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  #1  
Old 02-14-2002, 02:29 PM
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Join Date: May 2001
Location: Fort Worth, TX
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Question Fuel pump relay?

My new OVP relay that I ordered from the site came in today and my problem still exists. My fuel pumps cut off and the engine dies. I can't say that it has a pattern to it, %70 of the time it will start and run for about two minutes and then the fuel pumps cut off. For two months it would not start due to this, but the other day it started and ran fine enough for me to drive it around my neighborhood. They next day, no fuel pumps. I believe they are the original pumps and quite audible, believe they need replacing, but I don't think that that is the current problem. My old OVP rattled when I shook it so I replaced it. There was some corrosion on the old OVP so is it possible that my fuel pump relay needs replacing as well due to corrosion? They look in good condition.(002 545 16 05 & 002 545 18 05) Is there something that I am missing? '83 BMW 733i was totalled by a Cadillac last week and the rental car is a Pontiac!
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Old 02-14-2002, 03:09 PM
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Does the fuel pump relay feel "warm" when it cuts off. Mine did and when it cooled it was ok so I replaced it. New one did the same thing. One of my pumps checked bad so I replaced it and seemed to cure the problem.
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Old 02-14-2002, 06:52 PM
benzat
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mine did that when my fuel pump relay went out..but I did replace both. first replaced the fuel pump and it didnt run then I replaced the relay and it ran fine.

mine died on me and it would start then run then when it was shut off it wouldnt start. had it towed home and started it the next day. then it wouldnt start again.

if your car is like mine you can jump 2 pins on the relay and see if it will start.

mine is a 1982 380 SEC I have the CD for that car and can send you some info on jumping the relay if you need it

benzat

1982 380 SEC
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Old 02-15-2002, 01:56 PM
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Started this morning and it ran for it's two minutes and died. I checked the fuel pump relay and it was not "warm" at all. Shopping for fuel pumps...
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Old 02-15-2002, 02:08 PM
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Make dang SURE it's the pumps. They are expensive and it probably has two.
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Old 02-22-2002, 10:49 AM
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Which is it?

Okay Cap'n I want to make sure which it is before I buy anything. It seems to run fine IF I touch the gas pedal, leave it to idle without, it dies I have seem to find, could be nothing. I am clueless and getting frustrated.

Do old fuel pumps put some kind of drain that may make the fuel pump relay react? The fuel pumps are being cut off by something but I cannot figure out what it is. Then again I can get it to run for many minutes at a time.


Should I buy a new relay along with the new pumps?
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1980 300SD
1987 560SEL SOLD@216K
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  #7  
Old 02-22-2002, 11:26 AM
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yal yal is offline
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You have to check the current draw on the fuel pumps. If your fuel pumps are bad they will draw to much and eventually fry the relay. Its a which came first the chicken or the egg scenario.

Check the fuel pumps first then you can safely say it is the relay.

Check this thread:
Fuel pump or Fuel p relay? Doc,Benzmac,SteveB

Last edited by yal; 02-22-2002 at 11:43 AM.
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  #8  
Old 02-22-2002, 02:50 PM
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Re: Fuel pump relay?

Quote:
Originally posted by SqueakyBrake
My new OVP relay that I ordered from the site came in today and my problem still exists. My fuel pumps cut off and the engine dies. I can't say that it has a pattern to it, %70 of the time it will start and run for about two minutes and then the fuel pumps cut off. For two months it would not start due to this, but the other day it started and ran fine enough for me to drive it around my neighborhood. They next day, no fuel pumps. I believe they are the original pumps and quite audible, believe they need replacing, but I don't think that that is the current problem. My old OVP rattled when I shook it so I replaced it. There was some corrosion on the old OVP so is it possible that my fuel pump relay needs replacing as well due to corrosion? They look in good condition.(002 545 16 05 & 002 545 18 05) Is there something that I am missing? '83 BMW 733i was totalled by a Cadillac last week and the rental car is a Pontiac!
Hi Roy & others

This problem occurs particularly after the engine has been running due to the pressure relief valve located at the back of the pump inside. It is activated by a small spring which in time weakens and do not allow pressure to be relieved.

As the pump is driven by a permanently excited electric motor (when the engine is running) the pressure is reduced. After stopping, the fuel reservoir maintains pressure in the system to facilitate starting and with this pressure if the valve is stuck it develops an inner leak.

When this happens, if you tap the pump firmly it releases the pressure valve and the engine starts again. When the tapping affair becomes more frequent, it is time to replace the pump.

However, Mercedes have realized this and they provide a Check Valve which can be installed by replacing the existing hollow screw to the pipe connection to the pump, effectively providing a secondary pressure relief valve and avoiding having to buy a new pump. ( $7.50 for the Check Valve).
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