Bubbles in IP fuel return line
 

Trying to diagnose why i have air bubbles in the fuel return line (back of IP returning to spin on filter) of my 300D.

At idle no bubbles show up but as throttle is increased the bubbles begin and increase as throttle increases to almost a froth. No fuel leak visible from above will check underside of IP later today/tomorrow.

No bubbles visible in other fuel lines.
Pressure relief valve is tight (location of fuel return line banjo bolt).
Car idles fine, no shaking or rocking as throttle increases.

I believe this problem existed before, but here is work just performed:
Replaced camshaft - 2 lobes were badly pitted and discolored (lobes 8 & 9)
Replaced rear rocker arm spindle - bent probably a 3/16" over the rear third
Replace cam towers 4 and 5 associated with bent cam spindle
Replaced rocker arms 8 & 9 - discolored and faces showed wear
Replaced timing chain - 2mm method showed 4+ degrees...so while i was in there

Injection Pump in not original to the car, was bench tested/adjusted prior to install several years ago. Car sounds and runs better after above work but still sluggish.

thanks,

chris

Do you have the original primer pump? Or has it been replaced with the new style? Sounds like when its being throttled the pressure is building up and your sucking in air.

http://www.peachparts.com/shopforum/diesel-discussion/109076-heres-my-payback-diesel-primer-pump-replacement.html

cooljjay - Yes, newer style bosch primer pump is installed...but i will check nut for tightness.

thanks,

chris

Another place I would check are the rubber lines under the fuel tank above the rear. If ones is cracked and seeping, it could also cause air to get into the lines....they are usually over looked

The Hand Primer and the Hoses that Connect the Plastic Fuel Filter are on the Suction Side.
See if you have any wet Fuel Lines from the Tank on forward.

On Mine one of the Metal Tubings under the Car Rusted through.

cooljjay - I did replace all those lines several years ago but you never know - will check them. If they were leaking i believe bubbles would show up going into the pre-filter?


Diesel911 - Was just under the car repairing a small hole in center muffler (car in garage) and did not notice any wetness. Will trace rubber and metal tank to fuel pump lines. If there is air entering the system prior to IP, wouldn't the bubbles show up leaving the spin on filter in route to IP?

thanks,

chris

Hmmm I wonder if you are missing a crush washer some where? I am also wondering if its normal, not really air bubbles but fuel voids? I would think you would have an idle problem.

What is a fuel void?

Tomorrow i will take a look at how my 116 (300SD) fuel return line segment behaves from the pressure relief to main fuel filter as it has the same 617 engine and similar injection pump while working the throttle.

Bubble.

Your problem may also be a restricted pickup screen in the fuel tank. Feed your lift pump with a container of fuel to see if you still have the bubbles at higher rpms. This may help you decide where to look.

I am not a great fan of reversing the fuel pickup and return lines in the engine compartment. The fuel tank should be half full to do this and it is another method of clearing or condeming the fuel pickup from the tank.

I did replace the screen about 4 -5 years ago along with all the fuel supply/return hoses. FWIW original screen was clean. Still could be an issue.

thanks,

chris

Found bottom pre-filter clamp slightly loose but not wet. Also tightened top pre-filter clamp. All other fuel connections look good.

Still need to check rear fuel hoses at tank.

Need to wait a couple more hours to give my JB Weld center muffler patch a full 24 before testing with engine running.

thanks,


chris

That is part of the Mystery.
All of the Lines with the Exception or the 2 sections of Hose (cheap to replace with 5/16" ID Fuel Hose from any parts store as it is rated for Diesel Fuel) that attache the Plastic Filter to the the Lift Pump on are under pressure. So in theory there is no way Air can get into the Lines from that point on.

Do you know if you have an MW or M Type Fuel Injection Pump?

Several times I have chased air issues in the fuel system. In a few instances I used segments of clear hose to provide visual inspection. So if you want to eliminate the possibility of a section of the system as culprit. Install a section of clear hose. no air, then move on to another section until you isolate where the air is getting in.

Either way its a pain in the butt. Good luck.

The consensus on this issue appears to be that the improbable is possible, which I agree with. Along that line of thinking, I suggest it is worth also taking a good look at the IP return line from the relief valve, as well as all connections and seals on the fuel filter stand. I suspect that the problem lies somewhere in that area, probably at one end of the clear line.

I had compression air coming in a reman injector ... took me months to figure it out. I suspect that is pretty rare and in my case the car would not even run. However, that is where the froth would show up, in the return line on the back of the IP, not on any of the other lines. ckamila, if you recently replaced the injectors or if there's any chance you may have damaged a nozzle while doing other work, it might be worth considering. I think it was a pretty bizarre thing, though. Are your lines to and from the secondary filter clear enough to be really sure there aren't bubbles? I replaced them with new clear ones before feeling confident there were no bubbles in them ... before that they were browned and I had some doubts that maybe I wasn't seeing a froth in there.

Everything appears tight enough from the tank to the lift pump. Connection at the lift pump are more challenging and will look at tomorrow. All banjo fittings are tight too.

Looks like i have a little less air/froth in fuel return line but need some natural light to see better. Problem is far from resolved.

JB Weld center muffler repair looks to be holding so far at low temps.

thanks,

chris

Well, yes, i did just have my injectors cleaned an balanced. IF i pop test them for spray pattern and pressure setting, will that be enough to tell?

Also i don't have any idle issues or an unbalanced engine as more throttle is added. Seems if i suffered from the same issue you did there would be other signs.

Return line is new so nice and clear. The other 2 (from the lift pump to primary filter and from filter to IP) are brown and yes harder to tell for sure no bubbles are passing.

I'll see if i can post some video of the bubble surge tomorrow.

thanks,

chris

On my faulty injector, when the fuel-line nut on top of the injector was cracked, bubbles/froth would come out interminably (which for a long time I had assumed were coming from the IP). You could try just cracking the nut on each injector, one at a time, and looking for bubbles (including as you apply some throttle). If none of them bubble I don't think that's the problem. If you're seeing air coming out of one line, you could try taking that one out and pop testing it ... if spray pattern and pressure are OK, I don't think you have a nozzle problem. I wish I had taken my faulty one to get pop tested (or dissected) but I needed to send it back to get the warranty honored ... would have been interesting to see what it did.
I do also think if you had this problem, you would be having more issues with the way the engine was running. Mine would only run on three cylinders, and if I tightened down that line, it would airlock and stop running altogether.
I would probably pursue the simpler solutions first (leak on the supply side of the lift pump), but I thought it was worth mentioning that it is technically possible to have air get into the pump on the other side.:o

I may have overlooked it, but what's the problem other than seeing bubbles?
I was chasing mine dying out on me forever. Replaced all the lines, clear in the engine bay and had/have bubbles everywhere. Could never find the source of the air getting in. After all was said and done, a sticking lift pump was what was causing my issues. I still have bubbles, but I am so excited the dag-on car runs now, I don't care about the bubbles!

Yes, if where the Nozzle Pintle seat in the Nozzle is buggerd up combustion gas will get inside of the Injector. When you take the Injector apart you will see Carbon inside.

It will also happen if the Injector Spring breaks but that will give a noticiable miss.

I think it would be easier to leave the Injectors on the Engine and replace the Fuel Return lines with ClearTubing and see if you are getting bubbles out of the Injectors.
For a temp look I suppose any cheap clear plastic tubing might work.

If you want to leave the clear Fuel Retun Lines on the Injectors some Members have used: 1/8" ID
Oregon (as in Chainsaw) Brand, it is a Tygon fuel hose.
Tygothane (Saint Gobain is the Manufacturer)
U.S. Plastics is the retailer.
That they bought at a Lawn Mower Supply Shop.

.

Youtube video link IMG 0104 - YouTube showing air in return line. Best view around the 1 minute mark since video is rotated 90 degrees..

chris

Did this air in the line cause any problems? I have had a perpetual rocking of the engine at idle that seems to come and go(none when cold). I also have these bubbles but at a much higher rpm. My car has loads of power and I have the ALDA valve bypassed with very little smoke at full throttle. I just wonder if in my case my pump has a problem internally. The shake has improved over the 3 years I have driven it but in neutral it still shakes with a audible miss at the tailpipe. In gear it will almost smooth idle, but it comes and goes. The biggest improvement came with 2 gallons of atf added to the fuel. I have done every thing except compression checked the engine.

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Yep, I had air bubbles in my clear line going to the IP in a vw, Everything was tight, good filter, good fittings... but had a restriction coming out of the fuel tank due to rust (in the tank). The the diesel fuel pump is so strong (it circulates way more fuel than is actually injected) that if there is a restriction in the suction side of the fuel line system it sucked air in through perfect hose clamps. I think that's why bubbles are so common.

I was sucking air somewhere on my engine. I have the 124 version with an OM603 but the concept is the same on your 123 with OM617.

I replaced the 3 clear lines, that have banjo bolts, between the lift pump, the filter, and the IP.

I have clear return lines (Viton tubing) and before I replaced the 3 supply and main IP return lines, I had bubbles in the injector return lines at idle and when I revved up the engine in park (obviously I could not look at this while the car was going down the road...).

It caused difficult starting, it ran like crap once it was started, and idled rough until it had run for about 30-45 seconds.

After replacing the hoses, no more bubbles in any of the lines at all now. The above symptoms all went away.

The reason the lift pump circulates more fuel than is needed to burn is so that the excess fuel cools the injector nozzles and the IP. Also you never want to starve the IP of fuel.

Last week i did run a closed system - connected the IP supply and return lines to a bottle of fuel and had the same issue. Idle and starting are fine just lack of power from the foamy air/fuel mix.

I have since rebuilt a fuel pump and will likely try replacing soon.

I did have a cracked line from IP rerun line which i replaced. Since it's under pressure, i don't believe air would enter there.?

BodhiBenz1987 - Cracking the lines did result in bubbles/froth coming out.

Will see if the rebuilt lift pump changes the issue.

Thanks,

Chris

The thread is a bit old, but it seems that you raised the issue of air coming out of the IP return line, which is a problem I (and others) are experiencing. What did you do to confirm that compressed air came from the injector?

I have a thread diagnosing this same issue if you wish to contribute. Thank you!

http://www.peachparts.com/shopforum/diesel-discussion/412973-om617-injector-return-fuel-flow-rough-idle-2.html

Theseus -
Never resolved the issue. Son totaled the car so we will never know.

-chris

Sorry, that is unfortunate.