Fuel pump? Or other issue?

ntranced · Postby **ntranced** » Tue Oct 08, 2013 11:36 am

Went for a drive down to the South coast over the weekend in my 02 MX5 and ran into some worrisome car problems. Was driving for about 1.5 hours and a bit of spirited driving through some mountains, the engine spluttered; revs dropped suddenly and back up for about 15 seconds until it completely cut out.

Got it stopped on the side of the road and it wouldn't start up again, engine would crank but wouldn't start. Tried starting about about 5 times but nothing, limited mechanical knowledge but suspected a fuel issue, only fuel related fuse I could see was the injectors, pulled that and a hum/buzz from the engine bay would stop so wasn't that. Last thing I did was pull the battery terminal and put it back in (in case of immobiliser issue) but it didn't start either.

Kicker was, a second attempt after pulling the battery, it fired up fine and started and was fine for driving for the rest of the day (fine for more twisties and a 2 hour drive home), started perfectly every time and no spluttering at all.

The other reason I suspect fuel pump is that very occasionally the car doesn't start first go (cranks okay) and requires a second go. However this is very rare and the second attempt it fires up immediately. When starting the car, I tend to always wait til the beeps are finished before starting.

Question is, how do I rule out the other issues of CPS or fuel regulator (or other?) or diagnose an issue which isn't easily replicated.

Appreciate any input.

93_Clubman · Postby **93_Clubman** » Tue Oct 08, 2013 12:02 pm

Sounds like the NB's green EGI relay in the fuse & relay box in the engine bay. EGI relay was also the black Fuel Inj relay on the NA. There was a Mazda Techincal Service Bulletin about the relay in 1991 - prior to that I had the issue in my NA6. 'Shuey' was also having the same issue in his NB8B until recently.
viewtopic.php?f=55&t=41606&p=534500#p534500

ntranced · Postby **ntranced** » Mon Dec 30, 2013 9:53 am

Bumping this thread as it just happened today, was able to get a feel of more symptoms and noticed that when it was spluttering/surging under throttle, it would be extremely rough. Say I was revving to 2.5k, it would drop to say 2k and surge back and forth. If I opened the throttle a bit more, it would surge back and forth to that point. However, shortly after, it seemed like the max I could rev to would decrease.

Like I'd be able to get to 4k, and then it would slowly max out at 3.5k, then 3k, etc. I turned off the engine and re-started once and it would still surge. While it was surging, it would idle fine until a little bit later where the surging would begin as well until it cut out completely. Left it off for a while, checked under the bonnet for anything out of the ordinary, but nothing. Re-seated a couple of the fuses in the front and tried to start the car.

This time, it started up first go, revved it a bit and the splutter/surge wasn't there, let it idle for about 5 minutes and it was still okay. Was able to drive the car into the car park 10 minutes away.

I'm gonna order a replacement fuel pump and the EGI relay, any other suspects you guys think?

93_Clubman · Postby **93_Clubman** » Mon Dec 30, 2013 10:25 am

Make the fuel pump a lower priority, & do EGI relay, then cam position sensor, & then crank position sensor if the problem persists after each one - see here for links:
viewtopic.php?f=29&t=61318

Ref EGI relay, in addition to wreckers, you can also find them on ebay, where a number of us have bought them - eg:
http://www.ebay.com/sch/eBay-Motors-/60 ... 5b4&_sop=3

Diagnostics on page 2 of this thread might also be of use:
viewtopic.php?f=29&t=59479&start=15