Miata Mailing List: September 1992, Message #74
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   From: (none)
Subject: Re: My Miata Needs Better Gas!
   Date: (none)


In message <9209291945.AA05863@voyager.austin.ibm.com>,
moore@slt.ncsc.navy.mil writes:
> My '91 Miata (silver base package) suddenly, and I mean suddenly, began
> requiring premium unleaded last year (around the 18k mark); anything less,
> and I've tried Exxon, BP (aka Gulf), and Amoco, detonates badly under hard
> acceleration, usually second to third.  The transition from surviving on the 
> cheap stuff to demanding the expensive stuff ($1.24.9 down here right now) 
> happened over a month's time at most.  I'm the sole owner and the engine's
> not been thrashed at all (well, okay, but just enough to break it in), and I 
> installed splitfire spark plugs (properly gapped) when the trouble started.
> 
> Now here's the weird part (and hopefully it's just coincidence): at about the
> same time my wife's Bronco II experienced similar gas problems; she switched
> to premium, then back after a few months, and she experiences only minor (?)
> knock.

Definitely weird -- sounds like one for the Tappet Brothers, Click and Clack!

I'm at 55K miles on a '90 model, and have *never* had problems with pinging or
knocking with the 89 octane (87 uleaded is the cheap, recommended stuff; 91 or
92 unleaded is the highest generally available) I put in it.  I'm also running
splitfire plugs, good condition wires, timing seems to be OK, etc.  Most of
the miles have been put on here in Austin (400-600? ft. altitude, moderate to
heavy humidity, hot summers, mild winters), but I've also driven the car in New
Orleans, the Adirondacks and in the mountains west of Denver without problems.
My Dad's '87 Nissan pickup truck (2 or 2.2 liter overhead cam inline four,
with *two* spark plugs per cylinder) starts to ping on the 87 octane stuff but
smooths out on the 89.

Did you have some interesting shift in the weather lately?  (Nah -- wouldn't
make enough of a difference.)  Have owners of your local gasoline distributors
been seen together coming out of private restaurants?  (Hmm.  Conspiracy
theory types would go for it.)