Sequence of Events (1989 6-cyl, EFI, 5-spd manual.)

The Fan Clutch needed replacing. On my way to a friend's garage, the water pump shaft broke and the fan belt broke. After replacing the water pump, fan clutch and belt, the Tachometer is malfunctioning. Before this happened the Tach worked perfectly.

Now, with key in off position the RPM is Zero but when engine is started the RPM jumps immediately to 2200. It stays totally steady at 2200 and drops back to Zero when key is turned off. 2200 RPM was probably the RPM at the time the belt broke.

I looked for a broken wire that may have been caused by the broken fan belt. Didn't see one and also didn't know where to look for one.

Could the abrupt stop of the alternator cause this?
What 'feeds' the tachometer?
Does anyone have a schematic showing the tachometer wiring?

 

First, what year and model is your truck? How many miles are on it?

You do not have a fuel pump shaft. Your fuel pumps are electric and depending on the year, are entirely in the tank or mounted on the frame rail roughly under the driver's seat and in the tank.

So what broke when the belt broke?

The tachometer is completely independent of the fan clutch or belt.

My guess is that you knocked a wire loose while you were working on it. Look under the hood for anything disconnected.

 

Thanks, I goofed. Please view my edited post.

 

The tach gets its signal from the negative side of the coil. Unfortunately, I don't have a wiring diagram but subford may along shortly with one.

 

quote
I looked for a broken wire that may have been caused by the broken fan belt. Didn't see one and also didn't know where to look for one.

Could the abrupt stop of the alternator cause this?
What 'feeds' the tachometer?
Does anyone have a schematic showing the tachometer wiring?


You should have a green wire connected at the coil neg - side which in the inboard side of the coil, it is marked as such. Then there should be a white wire to the light switch, a red wire to the ignition, and a black wire to a good ground...I suppose that the abruptness of the incident (loosing a connection and possible grounding, depending on how and where the wires were connected), could have caused internal damage to the gauge.