Onan 12.5 Civilian model - Steel Soldiers::Military Vehicles Supersite

patracy · 12-13-2011, 13:43

I picked up a Onan 12.5 generator last night. Basically it's the same as the MEP-003. At lunch I tried starting it but wasn't getting any fuel. I checked the forums and found mention that the center bolt on the hyd. head can stick. I took it apart and found the valve slightly stuck in there. Removed and cleaned it, then worked the lifter up and down several times until I could see that it moved and rotated freely with the engine running. The fuel lift pump was squirting fuel freely through this point. I reinstalled the valve and threaded housing until it bottomed down on the pump. I placed the cap back on and tried spinning the engine over with the lines removed. I didn't get any fuel. I finally tinkered around and realized the valve was staying closed in the center and not feeding pressure to any of the other ports. I backed the threaded portion out a little and placed the cap back onto it. After that, when I rotated the engine all four ports squirted fuel one after another. I reinstalled the lines and left them loose to the injectors. I turned it over a bit until I had fuel dripping from the injector bodies and tightened them down. I can spin the engine over, but it doesn't seem like I'm getting any fuel still. I've sprayed the engine with a little bit of starting fluid and it picks up in RPM's but never runs.

Should I try removing the injectors next and try cleaning them?

The generator has sat for a number of years. The fuel that was drained was very brown and nasty looking. I've filled it up with fresh diesel fuel. But I'm wondering if the injectors are in as bad of shape as the IP was.

patracy · 12-13-2011, 14:16

Well I decided to pop the injectors out of the head to see what they're doing. And I'm not getting any fuel out of them. I do get a dribble of fuel out of the lines when cracked on the cylinders. But nothing out of the injector tips. Guess I'll start taking them apart to check them.

Crawdaddy · 12-13-2011, 15:17

I seem to recall reading that you need to count the turns when removing or dissasembling the injectors. I don't recall all the details about it, but something you might want to check out before ripping them apart.

Keith_J · 12-13-2011, 15:40

Sounds like the needles are stuck in the injectors. If soaking in solvent doesn't work, reassembling without the needle springs and then using the injection pump's pressure may free the needles.

If not, any diesel injection service shop that works on Bosch products should be able to help.

patracy · 12-13-2011, 15:51

I removed the cap/spring/spindle from one injector. I left that connected to the line and tried turning it over, nothing came out of the injector body. Not sure what way to go now.

Carl_in_NH · 12-13-2011, 15:59

Focus on low pressure fuel to the injector pump, and then the high pressure side of the injector pump. Sounds like IP issues, not injectors. EDIT: What makes me think this is there should be quite a bit of fuel from the cracked lines - not just a dribble.

Crawdaddy · 12-13-2011, 16:14

What Carl said makes me remember a mistake I made when I was priming my pump: when priming the injector lines, make sure the throttle arm is up to ensure plenty of fuel flow to purge the injector lines.

quickfarms · 12-13-2011, 16:22

Since you posted that the unit had been sitting for years and the old fueld looked like muck it is very possible that both the injectors and pump need to be cleaned and rebuilt.

I have a Kubota powered generator that had siminalr issues and we had the injectors and pump rebuilt and it started right up after we reinstalled them.

Keith_J · 12-13-2011, 16:43

Even at max fuel, each stroke of the injection pump is a bit over a thousandth of a cubic inch. About a half drop.

Take the injectors out and soak in Berryman B12 carb cleaner.

patracy · 12-13-2011, 16:54

Lift pump is working, when I take the cap off the HH I get a couple foot stream from the lift pump squirting fuel out. I took apart one injector, it seems the needle is stuck on it. I was able to get it loose and the nozzle would squirt a stream of fuel with the spring and spindle out. But once I reset the spindle and spring it no longer flows. I'm going to a diesel shop to have them cleaned/flowed.