It could be the fuel pump, it may be ok at low revs but if it can’t keep up at high revs you may get missfire but I’d also expect knocking and no power from a lean ratio. Not that you would hear knocking in an S1.
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Did you use something to clean the inside of the tank out? Have the tank out of our S1 at the moment and keen to flush out the insides before repainting the outsides.
Yes I was guided through trawling on seloc to the Bilthamber range
I used their degreaser followed by deox c
I used 2kg in all, initially 500g with around 3ltrs of hot water that I sloshed about over the course of an hour, rinsed then filled the tank up and leaving it over night with the remaining 1.5kg.
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Looks good, fingers crossed this fixes it. If nothing else, with a new fuel filter the only thing that could be wrong with the fuel system is the injectors, which are relatively easy to have checked.
All back together with a new pump.
Good news is the car runs again.
Bad news is it still imposes the 5.5k limiter!
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Damn, any fault codes?
Has it always done the misfire then the imposed lower limit since you have owned it, or just started one day? Any other work carried out just before it started? Does your car have the 190 kit fitted?
Other than having the injectors checked/cleaned, it sounds like you have done most of the sensible checks and changes.
Other things I’ve seen over the years, bad earth at the cylinder head by the dipstick - this is the main earth for the injectors and coil pack from memory - bad earth at the chassis/gearbox earth point, make sure that the shaped washer is still fitted to the chassis - this normally causes issues when starting, but worth a check - poor connection/water ingress at the main engine loom connector under the coolant header tank, poor connection/water ingress around the relay box and engine ECU behind the seats - Exiges use the same bulkhead, with a couple of extra holes, as an Elise, but no boot lid hinge, but the holes are still there, there was a TSB about blanking them over, but have seen some that still hadn’t been done - there’s a resistor in the loom in the crank sensor wiring and I vaguely recall one where the resistor was breaking down.
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A fix, which you may not want to do, is to get an emerald ecu and adapter loom and get it mapped. You will get more power.
I did this when I had horrible problems with the std ecu which turned out to be the O2 sensor. The problem I had with the emerald was poor running in different conditions, wet, lights on, wipers on and passing the mot. Maybe mine was mapped badly.
So looking through dates (this has been going on since June!) I did a few things in the weeks leading up.
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removed a very old standard exhaust replacing it with a janspeed and a Decat.
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fitted a PRRT.
Think I’ll stick the cat on…you never know!
I will double check the earths but from an
Glance they all appeared okay.
Oh and I believe the 190 kit is fitted, ECU has “P” written on it in black marker pen.
Ah nightmare!
Anyway, you’ve done quite a bit already, is the below correct with regards to what you’ve checked/replaced/ruled out? I’ve noted down some things from the top of my head and put ‘ok’ for things that I think you might have done, but please correct it as appropriate.
IGNITION:
leads - ok
coil pack - ok
injector resistance
FUEL:
pump - ok
filter - ok
FPR - ok
injector spray pattern
TIMING:
cam timing
ECU:
module
AIRFLOW:
TBs (free to move, balanced, etc.)
IACV
exhaust flexi/cat restriction
ECU INPUTS:
lambda - ok
crank sensor - ok
IAT
MAP - ok
Ambient pressure - ok
speed sensor
coolant temp
TPS
alternator output DC volatge and AC ripple
ECU OUTPUTS:
injectors
coil pack
tacho
IACV
It’s worthwhile scanning through the list and see if there’s anything that you’ve missed and that you could quickly check. For example, does the TPS signal look ok, is the Inlet Air Temp doing something crazy, does it still happen with the IACV or lambda disconnected, etc.
I have a spare 190 ECU that you can borrow to test, but I’d be looking to rule out everything else first, if it were me. Where are you based?
By the way, the easiest method (that I know of!) to check if the ECU is a 190 is to check that the fan cuts in at 92C. This is a lower temperature to work with the 82C thermostat that should also be fitted.
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There’s a 47K ohm resistor in line with the crank sensor, and it’s located near the ECU plug; I think that’s what you might be referring to? You could visually examine the loom for signs of ingress, but I’d be loathe to unpick the loom tape unless an electrical test (continuity or earth resistance) indicated a problem there - it’s a complete pain and would be easy to damage another wire 
Thanks for this, good to put it all in one place now the list is quite vast!!
IGNITION:
leads - ok
coil pack - ok
injector resistance - 16.4 on all injectors, I assume since they are all the same this is correct?
FUEL:
pump - ok
filter - ok
FPR - Not replaced - how would I test?
injector spray pattern - Going to send the injectors off for a clean and test at some point soon.
TIMING:
cam timing - Not checked, but also no reason to believe there’s an issue given the car is fine at all other RPM’s?
ECU:
module -
AIRFLOW:
TBs (free to move, balanced, etc.) - Move free, need to get balanced.
IACV - How do I test this?
exhaust flexi/cat restriction - ok
ECU INPUTS:
lambda - ok
crank sensor - ok
IAT
MAP - ok
Ambient pressure - ok
speed sensor - ok
coolant temp - ok
TPS - ok
alternator output DC volatge and AC ripple - Whats the AC ripple?
ECU OUTPUTS:
injectors
coil pack
tacho
IACV
Are you using any oil?
Oil? In the engine there is some! 
I put a call into Dave Andrew’s to get the lowdown on taking the emerald route… he actually said can I not just remove the misfire detection module, although my understanding was there is no separate module, it’s just a program in the ECU?
When I had the 5500rpm limit I also learned of the misfire detection module and tried to find where is this fitted… as I understand it yes you are correct it is an ECU update so no physical unit to remove (unlike the Elise?). For me the issue was resolved with the careful reseating of the HT leads on the coil pack, lifting the edge of the rubber boot as they are pushed into position. I’m sure you’ve tried this but may be worth reseating them again to be sure.
Edit: the car could run fine on a drive then when idling on a few occasions I could audibly hear the light ‘pop’ sound of an HT lead just lifting from being properly seated. Carefully reseated it and hey presto no 5.5k limit
Yes.
Are you consuming any? Having to top up frequently?
Thanks yes I’ve also spent a lot of time ensuring the leads are well seated which I believe they are (not found one to have popped up yet)
Ahh, I’ve not noticed any significant oil consumption so far.