Weird hard start

[Shuttlemandan]

UPDATE

got my buddies snap on scanner to check my fuel trims and alcohol %. They were way off. Fuel trims were at -25 and my alcohol % was reading 75. Reset both of these and now the Yukon is starting and idling perfect.

 

[kbuskill]

UPDATE

got my buddies snap on scanner to check my fuel trims and alcohol %. They were way off. Fuel trims were at -25 and my alcohol % was reading 75. Reset both of these and now the Yukon is starting and idling perfect.

Now the bigger question... why were your fuel trims off???

-25 on LTFT means the truck is running rich.

Have you filled up with E85 lately?

If your ECM thinks your Ethanol content is that high then the fuel trims being rich would make sense because the higher Ethanol content requires a richer AFR.

 

[Fless]

Now the bigger question... why were your fuel trims off???

-25 on LTFT means the truck is running rich.

Have you filled up with E85 lately?

If your ECM thinks your Ethanol content is that high then the fuel trims being rich would make sense because the higher Ethanol content requires a richer AFR.

^^^ THIS. Highly likely if the sensor mis-reported the ethanol content. But why would it do that? As I understand it the NNBS ethanol is calculated by some kind of software, not a real sensor, but I'm not sure about that.

 

[wsteele]

A slug of bad gas might screw up the calculations it is making for how much Ethanol is in the tank?