Hey, at idle my engine jumps/studders and on a long acceleration in high gear barely pulling it feels like the gas kicks off to the motor for half a second then it happens again and again untill i get higher rpms. It screams up top but runs like hell on the bottom? any ideas... its a 99gmc with the 5.3l, cat back exhaust, and cold air intake.

 

You may wanna check on your fuel pressure. If you see an irregularity you may need a new fuel pump. How many miles are on your truck?

 

Over 112,000 miles

 

Its a jerky feeling and i can hear my exhaust go quieter then come back up again when it happens...like i said it happens VERY fast i cant even see a drop in my rpms.

 

Does it run like *** and then if you slowly lay intot he throttle is smooths out and stays great until you let off again?

Mine did that and I found the O2 wire laying on the header. It gave the O2 the wrong reading due to heat on the wires and made the truck run rich until it switched to open loop and ignored the O2's (usually around 40% tps). Then it pulled great until I let off the throttle again. Blew black smoke like diesel as well.

 

A little hard to diagnose without being there but my old SS did something similar when the cam position sensor went bad.... not 100% sure it will fix your issue but its something to look at.

Did you do anything recient to the truck? Sometimes a crank position relearn can fix the issue as well.

 

No it only happens at low rpm acceleration and smooth slow take offs....it sputters basically then seems to clear itself and its 100 percent again. Nothing has been done to the truck.... at first i thought it was my tranny overdrive messing up and making the truck jump but it does it with the overdrive off and i now hear its in my exhaust.....my tranny is gone though.

 

How do i do this crank relearn?

 

Is it just sputtering or sputtering/backfiring? If its not backfiring it wont be a position sensor issue.... more like a fuel/02 sensor. The relearn can only be done by a Tech2 or tuning software.

 

It doesnt back fire under acceleration what so ever just sputters below 2 thousand rpms under very light acceleration....like vmmmmmmm der der vmmmmmmm der der vmmmmmmmm...i tried sounding it out with words hope it works haha but thats what it does.