*Solved* Ignition "ON" position hum

Patty · Postby **Patty** » Sun Aug 30, 2009 2:16 pm

Hi Guys,

What's the light humming noise you can hear from the engine bay when you turn the ignition to the "ON" position?

Reason I ask:
A couple of days ago my NB8A would start and then stall right away which is weird because it had no symptoms leading up to this. I did notice that the humming was not there when I turned the key to ON. Anyway I started on the fuel pump diagnosis instructions from miata.net, removed windblocker, started to pull the plug/clips holding the carpet on the parcel shelf, decided I wanted the windows down, turned ignition to ON and noticed the humming had returned so I tried my luck and she started, which is great, but now I'm wondering why she stalled to begin with. Maybe my tinkering alleviated some earthed wires and it has something to do with that humming...

Pat.

JBT · Postby **JBT** » Sun Aug 30, 2009 2:59 pm

The humming sound you can/could hear is probably the fuel pump. When you started removing bits behind the seats you may have temporarily fixed an intermittent fuel pump wiring connector which caused it to operate properly again. Someone else had this problem a while back. Do a search for "fuel pump".

Patty · Postby **Patty** » Sun Aug 30, 2009 3:34 pm

I did do a search, and it helped somewhat but my problem isn't the same as ducktape's which had similar symptoms. The confusing part is that the pump is under the parcel shelf whereas I traced the humming to the engine bay near the throttle body (I can't pinpoint any closer than that)...

It's always been there so I take it as normal.

JBT · Postby **JBT** » Sun Aug 30, 2009 4:34 pm

Try this one. The humming may be the sound of the fuel pump being transferred to the pressure regulator on the fuel rail near the intake manifold.

Steampunk · Postby **Steampunk** » Sun Aug 30, 2009 8:40 pm

is it more of a high-pitched buzz that occurs for about just over a second, and ends with an abrupt "tick" noise?
If so then, as JBT stated, it's the fuel pump being primed, and yes, it does sound like it's coming from the engine bay rather than behind the seats.

Patty · Postby **Patty** » Mon Aug 31, 2009 1:33 am

Ok thanks for the tips guys, my under bonnet knowledge isn't all that crash hot but what it was, was a loose connector to what I think is the ISC/IAC valve :?:

I pushed it all the way in *click* and the hum is there all the time now while the ignition is ON. It's the part which sits right under the TB (butterfly valve) and feeling around it, it doesn't appear to have any lines attached to it. Is this normal (maybe I've identified the wrong part)?

Anyway it seems fixed now and my original fuel delivery guesses were completely wrong... Can any other NB8A drivers confirm this hum/buzz is normal?

oh and +1 respect to JBT for leading me in the right direction. +0.5 for red because it does tick when the plug breaks contact :lol:

Steampunk · Postby **Steampunk** » Mon Aug 31, 2009 12:55 pm

Patty wrote:oh and +1 respect to JBT for leading me in the right direction. +0.5 for red because it does tick when the plug breaks contact

I'm surprised no one else has some advice. I only wrote it cause I had a similar experience.
After I installed my aftermarket engine management system, and turned the key for the first time, I heard the buzzing and the "tick" and it scared the begezzus (cause obviously it didn't happened before) out of me. Lucky my best mate was with me and he rightly ascertained it was the fuel pump.