Only My Tach Works Properly...
 

Lately my gauges have been acting up, except the Tach.

Speedo has worked intermittently. It worked perfectly for the past 400 miles, then nothing one day, then began working again, now nothing. Can't seem to pin down the cause of the problem, seems to come and go with every drive cycle of the car, it never quits or begins working again when I am driving it, only when I turn it off and drive it later in the day, or the next day.

Fuel gauge has begun to read about 1/2 tank high when the car is first started in the morning, then settles back to the "correct" reading after a bit of driving.

Coolant temp gauge often bounces up/down 1/4 mark on the gauge so I never know if it is reading accurately. It mostly reads just below the uppermost white mark, not sure if this is normal or not.

Oil pressure gauge reads 5bar on startup consistently, settling down once the car heats up, not sure if that is normal. If I disconnect the fuel injection relay and crank the engine, it will climb to 5 bar with just the starter cranking - bad sender?

volt meter reads low consistently, about 12.5v with the car running, while actual charging voltage is 14.45 measured @ battery and jump post - can it be adjusted? I know from other threads that this is a common problem.

Finally, shift indicator rarely works, only seen it come on twice in one year of owning the car. The other night when the key was in position 2, indicator lit up (enigne off), a rare occurrence.

Could there possibly be an issue with the cluster as far as connectors or terminals??? It seems unlikely that all the different sensors are flaky, the fact that I have issues in almost all the gauges except the RPMs would lead me to believe this. Should I start checking voltage to the connectors behind the cluster? Or should I look somewhere else first? Any help would be greatly appreciated, I am going nuts driving around with no speedo and poor gauge readings.

Pull your pod, verify all the terminal screws are driven in tight. Spray the connectors with cleaning solvent, the scrub all grounds throughout the chassis. Worked for me.

So it definitely sounds like a connection problem? I will recheck all the grounds, then pull the pod and do a thorough cleaning.

I found ALL the terminal screws on the flex board backed out. Not sure how they didn't fall out. Previous repair at a local Porsche shop changed out the light bulbs (which does not require removal of the flex board), and managed to back the terminal screws enough to cause intermittent operation of the guages, namely the tach (which drove me nuts).

I use WD-40 on all electrical connections. Works great for cleaning, and protects for a long time.

I'm in the process of completely re wiring my dash and dumping the printed circuit. Ill post pics when complete

I just pulled the pod and connected just the cluster. When I hold the cluster by the sides and gently flex the white plastic base, the fuel and temp gauges jump around. After removing the 2 pin connectors on each gauge and all the screws, cleaning electric board with an eraser, and applying ox-gard, the gauges no longer bounce when the base is flexed, they hold a steady reading. I still can't get the upshift indicator to light with the key in pos 2 though - it used to occasionally. Anything else I should clean while I am in there? I have the tach out to clean the pins that connect to the threaded terminals, maybe that would help. Hopefully the speedo will work better too.

BTW I adjusted the resistor on the back of the voltmeter to the max, and it now reads just under 12 volts, which is closer but not close enough. Options?

Anthony10370, thats a great idea! I thought about that while I was removing the pod, should work great. Maybe I will do that as a winter project, definitely post pics.

Just finished putting everything back together. So far gauges do not bounce. However it seems I created a problem while I was in there, as my alternator is not charging now. All the dash warning lights stay on except for the alternator light when the car is running. I've had this happen before when my alternator quit, but this time I must have messed up the back of the voltmeter. Hopefully I can pull it apart again tomorrow morning before work. Any ideas?

As I understand it, the alt gets it's field/exciter voltage from the voltmeter, or something in the pod. Who knows, that resistor may be what controls the exciter voltage. I'd return it to it's previous state, fire the car back up with the pod uninstalled, just the connectors hooked up, and see what happens.

Found the issue. I checked all the connector pins which I knew were part of the voltmeter. The copper strip for pin 11 on the printed circuit board popped out from underneath the blue covering that allows the white plastic connector to slide on without damaging the copper strips, and got folded over on itself when I reinstalled the connector. The back side has adhesive on it, so It didn't conduct. Folded pin 11 back and reinstalled connector, now it works fine.

Sweet!

So far the coolant temp, fuel, and oil pressure gauges seem to read correctly, no more bouncing randomly. Voltmeter still bounces occasionally, but reads more accurately as I adjusted the potentiometer on the back. Speedo has not quit yet, only time will tell.

Shift indicator worked briefly today, still not sure why it works so infrequently. Anyone have tips for fixing this? I know it's not a neceesary piece of equipment, but I have seen it work and would therefore like it to work all the time.

Broken wire that makes contact once in a while, probably on very hot days because of heat expansion.

This information might help you for the 84 especially:

Odometer Repair Procedure w/pics - Rennlist Discussion Forums

Instrument Cluster Repair w/pics (Part II) - Rennlist Discussion Forums

Maleficio; I agree, there must be a wire/terminal that makes contact intermittently due to heat/vibration. Possibly one of the riveted connections on the back of the speedo which I think feed vehicle speed to the tach.

Landseer; great links, never thought it would be possible to solder on the plastic circuit board. I'll try some of those tricks next time I open up the cluster, which will be soon I think (there are some specks of dirt/lint behind the plastic bezel which are bugging me).

On another note, where is the temp gauge supposed to read when the car is up to temp? Mine reads at the topmost white line consistently. This seems a bit high so I am not sure if there is still some inaccuracy in the gauge/sensor, or my engine is actually running that hot. I replaced the thermostat with the correct temp range when I did the TB service. Old one was labeled 92 to 106 degrees F. Seems too warm. New one was marked 87 degrees F. Replacing the t-stat did not affect the gauge reading though, it read at the topmost white line even before the service.

Finally, should I be getting battery voltage to the terminal on the cluster connector that feeds the voltmeter? I believe i got somewhere around 10.5 - 11.5 volts when I was in there. Possibly why the gauge was reading low?

When i pulled my gauge cluster the second time, it rested in my lap as I fixed the loose screws. After reinstall, the coolant temp gauge read lower than it did before. I presume I maligned the needle position as I worked on it. At the same time, I installed Royal Purple coolant additive. I honestly can't say that the reading is accurate or not because of this combination.

My temp gauge reads dead center when driving in a normal cyclus. If I'm cruising along at, say, 55-60 mph, it drops a few millimeters. Spirited driving doesn't seem to have any influence.

But a mechanics thermometer in the bottle when its hot or tape one to the hose to get an idea of the actual temp

Good idea, I will have to do that, then adjust my gauge. If everyone elses gauge reads somewhere in the center, I don't see why mine shouldn't.

a better tool for monitoring the temps is an IR gun.
If your having funny readings on the pod also check the 14 pin connector above the hot post for corrosion

Funny you should mention that, because it just occurred to me to check that connection. That could explain why the oil pressure gauge is still bouncing. As for the voltmeter I am unsure, I am not getting battery voltage to the pins on the plastic gauge connector, so maybe clean CE panel real well too? And maybe even test wires for excessive resistance?