Tachometer Fluctuating

[TheCanadian007]

Hey Guys, I've gotta carb'd 2.2 '87 Horizon with the Canadian (kilometer spec) rally gauges. Just recently I've noticed my tachometer has been acting very funky.

Upon cold start up the tach reads fine at idle, but once I give it gas, it starts fluctuating and won't give a proper reading. Once the engine is warm, it reads fine at idle and up to 2500 RPMs, at which point, it jumps from 2500 to 3500 RPM. (Engine speed itself isn't increasing at such a rate.)

Once the engine is fully warmed up and hot, the tach works perfectly fine with no hiccups. I recently added Bosch fog lamps to my car and spliced into the power module wire, coming off the positive battery terminal. I tried disconnecting the fog lamps entirely and the tach still acts wonky. I also replaced the distributor (the previous one had a wiggly trigger wheel) and also swapped 3 different hall effect pickup coils, all to no avail. I even scrounged a spare rally cluster out of another Horizon and swapped it, still not fixed.

I can live with the tach issues, as it does give me a reading once the engine is warmed up, but I'm kinda curious if any of you guys have similar.

[dirtyglhturbo]

we all have had tach issues. its a gracked solder joint on the back/inside of the cluster. resolder and yer done.

[TheCanadian007]

Which solder joint might be the culprit? Many Thanks.

[dirtyglhturbo]

pull out the cluster, remove the tach module off behind the tach. remove the cover, and you should see the culprit right in that area.

[NAJ]

Actually it is easier to do them all. Took me 15 miutes while watching TV.

[dirtyglhturbo]

^ yea what he said. i also found my fog lamp problem in the cluster as well.

[Sittn86]

Ok, now I'm intrigued. Fog lamp problem caused by faulty solder joints in the gauge cluster?? I'm not challenging, just wondering. My Duster obviously needs to have the joints reflowed because of the tach/R turn signal indicator, etc. problems I've had since I bought the car (I know, I'm lazy ). But the fog lights? Mine quit working a long time ago & I've looked at it just a little bit, but not enough to figure it out. Does that circuit really run through the cluster?

[dirtyglhturbo]

yes. the headlamp switch sends the fog lamp feed through the cluster. i had no fog lamps for years, until i got pissed and really started checking it out. i kept thinking, it must be the headlamp switch, but then i was looking at the wiring diagram, and it showed the cluster. pulled it, resolderd the prongs on it and poof . fog lamps again

[Sittn86]

Well, I know what I'm doing Friday afternoon! Thanks for the heads-up! I have an FSM set for my '86, but not the '94, so I was never able to look at the wiring diagrams. Who knows, maybe it's more similar than I know.

[TheCanadian007]

Hello Hello, reviving an old thread here.

It's been months since I posted this, but I didn't get around to yanking the wheel and cluster out until now. Once the cluster was out, i removed the PCB (printed circuit board) from the cluster and reflowed / resoldered all the joints on it. I reinstalled the cluster only to find it doing the same thing; tach still fluctuating. I noticed on the front that there's a whole bunch of transistors and capacitors on there, could one of those be blown causing the tach issue? Any other ideas or recommendations? Many Thanks.

[NAJ]

There is a Tach Module on the back of the cluster.
Not sure how to diagnose the module and I do not have any wiring for an 87 Horizon but it still sounds like a connection/pc board problem.

[TheCanadian007]

Thanks!

Anyone else provide some insight?

[TheCanadian007]

bump bump

[NAJ]

Surprised nobody has responded yet.
I now have the wiring for an 86 Horizon, i can post it for you tomorrow if you think it will help.
Mitchell On Demand is not showing any diagnostics for gauge/tach malfunctions and my 90 FSM only shows "tach inop" so the earlier manuals are probably the same.

[TheCanadian007]

Yeah, sure, thanks NAJ. I'm open to any help that I can get. Was thinking of stopping by the auto wrecker and seeing if I can nab another PCB to plug in there, try and see if I can find one good one.

Any other replies appreciated as well, Thanks.