6.2 diesel has no power/runs rough

[Johnny89345]

Im new to diesel. I cab swapped my 89 c1500 for an 89 k3500 gmc with a 6.2 diesel. The truck has 80k miles on it. Now it starts right up and idles fine but has 0 power, less then my 305tbi. Sometimes on the highway i hit the throttle and nothing happens just starts to miss and stumble. So i changed the fuel filter and removed the bleeder screw above the housing and it vled the air within a few seconds which leads me to believe the lift pump isnt bad. Whats next?

 

[Johnny89345]

Maybe 0 power is a little exagerated. Lets just say the 305 would do laps around this motor

 

[Schurkey]

There's dozens of things that could be wrong.

Faulty injectors?
Plugged catalyst?
Faulty throttle cable?
Non-functioning turbo?
Plugged air filter?
Internal engine damage (Flat cam, broken rings, valves don't seal, etc.)
Faulty sensors resulting in "Limp Home" mode?

You could START by performing a cranking compression test, and then connecting a REAL scan tool to look at the data stream, and to check for codes.

The ancient 6.2 non-Turbo engines were total turds. There was a reason they went to 6.5, Turbo, and then to Duramax.

 

[90halfton]

305 will run laps around a perfect running 6.2

 

[skylark]

There's dozens of things that could be wrong.

Faulty injectors?
Plugged catalyst?
Faulty throttle cable?
Non-functioning turbo?
Plugged air filter?
Internal engine damage (Flat cam, broken rings, valves don't seal, etc.)
Faulty sensors resulting in "Limp Home" mode?

You could START by performing a cranking compression test, and then connecting a REAL scan tool to look at the data stream, and to check for codes.

The ancient 6.2 non-Turbo engines were total turds. There was a reason they went to 6.5, Turbo, and then to Duramax.

No ecm in an 89 with a 6.2.

 

[Schurkey]

No ecm in an 89 with a 6.2.

I learn something new every day. Thanks for that.

 

[Sparkysikes]

Diesel place is a great help with just motor stuff. I had a 6.2 and load her up with 2000# and see what she can do. Just not fast. There is a fuse under the black. Cover under hood passenger side. Tap that to the buss bolt right next to it. If you hear clicking its not the lift pump. Step 2 leave key in on position but motor off. Open the bleeder valve on the fuel filter. Ffm. If your not spraying fuel out that it's due to the fact that the oil pressure sensor is supposed to operate the lift pump but is not strong enough. Replace the oil pressure sensor and use it to trigger a relay. Or do as I did and intercept the lift pump wire under hood and use the injector pump kill switch to power it. There is a Huge difference when you do and don't have a lift pump working on these.


After that is done find a wrecked 6.5 turbo truck and get the turbo equipment off if it. Stay low boost on your stick injectors and you'll get nice power but a 25 mpg truck!

 

[jdla140]

What trans are you running? you may have a VRV issue or a TV cable issue, is the truck just gutless the whole time you drive? does it smoke?

 

[Johnny89345]

What trans are you running? you may have a VRV issue or a TV cable issue, is the truck just gutless the whole time you drive? does it smoke?

No smoke its hot a turbo400. Doesnt the vrc only control shift points?

 

[tinfoil_hat]

Poorly timed or badly worn injector pump, or you have an air leak somewhere between the pump and the injectors. Those would be my first guesses. Get a diesel shop to do a pop test on your injectors. I forget what the psi is supposed to be but it's very high. Like 15k. If you reused the fuel lines from the tank to the filter from the gasser then maybe they are too small and dont alow enough fuel volume.
There is also the CDR valve wich looks like a large tuna can. They don't really fail but they do get plugged. Rinse it out with diesel really well.
Low power is normal for these engines. They can barely outrun their own smoke. But if tuned properly, it is possible to get a legit 22-24 mpg, as long as you are not in a hurry to get anywhere.