Change fuel filter and see what happens. (Low cost). This should be done as part of routine maintenance at say 50k miles.
If no change then suspect relay next.
Stuart.

 

Thanks for your help guys, have concluded that the problem lies within the fuelpump/filter area. Had the car jacked up on the rear end and it started! Lowered the car and it went fine but later when I tried to start it nothing again. Went under and tapped on the pump/filter and hoses and it started again. Clearily there is something clogging the filter/hoses or the pump is going bad, what do you guys think?

 

snanceki: I have a filter and will change it asap, it was so rusty down there so I couldnt get the filter loose, have sprayed on some rust-desolving liquid and will try again today. Regarding the relay, I already tested with a new one and nothing, so my relay is working properly!

 

If the pump is very rust (its made of aluminium!) maybe the electrical connecxtions have corroded in the vicinity of the pump.

the fact that you have changed the pump relay does not totally rule out that the problem is a power supply to the pump issue but one thing at a time. Suspect a fragment of rubber from the inside of the fuel supply has become trapped in the vanes of the pump or the pressure relif valve (part of the filter assembly).

Hope you get it sorted.

Stuart..

 

The pump itself is not rusty at all (as I can see) but the metal that holds the pump and filter is rusty and the screw is also all rusty so I have'nt been able to release the pump and filter, but with this solvent I hope it will be easier. I can't see the connector until I release the pump, but I will defenetly check it out once I do that, thanks for the tip!

What other power issue except the relay and the eventually corroded connectors could there be?

Thanks again for your help, but one quick question: Does'nt the fuel from the tank go first trough the filter and then the pump? In that case the fragment could'nt have made it trough the filter into the pump? I too am suspecting that a fragment have got cought somewhere because when the car is jacked or I tap/hit the pump, filter and hoses it solves the problem sometimes (the particle changing position allowing fuel trough/pressure buildup). So I will start with the filter and hope for the best. I'll let you know how it goes!

 

I would need to check but I think the filter is on the pressure side of the pump so debris from the tank / inlet hose can get stuck in the pump.
The tank most probably has a guaze filter and also possibly the inlet of the pump.
The filter is likely after the pump since it also acts (on some models) as the pressure regulating valve i.e. AFTER the pump.
To check that power is getting to the pump place an indicator light or multimeter across the pump terminals.
Stuart.

 

Thank you again Stuart you are VERY helpful!

You are quite right that the filter is after the pump and the arrow on the filter should point towards the front (hose) of the car. I changed the filter and the problem remains so it is probably clogged in the pump or the pump is not getting good current. Dumb question: Shall I check the pump while ignition on or off? Check the DC or Resistance?

Also wondering what kind of hoses I could buy since these are in very bad shape (when I started to tighten the hose around the filter it cracked a bit). So I would like to buy new hoses, have pump with a thick and two thin and also the one in to and out of the filter. Have a feeling that I could get them at MB but at a much higher price then elsewhere.

 

Hi,
It's so difficult to cover everything in a single reply.

You need to check that the pump motor is receiving power (i.e. Volts). This requires the ignition to be on. However it isn't that simple. The supply initially comes from the Electronic Ignition Switch EIS as part of the auto start procedure. However once the engine is running the supply comes from a relay in the electronics box under the hood. The relay is held closed by a feed sensed by oil pressure. If the engine stops there is no electrical supply to the pump for safety reasons otherwise in an accident fuel could be pumped out due to severed hoses and feed a fire situation.
So do as I originally stated and set up an indicator lamp (12v low wattage) across the pump terminals which you can view from the drivers seat.
The lamp should be on when you turn the ign on and go off after a finite time (safety). When the car is cranking it should be on and of course when the car is running.
If there is power to the pump then you need to find the reason why the pump doesn't run. Either the motor connections, winding or brushes must be no good or the motor is jammed. This can be determined by doing a resistance check with the motor disconnected (equivalent of ignition off BUT this check should be with the wires disconnected from the pump otherwise you measure the resistance of the supply circuit rather than the pump itself). Not sure what the resistance should be but something significant i.e. ik ohm.

So if the pump is seized it is either debris from the tank or hoses OR the motor rotor has seized due to rust between the rotor and stator (water ingress into motor housing which is unlikely OR between the pump vanes and stator Quite likely if there is water in the tank from contaminated fuel/condensation over time).


Fuel hoses are made of special material to resist the corrosive nature of the fuel so its important you use a fuel grade hose. Many manufacturers also coat the inside of the tube with a coating which resists the fuel BUT is not very flexible. It is therefore quite important that the hose is not bent or wiggled to get over retention humps too much otherwise the coating flakes off and gets into where it shouldn't.

I can't believe that it is the case but the oil pressure switch that controls the fuel pump relay COULD BE somewhere adjacent to the oil filter. Are you sure you didn't damage any sensor or wiring when you removed the oil filter especially if you didn't use the correct type of oil filter socket and struggled with some "alternative tooling".

You also need to confirm that there is pressure on the injector rail as I stated previously. Checking the pressure here eliminates a jammed pump, blocked filter, faulty return / pressure valve, blocked/squashed feed pipes and various electrics all in one go. i.e. there is fuel at the injectors throughout your start and run process.

Hope this moves you forward somewhat.

Stuart

 

Wow Stuart I owe you alot for your help, you seem to know alot in this matter!

I will do as you have described and also test the pressure on the injector rail but regarding that I have some questions:

"Better still check fuel pressure on the injector rail on top of the engine. There is a schraeder valve to connect a guage to." - you wrote this in your previous post, what kind of gauge do I need, something only MB can do or can I buy this gauge at MB or some other supplyer?

Would you smell the fuel if it made to the engine room when you tried to start/cranked the car? In that case that you should be able to smell fuel, I can't when I try to start the car, but maybe you should'nt.

I don't think I touched any sensors or something like that when I changed the oil filter, but I will have a thurow look at the surrounding area, both from the top of the hood and under the engine.

Since I now have disconnected the pump and filter (holding them in my hand) I can see that the wiring looks intact, there are no cracks etc on the wire itself and the connectors on both sides look clean and nice. Is it possible to test the pump in the trunk while I have it disconnected or do I need an enclosed system eg. the pump needing to be connected to the filter, tank and the rest of the system? Also, if I would test the pump in the trunk now will the fuel tank release fuel or is that controlled by the pressure the pump makes? (I have the pump with 3 hoses, 2in and 1 out, if this is relevant.)

When I blow with my mouth trough the thick hole on the in-side (to remove the fuel inside) the fuel gets trough to the other side (small out hole). Could this rule out that there is something jammed in the pump or not?

 

Hi NoShame!

Fuel Pump. With pump disconnected from vehicle (hoses AND electrical supply from vehicle) apply 12volts and pump should run. Don't allow to run for more than a few secs.

Yes you should be able to blow thru the pump HOW EVER this does not mean that the pump is not jammed. There is a rotor inside that runs to very close tolerances and even a small spec of rubber can jam the rotor.

Of course the pump may run on the bench but not in the car if there is no vehicle supply. This is where the lamp across the vehicle supply terminals (with or without the pump connected) will determine if 12volts is present to run the pump.

WRT the fuel rail pressure most tyre pressure guages will do since these have a Schraeder valve fitting. However once the guage has fuel inside it it is not good to use it for checking tyre pressures. Of course there are special guages for checking the fuel rail pressure but my "make shift" guage will give you an indication of whether or not pressure is being generated at startup and whether this is maintained once the engine is running.

You will only smell fuel "in the engine compartment" once the engine has "flooded" and is basically coming out of either the exhaust or the inlet manifold. The fuel rail pressure will advise if there is fuel at the injectors.

TAKE CARE WHEN DOING THIS WORK SINCE FUEL VAPOUR AND SPARKS/ELECTRIC DON'T MIX. OBSERVE USUAL PRECAUTIONS TO PREVENT FUEL SPILLAGE AND ANY POSSIBILITY OF A SPARK.

Hope this helps a little.

Since this is becoming somewhat of a marathon have you checked that you have a spark (watch that fuel floating around at the back of the car!) by removing one of the plugs and observing whether there is a spark whilst the engine is cranking.

No fuel or No Spark = No Start!!

STUART