Onan generator not running...

[John & Cindy]

Hello all,

This is an Onan 4000 watt 

Model# 4.0bf3cr16000b

I am having an issue that seems like a lot of people have had with my onan, will run only while holding start button, plenty of gas in the tank so i pulled the fuel line to see if gas was getting to the carb no gas...i tapped on the feul pump and it started pumping gas so i figured the pump was done...installed new pump and same thing no gas but if i tapped on the pump housing it would start pumping...can anyone shine some light as to what could cause this, i was thinking the original not running n issue was either the oil sensor (has plenty of oil) or i have heard of the R1 resistor going out, but just dont get the reason the pump would work if tapped on...any help would be greatly appreciated.

Thx, J

[Daniel Long]

Grounds, specifically bad grounds. The ONAN gets pretty hot during running and so some bits get worn out during use. I used to be able to bang the genset with a rubber mallet to get it to start right, then realized all I was doing was jogging the relays and other electrical connectors to resolve the grounding issue. A good cleaning with electrical contact cleaner and making sure those clips are not totally fried to all the 2 billion white wires in the genset panel (why are nearly all the wires white?? Did someone just give up?). I've swapped out the two fuses back there for new knife types and replaced the start switch only to have two contacts just crumble on me. Not a good sign for continuity! Sometimes the exposure to moisture and not  being in the RV can age the contacts. Nothing  complicated but it is tedious to go through and clean and replace them.