Need help identifying bad IVR

Electrical and Ignition

  1. Chained_360

    Chained_360 FABO Gold Member FABO Gold Member

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    Howdy all, I need some help tracking down why my gauge cluster is acting funny. I'm curious if it's the IVR, because the problem itself is a bit of a doozy.

    It's a long story, so here is the short of it. My 68 notchback (360/904) has been running 'hot' for the past month and a half, but it has never actually overheated. The temp needle loves to stay in the upper quarter of the gauge, sometimes pegging if you turn the car on after it is warm. Sometimes it settles down in the normal range, sometimes it doesn't. But regardless of what the gauge reads, the car has never had an actual meltdown (shutting off, spewing coolant, etc.). I'm trying to find out why.

    The water pump was replaced two and a half years ago (admittedly with an el-cheapo unit), and the only mods to the cooling system is the flex-a-lite fan and absence of a shroud. The belt has enough tension and isn't slipping. Last summer, the car would do a strange thing where it would peg the gauge when It warmed up and then settle down in the normal range.

    Today, as I was trying to pinpoint if it would ''overheat" at cruise or idle, the factory oil pressure gauge started to move around erratically, which caused me to scratch my head, as the factory oil pressure gauge has never read anything since I bought the car. This is because the previous owner installed a mechanical oil pressure gauge under the dash.

    As for the fuel gauge, it never worked when I bought the car, and when I replaced the tank and sender, I never hooked it back up due to the reproduction sender stud not being long enough. I tried connecting it with alligator clips and whatnot, and couldn't get the gauge to read anything.

    Apologies for the shaky/incomplete information, this temp gauge issue has plagued the car since I bought it and I wanted to give the full scoop. I know a bad IVR will knock out the oil, temp, and gas gauges, but I don't know if a failing one would cause the cluster to act like this, because the way the car is now leaves the possibility that all three gauge issues are completely separate and just happen to be rearing their heads at the same time. The biggest tip-off for me was the oil pressure gauge though, but I'm not certain. What are your thoughts?
     
  2. 67Dart273

    67Dart273 Well-Known Member

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    You have an oil pressure gauge? (Not a light?) then you have a Rallye dash cluster. In that case the IVR supplies all three gauges, oil, temp, and fuel.

    It is nearly impossible for the IVR to be bad and causing this problem IF the oil gauge works "normally."

    This is likely a bad sender, the engine "is" actually running warm, or else the sender wire is damaged and shorting some of the time.
     
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    • Chained_360

      Chained_360 FABO Gold Member FABO Gold Member

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      It is a Rallye gauge, but the factory oil gauge has never worked until it went haywire tonight. The previous owner installed an aftermarket mechanical gauge that reads normally. I will replace the temp sender though, they're pretty cheap
       
    • harrisonm

      harrisonm Well-Known Member

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      What he said. The IVR feeds all three gauges, so approach your problem as though the gauges or the sending units are bad.
       
    • 67Dart273

      67Dart273 Well-Known Member

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      Oh so you only have one working gauge. Well then could BE IVR. One thing you can do is scare up some resistors to use for testing. This imitates the old factory gauge tester, here:

      Someone edited this photo "handily" to display the resistors involved. All three gauge senders and all three gauges operate the same scale

      c-3826-jpg-jpg.jpg
       
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      • cannucky

        cannucky The Guy With No Birthday

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        without having any guages that work it's pretty hard to tell if its the IVR , is it even an IVR or us it still the VR in the fuel guage ?
         
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        • 66jim

          66jim Well-Known Member

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        • Frnknsteen

          Frnknsteen FABO Gold Member FABO Gold Member

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          I don't know about the A body gauges. My experience is from when I rebuilt my '69 B body rally gauges. I would think you could test the IVR to make sure it is putting out the 5 volts needed, or if it is running high. Found an interesting video of someone testing them (It was on a '67 Fury, but the method should be the same).



          As volts go up, so will your gauge readings.
           
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          • 66jim

            66jim Well-Known Member

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            to read IVR voltage just remove the water temp sensor and measure from the sensor wire to ground. The IVR for stock gauges should be 5V. If its a stock mechanical regulator its a duty cycle averaged 5V
             
          • 67Dart273

            67Dart273 Well-Known Member

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            OP if you can take the cluster out there are some things you can do. I would ASSUME the IVR is bad and either build or buy a solid state replacement
             
          • Chained_360

            Chained_360 FABO Gold Member FABO Gold Member

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            Awesome, thank you all for the responses! 67Dart273, thank you for the picture of the resistance test, I will try that after I test the temp sending unit. I'll start by testing all the sending units as soon as I get the chance and report back here.

            And I do plan on pulling the cluster soon-ish to install a tach and replace the bulbs, so when that happens I will go ahead and replace the IVR regardless if it's good or not. Thanks again! I'll keep everyone updated as I make progress
             
          • ChuckDock

            ChuckDock Well-Known Member

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            I love this site. I had the same issue, gauges were pegging. I installed a new radio and had the dash out but not really sure what got disconnected. I read through this thread and the looked at my cluster and didn't see how it got ground at all so I made a ground strap, screwed it to the metal part of the cluster and put the other end to ground, problem solved!
             
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            • oldkimmer

              oldkimmer FABO Gold Member FABO Gold Member

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              Have u checked to see if the oil pressure wire under the hood is maybe touching something metal and causing the gauge to fluctuate Kim
               
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