Garf Posted June 8, 2007 Share Posted June 8, 2007 I have a puzzling problem - a (seemingly) temperature related reduced rev limit (down to 4,200 when hot) and need some collective help for ideas as to what it might be! I've done the usual Blatchat searches but found nothing similar. Car is 1995 1400K SS no further modifications. At the point the issue began I cannot recall any action taken against the vehicle/engine other than normal driving. Symptons:- When I commence a journey the car has a self "imposed" rev limit around 5,800-6,000 RPM (vs the expected 7,200 for SS) The rev limit light does not come on but the car behaves exactly as if it had reached it's MEMS ECU coded limit i.e. it pops and bangs a bit at the rev limit and you cannot accelerate the revs through it (it's been a while since I've done it at 7,200 but I'm sure it's the same). So effectively at "cold" it limits at around 6,000 (I say "cold" as I'm loathe to thrash it up from direct start so this is a few minutes / 1 mile down the road) As I drive further 5-10 miles / 15-20 mins (I'm assuming therefore as the engine progressively gets hotter) the imposed rev limit drops from 6,000 to around 5,000 and eventually reaches 4,200 by the time I reach work - approx 15 miles / 30 mins on. Frustratingly this now seems to happen on every drive I do ☹️ Actions taken to date:- Recently it went in for service/MOT at 7 Workshop who looked at it but unfortunately could not fix it on the day. They, and I, checked and where necessary cleaned the following:- o Crank sensor o Spark plugs o HT leads o Dizzy cap o General check of all leads & connections o Reset MEMS o Position of leads in case of interference o Changed battery (on my request as previous one was 5+ years old) Considering it "appears" to be temp related - any ideas ?? Neil Wilson Garfield - M100 EOW - Yellow/Green 1.4K SS Edited by - garf on 17 Jul 2007 14:39:38 Link to comment Share on other sites More sharing options...
MartinWoodham Posted June 8, 2007 Share Posted June 8, 2007 I'd try checking the temp sensors - 2 in the water rail beside the head. 1 is for the MEMS and I forget what the other one is for...! Clearly its a spark problem - have you tried replacing the dizzy cap/ rotor arm and all HT leads? Also check the dizzy for secure fixing? Martin Aero'd supersported ex-Roadsports B...anyone got a cheap LSD? Link to comment Share on other sites More sharing options...
LazerBrain Posted June 8, 2007 Share Posted June 8, 2007 The other temp sensor is for the temp gauge on the dash. cheers, Darren. Link to comment Share on other sites More sharing options...
Garf Posted June 8, 2007 Author Share Posted June 8, 2007 Martin - thanks. Have checked HT leads and dizzy but only cleaned and re-fitted not replaced - maybe a consideration soon! From my discussions with Chris at 7 Workshop the temperature sensor input to the MEMS only affects the IACV and idle rev setting. He didn't think it would affect upper end rev limits. Maybe someone has another opinion ........ Neil Wilson Garfield - M100 EOW - Yellow/Green 1.4K SS Link to comment Share on other sites More sharing options...
S47zz Posted June 8, 2007 Share Posted June 8, 2007 Must be the sensor that limits the revs - breaking down [increased resistance etc] when it gets hot, don't have K engine in my car but it has to be the sensor I described. good luck Link to comment Share on other sites More sharing options...
Jason Plato Posted June 8, 2007 Share Posted June 8, 2007 crank sensor and coil being affected by heat or in close proximity to each other causing signal interferance. or try someone elses ECU . here is C7 TOP Taffia Area Rep Link to comment Share on other sites More sharing options...
Peter Carmichael Posted June 8, 2007 Share Posted June 8, 2007 Coil is knacked Link to comment Share on other sites More sharing options...
Garf Posted June 8, 2007 Author Share Posted June 8, 2007 Again - thanks all for the quick replies. Dave & Peter - both of you have mentioned the coil as likely candidate - Peter was especially precise in his diagnostic - "knackered" !!! I think one of my first actions will be to replace the coil after re-checking dizzy and HT leads - just so I can learn from this why do you believe it is the coil and why does the temperature effect it as explained ?? Neil Wilson Garfield - M100 EOW - Yellow/Green 1.4K SS Link to comment Share on other sites More sharing options...
CAB Posted June 8, 2007 Share Posted June 8, 2007 Sounds like it could be the coil, the resistance changes with the temperature. The hotter it gets the weaker the spark. My friends EU3 K series Elise had the same problem with one of the coil packs, fine when cold but missing when hot. Old/fouled plugs, leads etc make it worse (but these can also cause the same problem). CAB Link to comment Share on other sites More sharing options...
Mark Durrant Posted June 8, 2007 Share Posted June 8, 2007 Neil I have a coil removed from my R500 that is in good condition if your interested. Mark D Comp Sec Link to comment Share on other sites More sharing options...
Garf Posted July 17, 2007 Author Share Posted July 17, 2007 It's taken me a little time to post back what the cure was - my excuse is that originally I was so overwhelmed at having full revs back that I then went on a mad driving spree whenever possible 😬 Initially (based on strong posts above) I changed the coil but this was not the solution. It was in fact the Crank Position Sensor (CPS) - a new one of these allowed free reving right up to the limit even when very hot. I assume that it has some resistance and this was breaking down - changing more so as the temp increased. Anyway all fixed and when it stops raining I'm off again Huge thanks to all those who posted replies Neil Wilson Garfield - M100 EOW - Yellow/Green 1.4K SS Link to comment Share on other sites More sharing options...
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