mx5cartalk.com

Firstly let me say that the Search function is again refusing to cooperate and Miata.net doesn't seem to feature anything on fuel pumps. Here goes:

I was shocked and amazed when my 5 surged a couple of times during a blast up Black Mtn last night. These felt very 'dead fuel filter' esque, so I thought the time had come to change it (I'd been meaning to do it for ages, as its the only filter I am yet to change in my 12 months of ownership).

Anyway, today I drove her straight to Repco to buy a new one. On the way back, she surged a couple of times before spluttering to a halt halfway up the hill on Belconnen Way. She wouldn't restart.

I set about changing the filter on the spot with the scissor jack. Just before I pulled the hoses, I thought I'd give her one last try, and she started as normal. At this point I was thinking that the blockage had just resettled within the filter.

I managed to gingerly cruise all the way to within 2km of my home where she did it again.

So I changed the filter. Sadly, after changing the filter there was no change. So now I'm thinking fuel pump.

I arranged for a tow home where I pulled the hose at the fuel rail to see if it was pumping. Logic tells me that an electric pump will be pumping when the key is in the \"on\" position. However mine was not. It was only spurting fuel when on \"start\". ??????

Have I got a dead fuel pump? The only other possibility I can think of is the coils, but am thinking thay would have given more of a rough idle in the leadup to dying.

It's probably time I invested in that workshop manual I know.

Also, after having a jolly good look around, I can't find where to access the fuel pump. Do you have to lift the carpet on the parcel shelf?

how dirty was ther old filter.......did any dirt escape the filter?

i think the fuel pump only starts working when the engine is being cranked & then stays on. you can get it going with the engine not started by jumping the test engine pins of the diagnostics box.

What Super said. There is a switch on the AFM that turns the fuel pump off when the engine stops turning.

When you changed the filter was there any pressure in the fuel line? If the pump is working there should have been.

You can check the fuel pump operation by shorting the FP and GND terminals in the diagnostics box and turning the ignition on - the pump should run.

If pump test OK, then maybe it's an ignition problem.

JBT wrote:You can check the fuel pump operation by shorting the FP and GND terminals in the diagnostics box and turning the ignition on - the pump should run.

If pump test OK, then maybe it's an ignition problem.

Thanks for the tips gents. Fuel pump seems to be fine courtesy of that test.

Any pointers for diagnosing ignition issues?

Try replacement spark plugs and leads. You'll be surprised how failure of these things (leads especially) manifest themselves. If no change, you'll have a spare set of those things and will then need to dig deeper.

Also check for any intake ducting leaks/cracks/disconnects.

JBT wrote:You can check the fuel pump operation by shorting the FP and GND terminals in the diagnostics box and turning the ignition on - the pump should run.

If pump test OK, then maybe it's an ignition problem.

What JBT said.
Normally the pump will come on when the key is in the on position and then click off after about 5 secs, I assume this is to presserise the fule system. You should be able to hear it doing this.

Also, under the drivers side dash (near Steering column) there is a large yellow relay. This is known as the Circuit Open Relay (COR). It controls the fuel pump, amongst other things in the 1989-1993 1.6l NA MX-5. By jumping the FP and Ground (GND) terminals in the diagnostics box you are bypassing the COR. Make sure the connections into the COR are not loose and that your earth connections are good as well, particually the earthing point under the windscreen wash bottle.

Good Luck.
J

Ha! The simplest of solutions has been found.


Seems that the otherwise splendid gents who did my 100k service last week didn't quite click home the connector running to the coil unit. On initial inspection it seemed fine, but when I went back over it, it fell apart in my hands. I clipped it back together and have found her to run perfectly since.

Thanks again to all who gave advice

Yay!