300TE possible fuel starvation.

[VmanC]

Hi all!

Just got my W124 300TE running after a 3 year layup but have a couple of problems I'm a little stuck with, hope someone can point me in the right direction .

1. First trip of about 70miles to the mot station (I've moved house but not car storage address) was fine, but after collecting it from mot garage I've experienced a running problem. Power will drop away to nothing when I try to accelerate, this developed after 20 miles or so but once it started it became gradually worse, in the end I was finishing the trip by stopping for ten minutes, then driving for about one minute when it would cut out again.
I'm thinking it's a fuel supply problem, either dirt in the system or fuel pump issues, any other thoughts please?

2. Also, the abs warning light is on, always has been since I bought it, this being the main issue for the mot. Are there any common reasons for this, if not, what is the procedure for testing the system?

3. I also have total failure of the central locking, I guess the system doesn't like not being used as my other two Mercs ( 300se 260e ) have the same problem after not being used for a couple of years.

Advice on any of the above would be much appreciated .

 

[BlackC55]

Because you have an ABS light on too I would suspect a faulty OVP relay.

 

[VmanC]

Thanks for the quick reply.

What is an OVP relay? and where on the car is it situated?

You say 'too', does this mean that two of my problems are related?

Thanks in advance, Vernon.

P.s. Just remembered, my cold start system has never worked since I've owned the car, could this be another clue or a totally separate problem?

 

[bolide]

Let me google that for you

Nick Froome
the independent Mercedes Estate specialists

 

[GP801]

Behind the battery - the relay with a fuse on top. It is partly responsible for the fuel pump working and many other systems on the 124. They can be repaired but a new one for ours was £65 from the dealer.

 

[BlackC55]

Thanks for the quick reply.

What is an OVP relay? and where on the car is it situated?

You say 'too', does this mean that two of my problems are related?

Thanks in advance, Vernon.

P.s. Just remembered, my cold start system has never worked since I've owned the car, could this be another clue or a totally separate problem?

The OVP fault can cause rough running and ABS warning lighs too.

 

[VmanC]

Behind the battery - the relay with a fuse on top. It is partly responsible for the fuel pump working and many other systems on the 124. They can be repaired but a new one for ours was £65 from the dealer.

Thanks for that. I have a 260E so will swap the relays and see if it makes any difference.

Thanks too to the specialists, I may be calling on your services in the future, good to know you're out there .

 

[balge]

Hi
if there's no courtesy lights as well, the central locking could be the fuse, it's 'C'...it happened to me!... fuse looked ok, but a quick twist in the seating got everything up again...quickly followed by a set of copper fuses off Ebay!

Don't forget to check the fuse on top of the OVP!


cheers!

 

[VmanC]

Hi
if there's no courtesy lights as well, the central locking could be the fuse, it's 'C'...it happened to me!... fuse looked ok, but a quick twist in the seating got everything up again...quickly followed by a set of copper fuses off Ebay!

Don't forget to check the fuse on top of the OVP!


cheers!

Thanks for that, the interior lights don't work as it happens so you could have hit upon it .
The car is kept about 70 miles away at the moment so I won't be able to check these things till I'm back with it early next week, but I will report back on my findings.

 

[VmanC]

Some success

I was able to check the suggestions today and am pleased to say, the abs light is now going out. Thank you again to those who pointed me in the direction of the OVP relay, the fuse on the top had indeed blown. After this was replaced, not only did the abs light work, but also the cold starting worked for the first time in my ownership.
I did take it for a short run and found that I had full power under acceleration, this is not conclusive however, as the fuel starvation problem didn't materialise until after 20 miles or so. It is ready for re-testing now so the 70 mile trip back to the garage on Thursday will tell me if replacing the blown fuse has cured the fueling problem too.

As for the central locking, well that still won't work despite there being a problem with fuse C. After cleaning the fuse the interior lights started working again, so any suggestions for what to check next would be much appreciated.

 

[GP801]

Can you hear the pump whirring for the central locking? If the pump is working then its likely there is a vaccum leak somewhere in the pipes. If pump not working then either the pump itself or the electric supply.

 

[VmanC]

Can you hear the pump whirring for the central locking? If the pump is working then its likely there is a vaccum leak somewhere in the pipes. If pump not working then either the pump itself or the electric supply.

Thanks GP, I can't hear anything but when I operate the drivers lock but I can see the button on the back door twitch slightly, could this be a clue?

 

[GP801]

Thanks GP, I can't hear anything but when I operate the drivers lock but I can see the button on the back door twitch slightly, could this be a clue?

It would suggest the pump is probably working. I suspect there is a vacuum leak somewhere. I think the pump is under the rear seat wrapped in some foam. Cant remember exactly. You could try putting a 12v supply across it to confirm it is working.

 

[balge]

The vac pump is indeed under the rear seat, drivers side iirc, as mentioned, all tucked up in a foam box.

Isn't the headlight adjuster run off the vacuum too? Does that work ? (hmm, don't think mine works actually, locks work ok though...)

What year is yours, wondering what ignition, there is a vacuum connection on some?

cheers!

 

[VmanC]

The vac pump is indeed under the rear seat, drivers side iirc, as mentioned, all tucked up in a foam box.

Isn't the headlight adjuster run off the vacuum too? Does that work ? (hmm, don't think mine works actually, locks work ok though...)

What year is yours, wondering what ignition, there is a vacuum connection on some?

cheers!

Mine's a 1988 model. Will uncover the pump asap and have a look. Thanks again

 

[VmanC]

update

Has now passed its mot, is taxed and on the road so I can drive it more to try and trace the suspect fuel fault.
Once again the 70 mile trip was fine for the first half but then the fault materialised. When I tried to accelerate with any more than a tickle of the accelerator she dies, and starts to shunt/kangaroo. This gets worse as I progress, at first I can keep going using a very light throttle, but in the end it will die away and sometimes stall. If I then turn the ign. off and wait a minute I can continue with everything fine, but the fault will quickly return. The longer I leave the engine off the longer it takes for the fault to return.

It seems to me like something is getting hot, maybe a fuel pump or relay , and then stopping working. I have swapped the ovp relay and one of the pumps, the one that sits by the diff on its own, with one from my 260E, but it made no difference. I guess I should try the other pump too, they do get very noisy.

Could anyone tell me which relay is for the fuel pumps, or suggest another component it would be worth trying?

 

[GP801]

Fuel pump relay is in the box behind the fuse box. I would be surprised if this were the problem as normally when this fails the car just wont start because the pump does not run at all.
I think its time to get an expert to have a look. Dont wish to worry you but when our 280 did something a little like this with an intermittent misfire it turned out to be the ECU that had failed. Not sure if the older 124s have the degrading wiring loom problem but it might be worth checking aswell.

 

[219]

The fuel pump relay may well be the culprit - it is the one with 'Kickdown' printed on top - you need to open it up and inspect the solder joints at the edge of the board in particular .

These joints often go 'dry' in old age and you may see breaks in the solder around the pins - these can suffer from heat over a long journey and go open circuit .

it is 5 minutes work with a soldering iron to resolder and make good as new again .

Because of where they are , fuel pumps can become covered in crud and can corrode away , the electrical contacts also corrode and this can cause problems - have you changed the fuel filter ? These can become blocked , restricting fuel flow .

The other well known problem with the M103 is that the distributor caps are very short lived ; the lowest allen bolt at the bottom is a royal pain to get at , but these can also cause all sorts of intermittent running problems and is worth looking at .

Engine wiring looms are not a problem on this model .

 

[VmanC]

Fuel pump relay is in the box behind the fuse box. I would be surprised if this were the problem as normally when this fails the car just wont start because the pump does not run at all.
I think its time to get an expert to have a look. Dont wish to worry you but when our 280 did something a little like this with an intermittent misfire it turned out to be the ECU that had failed. Not sure if the older 124s have the degrading wiring loom problem but it might be worth checking aswell.

Thanks again GP . I do hope it's not ECU related as the two I have to swap with are from my 260E and a 300SE I'm also scrapping, not sure if either of these will do

 

[VmanC]

The fuel pump relay may well be the culprit - it is the one with 'Kickdown' printed on top - you need to open it up and inspect the solder joints at the edge of the board in particular .

These joints often go 'dry' in old age and you may see breaks in the solder around the pins - these can suffer from heat over a long journey and go open circuit .

it is 5 minutes work with a soldering iron to resolder and make good as new again .

Because of where they are , fuel pumps can become covered in crud and can corrode away , the electrical contacts also corrode and this can cause problems - have you changed the fuel filter ? These can become blocked , restricting fuel flow .

The other well known problem with the M103 is that the distributor caps are very short lived ; the lowest allen bolt at the bottom is a royal pain to get at , but these can also cause all sorts of intermittent running problems and is worth looking at .

Engine wiring looms are not a problem on this model .

Thank you Derek, these are the types of things I'm thinking could/hope are wrong ( cheap and easy ). I'm away for the next week but will check on these Items when I get back.

P.S. Your black SE looks identical to mine .