Anyone know about the electronic pump unit #4? I know its one of the injector pumps. I get a fault code from time to time then it goes away. I used to get them on many of the units but i think it was a wire connection because it quit and Mack said if its indicating more than one and running fine it must be a connection. Also on these units, where are they located and do they ever need service. A buddy of mine had a broken spring in one and said he would like to replace all the springs because they wear out. It would be nice if there were some kind of photo or schematic explaining these very important parts and how to trouble shoot.

We had sent my pump to Mack 3 weeks ago. I kept getting 8-3 and 8-5. The truck had lost lots of power and started smoking black like a train. Turns out 3 of the pumps were out. I am not sure how to fix it yourself but I know Mack charged an arm and a leg.

My buddy (RM Plant owner) had his go last fall sitting at a stop light. He said it started running very poorly. They pulled the unit off and replaced it, cost around $500. The reason for failure is the rocker arm spring broke.

Just like on 99% of the cases with these fault computers. Just reset and keep going. Its probbably a connection.

Yeah Stick your probably right. I'd just like to dig into the system sometime or better yet get advice and maybe even photos or schematic from some one who has. Too bad Mack doesn't sponsor this site?