eightTfourTA

iTrader: (3)

My '84 TA has it's original gauge cluster with the 8000 rpm tach. Lately it's almost always stuck at about 1500 rpm, no matter what the engine's doing. It only moves if I go WOT and even then it just flies anywhere it wants. However, with the key in 'run' position the needle goes down to about 400 rpm like it always did, so I don't think (ahem) that it's physically getting stuck.
Any input before I start tearing things apart?
Next up, I bought a Nordskog LED Air/Fuel gauge. Should I use a separate oxygen sensor for this gauge, or tap it into the O2 wire, like at the ECM?
My tech manual tells me not to try to do a voltage check on the sensor, is hooking up a gauge considered the same? Of course the gauge instructions say to "hook the grey wire to the O2 sensor's wire". I tend to lean toward the tech manual, but I wanted to see if anyone else may have had experience with this.

------------------
DR Stevens
Car #1: my ride
1984 TransAm
305HO(L69) 95K & counting
750 cfm Q-Jet reman. by Holley
K&N filter
700R4/Superior shift-kit
3.42 lim.slip
underdrive pulleys
Accel HEI Super-Coil
180 stat/hi flow water
pump/Jet fan switch
dual snorkel /w/ hood louver
3" exhaust of some sort
partial emissions delete
Audiovox GM-250 DIN.5 stock-appearing radio /w/
10-disc Prestige changer
Car #2: My wife's ride
1991 Firebird/Formula
305TBI(LO3) 99K & smoking
K&N air filter
Hypertech Thermomaster Chip
Stock AM/FM cassette /w/ EQ, Jensen 400W amp, 12" Pioneer sub, 6-disc Jensen changer
more engine mods in the near future
"I'd rather flatbed an F-body than drive a
'Mudstain'.

TunedPort350

1) Sounds like you need a new tach.

2) I spliced my O2 gauge to the violet wire (under the dashboard) which goes from the O2 sensor to the ECM. That was exactly what the instructions said and I have had no problems. Just don't try to splice directly to the sensor wire (it is shielded), just splice in to the signal wire to the ECM.

Tim Burgess

The reason the shop manual says not to measure the voltage at the O2 sensor is that a low impedance voltmeter will load the O2 sensor output & its output voltage will drop, since it is a high impedance voltage source. A high impedance volt meter may be used to measure the output voltage of the sensor - or your A/F ratio meter, since it has a high impedance amplifier built into it. If the O2 meter has a "-" sense input for the O2 sensor, in addition to the "+" input, connect that to the O2 sensor ground wire at the ECM, as well.

Tim

eightTfourTA

iTrader: (3)

Ok, now I know I can hook up my gauge with no problems.
It was hot today down here, and the tach seemed to move a little more than it usually does. Still hanging out around 1500, but it was twitching up & down when the turn signals were on. Then when I went on the toll road and was doing around 75 mph which usually registered at about 2400rpm, the tach gradually settled in at 2000.
Any more thoughts on what I should be looking for to fix it?
I want to pinpoint whether the problem is in the gauge itself or another related component.

------------------
DR Stevens
Car #1: my ride
1984 TransAm
305HO(L69) 95K & counting
750 cfm Q-Jet reman. by Holley
K&N filter
700R4/Superior shift-kit
3.42 lim.slip
underdrive pulleys
Accel HEI Super-Coil
180 stat/hi flow water
pump/Jet fan switch
dual snorkel /w/ hood louver
3" exhaust of some sort
partial emissions delete
Audiovox GM-250 DIN.5 stock-appearing radio /w/
10-disc Prestige changer
Car #2: My wife's ride
1991 Firebird/Formula
305TBI(LO3) 99K & smoking
K&N air filter
Hypertech Thermomaster Chip
Stock AM/FM cassette /w/ EQ, Jensen 400W amp, 12" Pioneer sub, 6-disc Jensen changer
more engine mods in the near future
"I'd rather flatbed an F-body than drive a
'Mudstain'.

TunedPort350

The fact that it pulsates when the turn signal is flashing leads me to believe that there might be some wrong (or loose) with the printed circut board which is located behind all of your gauges. Are any of your other gauges acting flaky? I would first make sure that the gauge cluster is screwed in tight before I went and bought a new tach.

eightTfourTA

iTrader: (3)

All other gauges are normal; I had the cluster out about a year ago to fix some bulbs & free up my trip odometer (not fun). I made sure everything was put back together tightly and I even continuity-tested all the traces from point to point. I never took the tach out of the housing though, but it was working right at that point. It only seems to do this if the ambient temp outside is below 70- it starts coming back to life once the heat is on down here.
Looking at the schematics, the only other thing that I can see in this circuit is the tach filter-is this a problem spot? And where the heck is the bloody thing anyway?

------------------
DR Stevens
Car #1: my ride
1984 TransAm
305HO(L69) 95K & counting
750 cfm Q-Jet reman. by Holley
K&N filter
700R4/Superior shift-kit
3.42 rear/3.73 blew up!!
underdrive pulleys
Accel HEI Super-Coil
180 stat/hi flow water
pump/Jet fan switch
dual snorkel /w/ hood louver
3" exhaust of some sort
partial emissions delete
Stock-appearing radio /w/
10-disc changer
Car #2: My wife's ride
1991 Firebird/Formula
305TBI(LO3) 99K & smoking
K&N air filter
Hypertech Thermomaster Chip
more engine mods later
400W amp /w/ 12" sub

[This message has been edited by eightTfourTA (edited March 18, 2001).]