1972 250C No crank, no start

[billyjobs]

Just got this nice mercedes 250C project I'm working on. Bought her for an insane $500 price. The car was parked for about 3 years. Original owner reported that everything was working. It was originally cranking when I saw it. It was then towed over to me and now it is not cranking.

So far I've washed it, as you can see in the photo. And I've started to clean the engine removing oil build ups and dust. The car suddenly does not crank.

I've also changed the engine oil and all the 12 fuses. There are other fuses compartments there as well, but I'm not sure what they are.

I've swapped out the battery. All the lights are nice and bright. But once I try to crank, there is silence.

I've checked to make sure that the starter is going to the positive terminal, and chassis to the negative on the battery.

Could the starter or solenoid have went out? Is there anything else that could be the culprit?

Any troubleshooting advice would be great!

Thanks!

[engatwork]

Not in reference to the no crank issue you are, in all likelyhood going to have to go through 100% of the fuel system and clean and/or replace everything that has ever had fuel in it. I have just gone through something real similar in a 84 380SL. You can get a good idea of what the inside of the fuel tank looks like by pulling the fuel strainer. Plan on pulling, cleaning and re-lining the fuel tank if the strainer is blinded over with rust and debris.

[kraakevik]

Make sure the woven copper grounding strap to the starter has continuity and freshly cleaned connections--this tends to corrode, especially when the car is not used



Tim Kraakevik
kraakevik@voyager.net

[BWhitmore]

Not starting now may be an advantage as the fuel system really needs to be checked before starting the car. Serious and expensive problems will occur if started befote checking the fuel system. The braided ground strap is a good place to check for the non crank issue. Also check the neutral safety switch by moving the shift lever to neutral and moving the lever back and forth.

[billyjobs]

Thanks you guys.

I was able to get the car to crank. Very stupid issue. The gear wasn't fully on park. Wow.

The issue I'm having now is the fuel pump. When does the fuel pump pull in the fuel?
If I push the carburetor control rod should I have seen fuel? I've also looked at the fuel filter and it looks dry. I took out the fuel filter and tried starting the car to see if fuel will spit out of the pump, no fuel. I've changed a new fuel pump and with no success of being able to see the fuel get to the carburetors.

My question is what is the sequence of fuel when you step on the gas? Is there some kind of relay or fuse that could be preventing the pump to not work?

Thanks

[Frank Reiner]

bj:

Re-read posts #2 & 4 above.

[billyjobs]

Originally Posted by Frank Reiner

bj:

Re-read posts #2 & 4 above.

Yes but the thing is, I'm not getting a pumping action from the mechanical fuel pump. Right at the pump inlet and out.

So if the fuel pump is pumping, I can then start to back trace to the tank and see if something else is wrong. If fuel is not reaching the pump.

It's a new pump and I was able to feel the pump if I pressed it again something.

When does the fuel pump, actually pump? when the gas is pressed?

[Dr. Benz]

So pour a small amount of fuel into the carbs. If it barks a few times at least you will know that it should run. While its turning over via the engine, you should have a much higher cranking speed and that just might get the fuel pump to pull fuel up from the tank.
If the tank is empty or nearly so, it probably won't pull fuel that far. You could always hook your fuel line at the pump to a small can of fuel and see if it will fill the carbs. Be careful, open fuel can catch fire easily.

[billyjobs]

Originally Posted by Dr. Benz

So pour a small amount of fuel into the carbs. If it barks a few times at least you will know that it should run. While its turning over via the engine, you should have a much higher cranking speed and that just might get the fuel pump to pull fuel up from the tank.
If the tank is empty or nearly so, it probably won't pull fuel that far. You could always hook your fuel line at the pump to a small can of fuel and see if it will fill the carbs. Be careful, open fuel can catch fire easily.

Yes ok I will try that, as soon as I get my spark plugs in the mail. For now, is the fuel pump suppose to work when the starter cranks? For example, say I remove the inlet and outlet from fuel pump and crank the car, should I feel the air going in and air going out on the fuel pump?

Right now, I would put my finger at the inlet and outlet on the fuel pump and have my neighbor crank it, and I feel no pressure of it pulling or pushing.

Thanks

[JeffreyNMemphis]

Welcome Billyjobs!

You are in the right place to get information and resources to do these maintain, repair and restore tasks.

The mechanical fuel pump on my car was not working. The diaphragm failed. Fuel got into the crankcase. I could smell gas on the spark plugs.

I bypassed the mechanical pump with an electric pump and carbs got fuel and the engine ran properly.

Your fuel tank has a fuel strainer that could be clogged. Our host sells the fuel strainer for about $20.00. It is very possible for a 40 year old gas tank to be full of trash and clog the fuel strainer.

Have you checked all of the fuel lines to make sure they are in good condition? It is a fire hazard to have gas burst through an old dry rotted line while the car is running. If you disconnect the fuel line at the tank and nothing comes out, you have a clogged strainer. Does the fuel gauge work? If not, that would indicate gas turning to varnish and freezing up the lever on the sending unit.

[billyjobs]

Originally Posted by JeffreyNMemphis

Welcome Billyjobs!

You are in the right place to get information and resources to do these maintain, repair and restore tasks.

The mechanical fuel pump on my car was not working. The diaphragm failed. Fuel got into the crankcase. I could smell gas on the spark plugs.

I bypassed the mechanical pump with an electric pump and carbs got fuel and the engine ran properly.

Your fuel tank has a fuel strainer that could be clogged. Our host sells the fuel strainer for about $20.00. It is very possible for a 40 year old gas tank to be full of trash and clog the fuel strainer.

Have you checked all of the fuel lines to make sure they are in good condition? It is a fire hazard to have gas burst through an old dry rotted line while the car is running. If you disconnect the fuel line at the tank and nothing comes out, you have a clogged strainer. Does the fuel gauge work? If not, that would indicate gas turning to varnish and freezing up the lever on the sending unit.

Hi Jeffrey,

Today I checked the fuel pump.

I'm not able to get gas to the fuel pump.

I have disconnected both inlet and outlet and have had someone crank the car to feel if there is pressure coming from either side. This is brand new mechanical fuel pump. Neither side is giving pressure.
So I haven't yet checked whether the fuel lines were clogged. Yes the gas gauge is working and showing fuel level.

Should the pump be working during the crank?

What else could be wrong?

What electrical pump can be used to substitute? for 72 250c also was there a oil pressure switch installed too? Was it installed near the mechanical fuel pump or was in on the line somewhere under the car?


Thanks

[engatwork]

Follow the hose from the fuel pump to the gas tank. Get the correct sized socket and remove the part that that hose end screws in to. Be ready for a fuel shower. Let us know what the sceen looks like.

[billyjobs]

Originally Posted by engatwork

Follow the hose from the fuel pump to the gas tank. Get the correct sized socket and remove the part that that hose end screws in to. Be ready for a fuel shower. Let us know what the sceen looks like.

What is the 3rd hose?

1. There one that goes from "compensating tank" screwed to the crankcase.
2. There that one that goes from gas tank to fuel pump
3. Then there is a 3rd one from gas tank that goes directly to the carbs.

Really appreciate it guys, super noob to this vintage Mercedes and also my first carburetor project.

[BWhitmore]

Billyjobs- unfortunately the methods you are using is likely to lead to a real disaster (fire) or serious engine damage. Your questions lead me to believe that you may not have had a lot of experience working on gasoline engines in cars that have not run for an extended period of time. Once again - the entire fuel system (tank, tank strainer, fuel lines, fuel filters, and possibly carburetors) need to be checked before you start the engine. If you do decide to proceed on your current process, have a good fire extinguisher nearby.

[JeffreyNMemphis]

Hello Billyjobs,

Your fuel tank will have one outbound fuel house and one inbound. Your carburetor has an inbound that fills the carburetors and then excess fuel is returned to the tank. If fuel is not getting to the fuel pump it could be a few things.

Fuel pump has no sucking power. You can get a 3psi electric fuel pump from local auto parts store as a temporary solution. If you want to keep the original mechanical type it can be rebuilt or replaced.

Fuel tank empty. If you put more than five gallons of fresh fuel then move to next possible cause.

Fuel tank clogged. Three bolts hold the tank in. There is also a plug connected to your fuel level sender accessible from the trunk under mat and plastic cap to disconnect. There will also be two small hoses connected to he neck of the tank that ventilate to be disconnected. It is best to use a transfer pump to siphon out as much fuel as possible before disconnecting fuel lines and have a deep drain pan under the hoses when you removed hose clamps. As mentioned already be careful and make sure your workspace is well ventilated and there are no ignite sources nearby. Fire extinguisher close by is a great idea any time you are working on combustion engines or using solvents or playing with matches.

Cleaning the tank on a forty year old car is a common task that you can do yourself. POR15 tank renewal kit is less than $100.00. Look it up on YouTube for more information. You may prefer to have to have a professional shop clean your tank but ask if they coat it so you don't have rust issuse in the future.

Keep us informed. Your before and after pictures are inspiring!

Jeffrey