P.J

What about with the truck running/alternator charging? (To back check the gauge) and see what voltage(s) you are actually dropping out to?

Truck Girl

I have a friend at the local dealer down in Grants Pass, OR who lets me borrow their scanner if it is not being used by a mechanic. I checked the voltage of the charging system right after I changed the alternator and it read 13.62 volts with the truck at idle and the lights on.

P.J

Um, but what about with the grid heaters cycling? It has to be moving off of 13.6V on cold start........?

Shovelhead

You might want to have the batteries charged and load tested.
Especially if they're more that 5 years old.

bucket truck

I've had my grid heaters kick in at temps that weren't near cool enough for them to be needed. I have pulled into stores or at the house and left it running, come back out and the grids will be running. If it is kinda cool out and the coolant drops below 140* mine are comin on. As for the AIT sensor. You can clean it with carb. cleaner. Pull it out on look at it. If it ain't white, it could be givin a less than normal reading. Just my $0.02.

Bucket Truck

nickg

Your batterys are NOT fine they are technically discharged or dead! even though they start your truck, then your alternator has to full field to charge them, batterys that are full charged will show a voltage close to 12.8 or better, you cannot get a proper load test unless the batterys are better than 12.4 (12.8 would be desired)
I'd suggest you have your batterys tested to confirm their condition then go from there.
also test your alt output at the terminal on the alternator and at both batterys voltage should be within .01-.02 of a volt

Truck Girl

Ok, that should be easy enough then. Both batteries are less than two years old. They are Optima batteries and I think they should be warranted for 3 years. Yep, 36 months I just checked their website.

I'll try new batteries and report back in a couple days. Thanks guys!

Truck Girl

Alright Guys,

Just to be sure I checked the batteries again before I drive all the way into town tomorrow to get new ones and this time both are at 13.0V with the truck off. Today is cool again so the grid heater has been cycling. Perhaps my batteries were just undercharged from the old alternator dying??? So far today the voltmeter hasn't fluttered around like it was before when the truck was up to temperature. It moves ever so slightly when the heater comes on, but the rebounds in just a couple seconds like it is supposed to.

Thanks for all your help!

Truck Girl

Shovelhead

Good News.

nickg

TG
when you tested your batteries was it shortly after the truck was running?
here is what I would do
1. test the batterys in the morning prior to starting the engine. (record voltage)
2. I was going to say test alt output with the truck running, but I think you've covered that it is charging.
3. compare the alt output readings to the readings at the batterys, and take your readings on the battery post and take them on the battery terminals the readings should be the same. if they are not the same between the terminal & the post then its dirty/loose connections and that in its self can cause all kinds of charging/starting issues

4. I'd still have the batterys load tested, optimas are known to have problems, BTW which do you have red/yellow tops?

Truck Girl

I've got red ones. When I changed the alternator I cleaned the posts and terminals really well. They are nice and clean now.

I left my multimeter down at the shop yesterday so I can't check the batteries this morning. I'll give it another go 'round tomorrow. I think everything is back to normal now as there was no fluctuation at all yesterday.

nickg

TG
Thats a good sign, (wishing ya luck) it very well may have been that it took a while for the batterys to come back up to charge

thedblc

Have you tried disconnecting the grid heaters? There are 2 relays on the inside of the driver wheel well below the battery. They each have 2 small leads coming into them. Remove one lead from each relay and now the grid heaters cannot be started via the control unit. This would at least rule that out.

bigfish95971

Hi, I have 340k on my 99. The air conditioner will draw it down in the summer and the defroster cycling on off the air may do it also if the defroster is on (right two notches). Also, slightly weak batteries can do it. Unless you have torque converter lock-up problems the slight voltage fluctination should not be a problem in itself.
Jim

bsummit

I just had a similiar problem with my batt gauge. End result was my grid heater relays were bad. Don't know if they were stuck in the on position. I know the computer controls the relays but I replaced the relays and it solved all the problems I had. I don't know anything about the statement concerning the heaters disengaging at 26mph, but mine didn't stop at all. They stayed on at any speed until I disconnected them. My suggestion is disconnect the heaters and see if things go back to normal.