OM617 injector return fuel flow and rough idle
 

HI Everyone!

On my OM617, I've been experiencing rough idle since I bought it. It was extensively worked on by the previous owner (new injectors, filters, primer, service delivery valves, injector pump). He suspects air infiltration, so I replaced some lines with clear tubing.

When I prime my fuel system with a few pushes, any air easily passes from the secondary fuel filter to return to be removed. However, an air pocket exists from the injector return to the secondary fuel filter. Even though the engine starts easily, the air pocket still exists. I can only get rid of the air pocket after I give the car a lot of gas and direct it to the secondary fuel filter, then it is gone.

My concern is the fuel flow going through the return lines to the secondary filter. In comparison with the rest of the system, very little flows from the injector return. Could this be normal or is there is restriction? How much return flow is considered normal? Does that flow have a way to be measured?

Theseus
Murfreesboro, TN
84 300sd "Helga"

A large volume of fuel passes through the fuel injection pump housing and that keeps it reasonably cool.

Only a small amount of fuel enters the injectors and only a small amount of that fuel lubes the injector and comes out of the small return lines.

Do you see any air actually moving through the plastic fuel filter and if you can see through it the line from the Fuel Supply/Lift Pump to the secondary Spin-on Fuel Filter?

"(new injectors, filters, primer, service delivery valves, injector pump)" how much of that can be proven to be true?

Raise your idle speed to 850 rpm using the proper idle adjustment screw on engine block side of the Fuel Injection pump.

Do a valve adjustment.

Back out the Governor Idle Pin/Rack Damper Bolt and adjust it. Not despite one of the names it is called it is not the idle adjustment.

Normal to see a stationary air bubble in the pre-filter. If in CA, try renewable diesel.

I have an air pocket in the plastic fuel filter but don't see any air coming from the fuel tank. I have a very dark tube from lift pump to secondary filter that I will need a clear line installed to see air. If I rev it, air can be seen going from secondary filter to the tank if that helps.

You did not say if you replaced the 5mm O-ring on the Fuel Supply/Lift Pump. People buy the Mercedes Fuel Supply/Lift Pump valve kit because it is cheap and there is no O-ring in that kit.

I don't know if this is your issue or not because I have no experience with it.

Around 2010 I was looking up some injector stuff and I found a picture of a Injector set up so that the Nozzle end was sealed and under pressurized air.

What was being checked was the seating area inside of the Injector Nozzle. If it was not seated bubbles would come out of the top of the Injector.

I assume the air pressure was mimicking the pressure of compression
If this test is true if your Injector nozzles are worn air from compression can pass through the nozzle and out of the Injector and into the return fuel.

I don't know if that is what is happening or not. I worked in a Fuel Injection Shop for 5 years and no one ever said there was even such a machine for that type of test.

If air is not going into the Fuel Injection Pump I don't see it causing idle issues.

On the Stock Injector Nozzles: "Passages #14 and #15 get Plugged with Carbon. (All of the ones on my Car were so plugged and most of the ones I pulled from the junk were also plugged.)"
http://www.peachparts.com/shopforum/diesel-discussion/299084-monark-diesel-injectors-2.html

See post #6 for a better pic.
http://www.peachparts.com/shopforum/diesel-discussion/390059-monark-nozzles-question.html

Previous owner ("Junkman" on the forum) told me exactly what he did to the engine, which we've been documenting.

The injectors are all Monarks, and Greazzer rebuilt them recently.

In order to find out whether there is any restriction, I'll run a line from the plugged side of the injector return line. I will replace some more clear hoses and take a video. Your help is greatly appreciated! :):):)

Hi,

Below is a video of what is going on. You can see the air bubbles in the injector returns. Not really moving along as I would think. They could move when you rev it. Bubbles were clear yesterday but showed back up this morning.

https://youtu.be/IuHNebI6nsc

You have an "02" filter head which does not take a crush washer for the fuel filter bolt.
This is causing some, or all, of the air incursion.

It uses two o-rings.
The upper o-ring is 2.5mmX 14mm, and the lower o-ring is 2mm X 10mm.

I recently added more clear lines. Additionally, the secondary fuel filter was also overhauled with new O-rings as per previous suggestions. Serviced the bypass valve, stretched spring to 27mm. New crush rings for reinstall.

Source of air infiltration found in the fuel system. See video:

https://youtu.be/FH6y6KFP9JM

After revving the engine, air is emitted from the bypass valve of the injector pump back into the fuel filter housing and out the expansion hose. There is no doubt that air is coming out somewhere from the injector pump. From the fuel lines or primary fuel filter, I don't see air. The return lines from injectors appears to have very little flow like before. What is the reason behind this? :confused: :confused: :confused:

I inspected the injector pump delivery valves. All valves looked good with the exception of the two nearest the front bumper. Valve holders' outsides were badly corrosion. (see photos). Fuel (or water?) appeared to be dirty and clear for the corroded valve bodies. It was very smooth and clean on the valve faces, so I reassembled it with new copper washers for now, cleaned it and reassembled it. The beginning was rough, then smooth, then I thought "I have it", then it became worse. Sure enough, there was the same level of air infiltration.

Why is the corrosion occurring? If the valve body faces are still smooth and the valve holder nor delivery valve interface have been corroded, do those factors still cause concern?

For now, I have ruled out the delivery valves. I'm expecting a rebuild kit for the lift pump this weekend. Can you think of any other sources of air infiltration?

Looking at the 0:31 time stamp on the video, it appears that the pressure relief valve banjo fitting is not sealing due to mixed usage of crush washers and regular(??) washers.

It does appear he has an extra washer installed but that wouldn’t explain the air coming from the clear injector line.

OP, I went through a similar ordeal some time ago. People will tell you all sorts of places to look on the pressure side of the lift pump. However, considering the amount of air you have, I don’t think that makes any sense. This looks suction side to me, which means before the lift pump.

Have you checked the hard fuel line that runs under the car for pin hole leaks?
What about the gasket around the tank strainer? With that much air, you have your two sections of fuel hose and the primary fiilter, the two things I mentioned and that’s about it.

@Shern - I have noticed a very small amount of bubbles at the suction side, but far more comes out from the banjo bolt. IMaybe the suction side bubbles could have been cause from the return flow air? But mind as well rule that out too. I agree it could be a pin hole or maybe a tank fuel line. The tank screen could be completely clogged up, causing the pump to be fuel starved too. I remember some rust particles in the primary filter. I'll try bypassing the fuel tank and have it run off some diesel in a plastic bottle in the engine bay and see how that works.

I too have this exact scenario. The video of bubbles from the overflow valve could be my car, would like to solve. Checked everything...