High voltage, no tach, and in limp mode
Fleet Mechanic
Joined: Jan 2011
Posts: 1,709
Likes: 4
From: 8600 ft in Colo
Are you reading 18v with a meter on the battery, or reading it on the dash gauge?
If it's the dash gauge, check it with a meter at the battery. If that reads 13-14v, it's probably in the connections to the instrument cluster. That could also put the trans in limp mode...
If it's the dash gauge, check it with a meter at the battery. If that reads 13-14v, it's probably in the connections to the instrument cluster. That could also put the trans in limp mode...
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New User
Joined: Mar 2012
Posts: 14
Likes: 0
I'll check at the battery. I put a new alt on it last week, as far as I am aware the regulator is on alt. people said it was external but I have yet to locate it, and the parts store said it was internal.
Laughing Gas
Joined: Jan 2010
Posts: 1,055
Likes: 1
From: Surrey, BC, Canada
Depends on what alt you have, 3g its on the alt, 2g I'm not certain, and 1g is on the fender right next to the starter solenoid.
Mine is the grey box under the Solenoid. (Old crappy alternator)
This is the 3g regulator, the grey thing screwed onto the back of it. (Not your exact alternator, but close enough that you can figure it out)
It's entirely possible it's a short somewhere, but I highly doubt it's a "New" alternator, more likely a rebuild. It's also possible they put a faulty regulator on it when they did it. (Had this happen)
Mine is the grey box under the Solenoid. (Old crappy alternator)
This is the 3g regulator, the grey thing screwed onto the back of it. (Not your exact alternator, but close enough that you can figure it out)
It's entirely possible it's a short somewhere, but I highly doubt it's a "New" alternator, more likely a rebuild. It's also possible they put a faulty regulator on it when they did it. (Had this happen)
Fleet Owner
Joined: Jul 2006
Posts: 20,322
Likes: 789
From: Mi'kma'ki
i would take the alt back and exchange it for another.
it's obviously no good (likely the regulator) since the issue just started after the alt swap correct?
what happened that you lead you to believe the alt needed to be changed the first time? just not charging/batteries running flat right? they've been load tested? all grounds are good,and +/- terminals all hooked up correctly?
the parts store is correct.the alt in your '94 idi diesel truck is a 3G 130A w/internal voltage regulator.this alt replaced the old school alt w/external reg back in mid year of '92 on diesel trucks,with the serpentine belt.
it's obviously no good (likely the regulator) since the issue just started after the alt swap correct?
what happened that you lead you to believe the alt needed to be changed the first time? just not charging/batteries running flat right? they've been load tested? all grounds are good,and +/- terminals all hooked up correctly?
the parts store is correct.the alt in your '94 idi diesel truck is a 3G 130A w/internal voltage regulator.this alt replaced the old school alt w/external reg back in mid year of '92 on diesel trucks,with the serpentine belt.
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Laughing Gas
Joined: Jan 2010
Posts: 1,055
Likes: 1
From: Surrey, BC, Canada
Internal just means it's mounted to the back of it.
These old trucks the internal gauge's are notorious for not working properly. Mine "works" if I bash the top of the dash a few times to knock it to whatever voltage I want it to be at.
And I'm with FordF250HDXLT, something isn't working right, and I've had enough bad electrical nightmares with this truck to feel it's related to that.
These old trucks the internal gauge's are notorious for not working properly. Mine "works" if I bash the top of the dash a few times to knock it to whatever voltage I want it to be at.
And I'm with FordF250HDXLT, something isn't working right, and I've had enough bad electrical nightmares with this truck to feel it's related to that.
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New User
Joined: Mar 2012
Posts: 14
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Sorry if 3 of the same messages show up. Phones isnt cooperating. I bought a new alt because the gauge was showin 18+ volts, I replaced it and the same thing 18v volts. I just got the truck and I was aware of this issue. But for the price that the guy was selling it for I couldn't pass it up. So I've started going through all the grounds and cleaning them. I did find a broken one(button of cab to frame) haven't attached it yet do to my kid wanting to play, not sure if that is a factor or not but will do it when it drys up and off of work.
Elder User
Joined: Aug 2011
Posts: 915
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From: Sweet home Alabama
If you just bought it the PO may have tried to change it to internal, Start the truck and turn on all power as much as you can get lights,wipers,Radio etc take a reading it should not be over 14.5 to 15. MAX at 1500RPMs then turn off everything except truck and test again if its over 15V at idol Id say they goofed with the wiring.
Postmaster
Joined: Feb 2011
Posts: 3,560
Likes: 1
he said the gage reads 18+ but a real meter read 14.5, so if thats accurate, the cluster is giving a bad reading and throwing the rest of the system into confusion. alternator would appear to be fine, with the problem elsewhere
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