs will wander but you don't really want to see them higher than 5% unless there is crazy temp/elevation variance and compensation tables aren't cutting it.

Here is my client's LTFTs (440WHP Supercharged Honda S2000)


I've taken a peak at my friend's canned BMW 335i Stage1,2,3 tunes and I'm seeing variance of 30%+ in trims. Pure garbage if you ask me. You will feel anything over 20%. My S2000 starts to misfire if I’m 17% short on trims. It’s amplified if you're transitioning from a cell that has -15% trims and the following one is +15%.... so there's your serious hiccup. These trims are reactive, meaning error already occurred and ECU is compensating and filling in the gaps. Basically, it’s masking a bad/lazy tune or some issue/problem such as vacuum leaks, dirty air filter, etc.

 

New air filter today, cleaned both MAF sensors, reset memory by disconnecting the battery. Within 10-15 mins, LTFT climbed to +6 and +7% at idle/light throttle and +3.1% on both banks under boost.

Should I pay someone to smoke test it? Or buy a smoke machine?

 

I would do basic maintenance and checks, just because it’s the right thing we should all do anyways.

Now, I don’t know what other if any mods you have but I’d drive around and just keep an eye on these trims and report back.

Edit: Basically I wouldn’t freak out too much. Share a log if you can after a few 100 miles.