still trying to figure out stalling 300SD
 

1980 300SD. Virtually everthing done now. filters, dampener screw, valves, return lines etc.

Still stalls only sometimes. Yesterday I could floor the pedal with no increase in rev's or acceleration. Two minutes later was fine. I am thinking injection pump or clog somewhere. No shop seems to be able to find a clue. What could be going on?

Algae in fuel? (I am in Las Vegas though). Clog in tank?

Monaco, I am going to buy a black 1980 300sd in Las Vegas this coming Monday. It looks like you are having many problems on a 1980 300sd. Can you give me some advice on what to look for? The owner said it only has 45k on the motor. A/c, heater, and sun roof not working? How much do you think is going to cost me? He is asking $3600-4500. I am going to make a $3000 offer if the car is in good condition. What do you think?

I don't care if it's got a rebuilt motor, that seems like a lot of money for a 1980 with some known problems.

Tank screen is almost certainly plugged. Warm weather climates are the best (ha) place for bacterial growth in the tank, only marine applications are worse.

You will need to pull the fuel sender out of the top of the tank, accessable after you remove the first aid tray on the W123 chassis.

Also check for a leaking suction line from the tank to the lift pump -- the rubber under the fabric cover can go bad, and all that gets sucked up is air, not fuel!

Peter

That sounds like a lot of money to me. I'd sell you mine for less and I have brand new A/C system under warranty, valve job, fuel filters, and many other bits of recent work.

Sunroof and AC systems are trouble on these and expensive.

I am thinking that only fuel screen in tank and the vent line are left. It really must be one of those two (or both). Can anyone walk me through (slowly) how I can handle these myself?

Run the hand pump -- if fuel squirts out, it is shot and you need to replace it, especially if it is the old red knob you screw down type.

While operating the pump, listen for the hiss of air getting pulled into the suction line -- you should also check for the presence of fuel on the outside of the line. If fuel is present or you hear air leaking, replace the line. You will be able to see air bubbles in the clear plastic lines if they aren't brown, but I suspect they are.

If the pump handle is hard to pull up, or the spring loaded one doesn't rise, the tank screen is plugged and you are fuel starved.

Peter

Since I just did this I might Add....

To remove the strainer:

Syphon as much of the fuel out the filler cap as you can.
If only a few gallons is in the tank, skip this step.

Get a plastic tub that holds several gallons and place below the tank.

remove the clamp holding the rubber fuel line under the tank. If the fuel is just dribbling out, the strainer is probably clogged.
Drain fuel.

Remove the rubber hose at the tank outlet with a 19mm wrench.

Using a 46mm socket and ratchet, remove the strainer.

thanks. can I back you up one step further, where is the hand pump?

The hand pump is mounted to the transfer pump that is mounted on the steering box side of the injection pump. You un-screw the plastic knob and pump it up and down. When done pumping it make sure that it is tightly screwed back or it will suck air. Get under the car above the differential and un-do the tank feed line. See how well it flows or not at all. Most likely, the screen is plugged. The best way to get rid of the algae in the tank is to remove it so you can clean it out good. The only other thing could be the transfer pump is bad. I'd go with the plugged screen in the tank.
A temporary way to clear the screen is to remove the fuel cap then get a compressed air hose and nozzle. Remove the primary fuel filter and CAREFULLY...CAREFULLY blow air back thru the fuel line. DON'T use alot of pressure 10-20 psi. This will blow away the gunk on the screen and if the car runs good, that is the problem.

Remove the filler cap before blowing air into the tank, or you risk "balloning" it!.

Check to make sure the hand pump is good, too -- if it is the red knock type the boot inside will evenually fail, and it won't pump fuel, it just squirts on you hand when you pump it. Nasty, and that also means it leaks air while the engine is running. Replace it with the newer plunger type -- permanently sealed, you just push down to operate.

Peter

Monaco,
Try running the car with the fuel filler cap loose or removed. This will eliminate the tank vent.
Tom
'82 SD
'86 SDl

Can't you eliminate the tank screen by reversing the fuel delivery and return line?

Certainly you'd need to fill up the tank with sufficient fuel or else you'd get a false 'out of fuel' problem...but this would allow you to get fuel from the tank and bypass the screen for testing purposes.