3406c cat motor running weird.

I'm still running one and has over a million miles.

It runs really strong and I've had good luck with it. I know once they start having trouble, they can be a nightmare. The best thing to do is convert it over like you said.

 

Here is a manual on the peec engines, hopefully it can help you.

http://ww2.justanswer.com/uploads/yellowman99/2010-06-21_153420_PEEC_Manual.pdf

 

Ok, now the rest of story is now known. The little transfer pump on bottom of pump housing that have two fuel lines going to it. They have check valves in them. They go bad over time. Hand primer pump same issue. That old of truck fuel lines from tank to engine could be swelled up restricting fuel or cracked causing it to suck air. Or plugged filters from alge or water condensation.

 

PEECs like to lope once they get old due to where it reads the engine speed from. It reads off the front gear train and when it gets wore out/too much lash it send an erratic speed signal to the ecm. The ecm then compensates with more/less fueling and makes the loping worse. There is a TSB released to swap the speed signal to the flywheel housing. Make a more stable speed reading and helps out alot with the loping. See attached

As stated above the fuel system needs to be check for air in the fuel first. This will only fix the loping if the fuel system in in perfect shape. More then likely it is just air in the fuel.