siebertl

About once a month or so, my batteries are dead and truck will not crank over. I have 2 brand new batteries, battery lugs are clean, alternator has been sent in and rebuilt. Alternator guy said it could be a bad voltage regulator. I realize this is in the PCM, but I could do the old style regulator easy enough.

This only seems to happen after a long idle, 5 minutes or so. Voltage runs below 8 volts and radio/dash lights kick on and off. Voltage comes back up at speed. Could it be a bad voltage regulator?

Also, there are two pegs on the back of the alternator, I do have an electric fuel filter heater hooked up to one of them so when the truck is running, the heater is heating a veggie oil filter. I'm really not sure if I should be sucking power off of the back of the alternator for this, but it seemed like a good place to get power while the truck is running.

infidel

Could be your heater draws too much juice and the alternator can't keep up at low rpms.
Wedge a stick or snow scraper inbetween the seat and accelerator pedal to get the rpms up to 1200.
If it's cold your engine won't warm up at idle anyways.

GAmes

Sounds like an awful place to draw amperage to me. I'd wire the heater to a switched relay that only pulls power directly from the battery, and only when you switch it on.

traindrv

I'd try disconnecting the heater and see if problem goes away or not.

siebertl

I will try removing the heater.

Where do you guys pull a switched 12volt source from under the hood?

What is the function of the two posts on the alternator, what should thier voltage readings be?

GLH

loose alt belt

GAmes

What I meant was hook a toggle switch to a relay and pull power directly from the batteries. You do know how to wire a relay, right?

Santaclaus

I'm not familiar with the alternator on the 98 specifically but most alternator's only have one output terminal. Most other terminal are either the field terminals, or censor terminals for other things such as tag on matters or the computer system in the truck.
As stated before you really need to put a fuse/circuit breaker and a relay in any high power circuit.
Is it possible that the grid heater is cycling on considering where you live?

siebertl

I'm sure the grid heaters are cycling, but the alt should be able to push more than 8-10 volts. I had the heater originally hooked up to a relay, it stayed on a couple of times and discharged my batteries so that is why I went this route. I'm going to start by moving the heater back to a relay, I'm still struggling with a good switched 12volt power source though.

What is a good switched 12volt source to tap into under the hood?

Doj Dewd

buy a decent relay. cheaper ones can stick on as you described. i also agree with wiring direct from the battery with a switch and a relay to power the veggie oil heater.

BigErksG2

Amps is what you need to worry about, not volts. How many amps is your veggie oil heater (watts/ volts = amps). You might have to run an ignition relay or manual relay and pull power right off the batteries. If its cold enough to cycle your grid heaters on and off it might be a little cold to run veggie oil. unless you are on a long trip.

siebertl

The heater came with a 30 amp fuse. I imagine it pulls quite a bit. I've got over 100k on veggie oil and know that system well enough. I suspect the two posts on the alternator are for the pcm to sense what it is putting out. I'd like to know what the voltage reading should be between the two posts to rule out alternator defects.

Moving my heater to a relay is a good idea and I will do that, I'm hoping that takes care of the problem but I suspect there is something else lurking. I ran the heater this way for over a year and no problems. So, I'll move the heater this week, but I'd like to know about what exactly those posts do, what voltage should they push, and what is the black rectangular box on the back of the alternator????

Santaclaus

A little off-topic but with as much waste heat that the cooling system produces at highway speeds why would you use electric heat?
You might also consider putting a double pole single throw switch in line with the grid heaters. The reason for double pole is to keep the grid relays separate. From what other people say he only needed the grid heaters for starting, how disconnected my completely but then I live in full in North Florida.
Which MIDI system do you use?

rattlerbob5.9

Those two small terminals should NOT EVER have any extras hooked to them they are the field terminals that provide and regulate the alternator output. The voltage to the field circuits are provided by the pcm which controls the rate of charge.

Old-stuff

I agree with rattler. drawing power from the small ones may be confusing the charging system. The large output one is electricly the same as battery.
Yes you can convert to external regulater if the one in the PCM goes bad. There is a sticky on how to do it.
Ray