RedCat7 Posted November 30, 2013 Share Posted November 30, 2013 Catches for a split second then does straight away. Car was last put away running great after the Oulton Park Trackday but was wet. I thought it might be out of fuel but have added 15l without any improvement. Homestart guy changed the spark plugs (because they were black and the gap looked large to him and my corner shop is a motor factors). We then found that it would run on 3 cylinders when the HT lead 1 or 2 was disconnected but as soon as it was reconnected the engine would die. Tried disconnecting a reconnecting a few sensors. Homestart guy has never seen anything like it before but suspects duff sensor. Tried disconnecting a reconnecting a few sensors but to no avail. Opening the throttles doesn't help, just created a few back fires. Anyone got any ideas to try please? My next step was to get an MBE diagnostic cable. Link to comment Share on other sites More sharing options...
ChrisC Posted November 30, 2013 Share Posted November 30, 2013 I am no master, but assuming it runs on 3 three regardless if it's 1 or 2 that's disconnected, the it might be a connection to the coil pack / coil pack or plug leads. It's wasted spark, ie two plugs are fired at the same time, but it can't power both plugs, so when both plugs are connected the sparks are to weak. Once only one plug is connected the single plug is strong enough. Link to comment Share on other sites More sharing options...
revilla Posted November 30, 2013 Share Posted November 30, 2013 I may be wrong - I only really know the K Series setup - but I thought in a wasted spark system both plugs were is series at either end of the coil secondary, so removing one plug will prevent the other from sparking rather than making it spark more strongly as the circuit is broken. Suggests to me that somehow either of those cylinders firing kills the engine, so maybe somehow they are being fired at grossly wrong (advanced?) timing? Link to comment Share on other sites More sharing options...
ChrisC Posted November 30, 2013 Share Posted November 30, 2013 Then disconnecting one plug lead mean it's not running on three,but two? If Timing is killing the engine then surely this would effect its ability to run on three as much as it's ability to run on four? As said no expert :-( Link to comment Share on other sites More sharing options...
RedCat7 Posted November 30, 2013 Author Share Posted November 30, 2013 Thanks for you thoughts chaps. Just been out for more experimenting. I can get to run (just) on any 3 cylinders but only with throttles closed. Dies as soon as you try any pedal. Doesn't really want to run on 2 but on the one occasion it did it sounded like it was running on 2 rather than 3. Jim Link to comment Share on other sites More sharing options...
ChrisC Posted November 30, 2013 Share Posted November 30, 2013 Just has a look at the circuit diagram, and agree that disconnecting one plug kills two cylinders. I suspect the fact it dies as soon as the throttle is touched might suggest a throttle pot / position problem. Does the build manual give any throttle pot reference readings (volts or ohms) that you can check? Link to comment Share on other sites More sharing options...
RedCat7 Posted December 1, 2013 Author Share Posted December 1, 2013 TPS seems to be set and working fine. I measured TPS reading as 1.00v closed throttle, 4.56v fully open. A BC search suggested that 1.03v is optimum. It only took half a turn of the idle screw to raise the reading to 1.03v but that had no effect on the problem. Link to comment Share on other sites More sharing options...
Martin J Posted December 1, 2013 Share Posted December 1, 2013 Could it be the lamda sensor failing? They are known to pack up. I bought one off the web & keep it in the car on my Summer blats abroad. Link to comment Share on other sites More sharing options...
Stationary M25 Traveller Posted December 1, 2013 Share Posted December 1, 2013 unplug it and see how it runs. If ok .... you have your culprit. Link to comment Share on other sites More sharing options...
RedCat7 Posted December 2, 2013 Author Share Posted December 2, 2013 Unplugging the lamda sensor did not help. Any more ideas? Link to comment Share on other sites More sharing options...
Bio Posted December 2, 2013 Share Posted December 2, 2013 Crank sensor, plug, or wiring wet or damaged....The sensor tells the spark plugs when to spark. John Link to comment Share on other sites More sharing options...
RedCat7 Posted December 2, 2013 Author Share Posted December 2, 2013 Crank sensor connector and cable looks ok, is dry and is connected securely. The Homestart chap ran the engine on 3 cylinders with the HT lead connected to one of the old spark plugs, earthed on the outside of the block. We could see the frequency of spark stepping up as soon as the engine caught, suggesting the crank sensor is working. Link to comment Share on other sites More sharing options...
ChrisC Posted December 2, 2013 Share Posted December 2, 2013 I think your going to have to find someone with the MBE software to see whats going on, or a similar car local willing to try and swap a few parts. Chris, Link to comment Share on other sites More sharing options...
Z3MCJez Posted December 3, 2013 Share Posted December 3, 2013 Is the crank sensor done up tight. They can come loose causing intermittent problems until they eat themselves, which is a permanent won't run problem. Fitting the new one is engine out or special tool to access. Jez Link to comment Share on other sites More sharing options...
John Hughes Posted December 3, 2013 Share Posted December 3, 2013 Hi Jim You are welcome to use my MBE connector if needed. Unlikely to be the Lambda as that does nothing until the engine is up to temp. On a sigma disconnecting it will again do nothing until up to temp and then it will not run unlike the K series. I also have a spare coil pack if you want to try swapping that. John Link to comment Share on other sites More sharing options...
pugwash Posted December 3, 2013 Share Posted December 3, 2013 In days gone by the symptoms you have described sounds like the ballast resistor has gone. Do these modern engines have such a thing? Link to comment Share on other sites More sharing options...
Guest Posted December 3, 2013 Share Posted December 3, 2013 I experienced something similar on a motorbike where the PowerComander went haywire and sent the timing all to hell. Could be an ECU problem. Link to comment Share on other sites More sharing options...
andy bell Posted December 4, 2013 Share Posted December 4, 2013 i had an ECU problem and on off chance it is try the repair from MBE root before you try the get stung from Caterham solution. Thread is http://www.blatchat.com/t.asp?id=232038 but not saying you should do that :) Link to comment Share on other sites More sharing options...
RedCat7 Posted December 10, 2013 Author Share Posted December 10, 2013 It lives . John Hughes lent me a spare MAP sensor (amongst other goodies) and as soon as I tried it the problem was solved. I hear that originally the MAP sensors on sigma 150's were used to measure load instead of the TPS but nowadays they are disconnected and just measured ambient air pressure. The mounting of the sensor hasn't changed though. It is mounted with the nipple pointing upwards but with no hose attached. So I reckon rain water dribbled in through the bonnet louvers and down into the nipple. Needs a little hose fitted and bent over in a loop so the end points down. Nice warm evening last night so I was very pleased to get in what might be my last Blat before winter really kicks in. Thanks for all the advice gents and to John for the bits and pieces. I'll definitely have some fun playing with the MBE connector before I bring you that back! Link to comment Share on other sites More sharing options...
Martin J Posted December 10, 2013 Share Posted December 10, 2013 What a relief! Another top tip for anyone with the sigma 150 engine. On my 125 it is still connected to the throttle body. Link to comment Share on other sites More sharing options...
Domus Posted December 10, 2013 Share Posted December 10, 2013 Mine failed after about 6 months, I was on my way to a GTKY7 day at Caterham Midlands when the thing just stopped. I turned up on the back of a recovery truck. Nick Potter eventually got mine going by pinching a MAP sensor from a new car in stock. I was tempted to advise Jim but when mine failed it would not even catch never mind run for a few seconds so I assumed it was a different fault. Well done John, a handy piece of kit to have. Link to comment Share on other sites More sharing options...
Stationary M25 Traveller Posted December 10, 2013 Share Posted December 10, 2013 Wonder if this was the problem for the other Sigma owner that reported a problem the same day as your first post ?? Link to comment Share on other sites More sharing options...
Ian M Posted December 11, 2013 Share Posted December 11, 2013 Apologies for not posting but my issue was that the inertia switch had "tripped", seems that I had been a numpty when doing some electrical work! Link to comment Share on other sites More sharing options...
Stationary M25 Traveller Posted December 11, 2013 Share Posted December 11, 2013 That's good news too Link to comment Share on other sites More sharing options...
John Hughes Posted December 12, 2013 Share Posted December 12, 2013 Goof to hear it's all sorted Same problem on Sigma 140 Supersports as the MAP sensor is not connected to the throttle body but open to atmosphere. A piece of tube looped over works fine as long as not allowed to kink shut. MAP sensors are available on eBay for less than £15 Link to comment Share on other sites More sharing options...
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