Got an odd issue with my son's '97 DI (134k). Yesterday his speedometer start fluctuating wildly while maintaining a consent speed. At the same same he would lose power and the tach would drop to zero. Almost like the fuel flow stopped. Initially I though maybe a gear slippage, but no transmission noise or shift at all. The loss of power only lasts a couple seconds then the engine reengages like normal. Wondering if it's some sort of sensor I should be looking at.

 

Perhaps your Vehicle Speed Sensor (VSS) and maybe your alternator.

 

Have the same issue with my 98', but have never been able to get it to do it long enough to check it out. Have had the speedo jump to 70 while sitting still, and idle erratically for just a few seconds (like it was running out of fuel) and then back to normal. Occasionally it will do it a couple of times in a few minutes and then drive it for 500 miles without another occurrence. If you figure it out, let me know.

 

Definitely sounds like the VSS.

 

You can drive without VSS plugged in, no speedometer or cruise. But alternator, when it dies, kills tach, and makes other electrical things do wierd things. The brushes in the alternator loose then re-make contact. You may have a son driving about with an under charged battery. It will only last so many minutes, then fuel pump and other electrical things die. A plug in volt meter, like this $20 Walmast special, will show you system volts while driving. Expect 13.8 - 14.2 at idle. As load increases, may dip as low as 13.2. Alternator dies and it will drop to a value in the 12's, and decreasing quickly.

The drop to zero by tack while engine still running makes me think alternator, the small flying lead on back of it. Could also be a ground for the dash cluster. A small circuit board inside the dash cluster processes the VSS signal, and the tach, etc.

 

Thanks for the insight. I'll get that meter and check it out this weekend.

 

Turns out one of the wires to the VSS was frayed so I soldered it and now it's good to go. I'll still get that meter to make sure the alternator is healthy. Thanks