summerinmaine Posted March 17, 2009 Share Posted March 17, 2009 I was down in Baja for the past four-five days, and to pass the time during the boring RT from Mexicali to San Felipe I did a lot of fuel/mileage tests to help diagnose my cold running/bad fuel economy problem. I got @15-16mpg on highway running at 60-70mph, and at worst got @13.5mpg when I was desert running in crappy two track, lots of soft sand, and running mostly at 20-30mph (mileage and speed verified by my GPS). Not great, but nowhere near as bad as I feared. And the motor never got above 175F, even in the slow running. What I did find interesting as a side issue was that when my low fuel light went on (meaning two gallons left according to the manual) and I re-fueled, the tank would only take 12-13 gallons. That means that there are 5-6 gallons left in the tank. I verified this by intentionally running a long way to try to run out of gas (I carry ~4 gallons in cans as a reserve when desert running), but couldn't get it to run dry. The most I squeezed in with the light on and the fuel gauge riding on E for many miles (after running for 230 miles total) was 16.1 gallons. Long story short: Is there a way to adjust the set-point for the warning light and/or recalibrate the gauge/sending unit? If not, no big deal, but I do like things to work as advertised if it's a matter of adjustment. Link to comment Share on other sites More sharing options...
jeepdoggydogB Posted March 17, 2009 Share Posted March 17, 2009 I was down in Baja for the past four-five days, and to pass the time during the boring RT from Mexicali to San Felipe I did a lot of fuel/mileage tests to help diagnose my cold running/bad fuel economy problem. I got @15-16mpg on highway running at 60-70mph, and at worst got @13.5mpg when I was desert running in crappy two track, lots of soft sand, and running mostly at 20-30mph (mileage and speed verified by my GPS). Not great, but nowhere near as bad as I feared. And the motor never got above 175F, even in the slow running. What I did find interesting as a side issue was that when my low fuel light went on (meaning two gallons left according to the manual) and I re-fueled, the tank would only take 12-13 gallons. That means that there are 5-6 gallons left in the tank. I verified this by intentionally running a long way to try to run out of gas (I carry ~4 gallons in cans as a reserve when desert running), but couldn't get it to run dry. The most I squeezed in with the light on and the fuel gauge riding on E for many miles (after running for 230 miles total) was 16.1 gallons. Long story short: Is there a way to adjust the set-point for the warning light and/or recalibrate the gauge/sending unit? If not, no big deal, but I do like things to work as advertised if it's a matter of adjustment. My fuel light routinely came on when I would hit 190 miles and take 13 gallons of gas meaning I had 5 gallons left. My old 98 TJ was about as accurate, now that I have a pre 91 fuel sending unit my lite comes on with 19 gallons left in the tank :mad: Link to comment Share on other sites More sharing options...
jaekl Posted March 17, 2009 Share Posted March 17, 2009 That's better than my 86 with a 85 gauge cluster in it. The warning light is instantaneous and starts flashing with the sloshing fuel with half a tank. While the 88 with a 88 5/6th cluster starts coming on at the last quarter if the float falls long enough to make it think it is down to 2 gallons. Link to comment Share on other sites More sharing options...
HOrnbrod Posted March 17, 2009 Share Posted March 17, 2009 There is a "low fuel warning" module inside the cluster behind the fuel gauge, part number 83504281 for the 1990 and below. Probably not available anymore, but ya never know. They are preset to conduct when it senses xx ohms for xx seconds (66.5 ohms for 20 seconds on the HOs, don't know the values for the Renix clusters) and illuminate the warning light. These are replaceable but non-adjustable unless you want to "fool" your module by adding in resistance. Link to comment Share on other sites More sharing options...
summerinmaine Posted March 17, 2009 Author Share Posted March 17, 2009 Thanks for all the comments. It's pretty much as I suspected. I'll probably just live with it. Link to comment Share on other sites More sharing options...
johnj92131 Posted March 18, 2009 Share Posted March 18, 2009 How about adjusting the float arm in the tank? Should not be too hard to measure the resistance when your low fuel light comes on, then just bend the float arm so the float sits lower in the tank at that same resistance. I have done this with my Passat but not the Comanche. Link to comment Share on other sites More sharing options...
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