Fuel issues on 190d - PeachParts Mercedes-Benz Forum

tram · #1 02-13-2009, 09:29 PM

Bought a 1965 190Dc to tool around in. Rebuilt engine, repaint, new seals, yadda, yadda. "Quick Glow" upgrade, hand pump upgrade.

When using the "choke" at cold idle, it runs great. Get it down to warm idle speed and it suddenly developed a problem... it would suddenly bog and die, just like running out of fuel. Will not restart without massive bleeding of the entire fuel system. Runs great on acceleration or at speed, too.

When it quits, it acts like it's completely out of fuel.

Day before yesterday, it did it and refused to draw fuel from the tank. Drained the tank, pulled the sending unit.. and discovered that the PO had used silicone sealer to seal the send unit to the tank. Bottom of the tank is filled with it. I remove the tank, and flush it with all orifices open. The suction line on the car to the engine was plugged, so I freed it with compressed air and flushed it.

Reassembled everything, primed it, it fired right up and ran better than ever! Drove it around, pulled back in and it started loping, then shut down.

Exact same issue.

I've since replaced the new hand pump, replaced the fuel lift pump with a known good one off another known good IP. double- checked the lines for blockage, and replaced both fuel filters, as well as replaced every rubber seal and copper crush gasket on the fuel system.

Fired it up, ran great, no stalling at low idle, all is good.

Wrong.

I let it sit for about 15 minutes, went to start it again and... Fuel system acts like it's bone dry. Primer pump draws fuel from the tank like there's no tomorrow. Filter is full, BUT I keep getting air out of the bleeder on the top every time I open it.

Just for fun, I even exchanged fuel filter canisters in case there was a little crack at the top, or something. Still no start.

Injection pump: Good
Drip timing : Dead on
Linkage: Adjusted exactly per repair manual
Nozzles: New
Compression: Excellent.

Definitely a fuel issue. But where?

bobodaclown · #2 02-13-2009, 09:42 PM

did you put the correct seal on the fuel filter canister?

pselaphid · #3 02-13-2009, 09:47 PM

Does it have a fuel pressure regulator valve at a banjo bolt on the IP return? Hot fuel is lower viscosity, so a weak regulator has trouble holding pressure, especially on hot fuel. The various clogs you cleared up might have contributed to the problem. Just a guess, as I'm not familiar with one that old.

tram · #4 02-13-2009, 09:49 PM

Quote:

Originally Posted by pselaphid

Does it have a fuel pressure regulator valve at a banjo bolt on the IP return? Hot fuel is lower viscosity, so a weak regulator has trouble holding pressure, especially on hot fuel. The various clogs you cleared up might have contributed to the problem. Just a guess, as I'm not familiar with one that old.

Good point. Yes, it has that valve, and your theory makes sense. I think I have a couple more of those around.

Lycoming-8 · #5 02-13-2009, 09:54 PM

The later MB diesels have a fuel strainer screen in the tank. Not sure if this model has that, but if so it could be clogged and the symptoms would be as you describe.

tram · #6 02-13-2009, 09:56 PM

Quote:

Originally Posted by Lycoming-8

The later MB diesels have a fuel strainer screen in the tank. Not sure if this model has that, but if so it could be clogged and the symptoms would be as you describe.

Went thru the whole tank and screen thing already, as per my original post. It needed to be cleaned but that didn't solve the problem.

coachgeo · #7 02-13-2009, 10:04 PM

easy way to determine if air issues is part of your problem is to temporarily wire in a 12v fuel pump way back at the tank. This pushes fuel and nothing is sucked on beside the few inches to a foot of line you needed back by the tank. With pump on.... if this solves your problems...... then you know to look for air leaks.

Also pull you fuel cap off and see if your symptoms change. clogged breather?

t walgamuth · #8 02-13-2009, 10:52 PM

I am wondering it the po had treated the inside of the tank with a liquid liner material to combat rust and its peeling off.

tram · #9 02-13-2009, 11:09 PM

Quote:

Originally Posted by t walgamuth

I am wondering it the po had treated the inside of the tank with a liquid liner material to combat rust and its peeling off.

No sign of it. It looks like orangey- red silicone. It was on both sides of the sending unit rubber gasket, and had gotten all rubbery from the diesel, making a nice little pile right in the bottom of the tank at the pick up tube ring. Of course he must have used half the tube. "More is more better", right?

Stuff should be outlawed.

vox_incognita · #10 02-14-2009, 08:31 AM

Remove the hose at the suction line,dip in a transparent bottle of fuel.Operate the hand pump.When you push,does it return fuel to the bottle?If yes,remove the lift pump and check the two disc valves ,clean the internals,renew the o-rings(air might be drawn on the lift pump suction/delivery stroke thru an old inlet nipple o-ring and along the threads.If the check valve is ok,there will be no visible fuel leakage,and still air can be drawn in the pump .Are the fuel hoses new?
You can use an appropriate vessel as a fuel tank to see if the problem goes away...and then search for the solution somewhere else(tank,metal fuel lines...).
Hmm,what else...check also if it`s not a hollow bolt used to hold the fuel return union(#306 and 312),as the pressure required for proper operation would never be maintained,even with by-pass valve ok.

If you`ve installed the later type fuel filter cannister with union on top lid
,check whether the hollow screw #261 has the 1mm.resctriction orifice-for the same reason.Not related directly to air presence,but worth checking.
See also whether the thin copper seal of the new hand priming pump does its job.On mine I could crearly see that it sucked air without leaking fuel and had to remove the lift pump to tighten it properly again.
I believe you got rid of the old metal pre-filter and used a plastic transparent one...

tram · #11 02-14-2009, 08:34 PM

Solved.

In reviewing the OE parts book, I noticed that the metal front to rear fuel lines are each in two pieces, with a short rubber hose junction to join them.

Jacked up the car, found the junctions. Both were original, hard as rocks, and weeping diesel.

Replaced them both with fresh fuel hose and clamps, and have been running around in it all day without issue.

Thanks to all for the help!