I have a 1999 taurus and when I am going down the road sometimes the speedometer will fall back to zero or below and the engine seems to die down. As soon as the speedometer gets back to working it will pick back up and run fine. It usually takes a few seconds for the speedometer to come back to life. Only once did the speedometer not come back and the engine died completely, but after a few minutes it cranked back up and was ok. Please help if you have had this happen before or know the answer.
Thanks
Henry

 

To Henry from Hanky,
If you can, on the alternator should be a plug in connection which you can remove and this will take the alternator out of the system. If the problem is frequent enough try driving the vehicle with the alt unplugged. If there is a problem in the alt you should notice the problem will be gone. You can't do this too ( 1/2 hour) long because the battery will not be getting charged while the alt is disconnected. A shorted diode in the alt can produce the problem you are seeing.

 

Thank you I will try that after Christmas and see if that fixes the problem and let everyone know.

 

One thing I forgot to mention is that the speedometer starts jumping around all over the place for a few miles while the car runs ok and then it drops to zero and the engine starts cutting out until the speedometer comes back to life and then the car runs fine for a mile or two and then it all starts over again. I did disconnect the battery and it still did the same thing. Thanks in advance for all your help

 

Some Fords will share a circuit with several sensors and the vehicle speed sensor is one of them. The speed sensor could be the problem , but it can affect other sensors like Mass Air Flow and tps.