1973 220D Losing Prime Overnight - PeachParts Mercedes-Benz Forum

73220downer · #1 06-23-2018, 06:53 PM

First a followup to my last thread about a similar problem: I found a leak on the secondary fuel filter housing and fixing that solved my no-start problem

Yesterday I parked the car at a very slight upward incline for a change and when I went to start it took about 30 seconds of cranking with the accelerator to the floor before it finally fired up. Normally it fires on the first or second crank with only the idle adjust turned up. I know this may sound like a glowplug issue after parking it nose-down for a few hours I glowed it and started on the first crank like it usually does. There are no bubbles in the clear line from the lift pump to the secondary filter even when the engine is revved very fast with the car pointing up, so I would believe that rules out any kind of air leak from the tank to the pump (all fittings are dry also). The only time I do see any bubbles is when I use the hand primer pump (new style Bosch one). Is it possible for air to be getting in here when the engine isn't running, allowing fuel to flow back into the tank? Only other thing I can figure is the overflow valve, but I stretched the spring to 27mm as per the FSM about a year ago... I'll check this again to make sure the ball is seating right and the spring is still intact. There's also a very small leak on the bottom of the IP that very slowly seeps fuel when the engine is on... could that be part of it?

Diseasel300 · #2 06-23-2018, 09:51 PM

If fuel can get out, air can get in. Fix the fuel leak.

73220downer · #3 06-23-2018, 10:59 PM

The leak on the pump has been there since I got the car and I've parked it on steeper grades for longer times without issue but my thinking here may be influenced by the difficulty of the repair.

Short of getting a rebuilt pump what are my options here?

73220downer · #4 06-24-2018, 08:55 PM

Fuel appears to be leaking from the plate on the very bottom of the pump, does anyone know a source for a replacement gasket?

marco5 · #5 06-24-2018, 10:53 PM

Have the pump rebuilt by a professional diesel injection shop. You drive a 45 year old car and it's more then due for it. Diesel leaking means air getting in, as mentioned above.

Diesel911 · #6 06-25-2018, 03:20 PM

Quote:

Originally Posted by 73220downer

Fuel appears to be leaking from the plate on the very bottom of the pump, does anyone know a source for a replacement gasket?

There is the Fuel Injection Pump as an assembly which is often called the Pump but at the same time there is actually a Fuel Supply/Lift Pump attached to the Fuel Injection Pump. 2 Pumps.

What happens if you pump a lot on the hand primer before attempting to start?

You need to locate exactly what is leaking before you know what to fix. That is difficult to do unless the area is cleaned and degreased.

If this is a type of Fuel Injection Pump that is not lubricated from the Engine (no oil feed line to it). You need to add and or remove Lube Oil as per the manual.

On one side of the Fuel Injection pump body above the lube oil level is either a bent tubing or a plug.

As a tiny amount of fuel always passes between the Elements and into the Oil Sump of the Fuel Injection Pump over time the Lube Oil level in the sump rises and comes out of that bent tube and in fact leaks out of that tube.
The mix of lube oil and fue as it sits the lighter portion rises to the top and leaks out first and give you that Fuel smell.

If the Fuel Leak is not related to the hesitation to start then it could be you need to rebuild the Fuel Supply/Lift Pump as there is 2 Valves inside of it that eventually wear.

Diesel911 · #7 06-25-2018, 03:43 PM

Pic of the oil overflow tube that was common on the older Fuel Injection Pumps that contained all of their own lube Oil.

Anyway if Fuel is seeping out of that tube it is possible for you to think you have an exterior fuel leak.

Note that there is a pan on the bottom of the Fuel Injection Pump or expansion plugs.

If it has the Pan and it was leaking it should be leaking Lube Oil unless oil and fuel mixed inside of the Fuel Injection Pump.

Note that as the Elements wear (pluhgers and barrels) more fuel leaks past them and mixes with the Oil. You only see obvious leakage on Fuel Injection Pumps that have had extemsive hours of use on them or foregin material has gotten inside and scratched up the surfaces.

One of the itmes that can pass through filters is Water. If water gets in with the Fuel Inside of the Fuel Injection Pump Water has no lubrucating ability to it and can cause scratches and sometimes even sitting overnight inside of a Fuel Injection Pump Water can cause tiny amouts of rust that scratch up the insides of the elements.

marco5 · #8 06-25-2018, 10:26 PM

good posts diesel911. So he actually has to change the oil on the W115 diesel injection pump? I bet many ignore this.

73220downer · #9 06-26-2018, 02:21 PM

I've changed the oil in the pump recently, it was still pretty clean and didn't seem to have much diesel in it. I'm not sure the bottom plate is actually leaking itself, but fuel seem to accumulate there.

Diesel911 · #10 06-26-2018, 02:26 PM

Quote:

Originally Posted by marco5

good posts diesel911. So he actually has to change the oil on the W115 diesel injection pump? I bet many ignore this.

If the Fuel Injection Pump has a removable cap/breather on top (those caps are not always red or plastic) of it you can resonably be sure you are operationg only on the Oil inside of the Pump. And as I said that Oil eventualy gets contaminated with Fuel.

There is threads with instructions on how to change the Oil. One of the methods is you get something like one of those Turkey Baster squeeze bulb type syrings and attach a thin tube to it and stick that inside and suck out the old Oil and refill it.

Back around 1975 when I worked in a Fuel Injection Shop I was told by my Boss to put 40wt Oil in them and to be especially sure that the Fuel Injections Pumps went out properly filled with Oil before they left the shop. That is partly because many did not know you needed to put Oil in them.

It was common back at that time for the older Inline Fuel Injection Pumps to have their own Oil Sump.

rmasteller · #11 06-26-2018, 07:36 PM

This is also true for many Bosch pumps for gas engines. My w113 230SL has its own oil reservoir and "dip stick". That's just a small post on the screw-on cap. When these pumps wear, gas gets into the oil - bad news!