w123 wagon sooo slooow (not the first time!)

[a1anda2anda3]

I have a reliable if somewhat undead w123 wagon ive been driving heavily for over a year since bought in nh/vermont. This one is the slowest of the 3 ive owned.
I,ve:
Cleaned goobers out of the fuel tank and screen twice.
replaced both fuel filters at least once
Replaced most if not all of the rubber supply lines. No leaks.
Running on plain diesel
...and its just really slow still like 45 up some uphills on the interstate for instance.

The thing i suspect but dont understand is that black fuel bladder type thing nwar the spare tire that sedans dont have but all the wagons do. What does it actually do? Ive read its like an overflow....there appears to be a fuel line, one that is teed off sitting in the well rather than attached to that bladder thing. Can i somehow bypass the whole thing? Is the disconnected line ruining my fuel pressure?

What else am i overlooking?

[tangofox007]

Originally Posted by a1anda2anda3

What else am i overlooking?

I have seen the plastic valves in the lift pump get so gummed up that they don't seal properly. You can remove and clean them without removing the pump itself.
Additionally, the fuel filters can get plugged quite quickly.

[Bootsie]

Are you hitting the *shift points* as indicated on your speedometer? (one dot, two dots, three dots, = gears). If not, maybe a vacuum leak.

Lubricate and tighten all your engine bay linkages though.

Mine were so loose at first that when I was full throttle - the linkages thought I was actually only half throttle. The worst linkage was the one that goes down to the butterfly valve on the intake manifold.

After cleaning / lubricating / and tightening (if necessary) each one - I was finally going full throttle again. My thottie mount ball dissentigrated when I did this though. Watch out. It's a great piece to improve and replace, but its failure took me off guard.

[unkl300d]

Forum member greazzer sells re-springed Injection pump 'valves' or something like that.
Apparently the new spring he uses brings life back to the throttle.

[Rogviler]

If you unscrew the ALDA from the top of the IP and leave it off while driving, does this affect the power?

On mine that took it from dangerously slow to perfectly drivable. If this is the case you could dig into it and figure out why. Mine worked so much better that I ended up just leaving it off, but this is intended to be a diagnostic scenario.

[Diesel911]

The Fuel Supply/Lift Pump kit if you get an generic one is cheap and it has the 5mm O-ring needed to do the complete rebuild. The Valve Kit that Mercedes sells lacks that vital O-ring

If your Fuel Pressure Relief/Over Flow valve can be taken apart you can remove the spring and the ball bearing that is used as the valve an stretch the spring to get a free length on the spring of 27mm.

Check where the linkage pivots on the fire wall to see if it is not coming apart.

The Throttle Linkage rods have specific lengths they are supposed to be.

[Diesel911]

Air leak at the Hand Primer or other areas?

I had a small hole that rusted through the fuel inlet tubing under one of the clamps. The rubber was intact but that did not stop the rust.

Oddly it did not drip but seeped. I only noticed it by the smell when I worked on the rear Wheel near that area.

[jsb357]

maybe rig a small underhood tank to see if the problem is tank / line related or
engine / IP related.

might help narrow down the problem.

[vwnate1]

You didn't mention how recently you've adjusted the valves nor did you mention if there's any crud in the clear plastic fuel intake screen ~ if so there's prolly still lots of dead fungus crud in the fuel system .

The black thing is a vapor recovery system, replace the hoses with proper Diesel fuel hoses and forget about it .

Is this a turbo charged engine ? .

Once you've done all the basics look at the ALDA pressure sensing pipe ~ it tends to clog up over time and is easy to take off and clean out using your favorite de greaser ~ I use the Sam's Club Member's mark industrial degreaser cut 50/50 with tap water .

Check and clean as necessary the over boost protection valve, it too clogs up over time ad do the banjo bolts at each end if the sensor pipe .

[resto108]

The "black thing" is an expansion tank. The wagon tank is flat, so if you fill the tank on a hot day, the fuel will be ground temp and expand as it warms up. When it expands, it goes into the expansion tank. Has zero affect on performance.

[vstech]

What year wagon?

[vstech]

Check your carpet… have someone step on the accelerator pedal while you watch all your linkage.
Is your fuel line feeding the IP clear? If brown and brittle, it can leak air… and it makes it difficult to see air bubbles. Get new lines. They can be replaced with hardware store clear reinforced hose…

[upod]

Make sure the linkages are adjusted correctly and make sure the pivot on the firewall is not loose (I manufactured new ones if you need one). You need two people to check this. Sit in the car and with it off, push pedal to the floor. Look at the stop on the injection pump and see if it is hitting the full throttle "stop nut" on the injection pump (which is between the pump and the engine block). IF it is not hitting full throttle at the pump, you'll need to troubleshoot which linkage(s) are causing the problem.