Murphy’s Law by George Murphy

Ask George: Reviving a Barn Find

A number of members have contacted me about getting an older Mercedes-Benz going again after years of neglected storage. I just wish they had called before attempting to start the car, not after!

Because there are several issues that must be taken care of to assure that the car can even be started, much less driven safely, I will tackle them in order in a series of articles.

In this discussion, we’re talking about a car that was put away several years ago with no regard to preservation. The car was not prepared for storage but rather was simply parked indoors (or even outdoors) without any thought to long-term storage care.

Before attempting to start the engine

I cannot emphasize strongly enough: Do not try to start the engine before going through the fuel system completely. At best, you can do damage to the car. At worst, you can cause serious damage or injury to the car, the garage, and anyone nearby.

Warning: This is only a guide. Use common sense in handling gasoline and starting the car after extended storage.

First, remove the strainer from the tank and drain the old fuel out of the tank. Most older M-Bs with the tank mounted under the trunk floor take a 22mm hex Allen wrench to remove the strainer (you will probably have to rent or borrow one). It’s best to order at least two new tank strainers and fuel filters, as they may plug from debris in old fuel.

For models 100, 108, 109, 111, 113, and 114, the strainer is part No. 111 470 06 86. For others, consult the MBUSA Electronic Parts Catalog at www.epc.startekinfo.com/epc/welcome.jsp (subscription is free for North American models) for correct strainers.

After draining, flush the tank with diesel fuel until clean fuel runs out the strainer hole. Note: I did say diesel fuel. It will accomplish the same cleaning objectives as gasoline but is considerably less volatile. Don’t worry about having diesel fuel in your system; we’ll be draining it out thoroughly before starting the car.

To inspect the tank internals, remove the fuel gauge sending unit and, using a strong flashlight, look inside the tank for rust and debris. If it is seriously rusted, you’ll have to remove the tank and have it professionally cleaned and leak-tested.

Fuel-injected models

For fuel-injected models, remove the entire electrical fuel pump assembly (filter, damper, and so forth) from the fuel tank. If you have reason to believe that the fuel hoses are 100,000 miles or 20 years old or more, replace them. Clean the pump as follows.

1. Take the pump off the bracket and gently mount it so that the pump outlet is pointing upward.

Caution: Remember, we’re using diesel fuel (or kerosene) to flush the system and clean the pump; you’ll be using a 12-volt battery and jumper wires that will produce sparks when you connect power to run the pump, with potentially disastrous consequences if gasoline is used. In addition, the intake fitting of some electric fuel pumps may have a fine fuel screen, which should be cleaned.

2. Have a 12-volt battery nearby to use as a power source. Attach jumper wires to the battery electrical terminals and note polarity.

3. Fill the pump with diesel fuel through the outlet, then jog it electrically in reverse – pump (+) to battery negative; pump (-) to battery positive – for approximately one second so that the diesel fuel is expelled from the inlet. (Put a bucket under it.) The dirty pump will expel lots of dirt and crud. If the pump does not run when connected to the battery, try reversing polarity to get it going. If this fails, you’ll need a new one. On older M-B pumps, you can remove the end-cover screws and clean the rotor and rollers to free up the shaft. If frozen, you’ll need a new pump.

4. Repeat diesel-fuel flush until clear fuel flows out. Flush pressure damper and other lines on bracket and install a new fuel filter.

This procedure has resuscitated many stalled expensive fuel-injection pumps on cars that have been sitting for a while. It’s worth a try. I have salvaged pumps from several 280SE 4.5s this way also, much to the owners’ delight, and they are still working today after many miles.

The fuel-injection pumps have very close tolerances inside, and it doesn’t take much crud to cause them to lock up; the reverse flush can save you a lot of money.

Reinstall the pump and bracket in the car, but temporarily install a clear inline fuel filter between the tank and the fuel pump inlet. (For some unexplained reason, M-Bs do not have a filter between the fuel tank and the pump.) When fuel from the tank is finally running out clean (check the clear inline filter), you can restore the fuel lines to their original configuration.

After the fuel pump is hooked up, disconnect the fuel feed line in the engine compartment and use jumper wires on the fuel-pump relay to run the pump to flush the lines from the pump to the engine. As soon as clean fuel emerges, restore the fuel system connections. If the car is more than 25 years old, replace all rubber fuel hoses in the engine compartment, including the short injector lines found on EFI engines.

If injectors are plugged, remove each one and try cleaning with disc-brake cleaner. If they can’t be cleaned, new ones may be needed.

Carbureted models

For older models with carburetors and an engine-mounted fuel pump, disconnect the fuel line at the fuel pump and at the fuel tank. Flush the fuel line(s) with diesel fuel or denatured alcohol from the engine end back to the tank connections. Install a temporary clear fuel filter at the fuel-pump inlet if your car was not equipped with one originally, to catch any debris before it enters the pump and carburetors. Torque the nut to 120 Nm (87 ft-lb).

In the next issue: What to do before starting and driving the car.