Luke Beaumont Posted October 24, 2001 Share Posted October 24, 2001 Waah. It's been a fearsome saga getting even this far, but the fact is my oil pressure gauge/sender isn't working. This is K series engine in an '01 kit. It reads 2 bar at idle, but throttle movement causes the needle to gradually sag to zero. The gauge is getting the full 12.5V in, ground, and a clean connection through to the sender. With the sender disconnected, the signal voltage is around 7.5V. With the sender connected, and a voltmeter in parallel it reads just over 5V. Shorting signal to earth produces full deflection on the gauge. I'm baffled (short of replacing both components willy-nilly), Caterham are stumped (though they reckon the gauge should poke 12V to the sender), and I've got a trackday le weekend for which I'd really like to see oil pressure. Can anyone shed some light on this? Many, many TIA. Edited by - Luke Beaumont on 24 Oct 2001 19:51:37 Link to comment Share on other sites More sharing options...
EFA Posted October 24, 2001 Share Posted October 24, 2001 "Shorting signal to earth produces full deflection on the gauge." Luke, Your sender is knackered, or (unlikley in a newish engine) the pressure relief valve is faulty. Swap the signal leads for the temp and oil guages around. If the fault moves to the temp guage (which will now read Oil Pressure) its the OP sender. Fat Arn The NOW PROVEN R500 Eaterid=red> See the Lotus Seven Club 4 Counties Area Website hereid=green> Link to comment Share on other sites More sharing options...
Luke Beaumont Posted October 24, 2001 Author Share Posted October 24, 2001 Ta for the suggestion Arnie, but that just makes it weirder. Right way round: Temp gauge behaves normally, OP as described above. Swapped: OP (now temp) registers just enough to pull the needle off rest. Temp (now OP) sits about halfway, just over 80 and stays there irrespective of throttle. Oil pressure should increase markedly with throttle shouldn't it? This is an old K out of a scrapper, and I've wired up the old low oil pressure switch to the tacho shift light - this behaves normally as far as I can see (on with ignition, off shortly after the engine starts). Other than that, I assume it really is getting decent oil pressure - it wouldn't have lasted long at 7k rpm otherwise IWHT Link to comment Share on other sites More sharing options...
Fast Westie Posted October 25, 2001 Share Posted October 25, 2001 Luke Check the earthing on your instruments. When I did mine the only earth was through the senders giving some wierd results. The car in front is a Westfie1d wink.gif Link to comment Share on other sites More sharing options...
EFA Posted October 25, 2001 Share Posted October 25, 2001 Luke, The instruments are earthed to the wiper motor bracket under the scuttle abouve passengers left knee. Make sure the chassis has the powder coating removed where this ground is attached! Also check you have a good earth between the engine and the chassis - there should be a strap by the right front engine mount. Remove the strap and clean all paint and powder coating off the rubber bush mount and the chassis where the two smaller bolts hold this on. The v.regulators are internal in these instruments so earthing is now a very likley cause. If you can measure the resistance using a good digital meter (Fluke or similar) then you should get a value of less than 1 ohm across all earth points. Fat Arn The NOW PROVEN R500 Eaterid=red> See the Lotus Seven Club 4 Counties Area Website hereid=green> Link to comment Share on other sites More sharing options...
Luke Beaumont Posted October 25, 2001 Author Share Posted October 25, 2001 I've clocked the earthing arrangement, and the gauge sees 2 and a bit ohms to earth. Caterham are replacing the sender - fingers crossed that cures it. Thanks guys. Link to comment Share on other sites More sharing options...
EFA Posted October 26, 2001 Share Posted October 26, 2001 Luke, Thats still a bit of a high reading. Fat Arn The NOW PROVEN R500 Eaterid=red> See the Lotus Seven Club 4 Counties Area Website hereid=green> Link to comment Share on other sites More sharing options...
Luke Beaumont Posted October 26, 2001 Author Share Posted October 26, 2001 Rump. New sender made no diff, so I attacked the gauge earthing point, and now we read just under an ohm. Only snag is that hasn't cured it either sad.gif I don't think there's anything else I can do to get it working for the trackday tomorrow. What I will do is bring along the multimeter and ask another Caterham owner if I can read the voltage off the back of their gauge. Also been having enormous fun getting a Webcon shift light working tonight. Electrics, doncha love 'em [:] Link to comment Share on other sites More sharing options...
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