Hillcountrymac Posted August 4, 2014 Share Posted August 4, 2014 Hey guys,Replaced the ground cable yesterday.The one from the neg. post to the engine block(1990 MJ 4.0).While there I cleaned up the grounds and put it back together.Got in this morning and the oil gauge is pegged.Popped the hood and I had unplugged the sending unit when I did the cable.Plugged it back in and I'm still pegged.First question: with the key on the sending unit wire that plugs in the rear of the unit should be hot right? It is not hot,all gauges work except oil.What do ya'll think could have happened? Only thing I did was the ground cable that's it. Everything worked fine before I changed the ground,I did drive to to the Ace hardware unplugged,but that shouldn't make any difference,should it? I'm mystified in Texas. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 5, 2014 Share Posted August 5, 2014 It's a ground. Won't be hot. Change the oil also? Hit the sender with the oil filter wrench? Link to comment Share on other sites More sharing options...
Eagle Posted August 5, 2014 Share Posted August 5, 2014 How's your ground from the engine block to the body? Link to comment Share on other sites More sharing options...
Eagle Posted August 5, 2014 Share Posted August 5, 2014 It's a ground. Won't be hot. Change the oil also? Hit the sender with the oil filter wrench? Yes, I believe it will be hot. It's 12 volts from (through) the gauge to the sender, and the wire grounds to the block through the sender. If the wire weren't hot, that would mean the system is sending 12-volts through the block and out through the oil sender to the wire. 1990, so it's a Renix and has the "old" wiring. The resistance of the oil pressure sender varies from 0 to 88 ohms, with 0 ohms (no resistance) being 0 oil pressure, and 88 ohms being max (80 psi). A quick test is to take the wire off the sender, with the key on, and ground the wire directly to the block. That will be zero ohms of resistance, and the gauge should then read zero. Remove the wire and the gauge should swing all the way to the opposite end, to or beyond 80 psi. If the gauge doesn't read zero when the wire is grounded directly to the block, you have an open circuit somewhere between the sender and the gauge. If it does go to zero when you ground the wire, most likely the sender is faulty. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 5, 2014 Share Posted August 5, 2014 1990, so it's a Renix and has the "old" wiring. The resistance of the oil pressure sender varies from 0 to 88 ohms, with 0 ohms (no resistance) being 0 oil pressure, and 88 ohms being max (80 psi). The HO oil pressure sender is also 0-88 ohms; 0 ohms - 0 psi. OP, make sure the oil pressure sender male spade connector is mated properly to the output wire female end. Sometimes it takes a couple of tries to connect them properly if you still have the rubber boot over it. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 5, 2014 Share Posted August 5, 2014 90 Renix has a single spade connector at the oil pressure sending unit. It is a variable ground to the instrument panel gauge. Link to comment Share on other sites More sharing options...
Hillcountrymac Posted August 5, 2014 Author Share Posted August 5, 2014 Man thanks for all the help.I will work on it today.I will ground it to the block and see if it zeros.The old boot is on but is a real loose fit.Think I will replace the connection.I just doubt an open circuit because all it did was unplug.I have had weirder things happen,I replaced a condenser on my 82 EZGO and it would not run turned out the brand new condenser was bad,so maybe the sending unit went bad.Anyhow, thanks for all the suggestions and sorry about not getting back sooner,I got busy last night. Link to comment Share on other sites More sharing options...
Hillcountrymac Posted August 7, 2014 Author Share Posted August 7, 2014 It was the sending unit.Cheap chinese crap,lasted about 8 months.i replaced it with Bosch at least it has a lifetime warranty. Link to comment Share on other sites More sharing options...
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