No Power Under Load

[Rob Mac]

My 94 Silverado lacks power badly when I am towing.I have replaced map sensor,speed sensor,coolant sensor etc,also have reconditioned the injection pump. Some improvement is noted when not towing.Code 34 is coming up also. SES light remains on all the time. There is no smoke at all coming from the exhaust.
Any one got any ideas?

[65TD]

Look at the IP on the passenger side toward the front. The stepper motor is mounted there and could be jambed up by the wiring harness.

If you can see the rod that comes out of it check and see if it's moving at all while the truck is running. Check the plug on top. Check to see if it's mounting screws or linkage are loose.

The stepper motor controls timing advance. Without it your truck could have some power problems and cold weather starting problems.

Crank the truck with the ect sensor on the water outlet crossover unplugged and compare with normal start. There should be a noticeable difference if the stepper motor is working the timing will advance.