Digital Speedometer Issue

[boosted7]

Just picked up a beater coupe I need to use as a DD for a bit.

Reads 10km/hr or so at idle, on the dash and on the heads up. While in neutral if i rev the engine it will increase the speedometer readout.

While driving it is accurate(tested with GPS).

Intermittent as well. Wasn't doing it last night and is doing it today again etc.

Any common problems that cause this?

Thanks!

[xpertsnowcarver]

Start by downloading the factory service manual and learning how to understand the speedometer circuit.

[knate]

Start by downloading the factory service manual and learning how to understand the speedometer circuit.

Do you understand it? You are sounding a little condescending. It's not like he's just missing a speed signal.

I have not seen this in any analog dash 240s, but I had a HUD 240 that would do this while and I believe was more common when cold. It was so intermittent I never really dove into it. Since I've never heard of this on the analog cars it's probably something in the digital dash itself.

It sounds like some sort of electrical noise in the circuit, most likely from a poor connection. Cold temperature might make poor connections worse from shrinking metal. You might try reconnecting all the plugs that the speed would go through. Not just the ones at the back of the cluster, but I would reseat anything on the speedometer itself (including any screws that are used for connections). You should also try clean the contacts when doing this, make sure it's good clean metal making the connection. I haven't seen the back of the digital dash so I can't be any more specific than that.

I don't think it's related to the HUD since I believe that is just fed after the speedo and they both see the same problem.

And lastly if you do this, please let us know if it helps.

[xpertsnowcarver]

:tweak: Exactly what word or phrase comes off condescending? Please enlighten me by PM.

You're asking me if I understand how to use a FSM? Why would I instruct someone to bother with one if I didn't understand how to use one myself?? Nevermind, don't PM me... I'll just delete it.

^^That right there can be considered condescending.

[knate]

:tweak: Exactly what word or phrase comes off condescending? Please enlighten me by PM.

You're asking me if I understand how to use a FSM? Why would I instruct someone to bother with one if I didn't understand how to use one myself?? Nevermind, don't PM me... I'll just delete it.

^^That right there can be considered condescending.

Your wording saying to start by "learning how to understand the speedometer circuit" was a little condescending since the circuit is a simple one. I couldn't tell if you intended it to be or not, so that was me letting you know.

Since you are dense, I am asking if you understand the speedometer circuit so much better than the rest of us. The circuit you will find in the FSM is quite simple. Sensor -> Wires -> Speedo. Where does that get you when your speedometer normally works?

Your post added zero value to the conversation.

[xpertsnowcarver]

Right, since ^^^ adds far more value while I continue to stress the importance of learning to read a FSM. Carry on with your spoon feeding.

I forgot to add. Aside from coming off condescending. How do you find me arrogant in "knowing the speedometer circuit better than anyone here?" It's a rhetorical question. I never claimed such.

[boosted7]

Thanks Knate, probably is a connection/ground somewhere. Also seems to be more when cold as well. Wasn't doing it after a 5hr drive yesterday.

It is a HUD.

[knate]

Right, since ^^^ adds far more value while I continue to stress the importance of learning to read a FSM. Carry on with your spoon feeding.

I forgot to add. Aside from coming off condescending. How do I come off arrogant in "knowing the speedometer circuit better than anyone here?" It's a rhetorical question. I didn't.

This is not spoon feeding. If he asked why his speedometer had no signal, I would not have posted. That is something you can get from the FSM. There are a lot of situations where "Read the FSM" is an appropriate response. However this problem is not as straight forward as you seem to think it is.

The original poster asked a question which is NOT simply answered by the FSM. You can continue to stress the importance of reading the FSM all you want. Go read it yourself. Then please scan the page that tells you what to do when the speedometer works normally while driving, but sometimes shows erratic low numbers while stopped. It's not there.

You come off arrogant acting like you know the FSM is his answer, when his specific issue is not in there.

I'm done here. Apparently trying to help is discouraged in the tech section.

[lou's40sx]

Try: TunerClub.Net - Your Only Destination for Anything Related to Tuning - S13 Replacing a gauge cluster (http://www.tunerclub.net/content.php?38-S13-Replacing-a-gauge-cluster)

[boosted7]

So your saying it's my cluster that is causing this?

[Norty]

Not definetly anything. The speed signal is a pulsed signal and any kind of electrical noise could cause this. At idle with the car not moving there should be no or very little pulse because the sensor is not turning. It works off a worm gear in the transmission. But while driving down the road the signal is overcoming the noise thus making it read accurate. IF and only IF it is really an annoyance then you could dive into the wiring and solder connections at the hud display, but do so at your own risk because they diplay units and their connections are very delicate. It could possibly never work again! G/L

[boosted7]

Thanks norty!

[Charlie]

I want to know more about this as well.

I have a analog cluster and it does the same thing, but on idle/complete stops the speedo sometimes moves on its own. The thing is my speedo doesn't work most of the time. Most of the time the needle will just hang up there lets say 40mph. Before I would need to tap on the screen and then it will jump up to what I think is the actual speed I'm going, then when I come to a stop and go again it would stay at 0 again. Maybe my speed sensor is bad?

[dr.klawn]

i took my HUD apart when i purchased the car 7 yrs ago & it didn't work. i cleaned it with q-tips & elec parts cleaner that i dipped the q-tips into. i don't touch it now... just let it do it's thing & it's worked since. do u think ur speedo wires could b grounding out on tranny harness? 5-speed or auto?? i mean idk, just guessing....

[boosted7]

5speed. The HUD and digital dash readout work fine other than reading incorrectly while not moving. Dealing with some other issues first with the car before i start tackling this problem.

[EnnEssEnnKAT]

I have this strange problem. Only happens at cold and at idle for a short period of time and stops once driving.. Does anyone else guess the connections are to blame? I went from a needle type speedometer that worked fine, to a digital with HUD. It only started doing this after I installed the digital cluster.

Any additional input on top of the posts already in this thread?

[Mishkin_707]

I made I video of mine doing the same thing, only happens when it's cold, after the car is at full operating temperature its normal, it started like 7 years ago, haven't figured it out, also when it's cold my dash won't display lights or speed until my car is warmed up, again only in cold weather, summer time is fine, people say it could be the TCU but I haven't replaced it, although I did buy an Apex'i RSM to remedy the problem, that didn't work, the speed wouldn't read on there either, stays at 0 until the cluster comes on

[EnnEssEnnKAT]

TCU..what's that?

[Mishkin_707]

Timing control unit, little white box in the driver side kick panel near the fuse box

ALSO TO THE OP, there's a little knob next to the speedometer number display on the cluster, twist it left or right, it's to change it from Kph to Mph

[EnnEssEnnKAT]

I was in fact noticing that box wasn't secured down when I had my dash out the other day. I sort of just stuck it back and didn't secure it. Will look into fixing that.

[Mishkin_707]

Dunno if it would make a difference if it was bolted in or not but ya never know