6.5 TD will not throttle up

[Scottybo]

Hello I'm pretty new to the group I have a 1997 Chevrolet 3500 6.5 turbo diesel I love the truck I have 268000 miles I have done most of the normal 6.5 problems like bypassing the fuel pump relay relocating the PDM off the side of the injection pump a few other things has always been a great truck there for a while I got harder and harder to get it to run it would crank fine and idle fine but when you hit the the throttle it took a while before it would catch and throttle up once you got that first initial throttle up it was fine for the rest of the day but now it will start idle fine but when you give it fuel it throttles up to about 17 1800 RPM and smokes like a tar keel please note that injection pump was replaced about 3 years ago fuel filters are always change every 10000 miles when I started having problems I installed a bigger marine grade inline fuel pump that holds a constant 8 - 10 pounds shortly after installing the new fuel pump I had major issues therefore I put back old inline fuel pump that holds 3 to 4 PSI note I was having problems with starting and throttling up before I installed new fuel pump but after installing bigger fuel pump is when truck would not throttle up and run correctly any help would be much appreciated and this is my first thread if anything goes wrong I will fix it thank you

[Yukon6.2]

Hi
One of the problems was the pressure from your new pump,it was to high.You will need a pressure regulator if you want to put the new pump back in.
Do you use a colored additive?Sometimes if your fuel gets too colored the optical sensor in the injection pump will not be able to read through the fuel to do it's job.
Are you getting any codes?
Is the truck automatic?
Thomas

[Scottybo]

The 🚚 is a automatic and it does NOT throw any codes now that You say that i did start running heavy amounts of dyed fuel throught fuel system because it is a farm truck not long before problems started

[Scottybo]

Fuel pressure at t handle is at 4 psi with key on truck not running when you start truck pressure pulls a vacuum and is a - pressure.

[Scooby]

From my experience the lift pump should be able to keep positive pres sure on filters and injection pump. Never zero.

[Robyn]

You have one of a couple issues.

Plugged fuel line strainer in tank.
Failing lift pump

The fuel pressure can not drop below a couple pounds with the engine under load.

[Scottybo]

I have replaced sock in tank and lift pump puts out 3-4 psi

[Scooby]

The lift pump I just changed looked good sitting still at idle but when I ran a piece of tygon tubing out from under the hood and tied the gauge to the windshield wiper and took a drive with it as soon as I accelerated the pressure went to zero.

[JohnC]

Do you know the pump is good? Open the T-valve and run the line into a bottle. Jumper the pump relay and see how long it takes to pump a pint of fuel. I forget what the spec is, but I'm sure someone else will chime in. Or, just change the fuel filter and try again.

[a5150nut]

going to zero psi is normal as long as it isn't pulling negative pressure.

[phantom309]

use some clear tubing and run it from return line into a bucket and look for air bubbles,.
after i removed the factory fuel filter joke thingy, and added a full size filter,. my fuel pressure only dropped to 2psi or so,. and idled at 7,.