fuel trim issues and alcohol content high with 93 octane
a buddy brought his 2006 silverado over and i data logged it and pulled the tune. it had -19 percent fuel trims and was reading 74 percent alcohol content but he swears he only puts 93 octane in it. during the data log i let it idle for a bit and reset the fuel trims and gave it a couple revs. truck has btr stage 2 cam in it and no other mods besides no muffler (sounds ridiculous I know). tuned by a local shop not by me. i am wondering if the alcohol content sensor has gone bad or whats going on for it to read that high and not have e85 in the tank. ive never messed with flex fuel so bare with me. thanks for taking the time to read this thread. tune and log attached
also the fuel gauge doesnt work in the truck . idk if its a wiring issue sending unit or cluster issue or if its even relevent to the alcohol content sensor
02-05 L59's had a real sensor in the fuel line. 06 and up L59 is virtual flex so no sensor. I've seen that problem on a few 06-07 classic flex trucks and even on quite a few gen 4 virtual flex trucks. I believe the strategy is when more than 4 gallons of fuel are added the OS is supposed to try and recalculate the alcohol content by looking at the O2 switching so the fuel gauge not working may be contributing to your problem. All the ones I've seen had working fuel gauges and were just computing alcohol content wrong. Most I've seen were even using 100% gas. E0 or 100% is widely available here. One 07 Classic that had the problem was owned my a tech at a GM dealer was aware of his flex problem and he would just use his Tech 2 to periodically reset the E content to 0 when his truck would set P0172 and P0175 rich codes. He was even calling GM engineering support that dealers have and they couldn't come up with a fix on his truck. When I see the virtual flex problems the commanded A/F in closed loop is usually somewhere between 11:1 and 12:1 instead of the stoich for either 100% or E10 that the customer is using and very - fuel trims. I try and explain to the customer what is happening and offer to disable flex if they choose. Most choose that and say they never run E85 and never plan to. Even if you run E10 it would be no different than running a non flex on E10. Or if E10 is all you have you could disable flex and set the entire stoich table to 14.1.
Thanks a lot man that was exactly what i needed to know. I will inform him tomorrow and go from there. When the truck was tuned for the cam the tuner never took his top speed limiter completely off so he is wanting me to do that for him in the near future. Turning the flex fuel off is as simple as setting the tab to disabled correct?
Thats good to know. I know of a fuel station that has e85 about 10 miles from me and was telling him he could pick up a little bit of power if he would run it. He wants me to put a new pump assembly in it in the next few weeks. I will try to remember to come back and update you on if that fixes it. Thanks again for the insight.
Reply With Quote
