Towing Power (or lack thereof)

So I recently picked up a ‘93 K3500 with the 6.5L diesel. This is my first truck so please excuse the newbie questions.
I have made several trips with a steel 3 horse BP trailer (approx 3,000lb curb weight) back and forth along highway 3 in BC Canada. For those that don’t know it’s fairly mountainous, some steep grades, the worst of which is 9% I believe.
Now I know this truck is never going to win any speed competitions, but I expected a tad more power. Going up hills she sucks, and not in a good way. I thought it was an air problem at first but after shaving two hours off my best (empty truck, empty trailer, in Drive) time by being in Overdrive (with no load) I got to thinking.

So I did a test:

In Drive, the truck struggles to maintain speeds over 80km/h and is running about 3100rpm. She has zero power on a hill, can’t maintain speed, and the pyro tells me she’s hot.

In Overdrive, the truck cruises and easily does 120km/h without passing 2500rpm.

Today’s test was with an empty truck.

Is this normal for this truck? Is there something I should have looked at? Again, I know she’s not built for speed but I thought she’d be able to do a bit better ...
I didn’t get a lot of history from the guy I bought it from but he told me the glow plugs and wires were done recently, and he upgraded to a 4” exhaust (but did not do the crossover pipe). I know she needs her injectors done, they’re on order, along with new lines.

At 3100 RPM's, you're against the governor (power/fuel diminishes until the actual governed engine speed). No power there. That's it. Boost is limited from there, so the EGT's go up too, exiting the turbo efficiency range. If you have more power in OD/4th, it's because the IP isn't limiting and boost is plenty. More boost at lower RPM means cooler running, and it's also closer to the torque peak. The more weight you have in tow, the more meaning this has. If your injectors are tired, a new set will change the entire outlook. Probably the single best upgrade you can do is freshen a tired set of injectors.

If he put a bigger exhaust on it then you probably don't have the snorkle on the intake, but it's worth looking. (Where is the air filter getting its air from?)

The '93 waste gate is just a spring in a can. Do you know how much boost you're getting? And, yeah, at 3100 RPM it's going to act like it's got n power because the governor is cutting in.

The intake is the stock that goes down the side of the quarter panel and ends up somewhere under the bumper or behind the headlight?

I don’t know how much boost I’m getting, how is that measured?

And I know this will make me sound like a total noob but what is EGT?

He put a bigger exhaust on but did not do the crossover pipe. How much does that impact performance?

I can get stock GM replacement injectors in Canada from Lordco. I was planning on ordering a set of Bosch injectors from Accurate Diesel online but I’m no longer certain I’ll be able to get them shipped to Canada.

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Originally Posted by Eeyore93

The intake is the stock that goes down the side of the quarter panel and ends up somewhere under the bumper or behind the headlight?

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Yes. It is very constricted, and with age it can get sucked shut under heavy loads.

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I don’t know how much boost I’m getting, how is that measured?

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You'd need a boost gauge, basically a pressure gauge plumbed into the intake manifold after the turbo.

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And I know this will make me sound like a total noob but what is EGT?

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the pyro tells me she’s hot.

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That. Exhaust Gas Temperature.

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He put a bigger exhaust on but did not do the crossover pipe. How much does that impact performance?

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Can't hurt. Anything that reduces back pressure is a plus. There are mandrel bent crossovers that help. Not much more you can do because of the manifolds themselves.

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I can get stock GM replacement injectors in Canada from Lordco. I was planning on ordering a set of Bosch injectors from Accurate Diesel online but I’m no longer certain I’ll be able to get them shipped to Canada.

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I'll defer to some of the injector and overhaul experts for this one. I'll just say there are good rebuilds and not so good ones, and new.

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Originally Posted by JohnC

Yes. It is very constricted, and with age it can get sucked shut under heavy loads.

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I kinda got the impression she was trying to breathe through a straw. What’s the best way to improve this?

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You'd need a boost gauge, basically a pressure gauge plumbed into the intake manifold after the turbo.

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I will add that to the list, I wanted to move the pyro gauge anyway, the guy who installed the one on my truck put the gauge down behind the steering wheel for some dumb reason.

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That. Exhaust Gas Temperature.

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Ha. That makes perfect sense. Good thing I’m pretty ;P

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Can't hurt. Anything that reduces back pressure is a plus. There are mandrel bent crossovers that help. Not much more you can do because of the manifolds themselves.


I'll defer to some of the injector and overhaul experts for this one. I'll just say there are good rebuilds and not so good ones, and new.

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Originally Posted by Eeyore93

I kinda got the impression she was trying to breathe through a straw. What’s the best way to improve this?

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Just remove the tube from the inner fender and recycle it. There's a screw somewhere along the fender, and I think (it's been almost 20 years) it's clipped in behind the headlight.

You will be a happier guy if you read up some on adding a better turbo for towing,.
The little hair dryer thats on there starts to choke up after 2000 rpm.
It creates a ton of heat,. At 3100 rpm its a road block,.
Read up on pulling the lid off your mechanical pump and giving it a 'little' more fuel,. I will caution you tho,. Too much will only make it hotter with the stock Gm3 turbo.
Check out The HX series of turbo's
You can buy adapter kits on e bay.
Lots of info on this forum and on the net,.. have fun,. 6.5's are addictive to some people,...������������

So my new injectors are in the mail, as is a new crossover pipe. I have gauges coming and a new air intake. In the meantime I took a little time to figure out how she likes to be driven. Just completed the above mentioned trek through the mountains with a small load (1200lbs or so on the box and an empty car dolly). Drove to my RPMs not to speed so I kept her between 2000 and 2500 rpm. I let her have OD on the downhills and some of the flat stretches. Did the trip in 7 hours and had a phenomenal 14.92L/100km fuel consumption. The power is there if I put aside my expectations and drive her right :D looking forward to giving her a little TLC