OK, I've been around this block before. I have posted about the surge my truck has from 45-50 mph when truck is not under load, just easing down the road. Well to add a little info, I change my water pump this morning. While monitoring water levels After changing out the pump and filling up with water I noticed a few things. When I first started the truck it ran fine, smooth idle for about 10 mins. Then it started to miss just a little and progressively got worst. I put the air conditioning on to help warm things up and get the thermostate to open, When the air conditioning compressor was ingaged the truck ran fine under the little extra load. As the compressor would kick off the truck ran rough. I got in the truck and turned the air conditioner off and just pressed down on the brake pedal, the truck ran smooth, let up it would run rough. Just the extra little load helped. Put the truck in gear and all is smooth. What ever is causing this is working both problems - rough idle and surging at 45 mph. Could this be injectors? Any thoughts or ideas?
Thanks Gene

 

Any codes?

 

mkrenn, No codes......

 

Did you check fuel pressure? If that looks good, your 44 could be on its way out. How many miles are on this pump?

 

VP44 has just been changed, fuel pressure is 15psi. I have changed all sensors and APPS. Its strange that it continuously misses with no load on the engine (after it warms up). Any small load and the engine runs smooth.

 

Got me. Anyone else?