Onan 12.5 Civilian model

[patracy]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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.

 

[Keith_J]

Sounds like there is some serious dirt in the injectors. When the injector "fires", the needle lifts, allowing flow. This means there has to be room for the needle to move back. This along with normal internal leak down is why the injectors have return lines for fuel.

 

[patracy]

I dropped the injectors off at the diesel shop, they hope to have them checked out maybe by the end of the week. But I'm questioning the IP now. When I got home, I plugged the return line and turned it over. I get fuel out of all the four ports. But I was able to take a rubber band strap and place it over a port and block the fuel from coming out. I'm guessing it's not putting out enough pressure as well.

 

[Keith_J]

Odd. Pressure usually isn't the problem if you have volume.

 

[patracy]

I'm going to wait on the injectors first. I'll plug one up and see what it does with the pump first. If it still doesn't work, I'll replace the IP then.

 

[patracy]

Ok I've been reviewing the documents I've recieved on the pump. I had the delivery valve backed out. That allowed it to flow the ports out like it was doing, but it's not fully pressurizing the ports. Looking at a cut away, the DV should be flush with the housing. The DV allows fuel to flow through it. I'm going to pop it out and soak it. Then I'll put the DV back in and flush to see if it flows.

 

[patracy]

Just pulled the DV apart and screwed it back in flush. It's clean and free now, but it's still not flowing. Looks like I've got issues in the IP. Just wondered if there's anything else I can do to get the head to pump again.

 

[patracy]

I'm thinking now the injectors are fine. I pulled IP and found that the plunger is still sticking at the top of the stroke. I've squirted a mixture of gun bore cleaner with PB blaster in it to see if it will unstick. I tapped it back and forth a few times. I'm able to place the tappet face on a block of wood and press the plunger down. But it will not return to bottom. I'm not sure exactly how to dissemble it without damaging the pump. It seems that the tappet will go to the bottom, but it will not pull out. I tried removing the allen key screws for the head, but I assume the plunger retains it together to the base under that tappet. It looks that way from the cut away I have.

 

[Keith_J]

Squirt some Berryman B12 Chemtool in the plunger area. Let it sit for a few minutes and try to work it. Don't soak more than 30 minutes as it swells o-rings.

Since you have pulled the pump, Ambac has the manuals online. http://www.ambac.net/E64A353CC6034BE685460A71FD30F2F6.asp Should be a model 050, read the Diesel_Fuel_Injection_Pump for disassembly.

 

[patracy]

I studied the Ambac IP pdf I found online and figured out how to tear down the pump. The throttle lever was the part that was causing it to not tear down. Have all the parts soaking in parts cleaner now. It was a mess! There was dirt/rust/crud all in the housing. The plunger was stuck and once it was all broken down I was able to get it free. It made a light pop sound when it became unstuck. I'm going to let it soak the rest of the afternoon and reassemble it this evening. I've got to study up on how to reinstall/time the engine as well. Maybe I'll save this pump after all.

 

[patracy]

I'm making progress!

I reassembled the pump and reinstalled it. I didn't have a brass 1/8" rod so I used the back end of a drill bit. I don't see how it could harm it unless I was being hamfisted on install or somehow forgot to remove it after install. (I could see it breaking the gears off the pump) I lined the engine up to the PC mark and locked the pump in per the guide and reinstalled it. I purged the fuel to the pump and plugged off the return line. The four ports are now flowing fuel now with the delivery valve cranked tight. (It was only flowing to the four ports before with the DV loose, this was the lift pump pushing the fuel through, not the IP) I'll see how it goes when the injectors come back from the shop.