350 TBI - No Power When Towing?

[95k2500]

We had our 26 1/2' fifth wheel out this weekend and while the tow itself was fairly short in distance (say 10 miles) with a couple of gradual inclines, the truck really struggled with the load going uphill on the highway, much more than it ever has before. The truck would downshift from 3rd to 2nd to get the RPM up, but it didn't actually gain any power... in fact, it continued to slow down while maintaining 3K rpm... definitely didn't feel right at all.

Once back on the flat surface, it picked right up again and was cruising at highway speed no problem.

Is this a sign of a bad engine or are the other things I should be looking at?

Truck is a 1995 K2500 4x4, 350 TBI, 4L80E, 4.10 gears.

 

[thz71]

Definately not the engine honestly that's way Tok big of a trailer to be pulling with your truck and sounds like a tranny problem to me

 

[skylark]

That trailer should be fine. If a tbi has low power but still runs reasonably smooth, I look at fuel pressure followed by compression.

 

[95k2500]

It runs well... though even unloaded I noticed it does struggle a bit on the hills, I live in a pretty hilly town with some steep slopes and it definitely doesn't 'cruise' up those hills with ease, though I never thought of that much before.

Trailer should be fine, it's under 7,000 lb loaded.

What sort of issue would the transmission have that would cause this? Didn't feel anything slipping... more like the truck was either starving or getting too much fuel (not really sure) when I was pushing the pedal down.

 

[96Z71ECSB]

As skylark stated, I would start with checking the fuel pressure.
Also check the fuel filter/ air filter/ PCV valve.
A partially plugged catalytic converter would cause that sort of behavior also (if the cat is still there ).

 

[thz71]

That trailer should be fine. If a tbi has low power but still runs reasonably smooth, I look at fuel pressure followed by compression.

from somone who tows with a 350 tbi almost daily I can tell you that it won't hold 3rd up a hill pulling a 26 ft trailer

It runs well... though even unloaded I noticed it does struggle a bit on the hills, I live in a pretty hilly town with some steep slopes and it definitely doesn't 'cruise' up those hills with ease, though I never thought of that much before.

Trailer should be fine, it's under 7,000 lb loaded.

What sort of issue would the transmission have that would cause this? Didn't feel anything slipping... more like the truck was either starving or getting too much fuel (not really sure) when I was pushing the pedal down.

If its not pulling any harder in 2nd gear at 3k then it is in third at 3k that makes me think tranny and are you towing in OD?

 

[SkyHighColorado]

Clogged cat is where my money is. I had my cat fail and shot crap out into the tailpipe and it clogged causing an instant lack of power especially under load and crap MPG. Once I punched the cat out with a metal rod and floored it my performance was great and it was freaking loud!

 

[95k2500]

The campground we pulled it out of on Sunday had a very steep incline and it seemed to pull it up that fine... course that was at low speed and 1st gear.

No OD for highway, D only. I've pulled many trailers in my life.

So what would be the issue with the tranny if it downshifts and up shifts fine? That is what I am not understanding.


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[michael hurd]

If the fuel pressure is good, the injectors are spraying properly ( can check the spray pattern with a timing light ) I would place a bet on a convertor / muffler issue. There may be a collapsed baffle that is partially blocking the flow in the muffler. May not show up under light load / low rpm, but higher RPM equals more airflow through the engine.

This is assuming there is no MIL lit up, and no codes stored, as well as good compression. Would be good to have an idea of the mileage on the vehicle as well as the tire size... 4:10 ratio should be quite adequate assuming that the tire size is stock or close to it. Larger oversize tires will negate the lower gearing.

Have you changed the fuel filter lately? If that is getting clogged or there is a bit of water in the paper, it will not flow the proper amount of fuel that is needed for heavy engine load.

 

[95k2500]

275,000 KM on the truck... no cat (was removed by the previous owner)... but I will start digging around on the fuel system and see if I can uncover anything unusual.

I appreciate the tips... it's a solid truck and shouldn't really have an issue pulling our fifth wheel, it's definitely within reason in terms of weight, etc.