I suspect fuel pump issues, please validate

Tiny
DUCTAPESUPERHERO
  • MEMBER
  • MERCEDES BENZ
I suspect fuel pump issues, please validate. I'm driving a 1989 300E with an in-line 6 3.0L block, which has been having a difficult time starting when cold for the last few months (60ºF or 21ºF outside, no real difference). I've found that turning the key several times from off to on(while hearing the fuel pump work. A barely auduble uumm*thump) will make the car more likely to start up. Even then though, the first couple times that it starts, it idles at 400RPM and will die if I try to give it more gas. Once I let it idle for 2-3 minutes, it is a little laggy, but will rev up on command; after 3-4 minutes, it is wonderfully responsive.

Once the block is warmed up (or perhaps because there is still fuel in the lines), it'll start without a problem, idling at about 1000RPM. I'm not sure if it is a block-temp issue or if it is just that when the block is warm, the fuel lines are full from being recently run.

Today, I went out to start her and there was no mmmmm*thump* (but the car had power) so I suspect that my fuel pump is not pumping at all.

Here is my plan of action; I'd like to know if I'm attacking it from the right angle. This is my daily driver and she's stuck across town and my budget is low at the moment. I'll be doing the work myself.

1) Get to fuel pump and test electrical to make sure it is getting power. I don't think that this is the issue because I've been having problems when the pump was obviously getting power when I was having related issues.

2) If it is getting electrical power, feel it while it should be working to see if there is any motion.

3) If Fuel pump is inactive but is getting electrical power, replace it. I've found replacement pumps for as low as $135, but if you have a better connection (or if you sell it for $150, I'd rather buy from you to appreciate your feedback.


Thank you for your feedback.
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Saturday, January 13th, 2007 AT 8:56 PM

6 Replies

Tiny
DUCTAPESUPERHERO
  • MEMBER
The vehicle has about 190k miles on her (odometer died at 176k), and an unrelated bad power steering pump.
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Saturday, January 13th, 2007 AT 9:12 PM
Tiny
CLEAVAGE4U
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My Daddy says a loud hummin' pump is a pump in trouble. He says, when you drop that tank down you can check for power but it's probably gonna be there.

He says the pump was on it's way out when you had to keep turnin the key, cause the fuel would just drain back into that lil ol' tank.

I thought it was really cute the way you said the car went, "mmmmmmmmmm*thump" and was wonderfully responsive ater she was warmed up :wink: I'm kinda like that too!

I hear those Mercedes are real fast cars.
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Saturday, January 13th, 2007 AT 9:15 PM
Tiny
DUCTAPESUPERHERO
  • MEMBER
Thank you very much. I'll go ahead and order the part and let you know how it goes.
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Saturday, January 13th, 2007 AT 9:19 PM
Tiny
CLEAVAGE4U
  • MEMBER
Oh Mr Duct tape,
Thank you so much for givin me a reputaion! :Wink:

My Daddy wanted to say that you shouldn't be buyin' no cheap pump cause you might be having to do this twice. An since this is your daily driver an you're goinna be driven the mistress, you might wanna drop that tank down and see what kinda shape that sendin unit is in. When I'm in the area where my high beams are on, seems that thers a lot of salt that does some kinda corrosion things to the lines.
If you're in a warmer climate it may not matter, but if you are, you better invite me out, in that fast car of yours :D
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Sunday, January 14th, 2007 AT 8:49 AM
Tiny
DUCTAPESUPERHERO
  • MEMBER
I'm ordering a brand-new Walbro pump, which will hold me over at least until I can get a bit more cash and take care of all her other little flaws. These things always happen in the perfectly bad times, so we'll see how she does.

My part won't even be sent out until Tuesday, so I've got a bit of time to wait and rely on public transportation.

Portland weather is not too cold, and we don't use salt to de-ice the roads much, but rather some sort of bidegradable chemical liquid. I'll check the lines anyway and hope I shouldn't have to replace 'em to get this going. This'll be my first doing major work on the 'benz (although I rebuilt the engine on the Bimmer I had for 17 days - she was t-boned and totaled the day after I finished the project), but I know enough German to get by, so I should be fine.

Thanks again for your input.
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Sunday, January 14th, 2007 AT 10:34 AM
Tiny
2HOWARDS
  • MEMBER
Before you install that pump you may want to consider a vacuum leak. This will make the car idle high. It will also create a long cranking condition (lean mixture). There is also a throttle switch that will do the same thing. To check this remove the air cleaner and manually move the throttle, there should be an audible click. This click should be heard when the throttle is moved no more than 5 degrees. You may also be losing fuel pressure however this will not most likely be cured by fuel pump replacement. For this you will need to take it to someone who has a pressure gauge. They will need to check the system and control pressures. High mile cars can also leak fuel into the intake causing long crank times however, I feel you have a cracked vacuum line. Check the simple things first then take it to a shop that can check the pressures. This can tell you if there is a restriction (filter) or an internal leak. Loud fuel pumps could be caused by a restricted fuel filter.

Hope this helps.
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Monday, January 22nd, 2007 AT 11:24 PM

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