Voltage gauge shows really high

[cason234]

Hello fellow IDI enthusiasts!

I have a 1990 F250 with 7.3 IDI 4x4 ZF5...... I bought it about 6 months ago, and I don't think I've posted anything about it here yet. It looks like crap outside, but I'm fiddling with it here and there to bring it up to *****. So far, lots of cleaning in the interior, new headliner, new door panels, new door handles, interior cosmetics just to make it nice to drive. Mechanically, new rear brakes / rear axle seals / new front break lines / all new fluids, etc. Just put in a new steering column (it's fixed, to replace the floppy tilt column). While I was at it, I bypassed the ignition key entirely, and now have a single switch, and a push button starter. Then, I capped it off with my little MOMO steering wheel....... This truck is a pleasure to drive! Nice and tight, with NO rattles (other than the ol' IDI thrashing away under the hood!)

Here's my challenge: the 6 months I've owned it, the voltage gauge has always been on the LOW end of its range..... the dash lights have always been fairly dim, and the interior heater fan turns relatively slowly, and the wipers are slow. HOWEVER, it always starts with no problem, and the batteries seem to function just as they should.

Recently, the voltage gauge needle started swinging WAY over to the right (high) side of the gauge. As it does so, the dash lights go full bright, the headlights are noticeably brighter, and the interior fan gains speed. It only does this when the engine is turning at cruising speed. As soon as I slow down, the gauge goes right back to the low end of things again....... And, as I accelerate, back up she goes!

Is this a voltage regulator? A bad alternator? A bad ground (I have a feeling this may be a factor, but haven't looked into it yet)? Anyone else have the same experience?

Here are a few pictures:

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Here's my push button start / Momo steering wheel

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[Comptech]

Make sure the ground from the body to the negative post on the battery is intact.. For that matter look for a ground from the engine to the body as well.

 

[Comptech]

Set a voltage meter to d.c. Put leads on your battery, observe voltage at idle and slowly bring RPMs up while watching the meter. This should give you some indication of what the charging state is.

 

[cason234]

Thanks Comptech - what values should I be looking for? (ie: what's 'normal' voltage for a properly functioning system (I assume 14.2 volts or so))?

 

[franklin2]

Most newer cars and trucks run about 14.5v, but my 89 diesel runs the old school voltage of about 13.8v when charging. When my batteries are fully charged and there is not much load on the electrical system, my dash gauge (just like your 90) runs right in the middle. It will be to the left of middle after starting, way to the left when the glowplugs are glowing.

 

[cason234]

Most newer cars and trucks run about 14.5v, but my 89 diesel runs the old school voltage of about 13.8v when charging. When my batteries are fully charged and there is not much load on the electrical system, my dash gauge (just like your 90) runs right in the middle. It will be to the left of middle after starting, way to the left when the glowplugs are glowing.

Yesterday evening, I connected my multimeter to the battery...... started out at 11.8 volts at idle. I revved the engine slowly up to around 1800 RPM or so, and the voltage went all the way to 17.9 Volts (and held steady as long as I kept the revs at that level). Last night, I noticed that one of my headlights was burned out. Went to replace the bulb, and when I pulled it out of the headlight housing, it was shattered (not because I damaged it while pulling it out)! I figure the high voltage must have been the cause of that! ....... is this a bad voltage regulator?

NOTE: also removed, cleaned, di-electric greased and reattached the battery to battery ground connection. It seemed to be fine as well.

 

[DrCharles]

11.8 means it's not charging at all, 17.9 is pretty much wide-open. Yes, you will burn out a lot of bulbs if you run them at that voltage!

It is possible that a connection to the regulator is intermittent, but you aren't seeing it jump from 11 to 18 and back again. If it's a smooth transition as you increase the revs then the regulator is defective.

 

[cason234]

Thanks Dr. Charles..... I'll replace the voltage regulator and see what that does (while I'm at it, I'm going to replace the negative battery cables too..... they look a bit sketchy).

I'll update once I've got this figured out.