Hi guys, Im really stuck here and I know it must be something simple, but trying to find it is a different matter. A wee while ago my oil pressure gauge was working, then not working, I decided that it must be the sender unit and replaced it, then the gauge didn't work at all so purchased lee's spare gauge which I don't mind keeping as a spare anyway. I fitted the new gauge and no succsess. I have tested + wires at both ends and both have power and would like to know if: the engine has an oil pressure switch also fitted somewhere? or could there be a bad earth somewhere? All the fuses are fine etc etc but don't know what to try next. Any suggestions would be really appreciated as I don't really want to drive the car this way.
Try a temporary Mechanical oOil Pressure Guage,Buy it at ant Auto Part Store . then see what your getting,to make sure you have Oil Pressure.
Hi Harry, Thanks for that, I bought one and tested, good news in a way, I am getting a reading of 6.5 bar so oil pressure seems fine, so must be an electrical problem somewhere or a faulty new pressure sender?
So far I have been all over the car and now looking into wiring (or could it be a faulty replacement pressure sender?) I have been cross eyed looking at the old wiring diagram in the manual and see that there is a grey wire with black stripe that runs to the pressure gauge but not sure if this wire also runs into the wiper motor and switch colum. There is definatley power going to the sender and the gauge but none seem to work, and there is plenty of oil pressure as I have used a tester kit on it. Is there any way of testing the sender itself to know if that is faulty? The gauge is reading stone dead, please hope that someone out there can help.
Do your eyes a favor and get a set of Paul Bennett's stupendously awesome (my daughter's term) wiring diagrams: http://www.ferrari308gtbi.com/
Eric - Thanks for the endorsement *********** Stephen - the sender is a variable resistance which changes under pressure like a volume control potentiometer. The sensor resistance can be read with a volt-ohm-meter or multimeter. Is that term the same in Scotish? Set your multimeter to ohms and place one lead on ground. Remove the gray/black wire from the sensor then measure and note the resistance of the sender unit. Having now found the resistance at no oil pressure, have someone start the engine and measure the resistance again. A different resistance should mean the oil pressure sender is ok. Next bring your attention to the gray/black wire which makes no stops between the sensor and the connector under the dash a short distance from the gauge. You need to establish the integrity of the wire, that it isn't broken along the route from engine to cabin. Reconnect the gray/black wire at the sender. Open that connector under the dash which has the gray/black wire. Use your ohmmeter (one lead on ground) at the gray/black wire at that connector (key off - engine off) which should see the same resistance which you measured directly on the sender unit. Then reconnect the connector and make certain the ingnition key is off. Measure resistance looking for that same resistance as directly at the gauge. Assuming you can read the sensor resistance all the way to the gauge, you could do as Harry suggested and buy a cheap oil pressure gauge and see how it works connected to the gray/black wire. I don't think you will need to. You said you have voltage at your dash gauge with key on, so at this point your oil pressure gauge must be faulty. Chances are you will have found a bad connection along the way of resistance measurements, very possibly at the gauge or the large connector under the dash. GL ___________________________ http://www.FerrariDiagrams.com
Hi Paul, Thanks a lot for you help. I haven't done the ohm test yet but will do so in the morning, but what I did do was run a few tests and for some strange reason there is no power coming from the grey black wire at the sender, although there was the last time I checked. I do as a matter of fact have a spare pressure gauge, so tonight made a connection with power to and from the gauge and sender and grounded it, instead of the gauge reading 6.5 which it did, the needle would move about 1mm backwards in the opposite direction, so it seems to me I may have 2 problems? broken wire and faulty new sender? I will do the ohm test and let you know, thanks again. stephen ps. I also have a pressure testing kit and done that test, pressure is fine and showing 6.5 at idle so at least thats ok.
After I wrote the test I thought to reverse things but was to tired to edit it. Probably easier to measure the sensor resistance without the wire attached, then attach it and move into the cabin. Reason for disconnecting the wire is to eliminate any resistance from the gauge circuity. After you remeasure the sensor resistance at the cabin end of the gray/black wire and find it the same as when directly on the gauge, you can reconnect the wire to the gauge, then start the engine and see if the resistance changes. Doing it this way you don't need a helper to start the engine. The sensor has a finite resistance without any pressure but a different gauge doesn't know what that zero pressure resistance is. So it's not uncommon for an unmatched gauge/sensor to read minus or backwards needle at no pressure. Not to worry. GL
Thanks Paul, will give this a go tonight, just thought I would add that the pressure gauge I used to test as a secondry one is an identical one to the one in my car,so I connected the power source in the wrong direction? ie power the guage first instead of the sender? will this matter? or the sender is shot? will post some pics later might be a good idea? stephen
Ok, no pics yet but will tell you what happened. I pulled the clocks out from the dash again tonight so I could check the grey and black wire and to my surprise from last fitting the new oil pressure gauge, noticed that the black and grey wire had popped off the connector on the gauge!!! as there was a bit of strain there, I made an extension wire to give it some relief from popping off again. So now I have power restored to the black and grey wire at the sender end in the engine. I started engine but still no reading so checked the resistance in ohm and the sender is reading 63.9, I then checked the ohm from the clocks end and it reads 63.8. I started the engine and the reading went to 0 then 1 and no reading on the gauge, I tried my old gauge back in and the same....nothing. Could this indicate the my sender is shot? or am I looking for something different? Although there is now power at the senders grey and black wire, now that I have reconnected it to the gauge side, there is no power at the grey and black wire on the gauge side but there is power to the green wire, Im sorry just need guidance on this as I go.
