What would make fuel trims high when engine is cold but OK after warmed up?

[kev0]

Don't know where to start with this.

Fuel trims positive when cold, but after 5-10 minutes of driving, car would stutter and then become normal. I monitor my fuel trims live with my EcuTek app and right when the car stutters (RPM's drop then go back up), my fuel trims are OK.

What would you guys suspect to be the problem? I'd say vacuum leak, but I don't understand how a leak would fix itself after car is warmed up. Happens both on E85 and 93 Octane gasoline.

I understand that fuel trims may be high during cold starts, but mine are extremely high. It's so high it throws off a lean code.

[tomm.brz]

vacuum/charge leak would put very negative trims
more likely an exhaust leak that fix itself with exh headers getting hotter and expanding?

maybe post a log, starting it even before cranking
and add Fuel Quantity in the log s values
we could maybe try to understand if the lean code is real os it s the lambda sensing fresh air

[kev0]

Originally Posted by tomm.brz

vacuum/charge leak would put very negative trims
more likely an exhaust leak that fix itself with exh headers getting hotter and expanding?

maybe post a log, starting it even before cranking
and add Fuel Quantity in the log s values
we could maybe try to understand if the lean code is real os it s the lambda sensing fresh air

https://datazap.me/u/kev0/drive-back...ta=21-30-32-45

Hi, that is a datalog of my drive. Towards the end is where you see my fuel trims 'normalizing'. Can you please take a look and use your knowledge to maybe see what is causing my fuel trims to be out of line?

My tuner said he already applied about 30% correction to the tune and is still seeing fuel trims acting weird. From the datalog, can you safely assume that it is indeed an exhaust leak?

[tomm.brz]

will take a look

but a cold start log would also help
difficult to say actually, it does seem an exhaust leak
bring your car to check the exhaust, and see it the lambdas are well screwed in

[kev0]

Originally Posted by tomm.brz

will take a look

but a cold start log would also help
difficult to say actually, it does seem an exhaust leak
bring your car to check the exhaust, and see it the lambdas are well screwed in

https://datazap.me/u/kev0/cold-start...ta=21-30-32-41

Here is a better log, hopefully. I started datalogging right before I started the car up. As you can see, fuel trims are fine during the cold start, but after the initial RPM drop you normally get from a cold start, it starts to shoot up.

Can you tell what the problem could be based on the datalog?

Thanks again

[tomm.brz]

now it s a better view
i think no leak

Seems there is a problem with the port injection, as soon as it goes 100% PI, the afr goes lean and fuel trims shoot crazy up

Did you have this problem just lately, or since beginning of.tuning?

Did you change injectors or still have stock 228cc ones?

i would do another log adding the four Cylinder misfire values

[kev0]

Originally Posted by tomm.brz

now it s a better view
i think no leak

Seems there is a problem with the port injection, as soon as it goes 100% PI, the afr goes lean and fuel trims shoot crazy up

Did you have this problem just lately, or since beginning of.tuning?

Did you change injectors or still have stock 228cc ones?

i would do another log adding the four Cylinder misfire values

Thank you sir.

I bought the car used and I assume the original owner put back on all original parts, so for now, I assume it is stock PI's. That is what I told my tuner when he was creating my tune. This all started when I flashed the tune in my car and installed my supercharger. You may be on something about the PI because along with my P0171 codes, I also have P117B and P1170 which is related to the PI and DI computers.

Could it be possible that the PI are aftermarket and something much higher than stock? Would that make my car run lean if that is the case?

Thank you for your help.

EDIT: I forgot to add...my tuner made 2 maps for me, one is 100% DI at low load and other is 100% PI at low load. I switched both of them back and forth and fuel trims remained the same. Could that possibly rule out the faulty PI's?

[tomm.brz]

actually if you have now bigger injectors, but in tune you have the stock scaling of 228, you would have the opposite problem
meaning that it would flood with fuel through the PI injectors since the ecu thinks they are just 228cc and open them for more time

tricky...

check DI ECU harness, if everything is well grounded and... don't know. Never seen such a problem

it can just also be an electrical problem, also a simple one like a dying battery that doesn't hold voltage

could be vacuum leak, exhaust leak, clogged or damaged maf, failing o2.. can be a lot of things unfortunately

[kev0]

Originally Posted by tomm.brz

actually if you have now bigger injectors, but in tune you have the stock scaling of 228, you would have the opposite problem
meaning that it would flood with fuel through the PI injectors since the ecu thinks they are just 228cc and open them for more time

tricky...

check DI ECU harness, if everything is well grounded and... don't know. Never seen such a problem

it can just also be an electrical problem, also a simple one like a dying battery that doesn't hold voltage

could be vacuum leak, exhaust leak, clogged or damaged maf, failing o2.. can be a lot of things unfortunately

Sigh, this will be a long journey for me to figure it out.

My battery hovers around 14.4v throughout the entire log. I guess it's safe to say that I can eliminate the failing battery, right?

[kev0]

Anyways, I know that fuel trims don't matter during cold starts because the rear o2 sensor isn't heated up yet, but what if I have a rear o2 flex fuel kit? There is no rear o2 sensor for me to warm up anyways.. I just don't understand why my fuel trims are high before engine is warmed up.

It's frustrating!!

[ActionMaxon]

It could very well just be a vacuum leak when cold.

Generally speaking, engines leak everything more when cold. After it's heated up the engine and components have thermally expanded so leaks become less prominent or go away entirely once hot.

Try putting a vacuum gauge on it when it's cold. Then again when hot. If you have less cold there you go. If not, start digging into more sensor data.

Have you gone over intake clamps and whatnot to make sure there one wasn't missed during SC install?

[Fullcoverage]

Did you ever figure out your problem?

Originally Posted by kev0

Anyways, I know that fuel trims don't matter during cold starts because the rear o2 sensor isn't heated up yet, but what if I have a rear o2 flex fuel kit? There is no rear o2 sensor for me to warm up anyways.. I just don't understand why my fuel trims are high before engine is warmed up.

It's frustrating!!