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E28 (1982 - 1988)

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  #1  
Old 05-01-2014, 08:12 AM
earlalderfer earlalderfer is offline
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Mein Auto: 1986 BMW 535i/A
1986 BMW 535i

I have a 1986 BMW 535i. The car starts and runs for 15 20 minutes and loses power then stops. It seems like it is not getting enough fuel. I wait 5-10 minutes then the car starts and I can drive on before it repeats.

Is there a method to check to see which fuel pump - in-tank or external pump may have failed?

Has anyone else experienced this?
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  #2  
Old 05-02-2014, 03:30 AM
m735is m735is is offline
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Mein Auto: e23, e32, e34, e39
The car will run with a dead intank pump. You should get a fuel gauge and check the fuel pressure when it loses power, see if the pump loses power or pressure also.
There is a cheaper alternative to the intank pump as we'll, if that's bad. Chevy Vega fuel pump mod. Or go all out and replace both pumps with a TRE intank.
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  #3  
Old 05-02-2014, 07:45 AM
earlalderfer earlalderfer is offline
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Mein Auto: 1986 BMW 535i/A
Thank you for the response.
I will check the pressure ASAP. I am not up on the Chevy Vega pump mod? What is that and how to use.
And I not up on the designations...what is replace both pumps with the TRE intank? Do you mean original equipment pumps?
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  #4  
Old 05-03-2014, 04:00 AM
m735is m735is is offline
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Go on mye28 dot com and search TRE and Vega.
TRE is a high flow pump you mod to fit the intank, the Vega pump is the same as the one in there, just cheaper. With the TRE, you eliminate main external pump.
You can also search your symptoms and see what comes up. Maybe it's not fuel related.
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  #5  
Old 05-05-2014, 02:26 PM
earlalderfer earlalderfer is offline
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Mein Auto: 1986 BMW 535i/A
I checked the fuel pressure.....fluctuates 36 to 39psi at idle; pressure increases to 3 Bar when the vacuum line is removed from the FPR then back to 36-39 when attached. I let the car run in the middle of the day, hottest, A/C running on high, however could not recreate the same failure. Unable to check pressure during failure. At 36 to 39 psi would that indicate pump(s) is weak, when the idle pressure spec should be 40.6 to 46.4.
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  #6  
Old 05-06-2014, 10:21 AM
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Mein Auto: 2000 323i, 1988 528e
Quote:
Originally Posted by earlalderfer View Post
I checked the fuel pressure.....fluctuates 36 to 39psi at idle; pressure increases to 3 Bar when the vacuum line is removed from the FPR then back to 36-39 when attached. I let the car run in the middle of the day, hottest, A/C running on high, however could not recreate the same failure. Unable to check pressure during failure. At 36 to 39 psi would that indicate pump(s) is weak, when the idle pressure spec should be 40.6 to 46.4.
I would look at electrical and ignition components. It could even be a bad coil; I'm guessing that something is heating up and then failing.
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Old 05-06-2014, 01:43 PM
earlalderfer earlalderfer is offline
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Mein Auto: 1986 BMW 535i/A
I have replaced the wires, cap , rotor and coil as preventive maintenance when I acquired the car. Fuses and relays were replaced as preventive maintenance since the relays looked very old and weathered.

Is the lower than normal fuel pressure an indication that the fuel pump(s) could be weak? 36 - 39 psi vs 40.6 -46.4?
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  #8  
Old 05-06-2014, 01:57 PM
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Mein Auto: 2000 323i, 1988 528e
Quote:
Originally Posted by earlalderfer View Post
I have replaced the wires, cap , rotor and coil as preventive maintenance when I acquired the car. Fuses and relays were replaced as preventive maintenance since the relays looked very old and weathered.

Is the lower than normal fuel pressure an indication that the fuel pump(s) could be weak? 36 - 39 psi vs 40.6 -46.4?
It may be a bit weak, but the car starts and runs, so I don't think it's the pump itself; maybe the regulator, or the vacuum line to it. It seems like something other than the pump to me. Have you checked the speed sensor and the reference sensor? The fuel lines deteriorate over time and can be a problem after the engine compartment gets hot. I had a leak problem like that.
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Last edited by catso; 05-06-2014 at 02:04 PM.
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  #9  
Old 05-13-2014, 06:28 PM
south26 south26 is offline
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Mein Auto: 535i 1989
I had a coil that was starting to die and when it got hot it would die.


Andy
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