93 with grid heater and alternator problems

[JonWilson]

Im trying to figure out a problem a friend is having with his 93 5 speed diesel truck . the grid heaters have over the last 2 weeks begun to work very intermittently and now his volt meter is not wanting to jump to normal till after a good 15-20 minutes of driving. some days the grids wont come on at all making it a lot tougher to start in the colder weather the wait to start light will at times come on and you get a buzzing sound out of the relays almost like the pcm is telling it to do crazy things. when the wait to start light is on there is still not any power to the grids we've checked relays and wiring and everything I can think of . any suggestions ??possible pcm problem ,any thing would be helpful

 

[PToombs]

Sounds like the relays are bad. Put a test light on the grid side and turn on the key, see what you get. The buzzing is what clued me. They should just "click" on and off.

 

[JonWilson]

relays are not getting a signal to energize except intermittently so Im thinking that with alternator acting up and relay s not getting a signal that I might have a pcm problem any one think the same

 

[JGrefenstette]

you may want to check the alternator and see if its putting out any A/C voltage. it may have a bad diode. a/c can serisouly screw things up. also, have you checked/cleaned all the grounds and connections? its a good idea to put some dialectic gell on all the connections too.



i had one cold morning last week, turned the key and the grid heater did not come on. i new it was in the 20's and it needed to come one with the ignition, so i turned the key off and turned it back on again and it switched the grid on. extreme temps high or low will bring out the worst in any kind of equipment.

 

[PToombs]

Didn't realize you had no signal to the relay. I thought that the relays could be sticking on also, because you said the voltmeter doesn't come up for 15-20 minutes.

Could be the PCM. Hook it to a switch for temporary and see if it works then.

 

[Paychk]

Check the ground wires that are located near the battery, on the radiator support, these are for the PCM (computer). Also check that the engine to body grounds are clean bright & tight.