I have a 1997 12 valve diesel that has started to loose the tach, charging and oasionally the ck engine light and other red lights will flash on for a moment, then go out. If the truck is going down the highway, it will also loose o/d until the volts come back up to 14. Sound like an ECM going bad?

 

'97s do not have an ECM. They do have a powertrain control module however, and they rarely fail. It sounds like your engine speed sensor is giving you trouble. It controls the tach, cruise control, automatic trans shifting and alternator output. Very often the problem is chafed or broken wires or a bad ground. They do fail every now and then too. It is mounted above the damper, just to the left of center when looking down at it. If you remove it, the clearance from the damper upon reinstallation is .050 inch.

 

Sounds like your ESS sensor, the thing that tells the PCM the engine is running is getting flaky.

Do a search here on charging and you should get a good read.

Without Tach you also lose charging, ans well as OD and a couple of other things.

 

If the ESS is faulty it tells the PCM that the engine isn't running, nothing electronic will work.