John Vine Posted March 11, 2023 Share Posted March 11, 2023 #24: Glad the fuses are ok. Note that replacing the lambda sensor won't affect starting as the ECU will be in open loop until the coolant reaches around 60C. JV Link to comment Share on other sites More sharing options...
babymerc Posted March 11, 2023 Author Share Posted March 11, 2023 Hi John, yes the plug was resting on the exhaust primary. What is now stumping me is I disconnected the connector to the coil and I'm getting 12v there so presumably should get a spark at the plugs? Link to comment Share on other sites More sharing options...
ChrisC Posted March 11, 2023 Share Posted March 11, 2023 I would have thought the ECU will spark a pair of plugs from the coil pack using a switched neutral, not a switched live, so you would see 12v all the time.You need to know if the ECU is trying to start the engine or not. Without that information loading the parts cannon gets very expensive. Is there anyone local to you that can help, and has EasyMap? Link to comment Share on other sites More sharing options...
babymerc Posted March 11, 2023 Author Share Posted March 11, 2023 Hi Chris, not to my knowledge Link to comment Share on other sites More sharing options...
DW199 Posted March 11, 2023 Share Posted March 11, 2023 An engine needs compression, fuel and a spark to run.Sudden compression loss in a previously running engine could be caused by cam belt failure. I don't think it is common on the Sigma for this to happen but very easy to rule out. To check, remove the oil filler cap and whilst turning the engine on the starter the camshaft should be seen to be turning.Fuel is unlikely to be the cause as you say the plugs are wet. Can you hear the fuel pump priming when you switch the ignition on?Spark sounds the most likely culprit. I have an old school, very dim, neon timing light which I purchased in the mid 70s which I use as a spark checker. There are specific spark testers available. Halfords will probably stock one for around £10. You just connect it between one of the plug leads and sparking plug and see whether it flashes when the engine is cranking. It is worth having something to perform this simple check as it can save hours of fruitless fiddling when an engine won't start. Link to comment Share on other sites More sharing options...
babymerc Posted March 11, 2023 Author Share Posted March 11, 2023 DW199 Thanks for that. I must admit it's something I never considered and probably would end up with a bunch of bent valves if the cambelt had snapped, but nevertheless a simple check which I'll look at.John Link to comment Share on other sites More sharing options...
ChrisC Posted March 12, 2023 Share Posted March 12, 2023 Having suffered catastrophic timing failure (20 miles after an engine builder forgot to torque a Duratec crank main pulley), I suspect you would have noticed. The sudden bang and then the lack of noise, and assumed you would have mentioned it on the initial post.Just remember the ECU effect, if a timing light isn't triggering and therefore you have no spark doesn't mean you have an ignition problem. The ECU decides to run the engine, by controlling the ignition and fuel. Link to comment Share on other sites More sharing options...
Scotland North AR Posted March 12, 2023 Share Posted March 12, 2023 Hi, I've had this a couple of times with my Sigma after a winter lay up. The earth bolt in the centre of the picture gets corroded in the chassis resulting in nothing happening, turning over but not firing. There are four or five cables earthing to it. A couple of times a year I take it out, clean the bolt and the terminals, Copperslip and jobs a good un. Hopefully that might help. Link to comment Share on other sites More sharing options...
Area Representative paul richards Posted March 12, 2023 Area Representative Share Posted March 12, 2023 Nigel. Better to use dielectric grease and not copperslip. I use it on all electric connections on the 7 to prevent corrosion. Link to comment Share on other sites More sharing options...
babymerc Posted March 12, 2023 Author Share Posted March 12, 2023 Hi, thanks for that, I've cleaned that earth point. No bangs, cams are turning. I'm totally stumped Link to comment Share on other sites More sharing options...
babymerc Posted March 13, 2023 Author Share Posted March 13, 2023 Quick update. Had RAC out to it, he couldn't find the problem either. Couldn't interrogate ecu. He suggested trying another coil pack, which is coming tomorrow (even though the original one seems to check out ok) Link to comment Share on other sites More sharing options...
Area Representative DerekH Posted March 14, 2023 Area Representative Share Posted March 14, 2023 I have just had a similar issue with my 270S.I had the cam cover off to fix an oil leak, I didn't put the sealer in the corners when I replaced it last year.In putting the plug leads back on I must have pushed the in straight and didn't follow the cant on the engine.The plug cap is so soft it seems its possible to miss the plug, with the lead going all the way into the hole.Carefully refitted the plug caps and away she went.I can now get on with flushing out the old coolant.........DerekH Link to comment Share on other sites More sharing options...
babymerc Posted March 14, 2023 Author Share Posted March 14, 2023 Thanks Derek. I retraced my steps, even replaced plugs with an old set which I gapped to 1mm. Replaced my coil which I had taken off (new one hasn't arrived), gave the crank sensor connection a wiggle and away she went!!, so don't know what the no start was, which is annoying, but still leaves me with a car that won't pass mot emissions. Link to comment Share on other sites More sharing options...
Area Representative DerekH Posted March 14, 2023 Area Representative Share Posted March 14, 2023 I'm hoping my theory is right and I don't have a mystery gremlin hidingGlad your working again.Since I put mine away in November I have replaced an alternator and radiator.Hope all keeps going OKDerekH Link to comment Share on other sites More sharing options...
aerobod - near CYYC Posted March 14, 2023 Share Posted March 14, 2023 Hi John, if it was the crank sensor wiring causing the no start, your no ECU spark triggering would make sense. Assuming that it is not intermittently causing a misfire, I would look at the Lambda sensor next from an emission perspective. One basic test is to disconnect the Lambda sensor connector when the engine is warmed up. If it runs better with the sensor disconnected or there is no change, then I would suspect a need to replace it if it is more than 5 years or so old. Even newer Lambda sensors on Caterhams can be easily damaged due to the propensity to run rich from an engine mapping perspective compared with many other vehicles. Link to comment Share on other sites More sharing options...
babymerc Posted March 15, 2023 Author Share Posted March 15, 2023 Thanks James, got the car booked in with someone who is supposed to be a bit of a guru in this department on Saturday afternoon, so will let you know how I get on. Link to comment Share on other sites More sharing options...
ChrisC Posted March 15, 2023 Share Posted March 15, 2023 Crank sensor connection was your no start, you need to trace the wire and make sure it's not physically damaged near the starter. Link to comment Share on other sites More sharing options...
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