85 W123 Miserable Performance

[rmmagow]

Sort of well maintained car, valves, filters etc. I do take care of the old beast but performance has been really bad lately. Runs ok on level roads with good acceleration etc, but heading uphill, pedal to the floor it is struggling. I don't remember it running this lousy. I know it's no rocket ship and the tranny seems to kick down as required but it really feels sickly.
What's the big items to check? My Volvo turbo would collapse a hose once in a while, intake side and that killed my turbo. I think the W123 has some super critical things controlling the engine and turbo that need to be looked at, but I can't remember what. I've owned W123's for the past 15 years but lately my 85 has only been getting weekly runs and grocery store runs during the day. I do drive it once every couple of months for 300 miles at highway speeds.
Thanks

[Stretch]

There have been a lot of reports of poor diesel fuel quality recently.

If I remember correctly whunter has a method of sorting out crap fuel with two stroke oil - it seems to work.

(Must I link?)

[Zacharias]

The unofficial top 7 list that will cause what you describe:

1. Clogged fuel filters.

2. Linkage issue. If linkages have not been lubed in some time, they can bind and not provide full throttle.

3. Failing throttle bushing at firewall. This is the big rubber one that pivots. If it starts to come apart internally, it transfers less movement and results in same as #2. When it fails the car will barely want to move from a stop.

(TO check #2 and #3, have someone press down on the go pedal gradually to the floor, engine off of course, while you watch to see if the pedal movement translates to the linkage running vertically down to the pump actually moving to its full travel.)

4. Air leak into fuel lines somewhere. Make sure all the clamps are tight. Anywhere you see diesel leaking can probably let in air as well.

5. Deteriorated fuel hose sucking in air. No one pays attention to the shorty length of hose that connects the bottom of the clear filter down into the lift pump. These simply wear out, crack and can result in air being sucked in, with or without any visible fuel leak. Car may run fine on the flat but once under load it cannot cope.

6. Clogged strainer in fuel tank. If you ran the tank almost dry then filled up with a premium diesel containing injector cleaner, or dumped in some sort of fuel additive with cleaner properties, this can free up the crud at the bottom of the tank and deposit it on the screen, limiting flow.

7. Dragging brake caliper or stuck parking brake. The car should creep easily by itself on level ground when you take your foot off the brake in D.

[rmmagow]

Excellent guys, and thanks. I'll do my checking this week. With winter coming, I will set aside some time to replace the fuel lines. I thought I did the tank strainer but looking at my records It may have been on my earlier 83 W123. I know the car is still healthy but maybe it needs a bit more hands-on love to get it back.
Thank You.

[funola]

Originally Posted by rmmagow

Excellent guys, and thanks. I'll do my checking this week. With winter coming, I will set aside some time to replace the fuel lines. I thought I did the tank strainer but looking at my records It may have been on my earlier 83 W123. I know the car is still healthy but maybe it needs a bit more hands-on love to get it back.
Thank You.

Instead of replacing parts by trial and error till the issue is fixed, why not do diagnostics to pinpoint the issue? It's a lot cheaper that way. Zacharias pretty much covered everything to check, except ALDA/lack of boost..

What is your 0-60 time? My 85, in decent running condition is 14 seconds. After new Monark nozzles (popped and balanced), it went down to 13 seconds.

[Diesel911]

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

Another from hunter
Fuel injection pump starvation with a good lift pump
http://www.peachparts.com/shopforum/diesel-discussion/247039-fuel-injection-pump-starvation-good-lift-pump.html


Fuel Pressure Relief/Overflow Valve good pic an stretching
http://www.peachparts.com/shopforum/diesel-discussion/356193-adjusted-fuel-bypass-spring.html

[Wodnek]

Don't forget to check the banjo bolt on the back of the head. I had the same issue with my 85 a few years ago. I removed it, blew it out with compressed air, back to running like it should.

[rmmagow]

Originally Posted by Wodnek

Don't forget to check the banjo bolt on the back of the head. I had the same issue with my 85 a few years ago. I removed it, blew it out with compressed air, back to running like it should.

That was the thing I was thinking about. Clear hose to the banjo bolt? I'll scope that out in the morning. Thanks

[ngarover]

x3 on the Bango bolt and line... Had that issue on all 6 of the w123's I have owned. Never hurts to get a cheap boost gauge and see exactly what boost your actually getting, simple to install, 5 minutes tops.

Lift pump, I had that issue on my current w123, again, simple fix.

Check that most over looked tank filter.

Run a couple cans of Diesel purge through the system, it actually works wonders...

[ROLLGUY]

If your '85 is a California model with the trap-ox, it could be clogged. Best to install a bypass pipe. If not a CA car, disregard. Also, X however many +1 on the boost line. If you remove the banjo bolt from the ALDA, you should feel pressure between 2 fingers when the engine is revved. If not, there is a restriction somewhere. If it has a "T" in that line, then it may be loosing boost on the other line (blue flying saucer?)..Rich

[Zacharias]

If the plastic tubing that runs from the manifold banjo bolt across the firewall to the overboost switch then the ALDA looks old and feels really stiff, examine it carefully for splits.

I chased a similar problem on my w116 300sd and finally found that the tubing was split on one spot on its underside, absolutely not visible unless you grabbed it and turned it. So the ALDA was getting only a fraction of the pressure it was supposed to.

[300dOwner]

Don't discount air in the line...you mention going uphill you're pedal to the metal. When this happened to me it was air in the line...the secondary filter had a big bubble and when the car was heading uphill the bubble ended up blocking the fuel flow

[Graham]

I had low power problem once on my 85 300D. Solutions:

- First time, it was lack of boost. I used a simple gauge, but a mityvac or similar would do. Measured boost on line that connects to ALDA. No boost there?? I found that the rubber connectors on the valve on firewall that that line comes from had split. Fixed that and boost was fine. Saved having to check banjo bolt!

- Second time, I was busy, so had daughter take car to a knowledgeable Indy. Car came back running great. Bill was for $50 and said "Adjusted linkages" ! So yes, check all linkages from firewall up and replace plastic bearings or lube metal ones with some ATF. Maybe throttle is not fully opening? Can also affect shift points.

Good luck with it. My 300D turbo is still a rocket ship!

[rmmagow]

Well, simple things first. Changed the "clear" filter which on mine was an opaque white plastic and changed the canister fuel filter. Power is back. Dumping out the fuel in the canister filter it had a lot of black flakes, algae? Is there a recommended algaecicde to use in the tank? I'm going to order a tank strainer and run the car close to empty to change it.
This is apparently my whole problem although I did fill the fuel filter with diesel purge too before putting it back in. I need to drive it more and will be daily driving for a couple of weeks. Other issues will also be checked out just to get everything checked and ready.
Thanks for the advise.

[Stretch]

RI = Rhode Island doesn't it?

If so I'm surprised you are getting algae in your tank that far north. I thought it had to be warm for that. Was it a really warm summer for you this year?