NA6 wouldn't start

93_Clubman · Postby **93_Clubman** » Tue Mar 29, 2011 2:41 pm

Low km & FSH Australian delivered NA6 wouldn't start, but battery & starter cranked engine ok. No restriction in air filter or intake, however removal & check of a spark plug after cranking revealed it was dry, but that there was a spark. Further checks revealed fuel pump wasn't operating, but that there was power at the loom side connector at the top of the fuel tank where the fuel pump & fuel gauge assembly is located.

Removed & checked fuel pump - it worked! Checked continuity at terminals at top outside of fuel pump assembly connector & found resistence. Removed fuel pump wiring plug to top inside of fuel pump assembly connector, & found that the top connector of the wire (blue) from the positive terminal of the fuel pump, the corresponding terminal of the connector block at the inside top of the tank, & the plastic plug encasing the two fuel pump connectors were the problem.

Connector & terminal had a black coating which was producing the resistence, & the inside of the plastic plug had deteriorated, including the top of the partition between the two fuel pump connectors. Bought fuel pump wiring harness (including plugs) from GCG Turbo & modified it very slightly to fit. Top plug required shaving of a little plastic on its side & used bottom half of old harness to lengthen new harness (this allowed polarity of wires to be reversed, i.e. old blue to new black, & old black to new blue.

The fuel pump & fuel gauge assembly were otherwise in perfect condition, as was the inside of the fuel tank. The issue has come up on Miata.net a few times over the last five years or so - see last post on page one of the following: http://forum.miata.net/vb/showthread.php?t=247957

Attached pics are courtesy of the above post for anyone without a Miata.net logon. Pls note in this Miata.net example it appears to be the terminal & connector from the negative wire of the fuel pump. This may be due to different wiring in the US delivered cars, or simply that either wire is susceptable to this problem.

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manga_blue · Postby **manga_blue** » Tue Mar 29, 2011 8:34 pm

Nice one. I reckon that's the sort of problem you hope for just before you buy a car. Worth about a grand.

93_Clubman · Postby **93_Clubman** » Wed Mar 30, 2011 12:49 am

manga_blue wrote:Worth about a grand.

Two grand actually :shock:

is what Mazda quoted me to supply a new fuel pump/ fuel gauge assembly.

Meant to include that the fuel pump wiring harness pump plug is a Walbro GSSXXX type, while the top tank plug at the other end of the wiring harness is a Mitsubitshi type. If you can find one in Aust, Walbro fuel pump harness 94-614 is correct, although slightly short, or Walbro 94-646 (if you reverse polarity). Walbro fuel pump fitting kit 400-791 for Subarus also contains what appears to a Walbro 94-646, i.e. you need to lengthen & reverse polarity of the two wires supplied.

Btw, according to Miata.net threads this has affected NA6, NA8 & NB8. They also reckon it's called 'black wire' in the remote control plane community, but after further reading that seems to be due to NiCad batteries. Although the outcome, i.e. a black coating or build-up on connector & terminal, which intermittently & eventually breaks contact, is the same.

manga_blue · Postby **manga_blue** » Tue Nov 18, 2014 2:37 pm

A bit of a thread revival. I replaced the fuel pump today as part of a long and bitter campaign to find a full throttle miss.

I checked for blackwire and it was all good. After I'd put the new pump in I had a closer look at the old pump and while doing that some powder fell onto the table. It turned out to be some ultrafine metallic stuff, maybe part bright steel and part brass, which had collected in the base of the pump's electrical plug. It was almost 1mm deep and substantial enough to provide an electrical bridge between the terminals. :shock:

Sorry but I blew it all out before I thought to take a photo of it.

I suppose that with over 200,000kms on the car this was accumulated fine metallic particles deposited from hundreds of fuel fills.

Anyway, if you're checking for blackwire then all it takes is another 60 secs to check for this and clean it out.