'85 300TD dying out

[Stono-see-um]

My 85 300 TD keeps dying out on me. I have searched and read, searched and read, but cannot find a solution.
I have changed both filters, adjusted valves, bled injector lines and still she dies out on me.

Here is the situation. She is not my daily driver, so she sits a lot. I have to manually push prime it about 60 times to get her to start. She will idle all day long if I let her, but once I get her out on the road, she eventually bogs down and tries to die out. I pedal her back home and I start all over trying to get it to run. I have to pump the accelerator just to keep the RPM's up enough to keep from dying.

The last time I was bleeding the injector lines, I decided to find the ALDA, as I was curious where and what this mysterious thing was. I found it with no cover over it, like I have seen in pictures. The screw was very loose, so I just tightened it up using the adjusting nut. Could this have anything to do with it dying out?

NOTE: When I was bleeding the injector lines, I am not sure if all the lines bled out properly. Some bled a lot of fuel out, others not so much.

What direction should I be going with this? Should I be thinking about pulling the IP and breaking it down and rebuilding?

I purchase her about a year ago and have been steadily working on it here and there. Before I purchased her, the previous owner had the tank drained, screen cleaned and injectors swapped from another donor vehicle. He also ran a good bit of WVO/Jet Fuel through her as well.

Thanks for any and all help. Starting to get a little frustrated with it, but I enjoy figuring these unique beasts out.

[BrianCostello]

start simple,

Check the tank screen (I know PO did it, but check it anyway)

Then the fuel filters of course. But also the fuel lines. They degrade over time. Especially with WVO. . .it literally eats the rubber.

Once the screen is good, and the filter and rubber fuel hose is good. Move on to the return check valve. On the later W124 cars, its a fancy banjo bolt, I think the W123's are the same. it goes right into the IP.

having it die out sounds like fuel starvation. So it "should" be a straight forward fix

[Biodiesel300TD]

Sounds like you have an air leak. Having to prime the system after sitting for a while is usually the sign of an air leak. Make sure all your hoses are in good shape, and the clamps are tight. Does you primer pump squish fuel out when you use it. If so you need a new one and this could be the source of the air leak. If not it could just need a new crush washer. It's also a possibility that the lift pump it toast. This isn't common for most cars, but I've seen it happen a few times on cars that have run WVO without the proper heating.

[Graplr]

Originally Posted by BrianCostello

start simple,

Check the tank screen (I know PO did it, but check it anyway)

Then the fuel filters of course. But also the fuel lines. They degrade over time. Especially with WVO. . .it literally eats the rubber.

Once the screen is good, and the filter and rubber fuel hose is good. Move on to the return check valve. On the later W124 cars, its a fancy banjo bolt, I think the W123's are the same. it goes right into the IP.

having it die out sounds like fuel starvation. So it "should" be a straight forward fix

WVO does not eat rubber. High percentages of biodiesel degrade rubber fuel lines over time at a much faster rate than diesel or WVO. There are some people in the biodiesel world that use regular fuel line and change it out every couple years before holes wear into it.

It sounds like either a clogged tank screen or an air leak to me with possibly a worn lift pump if no air leaks and tank screen is fine.

Start by putting a clear hose on the fuel line right before the fuel enters the IP and look for bubbles. Or you could put clear hose on the return side to check for bubbles. If none then drain the tank and check the tank screen.

[vstech]

if you tightened the alda screw, you have totally eliminated fueling of the IP.
the screw needs to be loosened to increase power.

[cmbdiesel]

As far as rebuilding the IP, I refer you here...

Rebuilding injection pump

[barry123400]

There are a couple of clues here that the fuel tank vent may be obstructed.

Your having to repump up after sitting may indicate a remaining tank vacuum is drawing the fuel back into the tank while sitting. Plus engine dying out on the road as the vacuum intensifies once again. This denying enough fuel to the engine of course.

At least try leaving the filler cap loose to establish if it is the issue. Simple test.

[ah-kay]

By pass the main tank and hook up a bottle of diesel under the hood. Replace primary, 2ndary filters, check all hose clamps and go for a drive. This will eliminate a lot of unknowns. It has to be a air/fuel delivery problem.

Good luck.

[Diesel911]

In general it sounds like a Fuel Supply problem.

Most of the stuff has already been spoken about.
Except that your Fuel Supply/Lift Pump could be worn. Fastlane sells a Valve kit for that.

Long Fuel Pressure Relief Valve/Overflow Valve Thread
Fuel pressure relief valve adjustment - PeachParts Mercedes ShopForum

If you have more blow-by than can get our of your Crankcase ventilation system due to it being restricted or because yo have some Engine Condition that is causeing too much blow-by; pushes the Vacuum Shutoff Diaphram towards the shutoff Direction.

I have tried blocking entirely blocking off the Crankcase Ventilation Elbow with the Engine at idle and in about 7 seconds the Engine starts to loose rpms and acts like it wants to shut off. At that point I released it because the Crankcase Pressure can be hard on the Seals.
I tried it severl times with the same results.

[TnBob]

2x on ah-kays suggestion. Rebuilding the IP is waaaay down the list, as in last.

[Yak]

I've got little to add to the advice above, but based on your post count, I'll point out a reference to the unique shape of the TD's tank that might affect fuel supply: How does the tank screen work on a 123 wagon

I'd start with the basics and remove unknowns. ah-kays advice about a separate clean bottle of fuel is good, since that can isolate tank problems from engine problems; as is ensuring you've got a good boost pump.

I think I've read where the black Bosch pumps weren't recommended for WVO, so your PO may have kept the old "poker chip" pump for his WVO use (so-called becase of the thin white disk with ridged edges) and that could be leaky.

[Renntag]

I am dealing with a power loss issue in a W126 300SDL, so my searching brought me to this thread.

One thing that is not mentioned above:

Driving car, power loss happens.
Pull over, pop hood, loosen clamps to the prefilter.
Remove a hose.
Hear a sucking sound?
That indicates vacuum. There is fuel starvation due to a restriction.
This could be tank vent issue or a clogged prefilter, tank screen, pinched line......
This also indicates that the lift pump is struggling to do its job. If it made vacuum, its working.

Put it back together, have power again?
Drive until power loss.
Pull over, check fuel filler cap.
Hear sucking sound?
If there is a STRONG sucking sound then there is a venting issue.

Drive with the cap loose, power loss issue gone?
Chase the vent line for restriction. Blow out if necessary.
Replace any old hoses.

Also note that even a leaking manual prime pump will not be a source of air as the prime pump is sealed out of the system once locked back down. (This is mentioned many times in this forum).

Attaching a piece of clear 5/16" tubing on the return side will allow visual inspection for air bubbles. There should be NONE. Figure out where the bubbles are coming from. Maybe move the hose elsewhere to see how far "upstream" the air is present. Maybe a hard line is cracked with no visible leak? Under suction, air gets pulled in. Under pressure, fuel leaks out.

Best of luck.

[Stono-see-um]

Thank you for all of the wise words of advice. I may start with bypassing the fuel tank with a temporary one. Hopefully I can narrow down which end of the car the problems originates from.

I am guessing that by loosening the fuel cap and if that solves the problem, that would lead me to the tank vent? Where would the vent be located?

I noticed when I use the manual push prime, it gets tighter but not really tight like it used to in the past. I also had to help a friend out with their 240D that ran out of fuel. That push primer got really tight like mine used to. It is the black topped prime assembly.

The comment on me tightening the ALDA. The screw on top was wobbly loose. I just tightened the lock nut underneath the screw, so it's not able to move at will.

I will report back with my diagnosis. I hate it when I find a thread on my same problems and no one ever post their solutions!!

Thanks again!

[Biodiesel300TD]

Originally Posted by Stono-see-um

I will report back with my diagnosis. I hate it when I find a thread on my same problems and no one ever post their solutions!!

Please do, this is a good practice that gets missed in most posts. Posting what finally fixed the issue is very useful to future readers trying to troubleshoot their problems.

[Stono-see-um]

Originally Posted by Renntag

Also note that even a leaking manual prime pump will not be a source of air as the prime pump is sealed out of the system once locked back down. (This is mentioned many times in this forum).

If the manual prime is not locked back down, will this cause an air leak?

Here is what I have done so far with no change to situation:
Tried loosening the fuel cap.
Put a bottle with fresh diesel going straight into prefilter. I thought that solved it, then I was right back to dying out again.
Cleaned/Checked all banjo bolts I could find on or near IP or secondary filter, including the pressure relief valve. This valve looked very clean and seemed to function well.

Today I drained the tank and inspected the strainer. The screen was pretty clean. It had some light "gunk" on it but nothing that would hinder fuel flow. Some flakes of god knows what did drain out of the tank. This could have been restricting flow, but with me trying the bottle right at the prefilter, I don't think this is the problem. I can see some light debris in the prefilter, but only a few floaters here and there.
I notice when I manually prime, I get bubbles in the prefilter. Is this Normal?
She actually died on me today after I had cleaned all of the banjo's. This is a first that it actually died on me. Had to manually prime to get home. What is weird is if I am coasting into the driveway, pedaling it to stay running, then park, it will idle for as long as I want it to. Also, it almost always starts to have the trouble once I get up to about 3rd gear. Weird and I don't know if this helps anyone...

One more kick in the butt.. I got in it yesterday and noticed the Tach wasn't working. I think I found the culprit and I have attached a photo.