Fuel trim

[Jaredpear]

i have 1999 K2500 with a 454. 6 month old Bosch injectors, new fuel pump and just got new exhaust put on and passenger side pipe is missing it’s cat while driver side is still there. Driver side also has a leak at the cat flange. While driving fuel trims are normal and with 1-3% of each other but when I let off the gas the passenger side start shooting sky up into 20-30% positive fuel trims. If even hit positive 50% at one point which is as high as my scanner would go. I have no idea what going on. It wasn’t tis bad till I put on the new exhaust but still slightly did it. The cat was also missing before the exhaust, an help would be appreciated. Thank you all!

 

[1999gmc]

While you're at idle it is 20-30%. If so I would check for vacuum leaks. Possibly intake manifold gaskets. You could take it to a shop and have them smoke test it to make sure if you don't find any leaks. With it only being Pass side I wouldn't think it would be a mass air flow sensor. Are they original intake gaskets?

 

[Jaredpear]

While you're at idle it is 20-30%. If so I would check for vacuum leaks. Possibly intake manifold gaskets. You could take it to a shop and have them smoke test it to make sure if you don't find any leaks. With it only being Pass side I wouldn't think it would be a mass air flow sensor. Are they original intake gaskets?

Not even half a year old. Did head gaskets and every above that about 3 months ago

 

[Jaredpear]

Also it’s not 20-30% while idling, only when decelerating like coming off the the highway for example. Idle and with the gas pressed its normal

 

[1999gmc]

Hmm. Not sure. I'd say missing cat possibly causing it but you said it didn't have the cat before.

 

[Christian Steffen]

Could be a bad o2 sensor? Or perhaps an exhaust leak on that side?

 

[Jaredpear]

My collector gasket is very bad an has an audible exhaust leak, could it be that bad to cause that high of fuel trim readings?

 

[Christian Steffen]

Perhaps? Fix it and see. That or swap o2s around and see if the issue switches banks.