Advice needed 1980 380E

[Kerabo]

Well the rubber connection pipe seems to be ok.
As it only pumps from the tank when cranking it’s a bit hard to check the flow so I connected a wire from the pump and to the battery. With the feed to the CIS removed it pumps it’s mainly air and just a little fuel when I connect the pump.
The strange this is the cars owner had drained the tank and put back in 15L of clean fuel.
I would have thought 15L would have been enough to give a supply. Looking at spec reserve is about 12L?
Just a thought but is the reserve a manual switch or does it use it automatically ?
Thanks

 

[Pontoneer]

Well the rubber connection pipe seems to be ok.
As it only pumps from the tank when cranking it’s a bit hard to check the flow so I connected a wire from the pump and to the battery. With the feed to the CIS removed it pumps it’s mainly air and just a little fuel when I connect the pump.
The strange this is the cars owner had drained the tank and put back in 15L of clean fuel.
I would have thought 15L would have been enough to give a supply. Looking at spec reserve is about 12L?
Just a thought but is the reserve a manual switch or does it use it automatically ?
Thanks

The reserve is just a warning light which comes on when the fuel level reaches a certain level , there is a contact within the sender unit but there is no separate feed pipe or tap to be changed over as was the case , for example , on my Ponton .

When the tank was drained , how was this done ? Was the fuel siphoned out from the filler neck or through the hole for the sender unit ; or was the strainer removed from the bottom of the tank ? If the fuel strainer was not removed from the bottom of the tank and either cleaned , or ideally replaced , then it could well be blocked . I’d also wonder if the feed hose coming out of the bottom of the tank might have a blockage ?

The presence of air sounds to me more like a leak in one of the pipes as it is hard to imagine where it is coming from .

I’m now wondering about the components in the fuel pump pack under the car : the pump itself , the injection fuel filter and the fuel accumulator ?

This is puzzling .

 

[Kerabo]

The reserve is just a warning light which comes on when the fuel level reaches a certain level , there is a contact within the sender unit but there is no separate feed pipe or tap to be changed over as was the case , for example , on my Ponton .

When the tank was drained , how was this done ? Was the fuel siphoned out from the filler neck or through the hole for the sender unit ; or was the strainer removed from the bottom of the tank ? If the fuel strainer was not removed from the bottom of the tank and either cleaned , or ideally replaced , then it could well be blocked . I’d also wonder if the feed hose coming out of the bottom of the tank might have a blockage ?

The presence of air sounds to me more like a leak in one of the pipes as it is hard to imagine where it is coming from .

I’m now wondering about the components in the fuel pump pack under the car : the pump itself , the injection fuel filter and the fuel accumulator ?

This is puzzling .

I will ask what and how these things were done and get back.
Need to get it jacked up to get under
Thank you

 

[Kerabo]

Ok
We added more fuel and we have clean fuel and plenty of it at the CIS unit.
But it still don’t start.
With the pipe removed from the CIS head and a permanent feed to the tank pump fuel comes out from the injector pipe hole.
With my finger over the hole and cranking there is little pressure. I would guess not more than 10 psi.
So that can’t be enough to open the injector and spray can it ? I think I read they are 3 or 4 Bar?

Please just clarify this for me. The main pump is quiet high pressure but it has to be boosted inside of the CSI unit? So what gives the extra pressure as there are no electrical connections I can see and nothing mechanical to move anything.
I guess it’s time to look inside of the main head on the unit ?

Thanks for your input

 

[Bellow]

Check what was previously considered as a last chance filter. So far you have fuel at pressure up to the metering unit - but no evidence of it entering the metering unit.

Has the above been done?

 

[carat 3.6]

Please just clarify this for me. The main pump is quiet high pressure but it has to be boosted inside of the CSI unit? So what gives the extra pressure as there are no electrical connections I can see and nothing mechanical to move anything.
I guess it’s time to look inside of the main head on the unit ?

Thanks for your input

It is only the fuel pumps at the rear providing pressure, it isnt boosted inside the cis unit or anywhere else.

Never open the cis metering head unless you have the tools and parts to put it back together, once the membrane inside has been disturbed it cannot be reused.

Your issue is either:

A. As Bellow has suggested, you have a blocked gauze filter in one of the fittings at the metering head.

B. There isnt enough fuel coming from the rear of the car.

What I can tell you is that with the inlet fuel line removed from the metering head and the pumps running, it should be able to shoot fuel at least 8ft away. Not a very technical explanation but that's the sort of flow you should have going into the metering head.

 

[Kerabo]

Has the above been done

I have a good supply to the injection unit but will get it jacked up and check all filters.

He changed the pump himself as someone tested it and said it was no good but he says he changed for a pump with the same numbers.
I can only see one fuel pump but something has to increase the fuel pressure on route to the injection unit? If I can stop the flow with my finger it can’t be enough to inject?

Thanks

 

[alabbasi]

I've not read all the posts so I may be repeating what was already suggested. If the car is firing off for a second but not running it could be one of two things.

1) The injectors are clogged and it's just running off the cold start injector. This is common when you have fuel sitting in the fuel distributor or injector lines. The video below describes how to clean the injectors.
2) One of the ballast resistors have failed. There are two, one white and one blue. I can't remember which one serves which purpose but one is used to start the car and the other to keep the engine running. You'll typically seem them mounted on the inner wing close to the coil. Inspect them to make sure they're not damaged.

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

 

[Kerabo]

I've not read all the posts so I may be repeating what was already suggested. If the car is firing off for a second but not running it could be one of two things.

1) The injectors are clogged and it's just running off the cold start injector. This is common when you have fuel sitting in the fuel distributor or injector lines. The video below describes how to clean the injectors.
2) One of the ballast resistors have failed. There are two, one white and one blue. I can't remember which one serves which purpose but one is used to start the car and the other to keep the engine running. You'll typically seem them mounted on the inner wing close to the coil. Inspect them to make sure they're not damaged.

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

We have kept it running buy squirting gas easy start. I don’t feel it’s electrical but I am still learning on this one.
Is that the ballast resistor you mean ?
I removed the injectors and blew through with an airline and all sprayed what was in them in a decent pattern. I don’t have a tester to test them any other way.
I am feeling there is not enough pressure to open the injectors.
There are lots of parts to this I don’t understand yet.

 

[Bellow]

I have a good supply to the injection unit

To, but not into.
Pull what we think is the last chance filter and check it. There is no progress until it is known that fuel is entering the metering unit at the required pressure.

 

[Kerabo]

To, but not into.
Pull what we think is the last chance filter and check it. There is no progress until it is known that fuel is entering the metering unit at the required pressure.

This is as it says the last in line fuel filter?

 

[alabbasi]

Take the the fuel line that feeds the fuel distributor (as described in the above video) and direct it to a bottle then jump the fuel pump relay so that it runs. If you're getting about a liter for fuel in 30 seconds. The problem is in between that hose and the injectors.

 

[Bellow]

This is as it says the last in line fuel filter?

I don't know. And no one ever will until you spend the 5 minutes to check it out.

 

[DSM10000]

This is as it says the last in line fuel filter?

I would recommend that you listen to Bellow, Pontonerr and Carat3.6 et al and follow all of their suggestions in a logical fashion.

They all have significant and extensive knowledge

 

[Pontoneer]

You mentioned getting fuel up when the feed pipe is disconnected , but not at high pressure . I would suggest starting at the beginning ( the fuel tank ) and working your way forward ( following the flow of the fuel ) one step at a time .

I know you said the tank was drained , but you don't know how . If the tank was siphoned out rather than being drained from the bottom , there could be all sorts of crud in the bottom of the tank , possibly blocking the strainer inside the tank , which is there to prevent rust or other bits and pieces getting into the fuel line . If it hasn't been done , I would strongly suggest replacing the strainer .

The last W123 was made around 1985 or 1986 ; C registration was the crossover with the W124 series , so any W123 will be 40 years old , and the first ones came out in 1976 , so the car could even be knocking on the door of 50 years old ?

When I acquired a W124 diesel saloon a number of years ago , I gave it a good overhaul , and part of that was draining the tank and replacing the strainer as I knew the car had stood for about three years before I got it . Although that car was Diesel ( which brings its own problems because a form of algae will grow in a Diesel tank left standing and can clog up the lines , not an issue in petrol cars ) you can still have all sort of cr@p in a petrol tank , including water contamination and corrosion caused by this .

Here are some pictures of the outlet pipes from the tank on the W124 ( W123 won't be that different ) , the strainer ( note the state of the old one compared to the new one ; the same strainer fits a vast range of cars , and while I can't remember the cost , it wasn't that expensive or I certainly would remember ) . You also mentioned the fuel pump ( or one of them ) being changed ; here also there are a number of fragile and VERY expensive pipes , some with banjo couplings , which can easily crack ; if any of these are damaged , or just not sealed properly , they can draw air and cause poor fuel supply .





You can clampthe rubber fuel hose where it exits the tank , then undo the hose clip to drain the tank into a fuel can before removing the strainer ; again if little flows out , there will be a blockage in the tank , but the photos below will show why it is well worth checking this simple item .






Now , here are the SCARY ones ! If the strainer in your car is even HALF as bad as this one , you will have fuel supply problems , no matter how hard your fuel pump sucks . Oh , and don't over look the vent in the fuel filler cap , which has to let air in as fuel is drawn out - if this is blocked you will get poor fuel flow , plus the tank will slowly implode as it is constantly under suction - you can easily check for this simply by trying to start the car with the fuel cap removed .





I will post more below

 

[Pontoneer]

New parts going in . Note the part number on the bottom of the new tank strainer begins with 123 ; that shows it was originally used on the W123 series , but was the part supplied by my dealer against the chassis no for my W124 . I also replaced the rubber pipe as it would have been silly not to .





You need quite a large socket to remove the strainer from the tank ; I managed to buy one in Halfords .

 

[Pontoneer]

I have a good supply to the injection unit but will get it jacked up and check all filters.

He changed the pump himself as someone tested it and said it was no good but he says he changed for a pump with the same numbers.
I can only see one fuel pump but something has to increase the fuel pressure on route to the injection unit? If I can stop the flow with my finger it can’t be enough to inject?

Thanks

Some cars have one pump , others have two . I'd have thought a 280 ( a fairly thirsty car ; I've had lots of cars with the M110 engine and typically these are circa 20 mpg cars , less if you are lead footed , but even Miss Daisy would struggle to see 25 mpg from one ! ) .

Sometimes you have two pumps next to each other in the pack , but most often the pipe coming out of the tank goes into a first pump hidden up near the diff , then the output from that goes down to the pack with the second pump , filter and accumulator . It can be quite common for one pump to fail ( often due to rusted electrical connections ) and for the car to then run poorly on the second pump .

You should hear the pumps prime when you just turn the ignition on without trying to start the car , I've had numerous W123s ( 280E , 280CE , 280TE ) , plus W114 280E , W116 280SE , W126 280SE and they ALL ran the pumps for a second or so on just turning on the ignition , so this SHOULD happen . If you aren't getting this , besides faulty pumps , there could be an electrical problem with the power supply to the pumps . If you don't hear the pumps prime , I'd attach a meter to the pump terminals and see if they are getting 12V when you turn the ignition on / try to crank .

As Carat has suggested , take a hose from the end of the feed pipe in the engine compartment and into a fuel can or large glass bottle and see what is being pumped up whilst trying to crank .

Really you need to go through the system logically and one step at a time .

 

[alabbasi]

Some cars have one pump , others have two . I'd have thought a 280 ( a fairly thirsty car ; I've had lots of cars with the M110 engine and typically these are circa 20 mpg cars , less if you are lead footed , but even Miss Daisy would struggle to see 25 mpg from one ! ) .

All CIS cars have a single pump (even the 450SEL 6.9). The simple fuel delivery test is to jump the relay and direct the fuel to a 2 liter bottle. If you're able to fill the bottle with 1 liter of fuel in 30 second. There's no fuel delivery issue and it's likely that the FD is blocked. In some cases, you can press on the air flap to get the fuel pump going instead of jumping the relay.

In any case, that's not why I posted. I just wanted to let you now how glad I am for living in Texas after seeing the underside of your car

 

[carat 3.6]

All CIS cars have a single pump (even the 450SEL 6.9).

In any case, that's not why I posted. I just wanted to let you now how glad I am for living in Texas after seeing the underside of your car

Not necessarily, any UK Mercedes with CIS after 1984 generally has twin pumps. Some models had it earlier, some later, although it could be a USA vs UK market difference.

I do envy the climate you guys have the other side of the pond, I have friends in Arizona who are shocked at how bad some UK cars get underneath.

 

[Pontoneer]

Not necessarily, any UK Mercedes with CIS after 1984 generally has twin pumps. Some models had it earlier, some later, although it could be a USA vs UK market difference.

I do envy the climate you guys have the other side of the pond, I have friends in Arizona who are shocked at how bad some UK cars get underneath.

I was going to say that since I'm pretty certain my 280s had twin pumps , also remember posting with a US guy re his W126 500SEL bemused that his only had one downpipe each side , while mine had quad downpipes as standard ; there are a lot of market variations .

But yes , Al is correct , we do get underbody rust as standard equipment ! Though having said that , my current S124 is nothing like that and largely rust free ; I think the Diesel one had spent most of its life beside the sea , plus it was a late Indian assembled one , on an S reg , and they possibly had less rust protection than ones made for the European market . On the upside the Indian cars all came with uprated suspension , metal engine undertray , aircon and leather , plus a generally decent spec . The E250D with 5 speed manual box was also surprisingly economical for a normally aspirated Diesel and returned 50 mpg all day long .