95 C280 testing fuel pump relay? - Mercedes-Benz Forum

 
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post #1 of 5 (permalink) Old 05-07-2010, 01:27 AM Thread Starter
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95 C280 testing fuel pump relay?

I have a 1995 C280 that I thought the fuel pump was going out on. But after pulling the pump, it runs solid everytime I test it. I had assumed that the relay was good because the fuse in the top of it was still good.
But now that the fuel pump seems to be working I think the relay might be my problem.
can anyone tell me how to go about testing the fuel pump relay? Or give me a direction to my problem.

Thank you.
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post #2 of 5 (permalink) Old 05-07-2010, 04:00 AM
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what makes you think the pump is going out??? also just cause the pump runs doesnt mean its producing the required pressure and volume to let the car start and run. as far as the relay, you can check the resistance between terminal 85 and 86, should be .1 ohms or so. and you can check the resistance between terminal 30 and 87 should be about .1 ohms. this is when the relay is activated. really though never seen a relay cause issues. its either good or bad. i have seen bad ones but not ones that are going bad.
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post #3 of 5 (permalink) Old 05-07-2010, 06:11 AM
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Ditto. It might help if you tell us what symptoms you have leading you to believe it was the pump or is the relay. I had a fuel pump going bad (intermittant rough running and some no starts) on another car over a 3-4 week period. The final diagnosis was the pump. I asked the tech about the relay but somehow he determined it was not to blame.

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Last edited by Musikmann; 05-08-2010 at 10:28 AM.
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post #4 of 5 (permalink) Old 05-07-2010, 02:10 PM Thread Starter
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My reasoning for thinking the pump was going out was due to the car stalling out while driving and then not start at times. And it didn't sound like the pump was running every time I'd turn the key before starting.
My wife has ran the car out of gas a few times now due to the fuel gage reading wrong. I'm not sure if this is related to mt immediate problem or not. I've been telling her just to track her miles so that it wouldn't happen to her any more mainly because of me being a little lazzy and not wanting to drop the gas tank to replace the asend unit.
I bought a fuel pump through my local Bap Imports store but when I removed the old one I noticed they had sold me the wrong one. That is when I hooked up the old pump to the battery and saw that it was still running. But as mentioned, it might not be creating enough presure to keep the car running.
I will start by checking the volts on the pump and see what that comes out to be.After reading the above post I no longer believe the relay is my problem and I'm back to my original thought of the pump being bad.
i will post back after checking out the pump.
Thank you for your imput
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post #5 of 5 (permalink) Old 05-07-2010, 06:50 PM
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check the crank sensor too. they are a known issue on benz cars. usually they fail when the car is hot and will cause a no start issue. than after a bit the car will start when the sensor cools down.
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