Haunted Rally Gauges.

[MEK-Dangerfield]

I always thought of my car as a one of a kind, and this will probably prove it. I'll bet nobody had seen this, but I'm hoping for suggestions or wild guesses. This is something I should know about, and it has me stumped. 

Heading toward Carlisle last year on a Saturday, I got stuck in BIG time traffic with Topcat and Rusty S/E. I noticed every once in a while, my gas, oil pressure, and temp. gauges would apparently have a spike and go to just about max., then float back back to normal. I replaced the voltage limiter and the large capacitor on the back, but that didn't do the trick. I can't think of anything else.  It doesn't happen often that I notice... and I don't see this being a problem, unless in that rare occurance that I have a full tank of gas. I'm worried about the gas gauge might bite the dust.  Anyone have a guess???

  Mike

[4Cruizn]

    Got me??   

[FY1 RT SE]

Any chance you are blowing lights out also?

[MEK-Dangerfield]

Any chance you are blowing lights out also?

No. I know where you are headed, and I was wondering about the alternator/ voltage regulator too. I hardly ever drive the car at night, so that isn't much to go on. I did however drive it for a few hours with the lights on after Carlisle, and had no trouble. I would think I would see the dashlights, or headlights get bright if that was the case.  Thanks for the input. 

  Mike

[ShelbyDogg]

Mike, if you know that the voltage limiter is good, get yourself one of those digital voltage checkers, that plugs into the Cig lighter. That way when it happens again, look at the LEDs and voltmeter to see if you voltage is going high. You could have a grounding field, regulator, or field wire. Hi voltage or the limiter getting stuck is the only thing that could spike those 3 guages.  I bought a cheap digital volt reader with a cig lighter mount for about $5.00.  Look in JCWhitney, Boat-RV type stores.
Rob

[FY1 RT SE]

No. I know where you are headed, and I was wondering about the alternator/ voltage regulator too. I hardly ever drive the car at night, so that isn't much to go on. I did however drive it for a few hours with the lights on after Carlisle, and had no trouble. I would think I would see the dashlights, or headlights get bright if that was the case.  Thanks for the input. 

  Mike

Actually, those are not the items I was thinking about at all.  A loose/dirty ground or power connection was my first thought.

[MEK-Dangerfield]

Mike, if you know that the voltage limiter is good, get yourself one of those digital voltage checkers, that plugs into the Cig lighter. That way when it happens again, look at the LEDs and voltmeter to see if you voltage is going high. You could have a grounding field, regulator, or field wire. Hi voltage or the limiter getting stuck is the only thing that could spike those 3 guages.  I bought a cheap digital volt reader with a cig lighter mount for about $5.00.  Look in JCWhitney, Boat-RV type stores.
Rob

Thanks Rob. 

[pink panther]

hey Mike,
In the panther if I sat in traffic and Idle my guages sometimes drop, not talking stop light time, but in stop trasffic without rpms the guages go down quite a bit.

[MEK-Dangerfield]

Actually, those are not the items I was thinking about at all.  A loose/dirty ground or power connection was my first thought.

 Do you have any idea where I would look? Possibly the connections on the back of the gauges could be loose... but this spike happens so infrequent, it has me puzzled. The gauges fit tightly against the dash assembly, so I don't think it's a ground problem.  The power connection... I will have to explore that. Thanks again for your input.   I didn't think anyone would have a clue at this.  

  Mike

[ShelbyDogg]

You said the 3 guages pegged. Loss of voltage would be a different prob. Those 3 guages have nothing to do with a ground at all. The ground that they are getting is coming from the sending unit, that they measure. So your cluster being tightly grounded is moot.  Same problem would happen with the guage in mid air. The limiter or overvoltage, are the most likely suspects.
Rob

[Bullitt-]

Mike, I have done some research I believe I have a plausible cause for your symptoms. The only way I can see that this could occur would be an increase in voltage. The limiter should cut whatever voltage is available in half, but what if there was more than 12v available? In the '73 Dodge service manual in the alternator section I found this statement under Bench Test  (just the meat) "Field coil draw should be 2.5-3.1 amperes at 12 volts. A higher rotor coil draw indicates a possible shorted rotor coil or grounded rotor." This tells me it is possible for the alt. to produce more than 12v. Please do not run out & replace your alt. based on this, but it is the only source of voltage other than the battery in the system. Hope this helps
Wade

[FY1 RT SE]

You said the 3 guages pegged. Loss of voltage would be a different prob. Those 3 guages have nothing to do with a ground at all. The ground that they are getting is coming from the sending unit, that they measure. So your cluster being tightly grounded is moot.  Same problem would happen with the guage in mid air. The limiter or overvoltage, are the most likely suspects.
Rob

Never heard that the gauges pegged, they drifted up.  Where is the ground for the limiter at? Where are the senders connection points and also consider they are all tied together via the limiter.

Is the limiter you replaced new or just another limiter?  They are not the most accurate or stable units, (you should see the output on a scope) but are the best available.

[FY1 RT SE]

Mike, I have done some research I believe I have a plausible cause for your symptoms. The only way I can see that this could occur would be an increase in voltage. The limiter should cut whatever voltage is available in half, but what if there was more than 12v available? In the '73 Dodge service manual in the alternator section I found this statement under Bench Test  (just the meat) "Field coil draw should be 2.5-3.1 amperes at 12 volts. A higher rotor coil draw indicates a possible shorted rotor coil or grounded rotor." This tells me it is possible for the alt. to produce more than 12v. Please do not run out & replace your alt. based on this, but it is the only source of voltage other than the battery in the system. Hope this helps
Wade

Wade, good observation, however the alternator should always put out more than 12V.  Another thing to check is resistance through the wiring system. this can been done with a digital voltmeter by connecting the postive(+) of the meter to the battery stud of the alternator and the negative (-) of the meter to the POSITIVE of the battery. Run the car with the lights on (to create a load) and read the meter. You should not read more than .3 to .7 (thats tenths) of a volt. Do the same with the negative side of the charging system. Connect the negative (-) of the meter to the alternator case and the postive (+) of the meter to the NEGATIVE battery terminal. More than that and you have wiring that is not allowing normal flow of electricity

[ShelbyDogg]

Just 3 days ago, I have a "new" '74 Challenger that I found the firewall regulator putting out 17-18v. The headlights were both burnt out, guages not working, new battery. Right away, I threw that regulator in the garbage and replaced it. All that regulator does is ground the second field terminal on the alternator electronically, on and off, so that the alternator puts out the required 13-14.5v charging voltage. It gets it's ground being on the firewall. If it's a little loose it could cause all kinds of strange things. SO.......1. Check your voltage at the battery with a good digital meter. 2. Make sure that the voltage regulator on the firewall is securely GROUNDED. If the bolts that hold it to the firewall can't be tightened TIGHT because the holes are loose, unscew your pass.cowl vent and put a nut behind the firewall and snug it up.
Rob

[Bullitt-]

  just never had any experience.  I also like FY1RTSE's thought on a poor ground to the Voltage Limiter. I can see how if it lost ground it would stop functioning & stay closed allowing 12V to pass, thru. As to checking the amps from the alt. to the battery I don't think that is a factor here. A device that is designed to use X amps will use no more ( given it is functioning properly ) at the proper voltage no matter how many amps are available. Of corce all the checking when the problem is not occuring will probably prove nothing unfortunately.