This is generally a good sign.
I have seen engines that mis under heavy load typically have ring land , or piston / ring failures.
They tend to consume a fair bit of oil
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FPR - if the static pressure is ok, then this is doing its job ok
Cam timing - kind of agree, it doesnât sound like a timing issue if itâs a hard cut. Same for loss of compression.
TBs - just check that they are all closed with no throttle, and start to open at the same time. Basically make sure that the IACV or ECU ignition advance isnât trying to do something weird to compensate with something funny going on with the throttles.
IACV - block up the inlet to the TBs. (Pulling the plug could mean a constant air leak as itâs open below about 35% duty cycle). Just something to rule out.
Alternator - use a multimeter set to AC, connected to the OBD port. Rev the engine and check for AC which could indicate a failed diode in the regulator (could cause unusual behaviour in the ECU)
IAT - temperature used in conjunction with the MAP sensor for the ECU to calculate how long to fire the injectors for
Iâm just going to ask the obvious; are you absolutely certain that that the speed sensor isnât defective, the toothed ring corroded, screen damaged, etc.? It doesnât sound like anything to do with the engine internals, and if itâs intermittent (i.e. you can go past it initially) but repeatable under certain conditions, it sounds more electrical/sensor/ECU.
Thanks.
Iâve not checked fuel pressure downstream of the FPR, only going into the fuel rail.
IAT - this is correct from checking with my obd dongle
Same with the VSS, I have however seen reports of a sheathed cable being needed to fix a very similar issue⌠canât find many other reports of this cable though?
The thing is, there are so many different failure modes thatâs it simpler just to focus on what you have in front of you, rather than trying to find someone thatâs had exactly the same issue.
Having said that, suspicion still falls on that speed sensor. If it were me, Iâd be trying another sensor, checking the gap with a feeler gauge whilst spinning the wheel through various points, cleaning the teeth, measuring continuity resistance from the sensor plug to the ECU connector, visually inspecting loom and ECU connectors, visually inspecting wiring, checking resistance to earth on the loom, checking the screen has good continuity to earth, checking the screen is only connected at one end, checking the shape of the speed input to the ECU, etc.
Basically a complete health check of that aspect. Ideally, youâd temporarily run in a completely new twisted pair to the ECU, but itâs probably not practical as the Bosh ECU connector is a nightmare to de-pin.
If nothing else and youâve reached the point that you need professional help, documenting all the checks will reduce the labour they spend fault finding.
Can always try swapping the ECU too!
Misfire detection module was on the 111s, not the Exige.
The old post about the âspeed sensorâ I assume was really referring to the crank speed sensor not the wheel speed. If the crank sensor is noisy I would not be surprised if the ecu put the car in limp mode.
Try a new sensor.
Try packing the sensor away from the teeth with a washer or two under the bolts.
If you can, check the gap between the sensor and the teeth.
If you can. Connect a pc based scope to thd sensor and capture the wave shape as you accel, if should be a sine wave increasing in frequency and amplitude. The ecu reads the point the waves cross zero, it canât read the peaks as they move with rpm.
Pico technology make good pc based scopes.
If you go the Emerald route Iâd suggesting you to them to fit and map.
Wow, go to work for a day and loads of posts!
As ever from the other side of the service desk if you do take to a dealer/specialist, definitely take all the info you have and let them know the parts you have replaced. Do not be surprised if they recheck everything and charge you. To put it another way, in whatever you do for a living, if a customer brought in something that wasnât doing what it should be doing and said no need to check A, B and C as Iâve already done that and theyâre fine, would you just go along with that and get into more and more expensive tests/checks, only to find that the ÂŁ2 A item was the fault? That could trigger a slightly challenging phone call.
The wheel speed sensor definitely does upset things and triggers the misfire detection program. The Exige definitely has one, as I remember downloading them to ECUâs when the TSB was released. Itâs not an external box like an S1 111S.
190 kit normally had 190 written on the ECU in green pen/paint pen. The easiest way is to check the cam wheels, as the 190 kit has 3 marks and dowel locators on the inlet cam, fan should come in at 92 degrees and ideally the breather not breathing back into the engine.
Spacing the crank sensor will probably make matters worse, eventually it wonât start at all or get to an RPM where it cuts out. Replacement sensors are cheap however. If you get a willing volunteer, who doesnât get car sick, get them to watch the engine rpm as the 6100 misfire happens, if it drops to 0, then you have a starting point.
No need to unpick the loom just yet, just unplug bulkhead connector, ECU connector and look at relay box, to check for any corrosion or displaced pins.
Cam timing, unlikely, but have seen some cam sprockets come loose or have the dowel pin misplaced in the locating slots. Difficult to check without first removing the cam sprockets though.
Balancing is more a start, idle and pickup issue, as by the time your at 6k, they are just open.
Where are you based? Please donât say on the south coast. Please donât say on the south coast!
While the Lotus scan 3 tool is basic by todayâs standard, so is the ECU. If you take it to a dealer/specialist, make sure they have one that works or something that will talk to an S1 Exige properly, and ideally someone who can drive it!
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Its almost like you have worked on these cars for 20+ years John âŚ
Good advice. Wheel speed gave me a problem, fixed by cleaning it!
Iâm extremely grateful for all the advice and recommendations being given here folks.
How did you guess Iâd be south coast!?! Iâm on the Isle of Wight so limited options for proper technical advice.
We have an update though, I re-fitted the cat last night and went out for a blast with multiple pulls to 7+kâŚ.no issues at all!!
Whatâs the logic for the decat causing this then?
No lambda delete fitted to the de-cat maybe .
The lamba is on the manifold so remains in place regardless of cat or no cat.
Do they have a pre cat and post cat like on S2 k series ?
Just one lambda sensor on the manifold just before the flexi and cat, as Toby mentioned.
Iâm far from an expert on this, but I suspect the lambda does bugger all. Reasons for this:
- Stinky rich mixture even when warm
- When ECU switched to âclosed loopâ, the fuel trims donât seem to adjust correctly
- Workshop manual references the 340r 190 upgrade, and the 190 section intimates that itâs in open loop all the time
No idea why fitting a cat should make a difference, but maybe youâve disturbed something else and itâs âfixed itselfâ. The lambda isnât used with WOT as it will be open loop.
Ignoring the lambda, all youâve done is introduce additional resistance in the exhaust system; workshop manual also indicates that it runs better without a cat, which suggests that it should run ok without one. Also, plenty of people run without a cat and have no issue.
Either way, great result, enjoy those extra 2.5k rpms!
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Well done Toby!
That also sounds a very good car for that location, not that Iâve been to the Isle of Wight but Iâm sure Iâve heard there are some reasonably good roads to enjoy 
Great news, I donât understand why it has made a difference! New O2 or lambda fixed my car (190) from lots of low rev stumbles. As said above , itâs not used at high rpm or throttle openings. Mystery!
Thatâs weird, but also great news!
Have worked on loads of Exige/340R from start of production to today with no cat, both 177 and 190, and neither cared enough to trigger the misfire kit.
Thanks folks, so strange. Hopefully get out at the weekend to do more validation this has fixed the issue!
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