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Date: 10-11-05 06:13
From: Patnode
Subject: Tell me how my sealed mechanical fuel pump works??  
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My 76 2002 will not start, definitely not getting fuel, just got it back from the shop with a full tune up. I have narrowed it down to fuel, and lack therof.
Pulled the fuel pump off, plunger is working, good resistance, etc...I don't understand how this thing works, how does stepping on the gas bring the fuel fromt he rear of the car to the carb? It is obviously a suction force, but I cannot troubleshoot it. Was running just fine last week.Any pointers would be appreciated.
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Date: 10-11-05 06:24
From: steve howe
Subject: Re: Tell me how my sealed mechanical fuel pump works??
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With the fuel pump in the car you can disconnect the line to the carb and see if it is pumping gas. Pump it into a small container and don't smoke while you are doing it. It pumps gas into the carb bowl and the amount that goes in is controled by cutoff valve, when the bowl is fuel it closes the valve so no more fuel is allowed in. Hope that helps...steve
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Date: 10-11-05 06:28
From: Patnode
Subject: Re: Tell me how my sealed mechanical fuel pump works??
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Gotcha...but it is definitely not filling the carb bowl, my in line filter before the pump is partially filled??
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Date: 10-11-05 07:14
From: steve howe
Subject: Did you try disconnecting it at the carb? It sould be pumping a large
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volume of fuel, if it's not it is a faulty pump..
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Date: 10-11-05 07:20
From: Patnode
Subject: Re: Did you try disconnecting it at the carb? It sould be pumping a...
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Thanks Steve. I reconnected it, and pumped the gas pedal, no fuel, so it has to be the pump. What makes these things malfunction?
Thanks!
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Date: 10-11-05 09:06
From: canada rob
Subject: whoa... the engine has to be turning over!!
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URL: http://www.bmw2002faq.com/mambo/
mechanical pump only works if the engine is turning over. take the positive lead off the coil, take fuel line off the carb (put the end in a plastic cup) THEN turn the car over a few times and see if theres any fuel in the cup...
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Date: 10-12-05 05:35
From: mike
Subject: Coupla or three things to check...
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1. Check end of pump pushrod (goes from pump to camshaft). They wear. Ends should be squared off, not angled. While you're at it, check the pad on the fuel pump itself that the pushrod bears against. Some aftermarket pumps (those Italian ones) have soft steel pads, and they wear thru--then the pushrod won't activate the pump.
2. Check fuel lines upstream of the pump for air leaks...a mechanical pump can push gas thru a leaky line (output side) but will suck air instead of fuel if the leak is on the input side. And don't forget to check the fuel filter(s).
3. Remove pump from car and work the mechanism by hand: clamp in a vise, put short lengths of hose on inlet and outlet pipes, submerge inlet side in some kerosene (gas is DANGEROUS) and use a catch cup on the outlet side. Work the pump activating pad with a screwdriver (mimicking the pushrod's action) and see if it pumps. If it does, the problem is most likely one of the three above.
If it doesn't, it's time for a new pump.
happy troubleshooting
mike
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Date: 10-12-05 05:41
From: Patnode
Subject: Re: whoa... the engine has to be turning over!!
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Now this is making sense...will try today.
thanks!
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Date: 10-12-05 05:45
From: Patnode
Subject: Re: Coupla or three things to check...
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Thanks Mike, good things to check. The car has original fuel lines, I think, so I hope that is not the problem. Replacing the fuel line from the tank looks to be difficult.
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Date: 10-12-05 10:27
From: mike
Subject: The plastic line that runs from tank to firewall shouldn't be a worry
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unless it's been physically damaged by abrasion, welding torch etc. It's the rubber lines that connect the fuel pickup (at the tank) to the plastic line, and the rubber lines in the engine compartment that you need to check. They're all easily reached.
mike
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