lq4 electronic oil pressure gauge doesnt work
03-23-2012, 10:51 PM
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lq4 electronic oil pressure gauge doesnt work Ok guys this is my first post so I hope it's in the right place. So I've just got my 2004 LQ4 with a T56 into my 1971 El Camino. I just got to start it yesterday and when doing so my oil pressure gauge reads below zero. The gauge is a quad gauge and the temp, fuel and volt gauges all work fine so I figure the gauge has good power and ground. I did put a mechanical gauge on and it read 55 psi so I know I do have oil pressure. I took the wire off the gauge and grounded it and my gauge read maxed out so I think the gauge works. I replaced the wire from the gauge to sender and still no luck. I also attached a wire around the sending unit itself and hooked it to ground to make sure that wasn't the problem. I also attached an additional wire to the sending unit and touched it to the body to see if I had a good ground and my gauge read maxed out again. So I am thinking bad sending unit but when I crank the engine with the fuel pump fuse out so it wont fire the gauge reads 20 psi. Also if I pull the ignition wire so the starter wont crank when I turn the key to start the temp gauge reads max and the oil pressure gauge moves to 0 psi which from what I read is what normally functioning gauges should do. I have no idea what else to try. Anyone have any other ideas. Oh yeah I have a fully charged battery and a 4 gauge ground from battery to engine and 4 gauge ground from engine to frame and 10 gauge ground from engine to body. I am running a 4 gauge power wire from battery to starter and 4 gauge from alt to battery. Ignition starter wire is 10 gauge. Hope that's all the info needed. Thanks for any help.
03-24-2012, 09:40 PM
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Ok guys this is my first post so I hope it's in the right place. So I've just got my 2004 LQ4 with a T56 into my 1971 El Camino. I just got to start it yesterday and when doing so my oil pressure gauge reads below zero. The gauge is a quad gauge and the temp, fuel and volt gauges all work fine so I figure the gauge has good power and ground. I did put a mechanical gauge on and it read 55 psi so I know I do have oil pressure. I took the wire off the gauge and grounded it and my gauge read maxed out so I think the gauge works. I replaced the wire from the gauge to sender and still no luck. I also attached a wire around the sending unit itself and hooked it to ground to make sure that wasn't the problem. I also attached an additional wire to the sending unit and touched it to the body to see if I had a good ground and my gauge read maxed out again. So I am thinking bad sending unit but when I crank the engine with the fuel pump fuse out so it wont fire the gauge reads 20 psi. Also if I pull the ignition wire so the starter wont crank when I turn the key to start the temp gauge reads max and the oil pressure gauge moves to 0 psi which from what I read is what normally functioning gauges should do. I have no idea what else to try. Anyone have any other ideas. Oh yeah I have a fully charged battery and a 4 gauge ground from battery to engine and 4 gauge ground from engine to frame and 10 gauge ground from engine to body. I am running a 4 gauge power wire from battery to starter and 4 gauge from alt to battery. Ignition starter wire is 10 gauge. Hope that's all the info needed. Thanks for any help.
03-25-2012, 09:00 AM
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Do you have any idea what kind of resistance i should be seeing. I've been over the wiring a bunch of times. Since the three other gauges in the quad work I figure the gauge wiring is good. I ran multiple wire to the sender from the gauge and even did an extra ground. Seems like the wiring would be good. I will check the output resistance tho. I would try to get a new gauge but I've been trying to get a hold of dolphin (the maker of the gauge) for 3 days with no luck. Is there any way to tell what ohms the gauge operates of off so I can just get a new sender from someone else.
03-25-2012, 11:32 AM
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Resistance varies from sender to sender. I actually made a graph for SW sending units. Check it out on my webpage. It the February 16, 2011 entry:
http://www.buyrcars.com/jag.htm
Most of the SW-style sending units start with about 240 ohms at 0 psi of oil pressure. As oil pressure (psi) increases, resistance (ohms) decreases. (Note that I adjusted the SW sender output with a resistor, as discussed on the chart caption.)
There are other styles, though. Some start with 0 ohms and 0 psi and go up from there. It just depends on what type of sender you have.
To start to figure out what kind of sending unit you have, measure the resistance with the engine off, and then try measuring the resistance with the engine running.
http://www.buyrcars.com/jag.htm
Most of the SW-style sending units start with about 240 ohms at 0 psi of oil pressure. As oil pressure (psi) increases, resistance (ohms) decreases. (Note that I adjusted the SW sender output with a resistor, as discussed on the chart caption.)
There are other styles, though. Some start with 0 ohms and 0 psi and go up from there. It just depends on what type of sender you have.
To start to figure out what kind of sending unit you have, measure the resistance with the engine off, and then try measuring the resistance with the engine running.
03-25-2012, 11:45 AM
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Resistance varies from sender to sender. I actually made a graph for SW sending units. Check it out on my webpage. It the February 16, 2011 entry:
http://www.buyrcars.com/jag.htm
Most of the SW-style sending units start with about 240 ohms at 0 psi of oil pressure. As oil pressure (psi) increases, resistance (ohms) decreases. (Note that I adjusted the SW sender output with a resistor, as discussed on the chart caption.)
There are other styles, though. Some start with 0 ohms and 0 psi and go up from there. It just depends on what type of sender you have.
To start to figure out what kind of sending unit you have, measure the resistance with the engine off, and then try measuring the resistance with the engine running.
http://www.buyrcars.com/jag.htm
Most of the SW-style sending units start with about 240 ohms at 0 psi of oil pressure. As oil pressure (psi) increases, resistance (ohms) decreases. (Note that I adjusted the SW sender output with a resistor, as discussed on the chart caption.)
There are other styles, though. Some start with 0 ohms and 0 psi and go up from there. It just depends on what type of sender you have.
To start to figure out what kind of sending unit you have, measure the resistance with the engine off, and then try measuring the resistance with the engine running.
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03-25-2012, 09:19 PM
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03-28-2012, 07:03 PM
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Well I haven't had a chance to pull the old sending unit out to test it yet but I finally got a hold of the company I got my gauges from and told them what was going on and they said they would send out a new sending unit for free. I let you guys know if that fixes it.
04-03-2012, 10:30 PM
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Ok guys I finally got it all worked out. I got a new sending unit and put it in and it still didn't work. So after a bunch more of double checking grounds and gauge wiring I decided to run another new wire from the gauge to the sending unit. Still didn't work. So I tried a 12 gauge wire instead of a 14 gauge that it had and all of a sudden it worked. I guess there was to much resistance with the smaller wire or something. Thanks for all the help guys. Oh one last thing how do I make this post no active anymore?
