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LTFT Value?
- Thread starter The Fed
- Start date
Mak_Attack
Passed Driver's Ed
- Location
- Twin Cities
Long term fuel trim is a stored value that would remain the same as previously stored with the engine off. Short term fuel trim changes should be 0 with the engine off because there are no quick fueling changes being made without the engine running.
That I know, just wanted to verify the label changes.
You JB1/4, NPM, Dinan owners, what are your long term numbers?
Crud_muffin
Ready to race!
- Location
- US
- Car(s)
- e-Golf
I'm guessing it would be good to see logs comparing the same car, same pull before and after to see how both trim values are affected. Idle trim varies a lot and the total fuel map can vary through the rev range. I have no such logs so I am useless here.
My car was not running when I pulled the values. I'll check LT a few more times over the next few weeks. I figure there's a min/max range that's acceptable before you get a fault code, which is another reason I don't believe a piggyback can even be suspected. If you're "hot-rodding" a stock car all of the time your LT value has to indicate you've been using more fuel, right?
Crud_muffin
Ready to race!
- Location
- US
- Car(s)
- e-Golf
Exactly, it was showing the last trim value the moment before the engine shut off, likely idle. You're right also that it takes a great deal of trim before codes light up your Christmas tree. Guys can run 50% ethanol and still not see a trouble code.
Great article I found here that sheds light on trims (link below). On a stock tune, in theory you won't see long term trim at over 5% on prescribed pump fuel, and that goes for all the load range. In a [emoji241] piggy scenario, I'm not sure how the trickery works for getting the ECU to add boost, etc. JB4 crowd and their fearless leader probably know precisely. Guys?
https://www.matthewsvolvosite.com/forums/viewtopic.php?t=21123
George Smooth
Drag Race Newbie
- Location
- South Africa
The JB4 keeps the short term fuel trims in check by increasing fuel rail pressure. Its the only piggy back that does this. In turn we have seen hardly any changes that could be alarming on the ltft side of things. Over the years with more ethanol available at the pumps the ranges of acceptability value wise have increases and the ECU have been given the ability to adjust STFT at a much higher range which is part of the reason why the less inferior piggy backs work so well albeit at stock ECU AFR targets since they cannot change them.
I'm pretty sure if you drive for 30 minutes after removing your piggyback your fuel trims will be back to before it was installed. No?
George Smooth
Drag Race Newbie
- Location
- South Africa
The LTFT take very long to change. I reckon up to 5-6% higher than 0 there wont be any issue. If its higher they will most likely check for a weakness in the fuel system and start changing parts.
Crud_muffin
Ready to race!
- Location
- US
- Car(s)
- e-Golf
Thanks for chiming in on this, George! I assume you meant "doesn't take very long." Feel free to correct me.
George Smooth
Drag Race Newbie
- Location
- South Africa
I meant takes long. LTFT is average over whole driving cycle. So it takes quite a bit to make it change considering the amount of time over a driving cycle you full throttle.
Crud_muffin
Ready to race!
- Location
- US
- Car(s)
- e-Golf
Ah, that's something to think about. Using E20 and APR STG1 LO on my GTI, I see 5% LTFT and 0% STFT at idle and mostly 7-9% LTFT and 0% STFT at partial load/rpm areas of the map.
I've got to say, piggyback on a Golf R or IS38 seems to make a lot of sense. I mean, in comparing for example the APR+ tune graph for the R, it just seems like a JB device is going to get you a similar power delivery and thensome. Their tune doesn't seemingly add power below spool up, at 1,800rpm or so. That's my impression at least. The end user control aspect with a piggyback is very nice.