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M42 Fuel Pump Question


DUDOK

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Last night I got everything ready for the first try at starting the car.  The only thing I noticed is that with the key at accessory?(last stop before starting) I could not hear the fuel pump running.  I am using the standard in tank E-30 pump.  Should I be able to hear it charging the system?  or is it controlled by the computer?  or I have a dead pump or relay or I screwed up the wiring .. or?  thanks for any help in advance.

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I will assume this is an M20 setup, and the car did not start.

The pump will not activate until you move the key to the start position.  The trigger is the flap door in the AFM.

To test the pump, you could use the instructions in the Bentley Manual for the M20. (They bypass the relay with a jumper wire)  Or, of you remove the air box and reach in and move the flap door in the AFM.  If everything is working correctly, the pump will turn on.  If it does not work, you need to check if you are getting voltage to the pump.  Apply 12 volts to the pump terminals to check if the pump itself works. Then work backwards from there.

A common problem is the fuel pump relay.

 

You need to provide a lot more details about your build, what you have done so far, so that we can guide you in the right direction.  Was the engine running when it came out of the donor car?  What did you do to it?  Pictures will help too.

 

And finally, here is a pet peeve of mine.  What is your name?

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+1

first, everyone with an M20 or M42 in their car needs to buy and read the Bentley E30 shop manual....best resouce you can get.  (yes, this means YOU Clay...... :-)  )

 

 

second, yes the fuel pump is controlled by the ECU.  pump relay does not get signal to turn on until ECU sends it.  ECU will not send signal until it knows the engine is turning over with the starter (AFM flap opens from air being sucked in or crank sensor reading flywheel movement....depending on which engine is used.)

 

this is a safety feature....if engine dies in crash or fuel line breaks and ignition is still on, do not want a high pressure fuel pump feeding a fire.

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The E30 Bentley manual is awesome and an absolute necessity for any DIYer with an E30... but it does not cover the M42. (or the S14.)

So if you have an M42 E30, like I do, you need two manuals.  The E30 Bentley and the E36 Bentley.  And of course, the E36 M42 is not exactly the same as the E30 M42.  The induction is different and the E36 has a knock sensor.  But most of it is the same.

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