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  #1  
Old 09-07-2008, 11:04 AM
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250SEc Bad Fuel Pump?

Hi All,

I recently bought a 250SEc that hadn't been driven so much (see my previous thread on the car). Some time in its life, a 280SE engine was added.

When I drive the car, it starts very easily, and drives well with plenty of power, but after a while it looses power and will cut out on idle. When I first got the car it would run well for longer, but now it only runs 10-15 mins well before it starts running bad. The fuel pump on the car is very noisy (I can hear it whining, but its not the aweful sound my SLC's pump made when it was dieing). My first thought is that I might have a plugged fuel filter as the previous owner had let it run out of gas a few times, so I changed that, and the old one was kind of dirty but not that bad. I then went for a drive, around 40 miles and checked my new filter and it was still very clean.

I know I have a vacuum leak as my brake booster is bad, but I figure that would more cause bad idle than loss of power after a while. Thats why my thoughts are that my fuel pump is bad, but I wanted to confirm before i just start replacing parts.

Thanks,
Bryce

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  #2  
Old 09-08-2008, 01:02 PM
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You can check the fuel pump by pulling off the fuel line at the carbs, and cranking the engine. If fuel spirts out of the line, it's not the fuel pump. Sounds like a carb problem to me, but that's just a guess. RIDE ON!!
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  #3  
Old 09-08-2008, 04:02 PM
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Quote:
Originally Posted by flacollect View Post
You can check the fuel pump by pulling off the fuel line at the carbs, and cranking the engine. If fuel spirts out of the line, it's not the fuel pump. Sounds like a carb problem to me, but that's just a guess. RIDE ON!!
What carbs???????? Mechanical FI..........

Check the FP flow rate at the inlet line to the filter..you want 1 ltr/15 secs of flow. Just slip a hose over the ball flare and drop it into a measure container and turn ON the key.
If NO , then check the screen in the tank and the inlet screen at the FP inlet.

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2FG17RJ3A2GK0WJW00&yearid=1967%40%401967&makeid=MB%40%40MB%40%40X&modelid=250%2DSE%2D001%40%40250SE&catid=E%40%40Fuel+Delivery&mode=PA&subcatid=E1010@@Fuel+Screen&source=www.peachparts.com&clientid=catalog.mercedesshop
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Last edited by Arthur Dalton; 09-08-2008 at 04:15 PM.
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  #4  
Old 09-08-2008, 04:39 PM
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Thanks Arthur,

I assume that it would be best to take the car for a bit of a drive until it starts giving those symptoms and then compare that flow rate to when its running happily?

Thanks,
Bryce
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  #5  
Old 09-08-2008, 04:47 PM
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No..just do it cold.

If that rate is attained, then you know the next test step is the return line, so do that test first. If you get only 1/2 ltr/15 secs , you know one of the screens is partially plugged or the pump is bad. These MFI pumps are low pressure , but high volume [ Impeller pump], so it is the flow rate you are concerned with.
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Last edited by Arthur Dalton; 09-08-2008 at 04:55 PM.
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  #6  
Old 09-09-2008, 04:33 PM
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My recently sold 380SL had the exact problem. It's volume test was fine, but then after about 30 minutes of driving it would start to stumble under load and would quickly become undriveable. It happened a couple of times on my drive to and from work, in the same spot +/- about 50 yards. If I let it sit for a few minutes, I was able to restart and get to the office or home. .

And the worse it ran, the worse the pump sounded.

This turned out to be the tank screen.
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  #7  
Old 10-04-2008, 07:04 PM
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Firstly thanks all for the replies. Due to travel and the gestapo that run the apartment complex I live in, i was only able to finally work on the car today.

When i disconnected the fuel line and ran the pump, I did not get a smooth flow of fuel. During the 15 second test when i turned on the key there was a large volume of fuel that went for maybe 2-3 seconds, then it started to slow down, until there were regular pauses and more of a sputtering as it pushed out the fuel. The first burst was too much for my funnel so I wasn't able to measure the exact amount but I think I had 700-800mls over the 15 seconds.

the fuel I captured was fairly cloudy and brown.

So, my next step is to try and look at that fuel strainer thing. I wasn't able to remove it to day - using a search of the forum I found somebody who used an inverted spark plug removal tool - but while mine fits I don't have anything to turn it with inverted since its circular inside. I also went to a few hardware shops to either find a 24mm bolt so I can put some smaller nuts on it, or a 24mm hex attachment for my ratchet. the best I could find was a 16mm bolt and a 19mm hex. There is one more hardware shop I will try but I was hoping to see if anyone had any other suggestions.

Also, looking at the placement of the strainer and the fuel lines out of the tank, how does the strainer clogging up actually stop fuel delivery? it doesn't look like its anywhere near where the fuel comes out, from the picture posted earlier in the thread it looks like it just sticks up into the tank - unless the tank has some kind of false bottom to make it go through that central bit?

Anyway, thanks for the help so far - any other suggestions are much appreciated.

Bryce

NB: unfortunately driving around to find these tools resulted in the SEC being clipped by a tahoe. really looks like a jalopy now.
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  #8  
Old 10-04-2008, 08:31 PM
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The lines coming out of the front of the tank extend to the center of the tank inside. At that point , there is a swirl pot and the screen...
One line is supply and one is return.

Take the screen out and then blow thru both lines to clear them while the screen is out.

As far as the spark plug socket inverted trick goes , just go to any parts store and buy a decent plug socket that has the 3/8 drive square on the inside for the extension and the hex on the head............ Sears Craftsman is fine.

There is also other screens and a main filter , but start at the screen in the tank. An easy test for that is to just drop the line and check for a good gravity flow rate.
There is another test, but I will wait until you do this one as this is where you want to start [ at the tank]
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  #9  
Old 10-05-2008, 05:25 PM
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My '66 Coupe did this to the previous owner and he could only get about 30min out of the car, then it would shut down and not restart until it sat a while. That was his reason for selling it; he'd had it to a number of shops and no one could find the problem.

Amazingly, I drove it the 3hrs/240mi from San Francisco home without a problem. But a couple weeks later, it died on the way home from work and wouldn't restart.

Sure enough, there was a nice 3/8" thick plug of "stuff" built up on the screen inside the inlet fitting on the fuel injection pump. It's been fine ever since I cleaned that out.

A little hint for working on fuel lines while under the car:
1) Where some decent safety goggles that provide complete coverage, because if you remove a fuel line, splash yourself in the eyes, you're going to be in some serious trouble....and hanging onto that open fuel line isn't going to be your priority.
2) Tie rags around your wrists to keep the fuel from running down your arm, into your VERY SENSATIVE armpit, and down your side, chest or back.
3) Wash any skin that's been soaked in fuel thoroughly with soap and water to stop the burning and keep the methylethylbad**** from getting into your blood stream and liver.
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  #10  
Old 10-05-2008, 06:01 PM
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Thanks Arthur...

I wasn't able to find a spark plug socket (that I could use upside down), but I did find an oxygen sensor remover which I can put a 6" extension bar through.. looks like its slighly larger than the spark plug socket so hopefully slightly better fit too. I'll see next weekend when I get to the car again.

Bryce
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  #11  
Old 10-05-2008, 06:03 PM
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Quote:
Originally Posted by Todd Miller View Post

A little hint for working on fuel lines while under the car:
1) Where some decent safety goggles that provide complete coverage, because if you remove a fuel line, splash yourself in the eyes, you're going to be in some serious trouble....and hanging onto that open fuel line isn't going to be your priority.
2) Tie rags around your wrists to keep the fuel from running down your arm, into your VERY SENSATIVE armpit, and down your side, chest or back.
3) Wash any skin that's been soaked in fuel thoroughly with soap and water to stop the burning and keep the methylethylbad**** from getting into your blood stream and liver.
Thanks for the safety tips.. I hadn't thought of the rags around the wrists.

PS: Love the green coupe.
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  #12  
Old 10-05-2008, 11:17 PM
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Thanks for the kind words. Sadly, she's in horrible shape up close. This was probably a greymarket POS at some point, as it's a German sold model. All sorts of rust and much of it was filled with expandable spray foam insulation, squeegied off flush with the inner fenders and undercoated to match. 2 really bad paint jobs on top of the original, the top one of which is all checked and has solvent blisters popped everywhere. Literally...looks fantastic from about 10' away and then you get close and say OMG

But what can I say? She's a '66 250se Coupe...and I love her.
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  #13  
Old 10-11-2008, 08:37 PM
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First taksk today was to drain the fuel tank. To do this, I disconnected the fuel line from the fuel pump and drained it into some bottles. At first the flow was good, but then it would slow down drastically unless I reconnected the line and waited 30 seconds or so. Given that, it took quite a bit of time draining all the fuel left in the tank (about 12 liters). The fuel was almost the colour of ginger ale.

I then removed the fuel screen. It was dirty but not horribly so. Also a whole bunch of rusty dust came out and was caught in my oil change pan.

Given that, I spent the rest of the day removing the fuel tank. Took quite a while, but eventually I got it free and started sloshing some of the old fuel around in there. Looking inside, you can see the walls of the tank are a rusty colour, but it doesn't look too bad.

So.. while the tank is out, any suggestions for tomorrow to do anything before it goes back in? (Unfortunately I have to move the car sunday night). I was thinking of sloshing around some new fuel, as well as seeing if i can get some pipe cleaners for where the fuel line and return line go in.

I was also thinking of measuring the flow of connecting my fuel pump directly to my fuel can to see what sort of flow I get.

Anyway, any tips or suggestions much appreciated.
Bryce
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  #14  
Old 10-11-2008, 08:51 PM
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If there is nothing plastic inside the tank that's important (ask the folks here because I don't know) you can pure in some muradic acid, slosh that around and it will eat the rust right out leaving you with a shiny clean tank inside.

You can buy a quart of it from most hardware stores.

It is seriously some methylethylbad*****, so gloves and full coverage safety goggles and a charcoal mask are SOP.

When it's all said and done, you'll need to pour the rusty muradic acid out, and then rinse the tank with water several times, and then dry the inside of the tank with compressed air, and leave it to bake in the sun to make sure it's dry inside.
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  #15  
Old 10-11-2008, 09:23 PM
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Thanks Todd. There does not appear to be anything plastic inside the tank from when I looked in there.

Would it be ok to rinse it out with Petrol to re-install if I don't have time to get it dry or is the rinsing out with water and important step?

Bryce

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