It's a same your not closer because it sounds an interesting problem.
Your MOT emissions I suspect are caused by a all to common lambda sensor failure. It's happened before and will happen again, but I don't suspect it's the reason for the no start.
Can you check the fuses, unrelated shorts on seemingly unrelated circuits have caused no starts in the past. Example, speed sensor failure (also common) and indicator earth problems (that one is even on video).
What is interesting is you say the plugs are wet. Normally fuel and spark are not triggered by the ECU if it's not happy to run. I work on a Sigma that died on track, months after the last mechanic trapped the crank position sensor wire between the starter and the block. This car didn't spark or fire the injectors because it couldn't see the crank position sensor feed.
So with wet plugs I am assuming the ECU is happy, which makes me think about checking the wiring to the coil pack. The coil pack is less likely because it will normally fail for just two cylinders.
Ultimately I think your going to need the assistance of someone with the Easymap lead to learn what's going on. But check your fuses first ;-)
Thanks for that Chris. Checking the fuses will be my last throw of the dice. Will do this morning. As for easymap interrogating the car would be ideal. John
#21: Ah, ok. The reason I asked is that I'm assuming the tester meant high CO (carbon monoxide) rather than CO2. Also, a value of "over 9" is impossibly high for CO. Perhaps he meant 0.9? And even that is 3x the limit, and points to an over-rich mixture.
I'd agree that a dodgy lambda sensor is prime suspect for the emissions fail.. I'd also agree that Easimap is the best way to get to the bottom of your problem -- or rather, two problems, possibly unrelated: poor emissions and failure to start.
By the way, in #10 you said that you tested the plug for sparks by resting it on the "manifold". This may be a dumb question (in which case, my apologies), but did you mean one of the exhaust primaries (that is, something metal connected to the engine/chassis)?
#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.
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?
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?
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.
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.
It's a same your not closer because it sounds an interesting problem.
Your MOT emissions I suspect are caused by a all to common lambda sensor failure. It's happened before and will happen again, but I don't suspect it's the reason for the no start.
Can you check the fuses, unrelated shorts on seemingly unrelated circuits have caused no starts in the past. Example, speed sensor failure (also common) and indicator earth problems (that one is even on video).
What is interesting is you say the plugs are wet. Normally fuel and spark are not triggered by the ECU if it's not happy to run. I work on a Sigma that died on track, months after the last mechanic trapped the crank position sensor wire between the starter and the block. This car didn't spark or fire the injectors because it couldn't see the crank position sensor feed.
So with wet plugs I am assuming the ECU is happy, which makes me think about checking the wiring to the coil pack. The coil pack is less likely because it will normally fail for just two cylinders.
Ultimately I think your going to need the assistance of someone with the Easymap lead to learn what's going on. But check your fuses first ;-)
My detailed build blog
https://caterham420detailedbuildblog.co.uk/
Thanks for that Chris. Checking the fuses will be my last throw of the dice. Will do this morning. As for easymap interrogating the car would be ideal. John
All fuses check out OK, changed o2 sensor for 2nd hand one I had. No luck
#21: Ah, ok. The reason I asked is that I'm assuming the tester meant high CO (carbon monoxide) rather than CO2. Also, a value of "over 9" is impossibly high for CO. Perhaps he meant 0.9? And even that is 3x the limit, and points to an over-rich mixture.
I'd agree that a dodgy lambda sensor is prime suspect for the emissions fail.. I'd also agree that Easimap is the best way to get to the bottom of your problem -- or rather, two problems, possibly unrelated: poor emissions and failure to start.
By the way, in #10 you said that you tested the plug for sparks by resting it on the "manifold". This may be a dumb question (in which case, my apologies), but did you mean one of the exhaust primaries (that is, something metal connected to the engine/chassis)?
JV
#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
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?
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?
My detailed build blog
https://caterham420detailedbuildblog.co.uk/
Hi Chris, not to my knowledge
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.
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