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Author: Subject: MX5 fuel pump runs all the time
FFMan

posted on 21/7/20 at 09:41 PM Reply With Quote
MX5 fuel pump runs all the time

I've just acquired a Haynes roadster with MX5 running gear part built. The wiring was a mess so I tidied it up retaining all the loops and wires but removing the rear loom.

When i switch on the ignition the fuel pump runs, and i can hear fuel returning to the tank. When i got it i don't recall if the fuel pump did this, or it primed and then stopped.

In an MX5 i doubt you'd hear it either way but in the Haynes the pump is close by.

Can anyone advise ?

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theconrodkid

posted on 21/7/20 at 09:51 PM Reply With Quote
the pump should stop unless the engine runs, it is done with a dedicated relay, not a standard 4 pin jobbie

there was / is a really good manual "mellens.net" but dont seem to be working at the mo

[Edited on 21/7/20 by theconrodkid]





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FFMan

posted on 22/7/20 at 08:19 AM Reply With Quote
ok thanks

the previous owner says it has always done this. he thinks there is a jumper wire to the fuel pump relay.

is the relay a different colour or easy to identify ?

does the ecu control the relay, or does the relay have the prime timer built in, and once the engine is running, it's on all the time ?

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JAG

posted on 22/7/20 at 08:27 AM Reply With Quote
I have a Locost with the Mazda 1.6 from the MX5.

My fuel pump runs constantly; there's a feed from the tank (via the pump) to the fuel rail and injectors then a pressure relief valve (on the end of the fuel rail) and a return from the valve back to the tank.

I believe that is exactly as the original car - my engine is a 1994.





Justin


Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!

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FFMan

posted on 22/7/20 at 08:50 AM Reply With Quote
quote:
Originally posted by JAG
I have a Locost with the Mazda 1.6 from the MX5.

My fuel pump runs constantly; there's a feed from the tank (via the pump) to the fuel rail and injectors then a pressure relief valve (on the end of the fuel rail) and a return from the valve back to the tank.

I believe that is exactly as the original car - my engine is a 1994.


ok that's interesting. it's either a kit car hack or the original did the same and you don't notice in a sound-proofed mx5

Out of interest, you running the original ecu and using the mx5 loom ?

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JAG

posted on 22/7/20 at 12:15 PM Reply With Quote
quote:

Out of interest, you running the original ecu and using the mx5 loom ?



I'm running the Mazda ECU and a cut-down version of the original engine harness from the MX5.

This is the wiring diagram for the MX5 and I have replicated this on my car with the cut-down harness...

MX5 engine wiring diagram
MX5 engine wiring diagram






Justin


Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!

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FFMan

posted on 22/7/20 at 01:08 PM Reply With Quote
quote:
Originally posted by JAG
quote:

Out of interest, you running the original ecu and using the mx5 loom ?



I'm running the Mazda ECU and a cut-down version of the original engine harness from the MX5.

This is the wiring diagram for the MX5 and I have replicated this on my car with the cut-down harness...

MX5 engine wiring diagram
MX5 engine wiring diagram



thanks that diagram is handy

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gary gsx

posted on 22/7/20 at 02:09 PM Reply With Quote
Afternoon


Have you got the diagnostic plug in your loom? as you can put a bridging wire in there to run fuel pump obviously to test it maybe its been done and left?

Just a thought

Gary

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FFMan

posted on 22/7/20 at 02:37 PM Reply With Quote
quote:
Originally posted by gary gsx
Afternoon


Have you got the diagnostic plug in your loom? as you can put a bridging wire in there to run fuel pump obviously to test it maybe its been done and left?

Just a thought

Gary


i recall the diag plug is unused. i'll check the wiring later and it i find the bridge put in, remove it and see what happens.

I don't suppose it really matters but i like to get things right, or let them be wrong understanding why. Neither is the case at the moment

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FFMan

posted on 22/7/20 at 06:59 PM Reply With Quote
not quite sure how to attach an image here, but i found a shonky loop of cable on the relay plug. When I removed it (it kind of fell out), the pump doesn't run.

Feels like the loop is to an ign live so the pump runs straight away.

At first glance the colour of the wires on the relay connector do not match the diagram posted earlier.

Need to investigate some more...

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JAG

posted on 23/7/20 at 08:10 AM Reply With Quote
What year and model of MX5 does your engine come from?

You may have a different solution on your car.

My diagram is only applicable to MX5 1600cc Mk1.

[Edited on 23/7/20 by JAG]





Justin


Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!

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FFMan

posted on 23/7/20 at 08:20 AM Reply With Quote
quote:
Originally posted by JAG
What year and model of MX5 does your engine come from?

You may have a different solution on your car.

My diagram is only applicable to MX5 Mk1.


it's from a 98 NB so i guess that explains why the colours don't match. I have a Mazda diagram also but across many pages, i'll study that.

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gary gsx

posted on 23/7/20 at 08:40 AM Reply With Quote
Morning all


Mine is a 2000 1.6

I have two white/blue coming from main relay marked up as A and E on plug.

Then red/blue to fuel pump.

Then a blue/green that goes to ecu


Hope that helps


Gary

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FFMan

posted on 23/7/20 at 09:17 AM Reply With Quote
ok sounds similar.

My wiring (with the B5B4 marking upright facing you) left to right is blue/wh,red/bl,blue/wh

the back row is empty,empty,red

The first white/bl and red/bl where looped together.

In other cars, the ecu fires the pump for a few seconds to build pressure, then the pump comes on when the engine is cranking/running

according to my digram which is for a 1999 1.8 but the colours match, the blue/wh are joined in the loom which makes sense as they're the same colour, and this looks like an ignition fed live.

the red/bl goes to the pump. so the link on mine loops out the relay

My guess is either my relay is faulty, or the trigger wire (shown as green on my diagram) isn't providing a signal which according to the digram is straight into the ecu.

Later i'll put a meter on it and see.

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gary gsx

posted on 23/7/20 at 10:14 AM Reply With Quote
The wire that goes to the ecu goes to pin no 3N on mine, Do you have a coded ignition key with key reader etc?

Have you had it running?

Gary

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FFMan

posted on 23/7/20 at 10:36 AM Reply With Quote
quote:
Originally posted by gary gsx
The wire that goes to the ecu goes to pin no 3N on mine, Do you have a coded ignition key with key reader etc?

Have you had it running?

Gary


yeah i think it has coded ignition.

Yes it runs, not driven it in anger yet as other jobs to do, inc sort out that shonky relay link which would fall out given half a chance.

It looks as if the ecu grounds that wire to activate the relay, which i think it should do on prime, and when it sees the engine running. i'll get a meter on it later.

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