Two tidbits (the first is kind of an aside):
(1) From what I've just read, TR7 convertibles didn't "happen" until late
1978 and first appeared as 79 models (although it's likely some
preproduction convertible models are out there :-) Just a FYI...
Thanks to all who responded to my TR7 parts car request :-)
(2) I *finally* got my air/fuel mixture meter from JC Whitney. Please
allow 4-6 weeks for delivery. Ack! I also hate it that they saw fit to
charge $10 to ship a $35 meter. Anyway, on with the description.
The meter is made by a company called
Cyberdyne
205 Main Street
New Eagle, PA 15067
412/258-8440 or 8442
and I bet if you called or wrote to them, you could buy from them direct.
Their instructions are good; they are also *typed* (as in on a typewriter!)
Inside (you can see through the red plastic gauge face) is
*LM3914N (National Semiconductor I think)
*1 diode
*1 tantalum capacitor
*3 1/4 watt resistors
*1 1 watt precision resistor
*1 bar graph display, HDSP-4836 (with hp 135 I2 below it)
*3 display LED's which read LEAN, RICH, AIR/FUEL
There may also be parts underneath the circuit board that I can't see.
These parts are all housed in a very cheap plastic gauge housing and the
face is smokey red (?) plastic. You cannot open the gauge up without
destroying the housing.
Does it work? "The jury is still out" deciding that one. I've got dual
O2 sensors on my TR8 (yes, it's fuel injected). I used to set the idle
mixture by connecting up a good analog voltmeter to an O2 sensor and
tweaking the mix until I got a voltage somewhere between low and high (100
and 900 mV). Then I hooked up the O2 sensors back into the feedback loop
and that was that. NOW I figured I could use my new meter and watch
everything while I drive. I hooked it up and drove around. Nothing. Way
too lean to even register most of the time. I was mystified. The car's
been running just peachy for months now. I hooked up a cheapie voltmeter
to an O2 sensor and it didn't register. (I need to get a GOOD, high
impedance analog voltmeter which reads voltages in this range.)
Possibilities of what's wrong?
(1) Maybe the Cyberdyne meter is crap? I'll take it to work tomorrow and
put 500 mV across it and see if it measures somewhere midrange.
(2) Perhaps my O2 sensors have crapped out? That seems unlikely,
especially since they're only 15k miles old. (Note that I only use
sealants that say "safe for oxygen sensors"). Manual suggests replacement
every 30k miles so they oughta be worth 50k miles. I'll check them again
with a GOOD voltmeter from work tomorrow. YES, they were hot when
I was doing my testing.
(3) Maybe the fuel injection on the TR8 really IS running massively
LEAN? I've already tried tweaking the mix to full rich and it had very
little effect on the meter (although the car didn't run quite as well). I
put the mix setting back. After I check out (1) and (2), I may take it
somewhere and have them put a sniffer in the tailpipe and we'll see. It
certainly *seems* to run fine and not above the 18:1 mix the Cyberdyne
gauge says.
Any other suggestions?
Stay tuned! Meanwhile, for all you guys out there with data books,
exactly what IS an LM3914N? Write us back and let us know? I'd love to
*make* another one of these gauges and just mount the displays (I don't have
room for two big 2 1/8 in diam gauges).
jim
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