BigBrother-84 Posted August 13, 2023 Share Posted August 13, 2023 Hi Gentlemen! My road trip is coming soon, so I will limit Big Brother's enhancements for the moment. But there's a new issue that I will probably have to address. The fuel gauge hesitates with the fuel level. Let me explain: Starting the engine, it slowly goes to the good level. But during the drive, it fluctuates with the rpm. I noticed that, when the gauge shows a lower level than the reality, it's when the engine is going to idling (at a stop light or something like that). When the engine goes back to higher rpm, the gauge goes up too, reaching its correct level. It is not constant nor regular. Just from time to time, but it happens too often in my opinion. I did the "ground test" and the gauge goes to the max. So I suppose that my gauge and wiring are ok. Is it possible that the fuel sending unit is sensitive to the "electrical power"? Link to comment Share on other sites More sharing options...
81-F150-Explorer Posted August 13, 2023 Share Posted August 13, 2023 Possibly a bad varying sending unit ground. Possibly internal to the sending unit. Grounding the gauge eliminates the possibility of a bad gauge, but not a bad ground to the sending unit itself. --------------- It could possibly be related to the ICVR, instrument Cluster voltage regulator. --------------- How is the charging system? Could the voltage be dropping at idle? Link to comment Share on other sites More sharing options...
BigBrother-84 Posted August 13, 2023 Author Share Posted August 13, 2023 Possibly a bad varying sending unit ground. Possibly internal to the sending unit. Grounding the gauge eliminates the possibility of a bad gauge, but not a bad ground to the sending unit itself. --------------- It could possibly be related to the ICVR, instrument Cluster voltage regulator. --------------- How is the charging system? Could the voltage be dropping at idle? You’re right Ralph, this is logical and needs to be verified. But electrical diagrams do not show where the sending unit ground is located. Any advice? Link to comment Share on other sites More sharing options...
81-F150-Explorer Posted August 13, 2023 Share Posted August 13, 2023 You’re right Ralph, this is logical and needs to be verified. But electrical diagrams do not show where the sending unit ground is located. Any advice? It's grounded through the black wire in the connector. It connects to this ground via the sweep to the sending unit. The sweep rides on a resistor like spring, thus varies the ground as fuel level decreases. These sending units are known to have bad sweeps. I edited my original post with more ideas as to why the gauge can fluctuate. Link to comment Share on other sites More sharing options...
Gary Lewis Posted August 13, 2023 Share Posted August 13, 2023 It's grounded through the black wire in the connector. It connects to this ground via the sweep to the sending unit. The sweep rides on a resistor like spring, thus varies the ground as fuel level decreases. These sending units are known to have bad sweeps. I edited my original post with more ideas as to why the gauge can fluctuate. If the other two gauges, the coolant temp and oil pressure, don't do this then it probably isn't the ICVR as it serves all three. But if they do it is the ICVR. Having said that, I can't imagine why it would be tied to engine RPM save for an issue with the ICVR. That's because the battery voltage will vary with engine RPM, assuming there's a reasonable load on the battery such that the alternator can't keep the voltage at 14.4v at idle. So check to see if the other two gauges are acting wonky also. Link to comment Share on other sites More sharing options...
grumpin Posted August 13, 2023 Share Posted August 13, 2023 The way these gauges "work", I'd think it's from sloshing fuel, if the other gauges aren't affected as Gary said. Link to comment Share on other sites More sharing options...
BigBrother-84 Posted August 13, 2023 Author Share Posted August 13, 2023 If the other two gauges, the coolant temp and oil pressure, don't do this then it probably isn't the ICVR as it serves all three. […] So check to see if the other two gauges are acting wonky also. All other cluster instruments are perfectly stable. Just the fuel gauge that fluctuates this way. Link to comment Share on other sites More sharing options...
Gary Lewis Posted August 13, 2023 Share Posted August 13, 2023 If the other two gauges, the coolant temp and oil pressure, don't do this then it probably isn't the ICVR as it serves all three. […] So check to see if the other two gauges are acting wonky also. All other cluster instruments are perfectly stable. Just the fuel gauge that fluctuates this way. Then it shouldn't be the ICVR as it powers all three of those gauges. That being the case, maybe it is the slosh that Dane mentioned? Variations in these gauges aren't usually obvious since they are actually thermometers and the heat from the current running through the coil doesn't change very quickly. But perhaps you have a gauge that does react quickly? Link to comment Share on other sites More sharing options...
81-F150-Explorer Posted August 13, 2023 Share Posted August 13, 2023 Then it shouldn't be the ICVR as it powers all three of those gauges. That being the case, maybe it is the slosh that Dane mentioned? Variations in these gauges aren't usually obvious since they are actually thermometers and the heat from the current running through the coil doesn't change very quickly. But perhaps you have a gauge that does react quickly? Yes I agree, all three gauges would react... As for the sloshing, my fuel gauge will react to slosh, going around a turn, or going up/down hill but it's not very noticeable. ------------------- Is this something that happened recently? He did say that he changed the instrument cluster out for one with a tach... (or am I getting people confused?) Perhaps the replaced fuel gauge is more reactive than the older one he swapped in with the cluster? Still could be sending unit issues too. Link to comment Share on other sites More sharing options...
Gary Lewis Posted August 13, 2023 Share Posted August 13, 2023 Then it shouldn't be the ICVR as it powers all three of those gauges. That being the case, maybe it is the slosh that Dane mentioned? Variations in these gauges aren't usually obvious since they are actually thermometers and the heat from the current running through the coil doesn't change very quickly. But perhaps you have a gauge that does react quickly? Yes I agree, all three gauges would react... As for the sloshing, my fuel gauge will react to slosh, going around a turn, or going up/down hill but it's not very noticeable. ------------------- Is this something that happened recently? He did say that he changed the instrument cluster out for one with a tach... (or am I getting people confused?) Perhaps the replaced fuel gauge is more reactive than the older one he swapped in with the cluster? Still could be sending unit issues too. Yes, Jeff recently swapped out his gauge cluster. I wonder if the movement of the gauge was with the "old" or "new" gauge? Link to comment Share on other sites More sharing options...
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