Help: Suspected Bad IP on '83 300TD - PeachParts Mercedes-Benz Forum

pennintj · #1 08-12-2010, 09:15 PM

Yes, I've read all the "It can't be an I.P. because they never go bad!" posts, however I'm beginning to suspect something is wrong with mine.

Car: 1983 Mercedes 300TD with unknown miles. Car is a Grey Market import from West Germany (sticker under hood and inside door) Speedometer that was in it when I picked it up read 37X,XXX miles, and the speedometer didn't work. Previous owner said it hadn't worked since he'd had the transmission replaced a few years back, and he'd driven across country since then at least once.

Scenario: Lately it's been acting up, losing power especially once it gets below 3/4 of a tank. Suspected it was just "tank sludge" and I'd get to it, someday. About two weeks ago discovered that the linkage had been adjusted incorrectly to the fuel pump making it impossible to shut off with the "STOP" lever. Adjusted it and the car seemed to run a little better.

Tuesday gf was driving it to work when it stalled out at interstate speeds. Figured it was out of gas and called me to rescue. Filled with 3 gallons of fresh diesel, tried to re-start, no go. Towed home.

So far: Replaced the weeping fabric covered return lines with fresh clear tygon so I can see what's going on. Used the lift/hand pump to pump fuel back up to the fuel filter. *minimal* bubbles, but there are a couple. I've drawn fresh fuel through the incoming line using a hand-held pump and clear line. Looks good and flow is fine with minimal bubbles.

I've also checked the little check valve at the back of the I.P. and it seems to be working fine (it seems to hold pressure, then releases)

Have pulled the hard lines and attempted to bleed using the starter. I've also eliminated the vacuum system and applied my "Mighty Vac" to the fuel shutoff valve (holds pressure fine)

I can't get anything out of the hard lines. Despite cranking the engine till the battery died...three times.

There's no movement in the return lines (clear tygon) while the engine cranks, leading me to suspect the I.P. but I don't want to start yanking it out until I get a little more advice. I do already have two extras sitting in "parts cars" that I've accumulated (they breed I tells yah)

Background: Motorcycle & Scooter mechanic...I've worked on everything from 32cc to 2,300cc and that doesn't include the cars. If this were a gas engine I'd already be looking for a fuel pump. This is my first foray into Diesel.

-=Tom

toddyvol · #2 08-12-2010, 09:25 PM

Wonder if the fuel strainer at the bottom of the tank is clogged?

79Mercy · #3 08-12-2010, 09:27 PM

You did release the vacuum on the vacuum shut off valve while cranking the motor right??

dude99 · #4 08-12-2010, 09:47 PM

plugged fuel line perhaps?

layback40 · #5 08-12-2010, 09:54 PM

Tom,
Welcome to the forum.
We all hope that you can find out all you need to know.

It would be useful if you could put some details in your signature to help us all with comments.

Your described problem is common and normally suggests a fuel delivery issue.
Have you done a search for threads about this?
Has the car been run on WVO?

You need to start at the tank, the strainer in the tank may be blocked ( quite a common problem). It is likely that you may have a problem with bugs in the tank. This shows as a black deposit that blocks everything.

It sounds like fuel is not getting to the injector pump. Replacement of the 2 filters (primary & secondary is probably needed.

You could also have a problem with the lift pump. The one way valves can fail & so reduce the supply pressure to the IP.

Hope that helps !!

Good Luck !!

Biodiesel300TD · #6 08-12-2010, 10:35 PM

I would try swapping the supply and return lines in the engine bay. This will bypass the tank strainer and will tell you if the strainer is clogged or not. I would also change both fuel filters.

pennintj · #7 08-12-2010, 11:11 PM

Quote:

Originally Posted by layback40

Tom,
Welcome to the forum.
We all hope that you can find out all you need to know.

It would be useful if you could put some details in your signature to help us all with comments.

Your described problem is common and normally suggests a fuel delivery issue.
Have you done a search for threads about this?
Has the car been run on WVO?

You need to start at the tank, the strainer in the tank may be blocked ( quite a common problem). It is likely that you may have a problem with bugs in the tank. This shows as a black deposit that blocks everything.

It sounds like fuel is not getting to the injector pump. Replacement of the 2 filters (primary & secondary is probably needed.

You could also have a problem with the lift pump. The one way valves can fail & so reduce the supply pressure to the IP.

Hope that helps !!

Good Luck !!

No to the WVO. Thought about it, but not practical now.

I've been lurking on this as well as a few other forums for about a year, and I've been reading up on common fuel problems.

Fuel filter (clear plastic one) is fine & clear, and was replaced not long ago. Spin on filter was replaced a short while ago, but they're cheap enough.

Lift pump looks fairly new. BOSCH is still visible down the side bright and shiny. When I operate it, there's some *slight* bubbling visible in the intake line between the pump and the fuel filter intake line.

There's also some slight movement in the return lines, as well as the line between the IP Overflow(?) back to the fuel filter.

I don't seem to have a blockage coming from the tank, as I can draw fuel through it with an aux hand pump I use for draining scooter tanks. I'll see about drawing from the return line tomorrow.

Re: Fuel shutoff valve - Should I be using a vacuum to open the valve or close it?

-=Tom

79Mercy · #8 08-12-2010, 11:17 PM

You should not apply any vacuum to that valve, unless you want to turn the motor off. If you have a vacuum on that valve then no wonder the injection pump wasn't putting out fuel.

Diesel911 · #9 08-13-2010, 12:52 AM

Quote:

Originally Posted by pennintj

No to the WVO. Thought about it, but not practical now.

I've been lurking on this as well as a few other forums for about a year, and I've been reading up on common fuel problems.

Fuel filter (clear plastic one) is fine & clear, and was replaced not long ago. Spin on filter was replaced a short while ago, but they're cheap enough.

Lift pump looks fairly new. BOSCH is still visible down the side bright and shiny. When I operate it, there's some *slight* bubbling visible in the intake line between the pump and the fuel filter intake line.

There's also some slight movement in the return lines, as well as the line between the IP Overflow(?) back to the fuel filter.

I don't seem to have a blockage coming from the tank, as I can draw fuel through it with an aux hand pump I use for draining scooter tanks. I'll see about drawing from the return line tomorrow.

Re: Fuel shutoff valve - Should I be using a vacuum to open the valve or close it?

-=Tom

Even with the above your performance dropping when you get below 3/4 of a Tank of Fuel is an indication of a Fuel Supply Issue.

If your Euro Benz has the same type of Fuel Supply Pump on it as the Parts Cars do I would Try swapping that. (The Fuel Supply Pumps on M Fuel Injection Pumps are Different from the MW Fuel Injection Pump Fuel Supply Pumps.)

I would also do the Spin-on Filter change. If you think the used one is good put it in a Zip Lock Bag and that way it will if it turns out it was good you can use it.

Get some longer 5/16" ID Fuel Nose and hook it to the Plastic Fuel Filter and see if it will run with that Hose in a other Container with Diesel Fuel in it. That would buypass anything to the rear including the Fuel Tank.

kerry · #10 08-13-2010, 09:25 AM

I second trying to get it to run on an alternative bottle of diesel fuel. Run the input and return lines into the bottle as if you were doing a purge and see what happens.
Layback's question about WVO wasn't really about whether you personally have used WVO but whether any previous owner had. WVO will eventually destroy the IP.

barry123400 · #11 08-13-2010, 01:48 PM

Well I removed my post because I was not aware the injection pump was being continually shut off by the poster. I thought he just checked it quickly.

If the car still preforms better with more fuel in the tank than less you still have an issue that does not actually stop the car from running. Supply pressure is less with a low tank. Should not be this way if all is well in the fuel supply system.

pennintj · #12 08-13-2010, 02:21 PM

Quote:

Originally Posted by 79Mercy

You should not apply any vacuum to that valve, unless you want to turn the motor off. If you have a vacuum on that valve then no wonder the injection pump wasn't putting out fuel.

Ding Ding Ding! Yeah, I'm new...

Disconnected the vacuum pump, started again with a fully charged battery, disconnected hard line injector #1, cranked until it started pushing diesel, closed off the line & cranked some more. Started right up.

Basically, she ran it out of gas, and there was too much air(?) in the system to move before I ran the battery down. I overcomplicated a fairly simple thing it seems.

I'm going to spend the week re-plumbing the vacuum lines and try to see how bad the tank is. Then once I get it back on the road I'm going to try to re-start the Sedan (tank is already out waiting to be cleaned) and move from there.

Thanks again for the help

-=Tom