W124 230te stalling issues

[twothirty]

Good evening all. This is my first post here and I'm seeking a bit of advice.

I have a 1992 W124 230te which I have had for about 6 months. It's a lovely ride but has always had a buzzing noise in the boot which I assume is the fuel pump. I took it on a run today and drove 60 miles (motorway) without a problem but on the way back it started to hesitate and lose power. I slowed down and tried to continue on but it was very jumpy like it wanted to stall but would pick up again. When pulled over it would idle without issue, good oil pressure, temp gauge normal but same issues when pulling off again. I stopped for 20 mins and started off again and was ok for about 2 miles until the same happened again so I had to get it recovered. The car had the same issue in traffic about 3 weeks ago. We managed to get it home and was fine the next day and has been fine until todays run.

I suspect it is a fuel problem but am not sure what to check. The fuel pump is still buzzing in the boot but could this finally be on the way or would it work until it fails (i.e does performance of the pump degrade or will it just stop working)? It has been serviced recently and I have changed the spark plugs within the last month. Any advice would be appreciated. Many thanks.

 

[drabux]

My first day also.

The buzzing noise is probably the petrol pump. They tend to increase with noise as they age.

I've had the engine go into limp home mode - if that is what you experienced - a number of times with Saabs when, on occasion, given full throttle. Sometimes it happened because I over revved but at other times it was not so clear. I certainly wouldn't worry about it unless it happens again. You could always hook up a OBD scanner to the OBD port to look for error codes.

All the best,

Alanb

 

[krimat2005]

no limp mode on these engines, sorry. fuel pump will make noise, it's a good thing cos if it's not making noise then it' not working. but i can't help more.

 

[grober]

On estate W124s there are 2 fuel pumps- a primer pump up close to the tank and a 2nd one in the conventional position under a black plastic cover in front of the offside rear drive shaft/suspension. The primer pump is there to prevent cavitation in the main pump due to fuel starvation. The primer pump is often overlooked- some folks don't know it even exists! It sounds to me as if the primer pump has failed some time ago and the main pump has been running noisy- its actually cooled by the fuel flowing through it. My guess is its now on its way out and starting to overheat after a short time.
Another thing that causes fuel starvation/ pump overload is a partly blocked fuel filter- when was it changed last?

 

[twothirty]

Thanks for the replies.

Not sure when the fuel filter was changed (and not really sure where it is so I'll check my Haynes manual). Do you think the motorway miles may have disturbed some muck from the tank? If I replace the fuel pump(s) are they both the same and is it possible to fit on the driveway or will it need to go to the garage? Would be nice to get rid of the buzzing.

Thanks all.

 

[grober]

First thing to check is the fuel filter. They are about £30 from ECP and not much more from MB quote your chassis no when ordering!
Hengst Mercedes Benz | Euro Car Parts UK
Its located next to the main fuel pump under that cover I mentioned. item 38 in the picture It would appear from the parts diagram the pumps are the same part but I would try to test them first to see if either was at fault before buying as they are expensive. Working under the car on the fuel system can be very unpleasant- dangerous even ---- with spilt fuel and fumes so unless you know what you are doing have good access underneath and have the right fuel pipe clamps etc leave it to the garage.
There is a outlet filter in the tank itself which can get blocked and this might be getting worse with time I suppose- don't think the motorway trip would have done anything unless you let the fuel level down very low.


The other well known problem in this area is a faulty fuel pump relay- lots of posts on here about that.

 

[Stratman]

I had an old Daimler V8 (Jag MkII shape) with very similar symptoms. It ran OK under light loads, but on the motorway, where there is a higher continuous fuel flow, it would misfire and hesitate.

It turned out to be a blocked tank vent pipe, a rubber pipe that exited in the wheel well and whose end was full of mud. It was preventing air entering the tank to replace the fuel as it was being used. The poor old pump was straining against an ever increasig vacuum and failed to deliver sufficient fuel at higher revs.

 

[twothirty]

Great advice, thank you. I took it round the block today and seems ok. It seems a strange symptom as I took it all the way to Cornwall and back in Feb without a problem. I will try the fuel filter as the first job and if it's not better I'll get the garage to swap out the pump(s). Is it a time consuming job or just fiddly? Thanks again.

 

[grober]

Changing the main fuel filter would be a good idea. Its possible to renew the tank outlet filter/ strainer also--- it screws into the tank with an O ring seal but can be a bit of a fiddle due to access and corrosion. Your garage man should be able to test the output of the primer pump at the same time to see if its working. Next stop would possibly be the fuel pump relay. Last would be the fuel pumps since they are expensive. You can often pick up a good main fuel pump/filter/accumulator assembly at a breakers. Its hung from flexible mounts as a complete assembly under that black plastic cover I talked about. You just need to disconnect the fuel supply pipe from the tank and the outlet pipe leading to the engine- easy. The estate primer pump is a bit more difficult to get at

 

[twothirty]

So, no more stalling issues even on an 80 mile run but is getting harder to start from cold. It needs a good push on the throttle whilst turning over and some encouragement and will then idle (a bit low?) at about 700rpm. It had new plugs about 2 months ago but could it need a new distributor cap and leads?

Nevertheless, it seems to run ok once driving but is getting very hot (bonnet almost too hot to touch and steam when it rains even after a 5 mile journey with light traffic). The temp gauge sits at about 90 so not sure what to check - water pump, cooling fan? Thanks for any help with this.