Hello,

I’ve just finished a 4.8L LS swap out of a 02 Silverado into a 89 k1500. The motor runs smoothly when cold feels like it has some power and responsive revs but as the motor warms up it slowly loses its power. Takes all its might to go 45 mph at full throttle. We’ve done plugs and wires and redid the entire fuel system, still lacking power, seems like first gear is all reving then when it goes to shift to second it locks up and wants to somewhat go.

 

How did you hook up the throttle valve cable? If it's not right, you'll burn the transmission up fairly quickly.

 

Have you checked for any DTC's?

 

You have to make sure that you adjust the kickdown (detent) cable that should be hooked up to your carb, throttle body, etc.

 

Sounds like it's shifting thru all gears as soon as you take off. TV cable isn't hooked up right.

 

Was the transmission working correctly before? I was also going to ask about TV cable...

It also sounds like maybe the filter gets clogged and cut fluid flow? Wouldn't be the case if transmission was working properly before.

Are you using the 4.8 ECU? How is the ECU getting transmission information? Would it not have been better to run the matching 4L60e? 🤔 I guess that doesn't answer your question, just thinking out loud.

 

. Yes I am using a brand knew 4.8L ECU and the kick down is hooked up perfectly tight and maxes out as throttle is pulled

 

yes I have checked there are no trouble codes appearing

 

well it’s going to sound stupid but we used a nut and bolt and a metal place and custom fitted a bracket to angle the cable, we also held the throttle right and welded an adapter to the bottle of where the throttle cable pulls on to make sure it would pull fully tight when throttle was maxed out.

 

we have it hooked up fairly decently it maxes when the throttle does but we are lacking an extreme amount of power, we are going to do compression tests next to make sure it’s not a motor problem and then go from there, you can go full throttle and it almost sounds like it’s hitting a rev limiter at 3k rpm’s

 

Is this a joke "the kick down is hooked up perfectly tight and maxes out as throttle is pulled"... Seriously? How exactly did you figure out the geometry for the cable? Serious question as it is LIFE OR DEATH for the transmission... It is NOT a kick down cable.. or a detent cable.. It IS a TV cable and it controls ALL of the line pressure, and influences all of the upshift and downshift points... This is not something that you can just throw together and expect it to work properly because you got the cable to max out as the throttle is pulled... Not kidding it takes a LOT to get the geometry right. I'm willing to bet, without seeing what you have working-it is not right. How many HOURS did you spend measuring the various components to get the geometry right? Cutting and welding the brackets to make it all work-unless you bought something that was already intended to work with a 700? What did you use to verify the angles needed for the attachment point? Me thinks you will have a smoked 3rd and 4th clutch pack in your very near future. Can you post a picture of the cable where it attaches to your throttle body... A picture is worth a thousand words...

 

jesus dude sorry I didn’t mean to offend you just two kids putting together a truck. It shift through every gear everything is fine I’ll post a picture tomorrow.

 

 

we haven’t driven it more than a mile most we do is start the truck to move it around so it’s not in the way. If there’s anything that needs changed I appreciate the help but there is no need to get aggressive. I understand your trying to help.

 

and yes we did look up the geometry got it as close as possible… yes we took our time.

 

 

Not offended at all. Sorry if I came across as "aggressive"... Here's another site that has relevant information; https://www.bowtieoverdrives.com/Ins...s/TV_101-1.pdf
though it does not go into setting up the geometry on the intake side...

This guy does a pretty good job of discussing angles, distance, lengths, and what-not for setting up the carb/throttle body connection; https://purplesagetradingpost.com/su...o/700R4p1.html

Have fun and enjoy your project!

 

sounds kinda like when i left one bank of coils unplugged on accident one time. motor still ran but it was down on power.

 

Leak down test will give you much more info!

 

You said it runs good when cold but bad when warm. Sounds like when it goes into closed loop it runs bad. Are you sure your O2 sensors are working correctly? Or the tune is not good.