bigbrainonbrad
Feb. 2, 2012 4:32 p.m.

I left work yesterday got in the car and it would not start. Took the key out tried again, but listened to everything. When I put the key in and turned the ignition to the on position, I did not hear the fuel pump prime. Popped the hood and wiggled the fuel fuse/relay thing in the underhood fuse box. Got in the car and it started up.

Today when I got home from work, I tried to start the car and same as yesterday, no start. I jumped the gnd to f/p in the diagnostic box, turn the key to on and the pump primes. Car starts fine and runs.

I know at this point that the pump is good, but I'm stuck past this. What and where do I need to check. I have a second car to drive around, but the gas mileage suck compared to the miata.

Apexcarver SuperDork
Feb. 2, 2012 4:46 p.m.

How much is the relay? is just replacing it an option?

I had similar problems with the mustang some years back.. turned out to be a wire connector going bad, $ 0.25 fix. (after getting burned for a LOT of money with a dealer to fix it, not the alarm, not the impact shutoff, not a bad pump, etc)

spritedriver28 New Reader
Feb. 2, 2012 5:18 p.m.

Check with Flyin' Miata, but it sounds like the relay to me.

bigbrainonbrad
Feb. 2, 2012 8:29 p.m.

Where is the fuel pump relay?

Keith SuperDork
Feb. 2, 2012 9:14 p.m.

It's under the steering column - yellow. But if you can make it work with the FP jumper, the relay is working at least partially. That just triggers the relay in a different way.

The relay is triggered three ways: the ECU turns it on for a short prime and also keeps it on during cranking. Once the engine's started, a signal from the airflow meter keeps it running - that way, when you drive into a tree and the engine stalls, the pump stops so you don't die a fiery death. You can also trigger the pump using the FP jumper, which was nice of Mazda to do.

I suspect that if you pull the jumper out after the car has started, it'll keep running. Give that a try, it'll help isolate the problem.

The relay's a bit complicated, as it gets triggered either by 12v (ECU) or by ground (diagnostic connector). You may have just lost one coil in the relay, which would explain what's going on. A new relay would solve it.

The short term solution is to install the jumper and avoid driving into trees.

For some reason, you can also beep the horn using a jumper in the diagnostic box. But only in US cars, not the Canadian ones.

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