Jig Posted March 1, 2017 Share Posted March 1, 2017 Anybody got any experience of a kit build Sigma not registering oil pressure at first cranking? I'm waiting for some ideas from Derek, but thought I'd ask here.My pressure gauge does the usual little kick as it initialises, but there it stays whilst I crank the engine over for up to 40 seconds. Engine is full to the top of the dipstick (just over 4l from dry).I have had the connector off the sensor at the engine and verified that there is a good voltage across the pins for the green and black wires. The green/white pin floats to around 4.5v when disconnected and the gauge reads this towards the top of the range. I shorted the green/white and black (at the sensor connector) to ground the signal and the gauge dropped to zero. This gives me confidence that everything is working from engine to gauge so I should see something registering. I reconnected the connector to the sensor, ensuring that it mated well and tried again, but I get nothing. The needle does not move at all, as though the signal is grounded.Is it likely that the sensor is no good (or wrong type) from new or is there a reasonable possibility of something serious amiss in the engine? Link to comment Share on other sites More sharing options...
SM25T Posted March 1, 2017 Share Posted March 1, 2017 On our old Rover engines we have a single wire to the sender. You test the gauge and wiring by removing the cable and grounding it on the enine with the ignition on. The gauge shows max 100%. Is your 2-wire the sender core and an earth ? Check with CC before shorting the sender core though. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted March 1, 2017 Member Share Posted March 1, 2017 Are you turning it over with it prevented from firing?I'd put my money on a faulty sensor or bad connection. Not quite sure what you've done in the first of those two tests... How many wires go to the sensor (as in Ian's post)? Have you checked your engine earths? (Might not be relevant depending on above.) What's the resistance across the sensor terminals with all wires disconnected both at rest and while cranking?Hope they send you another quickly.Jonathan Link to comment Share on other sites More sharing options...
revilla Posted March 1, 2017 Share Posted March 1, 2017 Also on our old Rover engines ...I've know them take anywhere from 15 seconds to over 2 minutes to first pick up oil pressure when cranking. It's a horrible horrible time spinning them over any imagining what you might be doing to them I know.Have you removed the spark plugs to let the starter crank it over faster? That will help.Did you fill the oil filter with some oil before fitting it? That can help (bit messy spinning it on again though) especially if on fitting some of the oil runs back towards the pump, wetting the rotors and helping them seal. It also means it has to pump less volume of oil before building pressure.If you didn't put oil in the filter, you could try removing the filter. If oil pours out of it on removal, the pump was at least starting to work, after which pressure normally comes up very quickly. If not, add some oil before refitting it. You might be able to pump some oil with a tube on an oil can into the oil filter housing to prime the pump before refitting the filter. You want to pump oil back down the hole that leads to the outside of the filter rather than the central return.Not sure how much of this translates to a Sigma but I think it should. Link to comment Share on other sites More sharing options...
SM25T Posted March 1, 2017 Share Posted March 1, 2017 If your sender is mounted in a rubber hose .... it would have an earth and signal core. The sender unit simply varies its resistance with pressure ..... edited as i was thinking temperature sender when I typed ! Link to comment Share on other sites More sharing options...
revilla Posted March 1, 2017 Share Posted March 1, 2017 PS: Crank it in say 15 second bursts then rest it for a bit to avoid getting the starter too hot. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted March 1, 2017 Member Share Posted March 1, 2017 I've checked the wiring diagrams. Can't match those wiring colours: have you been able to?Jonathan Link to comment Share on other sites More sharing options...
revilla Posted March 1, 2017 Share Posted March 1, 2017 The sender unit simply varies its resistance with temperature.... or even pressure Link to comment Share on other sites More sharing options...
Jig Posted March 1, 2017 Author Share Posted March 1, 2017 I think that this sender generates a signal voltage. It is three wires, power, earth and signal. My test was to disconnect the sensor to let the signal float and then earth the signal wire and see if the gauge registered the difference. It did. That confirms to me that the wiring and gauge is functioning. It also rules out an earthing problem I think. I'll go and buzz the earths, though, to be sure.I haven't filled the oil filter, no. I'll see if it will come off easily. Advice from Derek is to ignore it and crack on! Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted March 1, 2017 Member Share Posted March 1, 2017 I haven't filled the oil filter, no. I'll see if it will come off easily. Good move. I was surprised by Andrew's comments, but the advice is obviously pragmatic and he's started a lot more new or rebuilt engines than me. My K fired immediately and the oil pressure was up by the time I'd looked.Jonathan Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted March 1, 2017 Member Share Posted March 1, 2017 ... Green, Black and White/Green (rather than Green/White)?Jonathan Link to comment Share on other sites More sharing options...
Jig Posted March 1, 2017 Author Share Posted March 1, 2017 ... Green, Black and White/Green (rather than Green/White)? Yep.The filter was nice and full of oil too. Going to start it tomorrow as per Derek's instructions, which he has confirmed. He suggests they'll rectify the sender at the inspection - apparently it needs a special tool to remove. Link to comment Share on other sites More sharing options...
revilla Posted March 1, 2017 Share Posted March 1, 2017 Ah that's good, I strongly suspect you had oil pressure but weren't registering it on the gauge. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted March 1, 2017 Member Share Posted March 1, 2017 Thanks for the update.According to the diagram you should have an oil pressure warning light with a separate sensor and a White/Brown wire.Jonathan Link to comment Share on other sites More sharing options...
Jim 123 Posted March 1, 2017 Share Posted March 1, 2017 I have a Sigma oil pressure sender in my hand. It has a normal hex head for spanner fitting. Is a special tool needed because of access? Link to comment Share on other sites More sharing options...
Area Representative paul richards Posted March 1, 2017 Area Representative Share Posted March 1, 2017 Sigma sender is a pig to access especially on a 150 with throttle bodies. I suspect that's why a suitable spanner is needed. Link to comment Share on other sites More sharing options...
Dorset7 Posted March 2, 2017 Share Posted March 2, 2017 A box spanner is the way to skin that cat. Link to comment Share on other sites More sharing options...
Area Representative Iain McCallum Posted March 2, 2017 Area Representative Share Posted March 2, 2017 I will concur with the box spanner as my oil pressure gauge started to play up and i suspected the sender but it wasn't at fault. I traced the wire back from the sender and found that a connector was attached to the chassis and it just needed connecting properly and latching. Somehow it had worked its way loose.Probably not your issue as you have checked the gauge - but you never know!Also it appears to get some sort of feed through the rev counter so might be worth a check of that wiring too.CheersIain Link to comment Share on other sites More sharing options...
Jig Posted March 2, 2017 Author Share Posted March 2, 2017 So, the oddest thing: I thought I'd give it one last look before taking Derek's advice and just starting her up. I decided to run a flying lead from the battery neg to the instruments to check for bad earthing. I clipped onto the mounting lug on the back of the gauge and got a spark, I also heard a fuse pop. Checked, and sure enough, the 7.5A instrument fuse had gone. I replaced it, and suddenly the pressure gauge sprung into life. The fuse definitely blew when I messed around with it, so unless this was some kind of brutal 'reset' then I am at a loss, but it is now working perfectly!Car started pretty easily and ran faultlessly, whilst I ran it up to temperature and checked the fan operation etc. No leaks, no odd noises. Happy day!! Link to comment Share on other sites More sharing options...
SM25T Posted March 2, 2017 Share Posted March 2, 2017 Good news. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted March 4, 2017 Member Share Posted March 4, 2017 Glad it's fixed. Presumably this was before you'd tested any instruments etc that use the same earth.... I am at a loss...I'd now disconnect, inspect, clean and reconnect that instrument earth and its eventual connection to the battery.JonathanPS: I'm kicking myself on this. I got to the engine earth but not that. Doh!PPS: Andrew can probably calculate the impedance or charge density or something of the instruments from the rating of the fuse that blew! :-) Link to comment Share on other sites More sharing options...
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