Speedometer AND tach still not working
06-01-2001, 01:55 PM
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Speedometer AND tach still not working
I have posted a few weeks ago that mt tach wasn't working. I hadn't fixed that as I was trying to get the car on the road. Now that I can drive it I notice that the speedo doesn't work either? All the other gauges work, what should I do is there a common wire here that I am missing? 
06-02-2001, 01:01 PM
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Shawn,
Ugh, the 1977 wiring diagram was not meant to be easily read. For 1981, they became very readable. The 1977 wiring diagram would say the tach and speedo have nothing in common. Let's make a big assumption for the moment that the instrument wiring in 1981 is a guide to 1977. The 1981 wiring diagram would say they share a common brown ground wire, which starts at the clock, to speedometer, to tach, to oil temp indicator, to fuel indicator to ground. If there was a ground problem between the tach and speedo, or after the tach and before the oil temp indicator, then the clock shouldn't work.
Did you take the engine out and just put it back in? If so, is the speedometer hooked up to the transmission sensor that sends signal to the speedometer (assuming you have an electronic speedometer)? Is the connector under the tunnel cover behind the front seats disconnected? I can send you/post the procedure to test the speedometer and it's sensor if you that would help.
Ugh, the 1977 wiring diagram was not meant to be easily read. For 1981, they became very readable. The 1977 wiring diagram would say the tach and speedo have nothing in common. Let's make a big assumption for the moment that the instrument wiring in 1981 is a guide to 1977. The 1981 wiring diagram would say they share a common brown ground wire, which starts at the clock, to speedometer, to tach, to oil temp indicator, to fuel indicator to ground. If there was a ground problem between the tach and speedo, or after the tach and before the oil temp indicator, then the clock shouldn't work.
Did you take the engine out and just put it back in? If so, is the speedometer hooked up to the transmission sensor that sends signal to the speedometer (assuming you have an electronic speedometer)? Is the connector under the tunnel cover behind the front seats disconnected? I can send you/post the procedure to test the speedometer and it's sensor if you that would help.
06-02-2001, 02:53 PM
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Yes the engine was out and put back in. I am sure the connection is attached to the transmission, is there a way I could have hooked it up wrong?
Clock working in a 911 haha thats funny. Actually mine is working so that can't be it.
I will have to double check the connection at the transmission, anything special to look for that I may have missed?
Thanks
Shawn
Clock working in a 911 haha thats funny. Actually mine is working so that can't be it.
I will have to double check the connection at the transmission, anything special to look for that I may have missed?
Thanks
Shawn
06-02-2001, 03:44 PM
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Shawn,
Check to be sure the connector under the cover in the tunnel is connected OK. Otherwise you may want to check to make sure that the speedometer sensor is sending info to the speedometer.
Here's how the factory says to test if the sensor is working correctly: Jack up the rear and put it on stands. If you don't have a limited slip differential, lock the left rear wheel (someone could just hold it to keep it from turning when you do the test). On the rear tunnel behind the front seats, take the cover off, and detach the connector, which is the line from the speedometer sensor to the speedometer. Hook up a buzzer to the line. Go to the right rear wheel and turn it at least twice. You should hear the buzzer sound 8 times for each two turns of the right rear wheel. If you have limited slip, then you don't need to hold the left rear wheel, but you'll hear 8 buzzes per turn.
It would be incredible timing if the speedometer sensor stopped working when the engine was taken out. I think I'd check the continuity from the wire in the tunnel to the speedometer, also. I hate shooting bugs like this....Good luck!
Check to be sure the connector under the cover in the tunnel is connected OK. Otherwise you may want to check to make sure that the speedometer sensor is sending info to the speedometer.
Here's how the factory says to test if the sensor is working correctly: Jack up the rear and put it on stands. If you don't have a limited slip differential, lock the left rear wheel (someone could just hold it to keep it from turning when you do the test). On the rear tunnel behind the front seats, take the cover off, and detach the connector, which is the line from the speedometer sensor to the speedometer. Hook up a buzzer to the line. Go to the right rear wheel and turn it at least twice. You should hear the buzzer sound 8 times for each two turns of the right rear wheel. If you have limited slip, then you don't need to hold the left rear wheel, but you'll hear 8 buzzes per turn.
It would be incredible timing if the speedometer sensor stopped working when the engine was taken out. I think I'd check the continuity from the wire in the tunnel to the speedometer, also. I hate shooting bugs like this....Good luck!
06-02-2001, 06:12 PM
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Bill I will do those checks.
As for the tach, I checked the wires. On the rear the red one has 13.7 Volts all time, as long as key is on.
The purple/black one has 7.9 when it is running, it does NOT change with RPMs is it supposed to?
Also at the coil the re are no volts showing at the coil when the engine is running???? This is from the positive wire on the coil??
Thats weird!
Shawn
As for the tach, I checked the wires. On the rear the red one has 13.7 Volts all time, as long as key is on.
The purple/black one has 7.9 when it is running, it does NOT change with RPMs is it supposed to?
Also at the coil the re are no volts showing at the coil when the engine is running???? This is from the positive wire on the coil??
Thats weird!
Shawn
06-02-2001, 09:01 PM
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Shawn,
I checked the voltages on my tach to see what they were and how they went with revs:
1100 rpm = 4.32 volts
2000 = 4.20
2500 = 4.16
3000 = 4.10
4000 = 4.01
The fact that this is different by up to 3.9 volts from your reading may not be important. I checked, and the 77 911S and the 81 911SC have different Bosch CDI boxes, different tachs, and different distributors. I don't know what all the differences are, but let's assume that accounts for the voltage delta. As you can see from my readings, there's not alot of swing, but there is voltage movement. So, a steady reading doesn't seem right.
Relooking at the 77 wiring diagram, the purple/black line may go to the distributor, but there is a junction with a wire joining the Bosch CDI (or "high tension ignition unit" on the wiring diagram). Is it possible that the wiring to the distributor isn't completely hooked up? I know it's a stretch...
I checked the voltages on my tach to see what they were and how they went with revs:
1100 rpm = 4.32 volts
2000 = 4.20
2500 = 4.16
3000 = 4.10
4000 = 4.01
The fact that this is different by up to 3.9 volts from your reading may not be important. I checked, and the 77 911S and the 81 911SC have different Bosch CDI boxes, different tachs, and different distributors. I don't know what all the differences are, but let's assume that accounts for the voltage delta. As you can see from my readings, there's not alot of swing, but there is voltage movement. So, a steady reading doesn't seem right.
Relooking at the 77 wiring diagram, the purple/black line may go to the distributor, but there is a junction with a wire joining the Bosch CDI (or "high tension ignition unit" on the wiring diagram). Is it possible that the wiring to the distributor isn't completely hooked up? I know it's a stretch...
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06-03-2001, 02:27 PM
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Don't recall anyone saying they pulled the back cover off and adjusted it themselves (although I do remember one person taking the back off to fix the wheel that spins the mileage). Only time I had anything done to the speedo was when I converted it from 85mph to 150mph. Sent it to North Hollywood, they put the new face on it and recalibrated it. And it is spot on the money at all speeds. I did check the Up-Fixin' series, and there were no references to adjusting a speedometer.
06-04-2001, 12:28 AM
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BILL
I have about 700$ in service manuals and none of them even touches the speedo adjustment subject.Anyway, your responses are priceless,you come up with some answers I could never find in any of my manuals. The bad part of this is that when I wake up for my 3am **** I wind up on this forum and watch the sun come up.Life is full of unacknowledged heros.
I have about 700$ in service manuals and none of them even touches the speedo adjustment subject.Anyway, your responses are priceless,you come up with some answers I could never find in any of my manuals. The bad part of this is that when I wake up for my 3am **** I wind up on this forum and watch the sun come up.Life is full of unacknowledged heros.
