Macchiman Posted June 17, 2015 Share Posted June 17, 2015 On my return journey from Italy after an uneventful 10 day trip through the Ardennes, Black Forest and various Alpine passes, I had the rather uncomfortable experience of my engine loosing all power whilst trying to avoid the 150 mph rocket ships in the outside lane of a German autobahn.Around 30 mins before the loss of power, I noticed that the oil pressure gauge was reading full scale (8 bar). The water temp was normal and the engine was running as normal, so I assumed that there was a fault with the gauge. Approx 30 mins later the engine died. I managed to coast onto the hard shoulder without loss of life (mine). Car is a 2010 1.6 Sigma 140bhpDo the POBC have any suggestions how to identify and fix? And why does an instrument malfunction kill the engine?ThanksPeter Link to comment Share on other sites More sharing options...
SM25T Posted June 17, 2015 Share Posted June 17, 2015 I wonder if this is the same fault that Mike Clark had on the Isle of Man with his Sigma. Turned out to be the over-long cable to the speedo sensor on a rear wheel .... chafed through at a cable tie and stopped the engine dead. Link to comment Share on other sites More sharing options...
ChrisC Posted June 17, 2015 Share Posted June 17, 2015 Quick look at the wiring diagram i am not surprised the instruments will stop the engine. I guess if you lose the tacho you lose the engine, but I haven tried it. The speed sensor is a good shout, it's connected to nearly all the instruments and including the tacho, green wire, if that had a short, you would blow the instrument fuse.The oil pressure sensor is not directly to the oil gauge, it seems to go through the tacho, via a white and green wire WG, and then a while brown WN. Link to comment Share on other sites More sharing options...
ChrisC Posted June 17, 2015 Share Posted June 17, 2015 PS I am surprised a ford dealer would have an MBE lead to hand to read the fault codes, you can't read them with a standard OBD reader. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 18, 2015 Member Share Posted June 18, 2015 First thoughts while you're waiting: Do you have the relevant Assembly Guide or Handbook with the diagrams and fuse list? If not please send me a Private Mail with your email address. Do you have a meter already? (And lots of appropriate fuses.) Instrument circuits that vary resistance to earth shouldn't be able to do this. So I'd start with one of the others. How does the wiring work for gearbox and wheel speedos? Is there a live feed and a live-ish signal return. If so that sounds like a clever suggestion as 3 wouldn't apply. Does ChrisC's comment about losing the tacho apply to all models and ECUs? Any recent modifications or work "near" the affected parts?Jonathan Link to comment Share on other sites More sharing options...
CharlesElliott Posted June 18, 2015 Share Posted June 18, 2015 Speedo sensor cable is my bet. Link to comment Share on other sites More sharing options...
Macchiman Posted June 18, 2015 Author Share Posted June 18, 2015 Thanks for the suggestions. I have a copy of the assembly guide and owners hand book, and a multimeter, though I'm not too good at deciphering the wiring diagram. Once I've got the car back I'll check the speedo sensor cable. Johnathan, are you saying that it is unlikely that the oil pressure gauge and sensor are the cause the problem? Link to comment Share on other sites More sharing options...
Leadership Team Garry7 Posted June 18, 2015 Leadership Team Share Posted June 18, 2015 I had the same issue, caused by a short in the speedo sensor head, cable was totally fine - try disconnecting the black multiplug (zip tied to a chassis diagonal behind the seat back bulkhead panel) for the speedo cable and changing the fuse again.Good luck, Garry Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 18, 2015 Member Share Posted June 18, 2015 ... are you saying that it is unlikely that the oil pressure gauge and sensor are the cause the problem?I think so. The two common wiring faults are open circuits and shorts to earth. For circuits that work by varying resistance to earth neither of those should blow fuses. All corrections welcome.I've never played with an electronic speedo on a 7, which is why I asked about the general way they work. I know there's something about the sensors and wiring in the archives and I haven't found it yet.JonathanPS: I like Garry's approach as a quick test. Link to comment Share on other sites More sharing options...
Martin J Posted June 18, 2015 Share Posted June 18, 2015 I had exactly the same thing happen (twice) on my sigma 125. I agree with above that the speed sensor on the off side rear wheel is a likely cause. Mine had deterioated over the years & eventually blew the instrument fuse. I obtained a new one from CC but that to blew the fuse after a couple of outings & left me stranded. I had no jack or wheelbrace with me so couldn't unplug it. When I got the car home via the recovery company I unplugged the speed sensor & replaced the fuse. All then ok but the moment I pluged it back in the fuse blew so it had to be that. Tip...if you are stranded, the car runs perfectly without the hall sensor pluged in, just no speedo working, but you could use a satnav for keeping an eye on your speed. I now have a second one from CC & all seems fine. There is another possibility however, my mate with his sigma 150 had the same thing happen. He was on route to caterham guru Mick Attree to have the cambelt replaced. He was towed to Micks place & Mick investigated & found a relay had overheated. All the relays have now been replaced & the car is fine. Mick suggested it is a good idea to replace the 7.5 amp fuse with a 10amp one & we have both done this. We are also off to Italy this Saturday so hopefully no reliability problems. We have tools & plenty of spare fuses. Hope this helps. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 18, 2015 Member Share Posted June 18, 2015 The thread about diagnosing faults with the electronic speedo sensor, and a recommended modification.Jonathan Link to comment Share on other sites More sharing options...
Macchiman Posted June 18, 2015 Author Share Posted June 18, 2015 Thanks for all the info and suggestions. Looks like the speedo is no. 1 suspect. I'll report back my findings once the car is returned.Thanks againPeter Link to comment Share on other sites More sharing options...
Ian B Posted June 18, 2015 Share Posted June 18, 2015 I think if I had a Sigma and a failure of the speedo sensor/cable could leave me stranded, I'd feed that circuit from a seperate fuse.Wonder if there's a "Workshop Notice" relating to this from CC (or if it's another of that well worn phrase WNSTB "we've never seen that before" ). Link to comment Share on other sites More sharing options...
Leadership Team Garry7 Posted June 19, 2015 Leadership Team Share Posted June 19, 2015 The real pain is that a new / spare costs over £60!! CC made me buy a new one send the old (1 month old) part back before they'd refund me. Link to comment Share on other sites More sharing options...
Macchiman Posted July 16, 2015 Author Share Posted July 16, 2015 Car is finally back in my garage. It's a long story, but better late than never!Checked the speedo sensor wiring and no obvious sign of insulation being worn away on the flimsy wire from the multipin plug down to the sensor.Gary7 mentioned that his sensor also looked OK but had an internal short. Is there anyway to test this before coughing up £66? There are brown, black and blue wires from the sensor.Thanks Peter Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 16, 2015 Member Share Posted July 16, 2015 Is this the sort of sensor that flashes to show that it's working?Jonathan Link to comment Share on other sites More sharing options...
Macchiman Posted July 16, 2015 Author Share Posted July 16, 2015 Yes it is, but I have now disconnected the sensor at the multi plug connector, and replaced the fuse. Engine started, ran for 30 seconds then blew fuse again, so it can't be the sensor. I suppose there could be a short somewhere in the wiring loom supplying the sensor, or something completely different............ Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 17, 2015 Member Share Posted July 17, 2015 I'm confused. Are these the current questions: Why did the engine stop? Is there a fault in the speedo wiring? Is the speedo sensor working?Jonathan Link to comment Share on other sites More sharing options...
Macchiman Posted July 17, 2015 Author Share Posted July 17, 2015 Jonathan, the current situation is:The engine stops because the instrument fuse blows.It was suggested that a fault in the sensor wiring, from multi pin plug to the wheel sensor, may be the cause. I have disconnected the sensor at the multi pin plug, and replaced instrument fuse.On switching on the ignition (with speedo sensor still disconnected) all guages respond, and ignition warning light is shown. Engine will crank, start and run for approx 30 seconds before stopping with a blown instrument fuse. Therefore it can not be the sensor causing the problem AFAIK.......I originally reported that some time before the continental breakdown, that the oil pressure gauge had gone full scale, and I am now wondering if the fact that the engine runs for 30 seconds before blowing the fuse may be something to do with the buildup of oil pressure on startup causing faulty oil pressure sender to blow the fuse. I will disconnect the oil pressure sender but can not identify it on the engine block, build manual refers to "Connect the black wire from the vehicle loom to the oil pressure sender on the LH side of the engine block."ThanksPeter Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 17, 2015 Member Share Posted July 17, 2015 Therefore it can not be the sensor causing the problem...Agreed.I will disconnect the oil pressure sender but can not identify it on the engine block, build manual refers to "Connect the black wire from the vehicle loom to the oil pressure sender on the LH side of the engine block."2010 Sigma 140: please can someone advise.Are we sure that the tacho feed is the crucial link between the instruments and the engine working? Is it feasible way to jury-rig that and seei if the fault disappears?Have you measured the battery voltage in that 30s initial period?Jonathan Link to comment Share on other sites More sharing options...
makingff Posted July 17, 2015 Share Posted July 17, 2015 My oil pressure gauge went full scale but didn't cause any issues with starting or fuses blowing. It turned out the gauge was faulty (I was able to borrow a spare from a blatchatter which proved mine was broken). Link to comment Share on other sites More sharing options...
DJ. Posted July 17, 2015 Share Posted July 17, 2015 The sensor is above the oil filter on a Sigma. The gauge would have resistance, so shouldn't blow the fuse even if you short it earth I think. Duncan Link to comment Share on other sites More sharing options...
Macchiman Posted July 17, 2015 Author Share Posted July 17, 2015 Thanks DJ.Disconnected oil presure sender, started engine and it ran until I switched it off!Restarted a couple of times at let it idle until fan cut in. No problem.I haven't been for a run yet, but looking good!Thanks to everyone, and something to remember if your Sigma blows the instrument fuse.Peter Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 17, 2015 Member Share Posted July 17, 2015 Progress!So the probable cause is: Something to do with the oil pressure sender, wiring or gauge is U/S. That takes out the instrument fuse. That takes out the tacho feed and the ECU goes on strike.?Around 30 mins before the loss of power, I noticed that the oil pressure gauge was reading full scale (8 bar).Back to 1: which way round does this circuit work?Jonathan Link to comment Share on other sites More sharing options...
Macchiman Posted July 17, 2015 Author Share Posted July 17, 2015 Must be the sender, as it is disconnected at the engine block. Wiring and gauge all still in place.Peter Link to comment Share on other sites More sharing options...
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