Fuel Trims Problem

[shifty909]

2018 Silverado 1500 L83 I had the DoD problem, and because I was replacing lifters I decided why not go with a better camshaft. I replaced cam (BTR stage 2), lifters, pushrods, springs, as well as timing chain, VVT solenoid (with 4 degree lockout), oil pump (had a pressure control solenoid code), and bought a tune file from a "reputable" tuner. Now my fuel trims are way out to lunch, it is overfueling badly, especially at low rpm and the tuner has somehow disappeared off the face of the earth. Other guy in town wants $1000 to redo the tune but I was hoping someone had some insight as to what I could do to adjust fueling/timing to make this thing driveable.bb2 rework.hpt

[gtstorey]

Need to post a log also.

[shifty909]

For some reason it isn't letting me upload the log file. Is there any other way to send it?

[gtstorey]

For some reason it isn't letting me upload the log file. Is there any other way to send it?

No. How long a log are you trying to attach?

[shifty909]

Apparently too big of a file. I'll do another log tonight and upload it as soon as I can

[tonn0297]

Apparently too big of a file. I'll do another log tonight and upload it as soon as I can

You can just zoom to under 20min, then export as hpt file and set a checkmark in "only visible range", no need to relog.

[Alvin]

You can just zoom to under 20min, then export as hpt file and set a checkmark in "only visible range", no need to relog.

That's a handy tip.

Who did the orignal file? Do you have the stock file to compare to?

[shifty909]

So the zoomed drive was a few days ago, did another quick log yesterday on the drive home. zoomed post drive.hpldrive 2.hpl

[shifty909]

Original file was done by a local guy who has since disappeared. I do still have a stock file.

[Alvin]

This has virtual flex fuel enabled. It can cause you to chase your tail with fuel trims. I would disable that, add a flex fuel sensor if you ever want to run flex fuel. After you do that.. set up a table in the scanner to plot fuel trim error against the MAF table. Use that to dial in your fuel trims.

I wrote about this for a article pending to be published on our website. There are likely grammar errors in this...

https://www.pcmofnc.com/2025/02/19/h...lex-fuel-work/

[Some GM vehicles are ?E85 capable? but do not use a flex fuel sensor, or fuel composition sensor.

A fuel composition sensor is installed in the fuel line and can sense how much alcohol is in the fuel. Lots of OEM GM cars came with fuel composition sensors but many did not. If they didn?t come with this sensor but are ?E85 capable? this means they are using Virtual Flex Fuel.

The way this works is this.

If your car seems lean on average, it assumes the alcohol content is higher than what it first assumes.

If your car is richer than normal.. It assumes there is less alcohol in the fuel.

Note: Fuel from a gas station can be anywhere between 0-85% alcohol with the balance remaining as gasoline.

That?s right. It assumes.. It guesses.. You can see where this is going.

Virtual Flex Fuel is not reliable even in 100% stock vehicles. If the vehicle is heavily modified and the tune is anything but 100% spot on.. It ends up chasing its tail assuming this or that with the alcohol content. Furthermore.. If you have a bad or dying 02 sensor? that is enough to derail a virtual flex fuel tune.

For that reason.. We recommend disabling virtual flex fuel. The good news is.. Everything that is capable of running virtual flex fuel is also capable of running a real physical flex fuel / fuel content sensor. So if you are serious about running E85 please contact us about installing a fuel content sensor.

Also, side note.. If you are going down the flex fuel road.. Reach out to see if it would even be worth it in your application. There are setups that LOVE flex fuel.. There are a lot of other setups that offer little to no gains. We don?t mind steering you in the right direction.

[2xLS1]

This has virtual flex fuel enabled. It can cause you to chase your tail with fuel trims. I would disable that, add a flex fuel sensor if you ever want to run flex fuel. After you do that.. set up a table in the scanner to plot fuel trim error against the MAF table. Use that to dial in your fuel trims.

I wrote about this for a article pending to be published on our website. There are likely grammar errors in this...

https://www.pcmofnc.com/2025/02/19/h...lex-fuel-work/

I think every gen 5 truck calibration has FF Enabled with Virtual even when they are not FF vehicles. The actual FF trucks will have FF Enabled with Sensor. Have you not noticed this? I'm pretty sure Virtual FF ended with the Gen 4s.

[Alvin]

I don't know if i've been burnt by a GEN 5 before. Easy way to tell for sure is scan ethanol content.

[2xLS1]

Because if it doesn't have a physical sensor it is not FF.