Hello all,

I have been experiencing high negative stft trims for a while now that I am trying to chase down with my limited time and knowledge. I have a weird issue happening and am wondering if you guys could help.me understand what causes this issue .....
when monitoring stft on inpa ( when car is parked) after starting car and letting it warm up to idle i see stft hover from low - to low + numbers. When I rev a little on neutral ( 2k to 3k) the -stft get a little worst up to about -12 or so.

When I put car on reverse or first gear and I low rev car, the -stft are a lot worst, seeing -20 and -25? (Also trying to keep rev around 2k or 3k)

What can cause stft to be worst when car is in drive or reverse instead of in park ? I am.trying to apply same amount of gas , etc .

thanks for tour input

 

I wouldn’t worry too much about short term fuel trims, since they are are calculated almost every second. You should be more concerned with long term fuel trims, which are a running average of the short term trims.

Google search the definitions of the two, and you’ll see what they mean.

 

thanks for the reply. Yes you are correct the ltft seems to be more important for the fuel trims , but the issue is that left and srft both jump quite high when reving car in gear . Goes to -10 ltft accompanied by - stft readings of -15 to -25 at times . I wouldn't worry much if the numbers were lower, but these digits are def not normal and it has caused a p0172 code a few times. The ecu is def struggling to keep it under control .

I just don't understand what causes the negative fuel trims to jump much higher when i rev in gear as opposed to when I rev the same rpm in neutral?

 

It’s probably the difference in engine load from stalling against the converter versus sitting in neutral.

 

Yes, if there is no load on the engine, the ECU won’t add any fuel.

If you are getting code P0172, what is the condition of the rest of the engine? Air filter? Mass air flow sensor? Spark plugs or coils?

P0172
https://www.yourmechanic.com/article...-blake-griffin

 

the VE and fuel table are never perfect, load, air density/temperature, fuel quality all affect it you really should ignore SFT unless they peg and start adding LFT

 

Thank you. So from the info I am understanding when the car is un neutral and we rev it , there is not much resistance against the engine . When car goes into a gear , the resistance from things like the converter will affect engine and the ecu will translate that into load and start to inject more fuel to compensate for the resistance?
sorry im just a newbie trying to understand

 

Thank You, I am starting to understand the term load better on how it affects it .
As for the engine it felt good until my newman ph2 went in. Have had timing checked by mechanic and it looks OK.

Previously had both o2 sensors replaced, new iridium plugs , wires, coilpack. ( have swapped to stock parts and still the same).

Injectors were upgraded to the bosch 380 cc (4 port) and tune adjusted by adrian .

Intake was new ddm foam intake this summer


I have ordered 2 new map sensors and gas cap for replacement . i hate to be a parts changer but they seem original still so i guess it isn't a bad thing. When I get it I will see where it goes .

I have disconnected the purge valve as suggested and the trims seems to get a little better , but not by a lot.

 

thank you. But fom what I am gathering online if both the ltft and stft don't balance each other out doesn't it become an issue? I mean if one is positive and the other negative as opposed to both readings being negative ?

In my case the - ltft of -10 and the - stft of -15 to -30 are probably what is triggering my ecu code ?

 

I'm sorry I missunderstood you had both short and long term trims

if short term trim is at max positive or negative for more than a few seconds it will increase long term trim in whatever direction it's going, i.e., SFT -30 for a few seconds will cause LFT to add negative trim. I do not have the logic for the check code handy but if it pegs out too long it throws the code.

too much fuel is a interesting problem, need more details on the car, is it completely stock? normally I see positive trims from air leaks, not negative trims from too much fuel. Airfilter clean?

 

Some details appear to be long time coming... you have a tune, and you're concerned about fuel trims? Have you had this conversation with your tuner? Maybe he's tweaking something in your tune that the engine doesn't like?

 

I see. Thank you for clarifying that .
as for the car being stock , no it.is not, I just realized I opened the post in the wrong part of the site, sorry.

As stated in one of the above posts it has ...
Ddm intake, 380cc injectors( bosch), detroit tuned bpvalve, newman ph2 cam .
Also replaced crap load of gaskets, new iridium plugs , new wires, new coilpack . New o2 sensors, new cam position sensor, new fuel pressure regulator. Have ordered 2 new map sensors since these look original on car. I am having new exhaust header and afr guage put in so will have mechanic check cat quality and if there is any leak in the exhaust manifold perhaps.
also have had adrian tune it and he has taken quite a bit of time to try and rework tune . He's been a great help

 

Yes I did have a tune by a member of the forum and i have spoken to them. He has taken a look at the tune and logs and has tried to correct it . We are going to try again when afr guage and new exhaust manifold installed .
In the meantime I am trying to diagnose and chase down the issue if its mechanical with my limited skills, that is why I am asking for opinions so I can continue to learn and hopefully fix the issue if it is mechanical and not a software issue

 

Do I understand that you changed the cam after the tune?

 

Tmap sensor. It was for me.

https://www.northamericanmotoring.co...-throttle.html

 

yes that is correct deepgrey, I had the car running with a tune to accommodate all other mods. After installing cam I had tune refined to accommodate the cam .

I purchased the car about a year ago , and did a bunch of maintenance stuff . This is starting to perhaps feel like a previous mechanical issue which wasn't picked up before the tune perhaps .
I'm also wong if my old mechanic ( didn't seem to be knowledgeable with minis ) screwed something up as I remember that since he swapped out my fuel filter I remember that weekend stinking of fuel outside rear side of car. He said it was a gasket they should have put in ? They were working back there also to replace my struts. I do remember that my first oil change after that ( with stock injectors wreaked of gasoline ).
So I am starting to wonder if they screwed something with the evap canister or lines and that may be contributing to this .
Or #2 if they pinched the fuel return line somehow ?

Does anyone know if there is anything in the fuel filter assembly tank that if broken can contribute to over pressurizing the fuel rail?

 

thanks ssoliman,
After a bunch of reading that is what my next step is. Seems that these little buggers can cause all kinds of weird things . I Bit the bullet and ordered 2 new mini map sensors and a new gas cap and hope it helps. The map sensors on my car look original perhaps so I will replace them and fo from there .

 

also thanks for the link, somehow had not seen your thread before. Yes it does seem quite close to what I am experiencing except for the car dying out. The idle is acting a little wonky , but the yo-yo or hesitation issue is definetely there and it has been annoying me since the beginning. It happens around 2800 rpm to 3600 or so. By watching inpa while driving it seems the ecu may be pulling and adding fuel very iraticaly when its happening, so I wonder if it could have been this tmap all along .
Also wondering if my ddm intake could have fouled up an already dying tmap sensor as the oil substance on those foam filters is disgusting,lol. I had to wring out my filter before install as it came soaked. May have to look into a fry k/filter in the future .

Well fingers crossed on my new map sensors when they arrive as this issue is driving me insane ....

 

Good chance tmap will fix. You should see your trims correct themselves right after install. I’d reset all adaptations after install…

 

Well ordered both genuine mini map sensors from pelican parts . One by the air intake and and one on the throttle body. Also got new gas cap as my old one the seal looked all cracked .

the one by the throttle body looks the same and I installed it and the gas cap. I reviewed the fuel readings and still the same .

Upon opening up the tmap sensor ( part # 12140872679) i was immediately put off by what I saw. Different looking sensor body, size and it sais right on it " continental/ china". Surprised as it came out of a bmw box. Well tried to install it and immediately got code "264 - Circuit - Manifold Absolute pressure / atmospheric, High input." Reset fuel adaptations and still running high -stft.

removed the tmap right away and put old one back on. Waiting on response from vendor. i found on this forum a past post about tmap issues, it seems I got the same one . Not sure if this is a new company making these oem parts out of China. I provided a few pics , my old sensor is on the right side .

 

That is correct. I had the same experience. Looks like the OE part has changed to the continental sensor. You have the right part. I’ll post link to my experience.

try cleaning the plug with electrical cleaner and check contacts and pins

 

Oh wait I already posted a link to my thread. Scroll to the end…

 

thanks for reply,

I did Clean contacts and pins before install. Started car , ran for a little and code came up. Put old one I reset code and no more code.

It seems that continental may be the new oem supplier, but I dont like the look of that sensor . Different lengths of the probe, casing is different, just can't put my finger on it . It just looks different .

Ecs tuning seems to have the proper sensor under that part number when I checked their website .

 

yes and thanks for the link. I had read your post and the exact same symptoms are occurring. Gots to say that for the very brief moment I did try the new tmap sensor the yo yo seemed like it was gone. I did feel hesitation but I think it was from the ecu pulling so much fuel .
after the code I searched and came up with this thread https://www.northamericanmotoring.co...ap-sensor.html and the op had the same.issue it seems . I don't think this sensor is correct . I contacted pelican and am going to wait on the answer. Like I said ecs tuning has the one which looks like my oem one on the site . Maybe they can chime in .....

 

yes sir. I understand where you’re coming from. I felt the same. It does say “china” on it…

I contacted fcp at the time. They informed me it was the new oe part.

let me know what pelican comes back with, curious for sure