C32owner

So we replaced my fuel sender with a second hand fuel sender to save cost on diagnosing a fueling issue I have been having. Upon checking both fuel senders, left hand side of the car, both fuel filters were pulled and looked quite bad.
Went to the local auto parts shop to try just to replace the fuel filter, however going through the catalogs it says "in unit" and not a replacement part, meaning if you want a new fuel filter in the sender you have to buy the whole unit??? Is this the case or has anybody ordered just the fuel filter, perhaps have a part number? For now we running the car without a fuel filter at all.

55Jeff

you have to buy the whole assembly for around 450$.

sexyxe

^^ what he said. Unless you completely remove it and then go custom. I think someone on here uses twin Aeroflow pumps with an inline filter. I think it might even be a return style system too

JoeNobody

Are you in America? Are the parts leaking or have fuel stink? If so have the dealer replace everything under warranty

2000UZJ

According to his profile he's in South Africa. Probably unlikely they will replace under US warranty but good suggestion

C32owner

Thanks guys. In South Africa stealership here will have a good laugh at us if we try get some sort of warranty claim from a USA story.. Anyway that's ridiculous that you have to buy a whole unit just for a fuel filters ouch.

Having major issues with my car at the moment which we can't seem to get to the bottom of.. It's seems when the car goes over 3000rpm the car falls on its face rough as heck running and have seen that the fuel pressure just dies to 1.5bar..way to low.. So we have changed fuel sender unit, replaced 2 new oem fuel pumps.. Basically new fuel delivery unit, have changed relays.. Checked spark plugs and coil packs..been going on for weeks now.. Am so irritated, can't wait for the fix to be found.

Rocman8

you changed the correct relays? this happens often where the wrong ones are replaced.

ajm55

Craig, unlike earlier model E55s, on my car the fuel pumps are staged. The one pump activates on start up and the other only triggers at about 2,500 rpm (or when the car sees boost - not sure). Although your's is a CLS, it is also a later model if I recall correctly and perhaps the activation of your pumps is also staged. If so, it seems to me that there may be an issue with the activation of the second pump. Try wiring an LED light (to be located in plain sight on your dash) to the second pump to see if its getting (and retaining) power when you get on the throttle. If it isn't, this will explain why your fuel pressure drops off when it does.

Shifter

The second pump only activates after 5 seconds of WOT. Are your connectors ok, not melted or look burnt? Also the relay connections?

C32owner

Hi Anthony, thanks for that. Ya really stumped on it.. But staged as you say is how this system operates as well. We think it's something electrical as the second pump doesn't seem to power up correctly.. We have changed 3 relays, I wasn't there but apparently still same issue. The relays in the trunk. I have asked to hook up a volt/amp meter on the second pump terminals and to the first one to see what each is doing.. It's got to be something electrical, there is no burnt relays or fuses anywhere.. Both pumps turn on I think during ignition if I recall correctly.. Starts perfectly it's only when going wot at around 3000rpm.. Pulling my hair out here.

Also as a matter of interest, when we bought the new Mercedes fuel delivery unit, which is basically the new fuel pumps unit on the right hand side of the car. When placing the order Mercedes did advise this was an upgraded unit replacing the old system. So after many struggles of not being able to start the car we finally realised that the electrical connector on top of the fuel delivery unit cap had changed the order of the wiring.. Eg old unit was black red, black Red... Now on the new unit the connector colouring is black Red, Red black... So basically the pumps where fighting each other leaving no pressure at the rail.. So we have the new lower portion of the fuel delivery unit in place with new pumps and have the old unit cap installed for correct wiring with the existing connector on the car.. So car has good pressure for start but just the issue with second pump turning on when needed under boost.. Strange though That at initial ignition and start both pumps are fine and operating together... Maybe something in this upgraded delivery unit that needs changing in the wiring???

ajm55

It's hugely frustrating - I know from my own experience. Sounds like it's electrical. Your pumps are new so it's unlikely to be a faulty second pump. I had a volt meter connected to each of my two pumps when I was having a fuel pressure issue. I can tell you that my second pump activates at about 2.500 rpm when I go about half throttle. You'll find the problem. Just have to follow an elimination process

C32owner

Ya thanks seems like we on the right track now, with it definitely being electrical, as we hooked up the voltmeter and the volts are stable initially then just drop off.. Trying to locate a faulty wire somewhere in the system. Seem to think the maybe a previously installed tracker unit from past history is possibly causing nonsense in the system as the old models used to turn off fuel pumps when the car is stolen.. So trying to Locate that..

Denroll

Have you checked the voltage regulator on the alternator? How many volts is it putting out at idle?

Rocman8

Do you have a picture of the locations where the relays were replaced?

C32owner

Unfortunately I don't have pics but I believe in the boot/trunk on the left and right side is relays that was changed... Volts are fine on the alternator.