Guest Terry Posted May 4, 2012 Share Posted May 4, 2012 We have an issue with the oil pressure gauge in our new R400. We have changed the sender unit, changed the gauge. We have spent 8 hours today doing the following: Unwrapped dash loom from beneath the scuttle. Taken all pins/sockets out of plugs, checked and reinstalled. Checked continuity on all wires, plugs etc. for oil pressure gauge We have continuity on the green/orange wire to sender from the chassis/engine harness plug. This wire changes colour at this plug to green/white to the gauge. ie: Continuity from gauge plug to sender plug We have a ground/continuity on BOTH sending units if checked between green/orange & black when disconnected from loom. Is this correct or are both sending units faulty? Would this not tell the gauge to go full reading? We have continuity with ignition OFF between green/white & white/brown at the chassis/engine plug with ECU connected NO continuity with ECU unplugged How/why is the ECU in the gauge circuit? Is there a bad/high resistance ground somewhere? Where are the main grounding points on the chassis? HELP http://www.blatchat.com/images/smilies/sad.gif Link to comment Share on other sites More sharing options...
Klasik-69 Posted May 4, 2012 Share Posted May 4, 2012 I believe that most sending units have high resistance at 0 psi and lower resistance as the pressure rises. Good way to find out is to put an ohm meter on the oil pressure plug with the engine off, then start the engine to see where the resistance goes, if it moves at all. If the resistance doesn't move or change between the plug and the engine block (ground) you either have no oil pressure or you have a bad sender. Two bad senders ? I kind of doubt it but its possible. Have you put a mechanical gauge in there to see where you are on actual oil pressure ? I would do that first. You could easily test the sender off the car with a couple of air fittings and an air pressure gauge. Most oil sending units are 1/4 NPT or 3/8 NPT. Get a an appropriate sized tee, screw in your male QD in one branch, the sending unit in another and a gauge in the third tee. Check resistance to ground at 0 psi, then check resistance at 50 psi. Grounding issues can be between the motor and the chassis (doubtful) or the carbon fiber dash and the gauges (more likely). With an ohm meter, you can check the grounding by measuring the resistance between the metal body of the gauge and the car's chassis. If its open or high in resistance, you have a problem and need to fix that. Good luck. Link to comment Share on other sites More sharing options...
yellowss7 Posted May 4, 2012 Share Posted May 4, 2012 Wiper motor and on the block to the frame rail on right hand side. Link to comment Share on other sites More sharing options...
MHKflyer52 Posted May 4, 2012 Share Posted May 4, 2012 Ground your gauges mounted in the dash if mounted in fiberglass or carbon fiber. Link to comment Share on other sites More sharing options...
Guest Terry Posted May 5, 2012 Share Posted May 5, 2012 Wiper motor and on the block to the frame rail on right hand side. Not sure I understand Link to comment Share on other sites More sharing options...
Guest Terry Posted May 5, 2012 Share Posted May 5, 2012 Thanks guys for all your suggestions. It now appears that we also have a faulty rev counter, we are convinced it's a ECU issue. Link to comment Share on other sites More sharing options...
yellowss7 Posted May 5, 2012 Share Posted May 5, 2012 Sorry, Terry, you asked where the grounds were. I understand that there is a ground using the wiper motor mount. Tom Link to comment Share on other sites More sharing options...
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