I just posted this in Electrical but here it is as well.
Speedhut fuel gauge and MeterMatch
Like a lot of others I’ve had issues with the Speedhut fuel gauge playing nicely with the stock fuel tank sender. I would get wild swings and was never really sure how much fuel I had. After some discussions on the Speedhut group buy thread I decided to get a MeterMatch from Technoversions. It basically takes the ohm readings from the sender and converts them to a more stable range for the gauge.
So here is how I attacked this. I tried to install it without pulling the sender and it was just not working. And during the course of this I was getting some erroneous readings from the sender. So I drained the tank all the way and pulled the sender. I brought the sender into the car so I could manually move it to see what was going on. I set the fuel gauge back to default of 240 empty and 33 full. I then used the MeterMatch to set full and empty calibration. To calibrate you used up and down buttons to move the gauge needle and then save it when you get it where you want it. I had a really hard time since a single button push moved the needle almost a 1/4 tank. I ended up getting it close with MM and then doing a final calibration with the gauge. This worked really well. I reinstalled the sending unit and rewired it with a new good ground and a dedicated sender wire straight to the MM. I have a 16 gal tank. I put in 2 gallons and the meter read 1/8 and was stable. So far so good. I put in two more and it was a little above 1/4. Still good but I wanted to try the lower mid point calibration. As before the button presses moved the needle a ton. But I noticed the needle wasn’t stopping at the same place. I found I could walk the needle around by different combinations. I went to the gas station and put in four more gallons and the gauge read 1/2. Four more and I was a little above 3/4. Went for a drive and the needle was really steady compared to what I had before. Let’s face it a lever arm sender is going to have a lot of movement and if the gauge isn’t designed for that sender then it’s only going to be so good. So I got back to the shop and contacted Brian at Technoversions with questions about the up down calibration. Here is his reply:
With regard to the MeterMatch, what you are seeing with the up/down resolution is on purpose. Most gauges use a fair amount of current, so if we made the buttons work at full resolution, you could be pressing one of the up/down buttons a thousand times to go from end to end. So we make the buttons move the amount in larger increments. But to make the points in-between accessible, we make the increments between up and down slightly different, so that all values can be selected.
This is hardly noticeable on most gauges, but on some electronic gauges, such as the one you have, much less current is necessary so you are working within a small range of values, so the resolution appears to be much coarser. But you should be able to get there.
So you can hit a specific target with the right combo but I will tell you it is a challenge. You can get the needle where you want it and after you take it out of program mode it changes. I set the upper mid point calibration the best I could considering the heat index in Florida right now and may revisit it in the future. From 3/4 tank and up I don’t care if it is accurate and truth be told as long as I can count on 1/4 tank being stable and accurate I’ll be happy.
So to sum up.
I would run a separate dedicated ground and signal wire first since in all reality that may have been the bulk of my issues. I already had the MM so I used it. If That doesn’t work for you then:
Purchase MM from Technoversions
Set the fuel gauge to default ohms since that is where it was designed to work.
Use the MM calibration to get the needle to full and empty as best you can. I wouldn’t get too crazy with the button pushes since you are going to set the final calibration with the gauge.
Recalibrate the Speedhut fuel gauge.
Install the sender and use known amounts of fuel to check calibration.
I plan on draining the tank when it reads 1/4 and if I have 4 gallons then I’m golden. I’ll update this thread after I drive it a bit as well.