Noob new to GM needs some help!

[2000YukonSLE]

hey guys, new here and glad i found the place. Ive searched through the forums for this topic and havent really come across anything. Anyway i just purchased a 2000 Yukon SLE newer body style with the 4.8L 4x4 etc nothing special. Installed a set of 20in rims and tires and a spectre 9900 cold air intake. Every morning i get in my ride to go to work and it rides good, seems to have plenty of pep. Later on in the day when i run out somewhere or go home, the truck seems very sluggish. Feels like its straining just to accelerate but i have no check engine light on. I have the hard shift from first to second and put some lucas in it and it seemed to help that issue somewhat, still a firm shift but not hard. Could this be a trans issue? Also, i have a very loud exhaust leak coming from somewhere, sounds like its right under the drivers seat, will an exhaust leak cause me to lose power? Is it because i have an intake with no exhaust yet? Any help would be greatly appreciated and I know some of you will prob say its because its a 4.8 lol but for the price i got it for i cant beat it. Thanks

 

[Sprayed99]

hey guys, new here and glad i found the place. Ive searched through the forums for this topic and havent really come across anything. Anyway i just purchased a 2000 Yukon SLE newer body style with the 4.8L 4x4 etc nothing special. Installed a set of 20in rims and tires and a spectre 9900 cold air intake. Every morning i get in my ride to go to work and it rides good, seems to have plenty of pep. Later on in the day when i run out somewhere or go home, the truck seems very sluggish. Feels like its straining just to accelerate but i have no check engine light on. I have the hard shift from first to second and put some lucas in it and it seemed to help that issue somewhat, still a firm shift but not hard. Could this be a trans issue? Also, i have a very loud exhaust leak coming from somewhere, sounds like its right under the drivers seat, will an exhaust leak cause me to lose power? Is it because i have an intake with no exhaust yet? Any help would be greatly appreciated and I know some of you will prob say its because its a 4.8 lol but for the price i got it for i cant beat it. Thanks

the harsh 1-2 shift is more than likely caused by the plastic accumulator piston being cracked causing it not to "cushion" the shift if it is banging into second.

Is the shift a slide/bang or just a harsh bang into 2nd?

an exhaust leak can cause severe issues if it is close enought to the 02 Sensors. Also if it seems sluggish please make sure it is in fact going through all the gears. You may have a issue with the transmission going into fail safe and you are stuck starting in third gear.

 

[2000YukonSLE]

Thanks for the reply, greatly appreciated.When i first drive it when its cold its a hard shift, after that it kinda smoothes out depending on how much gas im giving it. Im having someone fix the leak see if that helps anything. Also going to check plugs and wires. Previous owner said he did tune up 30k ago. If it is cats, what would you recommend, i plan on doing an exhaust and saw some universal converters for a decent price and some magnaflows for 450.

 

[Sprayed99]

Thanks for the reply, greatly appreciated.When i first drive it when its cold its a hard shift, after that it kinda smoothes out depending on how much gas im giving it. Im having someone fix the leak see if that helps anything. Also going to check plugs and wires. Previous owner said he did tune up 30k ago. If it is cats, what would you recommend, i plan on doing an exhaust and saw some universal converters for a decent price and some magnaflows for 450.

I understand you have a lot of questions but please answer mine above. Then we can move on to other diagnostic questions. I want to figure out the hard 1-2 shift first.

 

[2000YukonSLE]

bangs from first to second when cold, after warms up smoothes out, doesnt bang into 2nd just slides right in. shifts through all other gears fine. also, tow haul light does not come in so it stays in OD as far as i know.

 

[Sprayed99]

bangs from first to second when cold, after warms up smoothes out, doesnt bang into 2nd just slides right in. shifts through all other gears fine. also, tow haul light does not come in so it stays in OD as far as i know.

Yup that sounds about right for a cracked 1-2 accumulator piston. A new one is cheap (I pay about 3.00). This will require you dropping the transmission pan and its a great time to replace fluid and filter.

Now onto the other questions. Clogged cats can cause the loss in power, but it doesn't always come and go. Your best bet is getting on performancetrucks.net or LS1truck.com people tend to just toss the entire y pipe with the cats when going to headers and you can get them really really cheap... Like under 100.00 if those people are local to you.

Other than that I gut the cats, but I also have tuning software to take care of any unwanted codes from this process. This is not a good idea if you livein an area where emissions are a issue.

 

[2000YukonSLE]

awesome i appreciate the input...ill have to work on that this weekend..as far as the cats i wil check out performancetrucks.net see what i can find...would it be better to go stock with cats or just go aftermarket? emissions arent a problem around where i am..i could probably just gut the cats i have now right?

 

[2000YukonSLE]

was doing some research and found that some people say to unhook your batterty when you install a CAI. i never did. did it today and let it sit for about 20 min, hooked it up and it runs great...weird