240D Less slow on full tank? - PeachParts Mercedes-Benz Forum

efm-7 · #1 04-29-2015, 08:51 AM

I made an interesting observation.

I noticed that when I filled my tank from nearly empty, all the sudden, I was able to keep up with the other cars casually accelerating from the stop light!

Does this make sense or is it all in my head?

I'm thinking that maybe there's more fuel pressure before the lift pump when the tank is full vs when when it's nearly empty. (Gravity?)
Which makes me wonder if an auxiliary fuel pump will help alleviate the slight loss of power when the tank gets low.

cho · #2 04-29-2015, 09:15 AM

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240D and keep up with the other cars dont belong in same sentence

just joking mate,...yeah you might have worn lift pump....

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efm-7 · #3 04-29-2015, 10:11 AM

You know you're a 240D owner when you have every downhill on-ramp memorized.

Should I try to fix my "probably worn" lift pump or try to get creative with a auxiliary pump?

barry12345 · #4 04-29-2015, 11:08 AM

You rebuild the old lift pump and make sure you have decent fuel pressure present in the base of the injection pump. Cheap to do. Good articles in the archives of how to do it as well if desired.

The relief valve spring may also need adjustment as they age as well. This is not to be ignored in the 616 engines in my opinion. I personally like 18-19 pounds of base fuel pressure in the injection pump. Certainly no less than 12 pounds. This might cost you about ten dollars for a 0-30 pound liquid filled gauge from harbor freight or simular sources to do properly.

Actually there are some other factors that may add to the situation. For example a pretty dirty tank screen might flow a little better under more gravity pressure I suspect. Still these older lift pumps should be refreshed anyways with any suspicion. Again very cheap to do.

I would think a good test for the tank filter is to just unhook the fuel line before the lift pump to see if decent gravity flow is there.

Your keeping up with traffic was a memorial quote. Where you exiting a parking lot?

Actually I own two of the 240d beasts as well. I have made more runs at hills than runs at women in my day with them.

They are well worth basically doing a tune up on as you want or need all the potential power available in my opinion.

The minumin tuneup is check the valve lash. Check for too much chain stretch. Make sure there is good fuel pressure present in the base of the injection pump. Inspect the condition of the air filter.

All pretty simple and cheap to do. Valves need checked every fifteen thousand. Unless they have not been done for a long time. If so a rechecking of the first adjustment a week or so later should be done.

Only then you can you consider enrolling your our car in the 240 beast club.

We were going to make bumper stickers for members initially. Then decided nobody could read them anyways when passing us so fast.

All kidding aside I find them unique cars having substantial differences from the five cylinder versions. I have also been living with the delusion that the turtle ultimatley beats the rabbit. .

efm-7 · #5 04-29-2015, 01:04 PM

I've done the valve adjustment, pre-filter cleanup, replaced all filters, and I've had a local long-time diesel Mercedes enthusiast comment that my particular car is "powerful", so i'm guessing it's not horrible.

I've done a bit of looking around for the rebuild parts based on this post http://www.peachparts.com/shopforum/mercedes-parts-reference-library/271632-om616-lift-pump-repair-kit-w123-123-a.html and only one of the four parts needed is readily available. I don't know how willing I am to go on a fool's errand for this. Almost seems like I'd need to replace the lift pump altogether.

Oh another fuel system related issue i'm having is the crush washer on top of the fuel filter bolt, leaking and can't find a replacement. One place wants $25 for shipping for a $2.50 washer and refuse to mail it as a letter. Oh the joys of living in Canada.

Oh yeah... exiting parking lots... it's an exercise in preparing for embarrassment and having the "I'm sorry!" face ready. And boy do I ever love "No Right on Red" intersections

charmalu · #6 04-29-2015, 02:13 PM

I need to rebuild the Lift pump in our 240. at 375K she is getting a bit tired.
I think the surging I get at slow speeds may be the pump, don`t know.
I have a couple pumps off 617.95 engines that I`ll go through when I can find the darn kits I bought.

Filters are good and valves have just been checked a couple weeks back.
Finally had to change the VC gasket as it was weeping a bit. 5 years on a gasket is pretty good, and the cover has been of a few times.

240`s are the last best MB offered as to simple, manual everything, till they went to electric windows and sun roof.

I don`t need to go 0 - 60 getting through an Intersection. 0 - 6 is just fine,

Berry, I agree, the Turtle does win, I see more rabbits lined up in the PNP`s/JY`s than 240D`s.
The Rabbits are in a hurry to get there. LOL

I was looking at another 80 240D on CL last night......

efm-7... change the fuel Filter housing to one of the later versions like used on the 84 & 85. Look at the part# on yours, second to the last #s are 01. the later version is 02. They do not use the crush washer, just 2 "O" Rings on the Bolt Shaft. You won`t have to pull out your hair trying to stop the leaks.

Charlie

mach4 · #7 04-29-2015, 02:22 PM

I installed a fuel pressure sensor on my engine. It's really nice to be able to monitor that critical aspect of engine health. While it won't tell you what the source of low pressure is (clogged strainer, weak lift pump, clogged primary filter, clogged secondary filter or weak pressure relief valve) it will let you know what the IP is seeing and if it's low it's easy to monitor what fixed it as you swap out components. Otherwise you're kind of feeling around in the dark.

Having a baseline for normal operations allows one to be proactive rather than get surprised - like getting stranded on the side of the road when a filter finally clogs completely.

DeliveryValve · #8 04-29-2015, 02:27 PM

I would bet you have a clog vent or a clogged tank screen. Having a full tank puts less vacuum pressure in the tank and with a clog screen, a full tank can make the fuel flow past the clog.

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efm-7 · #9 04-29-2015, 02:59 PM

I know a the screen isn't clogged but it's possible that the vent might be. I did use one of those internal tank coater kits and the paint might have greatly reduced the internal diameter of the vent pipe.

However, if a clog were the case, wouldn't the tank collapse when it goes empty or at least go "whoosh" when I open the cap?

efm-7 · #10 04-29-2015, 03:00 PM

mach4 - how did you add a fuel pressure sensor?

mach4 · #11 04-29-2015, 03:53 PM

Quote:

Originally Posted by efm-7

mach4 - how did you add a fuel pressure sensor?

It's a bit of an unorthodox solution, but here's the thread on its implementation - http://www.peachparts.com/shopforum/diesel-discussion/362989-adding-fuel-pressure-gauge.html

barry12345 · #12 04-30-2015, 04:32 PM

There still should be the valve kits available for the lift pumps at many places.I think there is more than one manufacturer of them. Could be several brands using the same parts from one supplier though. Dealers sold a kit as well.

They are not expensive and ninety five percent of the time are all you really need to recondition a lift pump if required.

I cannot see them ever being totally discontinued. They are a reasonably high volume cheap parts that are economical to manufacture. New lift pumps are pretty expensive in comparison.

I also would replace the 240ds heavy piston loading spring in the lift pump with one from a 617 turbo car. Not absolutey required. Still It gives more output pressure. Plus hurts nothing.

This spring should still be available new or even just one off a wreck would be great. I cannot ever remember a member saying his got weak. Of course not until that long ago and even now few still ever check their fuel pressure.

My belief that this is far from wise and has not changed. Still even if I am wrong what does it hurt to have or verify some semblance of decent fuel pressure? Even the manufacturer wanted it periodically tested on their maintenance schedule.

It really helps in many ways as well besides my unproven belief. That low fuel supply pressure over a very long period with a 616 four cylinder diesel. Also wears out and destroys the first rod bearing in the engine. To a lesser extent it may also effect the 617 five cylinder engines.

A nice side benifit is it is reported more than once it makes the engine run quieter at speed as well. Any reduction of that cement mixer noise under the hood at speed has to be beneficial .Personally I figured these cars where all custom built for deaf people.

Our daughter used to claim she could hear me driving the tractor home a block away. What really hurt was there is a forty foot hill to that side of the house present as well.

If your friend states the car is powerful for a 240d and he knows his 240ds. The throttle linkage is probably in good shape. I estimate a lot of these cars are frequently sold off because of that common deficiency. I also suspect that the last owner never usually examined the situation since everyone claims they are just slow anyways.

efm-7 · #13 04-30-2015, 09:14 PM

a weird thing happened last year. The accelerator pedal had a good amount of resistance to it for the first 4 months of driving it, and then something gave and became much looser. What should I be looking out for? The car still seems to drive the same.

Also many people talk about lift pump rebuild kits being readily available, but I'm having trouble finding any. I'm usually good at finding things, but drawing a blank here

Lucas · #14 05-01-2015, 02:52 AM

Think about this, if you find something that will give a 10hp gain, that is more than 10%!

And pm'n about this rod bearing failure... But feel free to elaborate here is no one minds.