1993 300CE - Car ran fine - parked it for a year. Will not start - cranks fine - have spark on all plugs - no fuel in fuel rain - no electricity at fuel pumps. Replaced fuel pump relay - still no power to pumps. Have power at relay connector on two of the 4 sockets ( battery voltage on one, < 2 volts on another ) Reading the repair info I have it looks like the fuel relay is controlled by the N3 fuel injection computer. Need help on how to proceed - where to look.

Jumper terminal 30/87 at FP relay and see if rail gets pressure...[ with KO]

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A Dalton

Thanks for your response - I was not testing the fuel pump electrical supply correctly. It only works for 1 second with the ignition on and engine not running. After I learned how to test - I have power to the pumps and did get fuel to the rail. Car still did not start - I will check the ignition again tomorrow. I also suspect bad gas - it smelled " funny " when I changed the fuel filter. Again, thanks for your reply to my problem.

Check the fuse on top of the OVP relay..

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A Dalton

I checked it - its ok. I am thinking I might have a fuel pressure problem - how do I check the pressure on the fuel rail ? Just hook a gage to it ?

Yes ..right at the test port on the fuel rail

Car at idle with vac hose to reg connected:
3.2-3.6 Bar
At idle, vac hose disconnected :
3.7-4.2 Bar
System pressure after at least 30 min wait :
No less than 2.5 Bar.

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A Dalton

I hooked up a gauge to the fuel rail ( I removed the schrader valve ) and cranked the engine several times - no pressure on the gauge. I tapped on the pumps - still no pressure. I removed the gauge and found a small amount of fuel but no pressure. I alos checked the supply line from the tank - plenty of fuel avaliable - almost drown me. It appears the pump(s) are not working. Can I test by removing the filter line and checking for flow when cranking - or maybe hook up a gauge at filter discharge ? Is there any possibility the pumps might " free up " if run without being hooked to the fuel rail ? Can they be repaired ( look sealed ) ? It seems odd to me that both pumps would fail - as I mentioned the car ran fine a year ago. Any help / advice would be appreciated.

Go see my earlier posting...
....you put the gauge on the test port , put the key ON , and jumper pins 30 and 87 with the relay out...that gives you direct 12V to the pump/s...bypassing the relay circuit.

If that gets you pressure, the pump is OK, so the suspect is the relay is not gettins 12v to the coil side of the relay in order to activate it/s contactor set [ you are just manually jumping the contactor set at 30/87]
If still no pump, see if you have 12v at terminal 30. If yes , then the pump is suspect.

If no v to coil of relay, then the next suspect is the OVP relay ..

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A Dalton

I just went through this... Mr Dalton is the man...OVP fixed me... From the outside it looked fine, fuse was good, but the inside was a different story. OVP and be done!
Again Thank You sir!

You're Welcome.............

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A Dalton

Mr. Dalton

It has been awhile, but I had a problem with the cars starter and just got it fixed. I am now back to fixing the lack of fuel problem.

I did what you advised and jumped terminal 30 and 87 on the fuel pump relay and had voltage at the pumps. ( I also have voltage on terminal 30 with the relay pulled. ) The pumps make no noise and deliver no fuel.

I dont understand how both pumps fail at the same time, or are they somehow " tied " together?

Can I test them or do anything to repair or is it best just to replace ?

Any advice is appreciated - thanks for your time.

If you have 12 V power to the pumps , [ and I am assuming you mean right at the pumps ], then the pumps are most likely gummed up from the year of sitting or they are bad.
I would take them off , drain them and then put some carb cleaner in them to soak, then battery/bench test them..sometimes they will free up [ even a little tapping can help ]..
You have power to relay 30 and have manually jumpered to 87, so that assures V to pumps.. you also want to check the terminals/connectors at the pumps too.
A 12v test lamp will work better at the pump than a meter b/c you can see if the connections load drop with a test lamp.
The schematic shows both pumps 12v pos feed to have a connector X36 and the neg of each pump goes to ground..so make sure that is where you are taking your power readings from...could be simply a bad ground...

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A Dalton

Mr. Dalton

I removed the pump set and checked the individual pumps on the bench and they would bump but not run. After a great deal of carb cleaner and tapping / bumping they finally started running and sounded good. I put them back together and installed on the car. They sound and feel like they are running but I still have no gas on the fuel rail. My questions are:

Do you have to " prime " the fuel after servicing the pumps ? I drained all the fuel out of the system to work on it.

Can the pumps run but not pump the fuel - can I test ?

Restriction in the fuel line ? Can I blow air through the fuel rail test port back to the pump discharge ( disconnected ) ?

Any other recommendations other than these items ?

Thanks for any help.

Take the line feeding the pumps off and see if you have a flow from the tenk...in no, then blow thru it, back up thru the tank....there is a screen in the tank that may be plugged.

I should have told you to try the pumps with kero while they were out..also , there is a check valve on them..check that is not stuck closed from crap..
I am assuming you have replaced the filter.

http://catalog.peachparts.com/ShopByVehicle.epc?q=1993-Mercedes--benz-300ce--Coupe-Fuel--Delivery&yearid=1993%40%401993&makeid=63%40%40MERCEDES%2DBENZ%40%4063%40%40MERCEDES%2DBENZ%40%40X&modelid=6177%3ABT%7C9%3AMBC%7C1499%3AED%7C10000022%40%40300CE+Coupe&catid=240737%40%40Fuel+Delivery&subcatid=240780@@Fuel+Pump+Check+Valve&mode=PA

http://catalog.peachparts.com/ShopByVehicle.epc?q=1993-Mercedes--benz-300ce--Coupe-Fuel--Delivery&yearid=1993@@1993&makeid=63@@MERCEDES%2DBENZ@@63&modelid=6177%3ABT%7C9%3AMBC%7C1499%3AED%7C10000022@@300CE+Coupe&catid=240737@@Fuel+Delivery&yearid=1993%40%401993&makeid=63%40%40MERCEDES%2DBENZ%40%4063%40%40MERCEDES%2DBENZ%40%40X&modelid=6177%3ABT%7C9%3AMBC%7C1499%3AED%7C10000022%40%40300CE+Coupe&catid=240737%40%40Fuel+Delivery&subcatid=240743@@Fuel+Screen&mode=PA
It is rather time consunming for me to load all of these for you , so here is a tip for ya.
All these fuel delivery parts are right there in the Parts section on top of the page..so why don't you just click there to make it easy for us??
Thanks
Just click on 'Fuel Delivery" and there they are ..right in front of you.

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A Dalton

Mr. Dalton

I wanted to thank you for your help. I finally got the car running and it is doing well. I had to replace the fuel pumps. I got the original ones to run but they would not pump fuel ( vanes may have been gummed up ) but the ones from the salvage yard worked fine.

Again, thanks for your prompt replies and good advice. I really appreciate it.

Randy Dooley