Guys,

I've noticed my AFR gradually getting to near 17 the warmer my car gets and longer I drive it. What can be the cause of this? WB Sensor going bad, Injectors, plugs?

 

Widely discussed issue. From my experience it was injectors sensitive to heat and/or fuel temperature. A flex fuel sensor enabling fuel temperature correction completely fixed it for me.

 

sounds like an expensive fix, is there a low cost option? I am over dumping money into this car.

 

Said sensor and connector can be had for under $100 and there's lots of documentation regarding wiring and setup on here. ACDelco/Continental make the most common one.

https://www.summitracing.com/parts/a...hoCuZcQAvD_BwE

 

And way way cheaper if you source one used off a salvaged GM flex equipped vehicle.

That said, your issue is pretty vague. Did you confirm that some corrections aren't causing the discrepancy? And that your wbo2 isn't faulty?

 

I think the expensive ones are older models from back when flex fuel sensors were less common.
Now so many newer cars use flex fuel sensors, with economy at scale the newer models are significantly cheaper.
It was surprisingly affordable, I rolled the dice on one from amazon GM 13507128, pigtail, dorman quick connects <$100 total. Its genuine and works great.

Check your IAT sensor location, IAT temps, IAT correction curve. Another common issue is bad IAT sensor location, heatsoaked sensor when true IAT is cool, thus correction curve pulling fuel incorrectly.

 

Post your tune and a datalog of the issue. If it's just idle, EGO could help, or WUE might be completely wrong, or MAT correction, or, or, or. We're all just guessing.

 

No WB sensor issue from what I can tell I do have about 5k miles on it, the AFR gets up to 17 (lean) on idle after driving it for a good amount of time. I am not sure how a flex fuel sensor would make the issue go away. Does it also give a fuel temp? Isn't a flex fuel sensor for e85 only I use the highest pump gas available in Phx 91. How does a flex sensor correct the issue? Maybe the WB is old, or I need to get new plugs? I want a cheap fix with the least amount of work I might be asking for to much. Is 17 that bad at idle?

 

A flex fuel sensor monitors ethanol percentage and fuel temperature, enabling ethanol correction and fuel temperature correction. In many states the gasoline is actually ethanol 10%, and it fluctuates from different station and blends. My fuel temp needed significant corrections (Flow force 725 injectors). Now my VE table is stable and no longer need huge EGO allowance at idle.

 

seems easy to install and wire up to MSP does it need a tune after install? Or just turn on the sensor setting on MS and it does it automatically?

 

Yes it was easy to install. Place it close to your fuel rail on returnless system, place it on the return line on a return system. Ethanol correction curve is standard usually not touched. Fuel temperature correction, I tuned it at idle plugging in the correction it wants every change in 10F. I found the correction ended up being close enough to a straight line slope. Then confirm the rest of your VE table takes the correction well by driving.

There are other possible causes of going lean on long drives due to something heatsoaking. I feel like the need for fuel temp correction on high-impedance injectors are not emphasized enough. I kept chasing my tail until I noticed people seem to stop talking about this issue when they have a flex fuel sensor.