Hi Folks,

So I swapped in a new odometer gear (which seems to work fine), and now the tachometer is reading low. At idle the tach needle is under 0... ??? About 1500 rpm low.

I took a photo of the wires before removal, and replaced them in the same locations. Tach worked fine beforehand.

As I side note, I get the idiot award for putting the dash light dimmer switch knob up on the dash above the instrument cluster... The knob is living in the windshield defrost duct work now.

Thanks for any info.

Bert

Folks,

It ends up the tach needle rotates easily on it's shaft... I must have mishandled it during the gear swap. It took a few tries to reposition the needle, but it's close enough now.

Still need to check connections regarding those OBD codes.

When you have the tach out connect temporary wires for power and ground and retest. I vote for the needle loose or moved on the shaft. Or, maybe the face plate moved. The peg at zero still there?

Hi Bert,

You said your car idles below 0, did you mean below 1? Your idle should be at about 800 rpm. You also said that your idle is 1500 rpm low. Does that mean it idled at more than 1500 rpm before? Your numbers are out of whack.
--
Bruce S. near D.C.

Bruce,
To clarify, my motor has been idling around 750-800rpm and the tach is now reading a good 500rpm or so below the "0" on the dial, so the tach is off by 1000-1300rpm... Hard to tell exactly as there are no lines below "0".

Just drove the car, and it seems to drive OK. I just drive by ear and estimate the tach is 1000rpm low.

The tach is a mystery, as are the 1-4-4 and 2-1-4 codes.

"The tach is a mystery, as are the 1-4-4 and 2-1-4 codes."
The OBD codes suggest a bad connection.
https://www.brickboard.com/FAQ/700-900/EngineOBDCodes.htm

Maybe you just need to unplug and replug the connections the the cluster.
--
1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.

Unplugged, cleaned and replugged the connectors. Thinking the problem is elsewhere.

Thanks.

Looks like I have a short somewhere causing #6 codes 1-4-4 and 2-1-4.

The car seems to run OK. I did a 120 mile trip with the tach reading low.

I removed the gauge cluster, cleaned up some terminals and reinstalled. Car runs with tach low.

My guess is the gauge cluster is not the problem...

Any ideas where to find the short?

1991 LH3.1 system.

Newish CPS. Most everything else replaced at one time or another...

Bert, I can't help with the tach--but came across a dash light rheostat knob this afternoon. Send me your street address and I'll drop it in the mail. You can send it back when--and if--you retrieve yours from the vent :-) -- Dave

Thanks Dave, but I noticed the knob is just inside the vent and I may be able to get it with a magnet or something. I always love a challenge.

"I swapped in a new odometer gear (which seems to work fine), and now the tachometer is reading low"
The tach is separate from the speedo. It runs directly off the distributor. (red-white wire is high voltage from the distributor and can wreck the instrument cluster if connected to it.) Probably just a bad ground. No need to disassemble the speedo.
--
1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.

Thanks for the heads up.

Was not planning on actually disassembling the speedo, just remove from cluster as for gear install, check the contacts and replace.

Any specific ground points to check?

Never heard this complaint before, and I watch the odo gear troubles religiously.

What year? Grounds are done differently 92/93. Could be a poorly seated contact at the tach gauge? It gets its power and ground from the pins on the cluster board. Are the berg stick pins from the speedometer gauge properly inserted in the sockets of the cluster board? Just guessing that the tach ground is not quite at ground potential.

Anyway like Ted's tongue in cheek, I'd take it apart and go over every step you took. That's the troubleshooter's mantra, for we fix nothing that we don't break something else doing it.
--
Art Benstein near Baltimore

"I sleep eight hours a day and at least ten at night." —Bill Hicks

Thanks for the responses.

I did a search and didn't find this problem posted.. New to me.

I'll take it all apart, inspect in the process and put it back together. Will double check the grounding, and maybe clean some contacts.

FYI: It's a 91. I added the tach years ago and have had no issues.

Bert

Bert, I just had a look at a tach (large tach for cluster). The needle stops at zero; it cannot physically go below unless it got loose on its shaft. The "ground" theory is therefore wrong. Your gauge just got "knocked out of calibration."

The EZK codes are unrelated, I'm sure. I'd reset them, be sure they returned, and then carefully inspect the plug/socket for the CPS, and the ICU. There's nothing in the cluster for the ignition system at that level.

It makes good sense to try to correlate new troubles with work you've recently done, but sometimes the new troubles are more of a coincidental occurrence.
--
Art Benstein near Baltimore

"On his feet he wore…blisters." —Aristotle

Art, I agree that the tach and codes are unrelated. I just noticed both issues at the same time and wondered if wiring on the cluster could cause the problems.

I guess I'll take the cluster back out and see if I can "recalibrate" the tach needle.

I'll inspect the plugs and sockets.

this may sound stupid but before presuming causality i would remove the new installed odo gear and reconnect the tach and try it out.