MG MGB and MGB GT Tech Talk
As soon as I fire up the "B" the tacometer is all the place. Tried replacing but the same problem. My temp gauge reads high too even at 190 degrees its well past a half point mark. I have an electronic ignition and m s d. Any suggestions?
Is your tach designed to be ran off msd
Is your cars voltage while running around 14 volts
Have you triple checked your wiring
Hard to give this a go thru without actual having the car in front of you.
Talk to they guys with "sleepy" tachs. Maybe you could trade...
What msd are running.
They have lots of ignition products
MSD makes what they call a tach adapt for some installations. Sounds like you need one. If you have the instructions, it tells you all about it. I had to run one on the TR8 until I switched to a compatible tach.
when I installed my VDO tach the needle hopped around a bit. Found a reference that said to solder a small diode into the line, did it and it quieted the needle.
First of all, it would be helpful if you update your profile to show the year of your car. Early tachs were current sensing, later ones were voltage sensing.
The waveform generated by a MSD ignition is quite different and it is confusing your tach. The MSD manufacturer may have suggestions.
Regarding your temperature - have you checked your temperature with an infra-red thermometer? If it is reading high, then the instrument voltage stabilizer is probably bad. It will generally affect the temperature, the fuel and some years of the electric oil pressure gauge.
Sorry bout that. Its a '72, and it worked fine until last summer. I tried changing the tach once but no luck.
I do have a infrared thermometer. And I've recently changed the water pump, thermostat, temperature transmitter. I've haven't checked the voltage regulator yet. Not sure the brand of msd, but it big and red if that helps :/
Be aware that there were two different temperature sending units - but they are almost identical in appearance. If you use the wrong one you read either high or low (depending on the mismatch). Could that be your problem?
I *think* that 1972 was the year they switched to voltage sensing tach (or maybe it was 1973). If the white ignition wire connects to the tach (a white male wire and a white female wire) then it is current sensing. Else, it is voltage sensing.
Your MSD manufacturer probably has a list of tricks to stabilize a tach.