Won't start without tapping on the inj pump
 

I just bought my first Cummins, it is a 93 model and I got it for a song because the previous owner was having problems getting it to start. I figured out that when I tap on the injection pump with a wrench it will fire right up. If you don’t give it a tap then it will just spin over and never start. I figured it was probably the stop solenoid so I gutted it and still it won’t start without a tap or two on the injection pump. When it does start it runs great. It seems like there is a valve stuck in the pump but I am not sure where to look.

I am planning on transplanting the Cummins into my Chevy dually after I get all the bugs worked out of it. Thanks

Prolly a spring is sticking, I would assume. Wouldn't hurt to pull it apart using some of the how to's in the forum, and see if anything is hanging up.

Yeah, I got no idea.

Take the top off with the four Allen-headed bolts, like you were doing a governor spring install, and see if it's all varnished up in there.

I have the same issue, and mine is currently apart.
Mine had been run on BIO/WVO and it has a thin residue in it, BUT I have come to the conclusion that it's actually wear or damage related.

Yours may well be "gummed up".

Mark.

Thanks for the replies, I talked to a guy at one of the local rebuild shops and he said he thinks it is a broken or very weak plunger return spring. He said it would require a full rebuild. Does that sound right to you guys? He said it would run $575.

How could it run great after it starts and at the same time require a full rebuild?

"Full rebuild" is pump shop lingo for "we'll fix it". They operate on a one-cost-fits-all approach.

I guess they're thinking that the springs aren't returning the plunger, which would probably be more due to varnishing on the plunger than weakness of the springs. Return springs like to cause stall issues and crappy running issues as well as no start issues.

I'm with everyone else and gonna go with the gummed up approach.

Try putting some power service in it and run it some.