Filled up the truck all the way in the filler neck and the gage reads halfway between 3/4 and full.

All the parts are marked as shipped. Hoping for them this weekend.

 

And, I'd bet empty is below the E. How are you going to calibrate it?

 

Put my spare orig IVR in, start the truck and warm it up to where the gages sit, mark em, swap to the new IVR and adjust it to make the gages read the marks. Then go fill the truck and make sure full is full and fine tune from there.

Unless someone has a better idea.....

 

Pull the indicator needle off its pin, rotate to point to "full", and push it back on in that position?

 

That would work for fuel, but to get them all back would require pulling and reinstalling all three pins. I think I'd do what Don is planning - turn one pot and fix everything in one go.

 

Tim Allen's Home Improvement Grunt - YouTube

The electrically-heated gauges - those run by sending units on the vehicle (fuel level/oil press/water temp) - all look like so:

 

Sorry I am creating another rabbit trail in this thread, but here's a tip someone told me that seems to work when you don't know where the vehicle runs out:

If you look at the sending units on most vehicles, the float arm will go down and hit a stop when the fuel level is low, and the pickup sock is always a couple of inches below where the float stops.

So the tip as it was told to me is to keep an eye on the needle as you get near empty and you stop and go around turns, the needle will rise a fall slightly because the fuel is sloshing around bouncing the float up and down. As the fuel gets even lower, you will find the needle will settle down and just sit there. That means the fuel is below the float level where it rests on the stop, and you usually have about 3 gallons more less depending on the vehicle and the fuel tank design. So if the needle is sitting there dead on empty, you had better find a station somewhere.

 

That's a good tip. Makes sense. Thanks

 

Most of the parts arrived today, so I can get started on the second try.

 

And here we have the second attempt:



And here we have power:



The potentiometer is very sensitive, so I may try some other resistors to get it less sensitive and better tuneability. I have enough parts for 10 tries.....

If it stops raining, I may go put it in.

 

The sensitivity is why I suggested using a resistor in parallel to the pot. You cut the sensitivity to a max of 50% of what you have now.

But, if you can figure out what voltage you need, closely, then you can pull the pot and/or resistor and put in a pot that has little range so it is easy to tune.

 

Parallel or series? I used a 1k pot in this one. Being a wiper style pot, it works but not very accurate/precise. Which is irrelevant when I don't even know what voltage I need.

I am guessing the gages need 5.2v or so. Maybe up to 5.5v. I found a chart that gives resistor values to get specific voltage outputs with the LM338T, but without knowing the needed voltage...

I could put this one in, adjust it to where the gages match the stock IVR, measure the voltage and build another with fixed value resistors....

And the more I think about it, the more inclined I am to swap out all the gages for Autometers. That or just put the stock IVR back in and live with it.

 

Parallel. If you know roughly the resistance that you need, then use a fixed resistor of twice that value and a pot with a bit more than twice that value. Theoretically then, when you trim the pot down just a bit from full value you'll be at the overall resistance you want. And any change on the pot will be roughly half of that to the circuit.

But, the idea of using fixed resistors, or using fixed resistors with a pot of very small value is a good one. Don't give up now, you are too close to quit. If not for you then for the rest of us.

 

The reason I am questioning this is...

Drive the truck to the local Radio Shack for the last resistors, note the gages just before parking, come out and start her up and they sit different. Hmm. Driving to work all this last week the gages read consistent. All checks before were on dry days. Today it was raining. Don't know if that was the difference as the change was not much, only half a letter lower, but noticeable to me.

Might be the grounds. Could the wet change it? Do I need to seriously clean all my grounds before going any farther? Could the harness be getting wet?

 

If the engine/cab ground is bad it could make a difference when it gets wet. But, did you check the gauges after driving a bit? Did they go back up? I'm wondering if they cool off a bit while parked and take a while to get back to that point. Also, many gauges seem to have a bit of resistance in them and will come up a bit when rapped or shaken, so maybe driving with the vibration causes them to read higher?