13 replies to this topic

[makus0025]

I went to my first race last week and when the day was done I went to load the car back on the trailer and it would not start.

I traced it down to a fuel problem (no full pump noise) and then I went to the fuel pump relay and it has no power going to it.

All the fueses in car checked out ok (1 cluster under the dash and the other one under the hood)


Anyone have any ideas on what else to check why there wouldn't be power at the relay?

Thanks

[makus0025]

Does anyone know where the factory fuel cut-off switch is on 2000 miata?

[KentCarter]

Does anyone know where the factory fuel cut-off switch is on 2000 miata?

as far as I know... there isn't one.

[Keith Novak]

I have a different year so this might not help but on a '95, sticking a jumper in the diagnostic box between FP and GND bypasses the relay. It ran, you shut it off and then no fuel so something changed between key off and key on. If you don't hear the fuel pump with the key on and the jumper installed, my first thought would be ignition switch wiring. If you do hear the pump, then you probably ruled out that.

My year also has a largish yellow connector under the dash on the LHS of the wheel that disconnects the fuel pump, useful for depressurizing the system. I'd see if you have one and if it's connected. I'd also clean all the grounds. Many electrical problems turn out to be bad grounds.

[Ken Nesbit]

Not really a solution here, but maybe a lead to chase. On some fuel injection systems the fuel pump will kick on when you turn on the key and run for a few seconds to get initial fuel pressure, then when the car starts it switches over to full on. I've seen cars (Honda, but Mazda probably has something similar), where the relay for that initial blast of fuel pressure goes bad and it doesn't kick on before starting the car. The result is, if the car's running (meaning the fuel pump switched over to full on), it's fine, but if you turn it off it doesn't get that initial fuel pressure and won't start. The symptoms sound similar...for what it's worth...

[Bench Racer]

If you do not have the wiring diagram for your 2000 Miata enter "Yorba linda Miata" in a search engine & print out the diagram, study & understand the eletrical fuel pump eletrical system.

I went through a similar deal with my 1990 Miata.

[makus0025]

Ok here is what I have come up with

Battery is not dead (I can measure 12 volts on the fuses)

I do not hear the fuel pump coming on with the key in the run pos. or when I try to start it.

I pulled off the cover back by the fuel pump and check voltage on the 4 wire plug

2 were grounds and the Red with blue strip had NO voltage and the 4th smaller wire had 5 volts

I read a few places that this 5 volts is not a good thing and could lead to an ECU being bad but then I read 99% it is not the ECU


I aslo read it could be the fuel cut-off switch but I could not locate it. But I do see autoparts stores selling them for a 2000 so that is another twist


After finding out I didn't have 12 volts back by the fuel pump I went to the relay under the dash and above the pedals. I found the same red with blue stripe wire and check it out and the wire was fine from front to back of the car.

Then I check power going into fuel pump relay and 0 all the way around

No power going into the relay during crank or in the run position


I check the fuses under the dash and the ones under the hood.

I also check the main relay under the hood inside the fuse box and that one was clicking so I assume that one is fine.


Anyone have any tips on what to look for or is my ECU junk?


I will try the jumper and see if I can manualy get the fuel pump to go on, just to make sure the engine can fire and run

[makus0025]

If you do not have the wiring diagram for your 2000 Miata enter "Yorba linda Miata" in a search engine & print out the diagram, study & understand the eletrical fuel pump eletrical system.

I went through a similar deal with my 1990 Miata.

thanks for this site !!

I see that the main fues box has white/blue wire that should be hot leading directly into fuel pump relay

well yesturday I had 0 voltage on this wire when I checked at the fuel pump relay

[makus0025]

thanks for this site !!

I see that the main fues box has white/blue wire that should be hot leading directly into fuel pump relay

well yesturday I had 0 voltage on this wire when I checked at the fuel pump relay

Just wanted to give an update on the problem

It ended up being the main relay ( the big green one inside the fuse box under the hood)

Even though I could hear it click it was not making full contact to complet the circet. I took the top off the relay and could push the tab over manualy and make the fuel pump come on and the car would start


Anyone have an idea what makes these relays go bad? Seems like some other people are having the same problem.

[Tom Hampton]

Relays have a hard life. All relays will eventually, just like every other mechanical device.

Temperature, humidity, current, inductive loads, and mechanical contacts don't really go together.

Every switch off the relay causes some arcing, resulting in some carbon building up... and some deterioration of the contacts.

[trimless]

Last year at the NASA Nationals my 99 developed a mis-fire which I eventually traced to the main replay. Replaced the relay and have not had a problem since then. It's a cheap part so it should be in the spares box. You can also open up the relay and make a hard connection to both terminals effectively bypassing the relay to get by for a weekend as I did. You just need to be sure to turn off the main power switch when not running to avoid burning up the expensive coil pack.

[dmathias]

If we can put a man on the Moon, you'd think we could build a relay that last!!!!!!

[Tom Hampton]

Sure they can.... define "last". You tell me how long you want it to last... I'll tell you how much it will cost.

You won't like the answer.

[Tom Hampton]

Oh... and, we can't put a man on the moon anymore.