tach problems (not twitchy tach like others have had) repost from gen/newb forum

[diputz42]

before you all tell me to do a search and read other posts, thats been done. i dont have that spuratic jumping twitching tach needle like other have posted about. i posted about this before i think and i didnt get much of a response. heres the scenario

when the car is first started for a while (usually in the morning after it has sat for a few hours) the tach will read zero. even if i rev it up a bit, it reads zero. then usually, after a short drive (seems to me like once the engine has warmed up), the needle will seem to catch on the tach spinner. sometimes it doesnt even need to warm up and it will catch. like this morning for example, i started the engine, tach read 0. then i put it in neutral and dropped the clutch and the tach seemed to catch. the engine idles quite high for the first few minutes (i assume this is normal). when the engine is idling high, the tach reads 2000. then when the engine finally warms up and idles normal, the tach reads 1500 when it should be 750-1000 at normal idle. even though the tach reads 1500, i can tell by the sound that it is idling at 750. i ordered a pocket logger, so once i get that in the mail (next week), ill plug it in and see where its idling.

now when i start driving, the tach seems to lag. what sounds like 5000rpm will read 4000 on the tach. and what sounds like redline will read about 6000 on the tach. and when i rev up the engine in neutral and the rpm drop back down to normal idle, the tach seems to lag. what i mean is as the rpm declines towards idle and lets say is at 1500 and declining, the tach might read 2500 and be declining slower than engine speed decline.

now heres the best part. when the engine/tach is still in this condition and i shut off the car, the tach needle lightly drops to ~500 and sits there. THE CAR IS OFF! and this is the ghetto part: if i continually open and slam the door, the tach needle slowly gets shaken down towards 0. and when i finally do get it back down to 0, the tach will work fine.

my best guess is something's loose. but i dont want to open up the gauge cluster and mess with/up anything. im hoping someone here has had this problem and knows a quick fix for it!!

thanks every1

 

[LandoAWD]

Sounds like a general calibration problem.

Do you have aftermarket gauges?

Did it EVER work properly?

If I were in your shoes, I'd mark where the CORRECT needle positions are, pull the cluster, place the needle for the tach in the correct position and verify good connections and that there is no binding on the back.

 

[diputz42]

Sounds like a general calibration problem.

Do you have aftermarket gauges?

Did it EVER work properly?

If I were in your shoes, I'd mark where the CORRECT needle positions are, pull the cluster, place the needle for the tach in the correct position and verify good connections and that there is no binding on the back.

bone stock. no gauges

it DOES work properly... usually once the engine warms up and sits off for a few hours or if I slam the door enough times and "shake" the needle back down to 0.

if i continually open and slam the door, the tach needle slowly gets shaken down towards 0. and when i finally do get it back down to 0, the tach will work fine.

any more ideas/suggestions?

when did this problem first occur? i have no idea because i just bought the car a couple weeks ago :\

im hoping it has somethign to do with the timing belt... because the belts are getting replaced right now as im typing. would that be possible?

 

[tsigrl2016G]

i put a post up like two weeks ago...about tach prob.'s.
The 90's have this signal unit for the tach on the back of the ignition coil pack,,,but for mine , there's no unit on there. The factory manual says that the unit on the coil pack sends the signal to the tach. Since mine doesn't have the separate unit...i figure it's the coil. A friend of mine let me borrow a coil pack he had extra , I haven't switched them yet, so right now my tach's useless. But it was on zero one day when i started it up, and then as i drove it more during the day, it would kinda "wake up" and "seem" to work properly. Now, it pretty much lost all "pattern" and does what it wants. I haven't had much time to work on the car lately, even something as simple as switchin an ignition coil. But, the car's performance isn't effected at all, it's just annoying to have the tach not work. I'm pretty sure only the 90 and 91's (might just be 90's) have this tach. signal unit attached to the coil...the 90's have the square plug...but when i switch em i'll post if it made the difference. either way, the tach get's it's signal from the ig. coil/ sig. unit. Oh, and i believe the wire should be white if u wanna check that out.

kylei

 

[tsigrl2016G]

I switched the coils today, and definately no change in the tach. i'm gonna try some other things and post what i can figure out

 

[diputz42]

try this... its what happens to me

if you turn on the car while its real cold, rev it up to around 3-4k and see if the needle seems to "catch". then if you rev it up again to about 3k and you hear the engine go back to idle, does the tach read as idle when it sounds idle? then shut off the car. does the tach read about 500? if it does, keep opening and slamming your door until you kind of shake the needle back down to 0 while the car is off. then, when you turn on the car, the tach works perfectly if i remember correctly.

if you have these exact symptoms, weve got the same problems. if you got a few of these symptoms... we probably still have the same problems.

one new thing that its been doing the past couple of days is its making a squeaking noise from the engine if i rev it up even a little bit during the first ~20 seconds after i start the engine while cold. ever notice this before?

let me know what new finds you make. i'll do the same.