Short Term & Long Term Fuel Trims, who checks them??

[Newbe]

As the post suggest I was wondering if anyone records or checks there STFT or LTFT with a diagnostic tool?

I had a remap a while back and I was wondering if these fuel trims would show up any issues in your remap?

Does anyone know if the long term fuel trim is an average across the whole fuelling MAP, so includes all loading conditions? If so I'm guessing this would show up any fuelling or lean conditions?

Could you check it by going up through the REV range and recording the results in different gears and loads? I'm guessing this would show something up in the short term fuel trim if there was an issue? Ie reading high or low percentage?

The other question I have is around the MAF. Pre remap my MAF was at 5 g/s with a standard throttle body. I fitted an 82mm throttle body and it dropped to 4.5 g/s after install. Now I'm unsure if this was due to a small vacuum leak or the throttle body? Has anyone recorded this before? Anyway, after the remap it's now at 5.75 g/s, would MAF scaling cause this change?

I'm not experiencing any issue but I was just trying to record some data if I experience any issues in the future, plus wanted to make sure the remap isn't impacting the car in a big way, (I'm a nosey git)

Any input would be appreciated :thumb:

 

[deMort]

I use fuel trims when diagnosing standard cars ..

Piwis uses different values in a sense , i think durametric can see these as well .... i can see ..

Instant adaptation .. what you would call short term i guess ..

These are all long term ..

Long term adaptation at idle ..
Long term adaptation at mid range ..
Long term adaptation flat out ..

Rkat , Frau and Frao is the names we use for them .

Rkat being the most important as issues tend to show up more in that range.

Being mapped though i would expect it will run more on the rich side .

Instant adaptations are converted to long term .. so in a sense long term cancels out the need for a short term adaptation .

So by looking at these values we can see if its running too rich or lean in a rev range over time .

There are different settings for different models and years .. wideband sensors give a constant voltage for example and are far more accurate than the earlier switching type .. which is still used for Cat diagnosis .

Larger body for the throttle would lower the air flowing across the sensor .. a map is needed as you have done to compensate for this .

Rough standard maf setting is approx 18kgh .. ill let you convert that .

Basic settings below as i have said above .. your welcome to the rest of that manual if you want .. bit boring but worth a read i feel ..

let me know anyways .

 

[Newbe]

Cheers for the reply

18 kgh is 5 g/s , it looks like it dropped to 16kgh after fitting the throttle body and rose to around 20 kgh once the MAF was recalibrated.

I do have a diagnostic tool but I don't believe it looks at 3 long term fuel trims. It only looks at RKAT, I think. Looks like I'll be able to get some data. On the same screen I think I can get load, RPM, STFT and LTFT. I can also get all the O2 sensors and MAF.

Is RKAT at 1500/2000 RPM?

If I get to drive the car I'm going to record some data and see what it looks like, I maybe back :grin:

 

[deMort]

Rkat is idle or just above .. its upto 32kgh air flow on the maf .. that's about 1K max i would have thought .

Rkat is the most useful figure to be honest .. i'm not sure if the LTFT is Rkat or one of the others though.

If i have an eml light on and the code refers to adaptions out of limits its nearly always in the Rkat range .. as per the image i would see +/- 6.8 or so and that would indicate a too rich or too lean mixture .. i can use those values to look for an air leak or perhaps a leaking injector .

With a Mapped system i would kinda expect readings to be in the 4 range .. it will run richer as that's the whole point of a map .

readings though depends on the car .. as again per the image you can see 2 values for max for old and newer cars at time of publication of this .. if its wide band sensor then its a 30 % value from memory .. that's a later system .

Lets just say i have to study training manuals for the correct figures at times .. i certainly haven't memorised every value for every model lol .

record what you want .. i can try and explain some of it .. best person though would be Ken at 9E .. mapped cars and mods and hes the man .. i deal with standard stuff im afraid .

 

[timm996]

I had a problem for about 5 years where 2 times out of ten my car would start, then stumble and die, or just stumble, after about a minute it would clear and be ok. Even throttle would make it spit and run badly. Took it to porsche they could not replicate or find any issue, then did leak tests etc.
Anyhow got stuck in a long jam one day and it starting doing it again and died. Got me thinking, I looked at fuel trims, they were out. Suggesting it was sucking air, I took off the valve that goes to the fuel tank and found it did not always close when it should, so it was actually sucking in air from the tank and breather. Also got a temporary code 442 from memory. I replaced this valve with a pattern part 99611012953 and checked the fuel trims and they were back to normal.
Since that day, never had the problem again.

I am thinking if I had paid more attention to fuel trim I would have realised what was wrong.

 

[Newbe]

Funnily enough I was only looking to get some data, although now I've looked my tool is showing the fuel trims at 0% even when I'm driving and the fuel system appears to be in permanent O/L. Even when the car is warm and at steady driving it didn't change.

The cars running great though. I've emailed Icarsoft POR II, which is the tool I've got to make sure it does read these parameters when driving. I don't want to look for a problem which isn't there because the tool can't read them. :dont know: