FFMan
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| posted on 21/7/20 at 09:41 PM |
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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
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| posted on 21/7/20 at 09:51 PM |
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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]
who cares who wins
pass the pork pies
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FFMan
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| posted on 22/7/20 at 08:19 AM |
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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
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| posted on 22/7/20 at 08:27 AM |
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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
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| posted on 22/7/20 at 08:50 AM |
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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
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| posted on 22/7/20 at 12:15 PM |
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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
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
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| posted on 22/7/20 at 01:08 PM |
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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
thanks that diagram is handy
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gary gsx
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| posted on 22/7/20 at 02:09 PM |
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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
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| posted on 22/7/20 at 02:37 PM |
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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
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| posted on 22/7/20 at 06:59 PM |
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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
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| posted on 23/7/20 at 08:10 AM |
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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
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| posted on 23/7/20 at 08:20 AM |
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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
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| posted on 23/7/20 at 08:40 AM |
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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
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| posted on 23/7/20 at 09:17 AM |
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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
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| posted on 23/7/20 at 10:14 AM |
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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
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| posted on 23/7/20 at 10:36 AM |
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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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