Engine/Transmission (1994 - 1998) Voltage Gauge Slow To Respond

[fleahead]

I've noticed everytime I start the truck, the voltage gauge reads just about 12v then in about 10-15 secs it comes up to normal charge voltage of 13-14 volts. This may be normal, as I don't remember ever paying much attention to it. It does this everytime it starts regardless of how long it is shut down. Is this delay normal?

 

[WDixon27]

mine does that once in a while, been keeping a eye on it looking for a pattern

 

[RVPILOT]

It could be a sign that the alternator is getting weaker, i e brushes going out. but also the grid heaters cycling can cause this. I have disconnected my grid heaters as I believe the manifold sending unit was faulty turning on the heaters even when the weather was warm and after a long run. i don't need them where I live but the wire is still there and can hook it up if needed. Stormy

 

[WDixon27]

it's not the grids on my truck as it's much lower on the voltmeter then what the grids pull it down to

 

[fleahead]

Well, there is no pattern. It's each and everytime I start it. As soon as the engine is running the gauge reads the same as when the ignition is just turned on. (raw battery voltage). Then after about 15 sec it goes up to charge voltage. (13-14v) It doesn't drop off again except for the little dips caused by the heater kicking in and out. I just wondered if most trucks show charge voltage immediately or is there a little delay before the charge voltage shows.

 

[Diesel Gunner]

Hmm... My truck recently started normally and after I got going down the road, I noticed that my voltmeter was only showing about 12 volts. Odd, I thought. Then about 15 seconds later the check gauges light comes on and the voltage had dropped to less thatn 8. I kept on driving, but on the way back to the home 20.



After a day or so, I load tested the original batteries and they checked OK. Still gonna replace them before hunting season anyway. Had a low voltage code set, so I disconnect batteries, clean terminals (which were not dirty or corroded) reconnect, codes gone and everything has been normal for several weeks now.



Anybody have any ideas?

 

[J Shocik]

Fleahead, it could be the grid heaters doing their normal cycling. When starting the truck in colder climates, after the "wait to start" light goes out & you start the truck, the grid heaters will cycle on & off. You can see this by watching the alternator needle go to full left (discharge), then to the middle(normal). Depending on how cold it is when starting, it will do this a few times. I believe when temps are at and below 59 deg. the grid heaters kick in.



If you suspect a worn or bad alternator, watch the alternator gauge after the truck has been running & is up to temp (warmed up ). When idling at around 750 RPM, if the gauge is to the discharge side and goes to normal when increasing engine speed, you might need a new alternator. I have a '97 also & had to change it last Feb. when it was doing what I described. That took care of that. If you change the alternator & have to get one at an auto parts store like Auto Zone, make sure you get a 136 amp alt. The store computer will show the truck needing a 120 amp, but the CTD's take the 136's. Hope this helps... John

 

[tp0d]

I believe this is a normal part of the charging circuit. When the PCM detects a signal from the crank sensor, it waits a predetermined amount of time until it allows the alternator to charge. It probably is monitoring the state of system voltage before turning on the alt. The grids will cause a fluxuation, but normally it shouldnt go 3/16" below the middle line, once the alt is charging. I watch this happening every morning when I start up. . (the wait until charge and the fluxuation)



-j

 

[Andy Redmond]

How old are the batteries? More than age 3? Getting suspect unless they are optimas etc. .



If they and altenator are okay, its just the pcm as suggested most likely.