6.5 Feeling Sluggish

[Jacku21]

Hi all, I have a 95 3/4ton ext cab long bed w the 6.5 and 4l80 and 4.10 rear limited slip. I was merging out onto the interstate today and needed to pick up speed quickly. I put the hammer down and struggled to outrun a semi truck. Once she gets up to 80 she cruises fine. Low speeds are fine for power and torque but she seems to have trouble getting up to highways speeds quickly. Kicks down fine and screams. would like to diagnose this lack of power. Or is this to be expected from the 6.5? I get they were never powerhouses but this seems excessive. Suggestions?

 

[dbrannon79]

Welcome to the forum @Jacku21. what all has been done in the rhelm of mods from stock? first thing I would suggest is to install a clear line to the IP return, get a fuel pressure gauge on the inlet and a turbo boost gauge so you can see what all it's doing under load. installing those three might give us a starting point on where to start digging into.

 

[Stoney]

Welcome @Jacku21 mines a crew cab dually and same drive train , you shouldn't be having that sluggish of a feeling.. does it take off off the line good like at a stop light? If it's shifting fine and rpms runn up when you get on it I'd say it's in the trans, have you done any service on it lately? Fluid/ filter on trans.?. Long shot but is your turbo spooling up when you accelerate ?
Fuel filter changed recently?
As @dbrannon79 said you want to make sure your not getting air in the line.. and you won't always see fuel leaking even if there is a leak.. as he said a piece of clear line in the injection pump and a couple clamps on it only costs a couple bucks.. but will give you a world of knowledge.. also make sure your lift pump under the truck is actually running.. just cause the truck runs doesn't mean the pump is...

Oh and WELCOME TO TTS!! Glad to have you join!! You found probably the best group of guys for knowledge of these engines

 

[Will L.]

Welcome.
They started you on the right track. Only other thing to ask is when you stomp on it, is there any exhaust smoke to indicate plugged air filter. Otherwise do exactly as said for the beginning.
Post a list of the truck details and any modifications made in your signature line- that way we see exactly what we are dealing with on each post and you never have to type it up a bunch of times.

 

[Jacku21]

Welcome to the forum @Jacku21. what all has been done in the rhelm of mods from stock? first thing I would suggest is to install a clear line to the IP return, get a fuel pressure gauge on the inlet and a turbo boost gauge so you can see what all it's doing under load. installing those three might give us a starting point on where to start digging into.

It’s completely unmolested.

 

[Jacku21]

Welcome.
They started you on the right track. Only other thing to ask is when you stomp on it, is there any exhaust smoke to indicate plugged air filter. Otherwise do exactly as said for the beginning.
Post a list of the truck details and any modifications made in your signature line- that way we see exactly what we are dealing with on each post and you never have to type it up a bunch of times.

It doesn’t smoke at all.

 

[Will L.]

Ok, so need that clear return fuel line seen for no bubbles or other contamination like water.
What is fuel pressure at the ip inlet?
Where is the boost?

Everything else is going to be guessing and throwing parts at it.
These 3 checks are proper diag to occur next.