My (limited) understanding is that the CPS feeds into pins 73 and 79, and is the input to the ECU. It looks like to the ECU drives the tacho via output pin 58, and I assume that this is the drive to a stepper motor.
So my reasoning was that if the ECU understands the CPS signal to then drive the tacho, it probably means that that the CPS signal is sufficient. The signal will from the speed sensor will be pretty small, similar idea as the flywheel pick-ups on a marine DG, so the drive signal must be amplified from a circuit in the stack or from the ECU.
Probably not explaining it well so Iâll try again; the ECU reads the CPS square wave as an input, looking for a rising/falling edge to calculate rpm, and looking for the missing teeth to work out TDC. Using this information, the ECU outputs a signal to the tacho. So if the tacho is moving during cranking, that must mean that the ECU is receiving the CPS signal. I was theorising that if it is receiving and recognising the signal, then it was probably recognising where TDC was too, suggesting that the CPS might not have been the culprit for it not starting.
A bit of a guess, since these ECUs are a bit of a black box, and the circuit diagrams seem not to be in the public domain.
I used to call myself a Marine Engineer in a past life, and have a bit of experience with DGs, so figured youâd get the reference!
C8LGY
Ok now I follow and your first paragraph is correct. Yes once the tacho indicated the cranking speed the engine started, but initially there was no tacho cranking indication.
I donât know where abouts you started to read in this thread, but perhaps I should explain the issues I observed as a sequence of events with a single line of inquiry.
At Initial ignition turn on (no engine cranking) only the tacho needle moved backwards and returned to zero, the speedo stayed static. No tacho rpm indication when cranking, no start.
After a little fettling both the tacho and speedo needles moved backwards on ignition turn on and returned to zero. Still no tacho rpm indication on cranking, no start.
It was at this point I suspected the CPS output since I knew the ECU had been tested and
working on another Exige. Butchered the CPS, tacho indicates cranking speed and engine starts.
During all three points above the CPS had been sending a signal (AC voltage), see oscilloscope picture in previous post. Itâs the signal strength that is the issue. Which is why I contacted Lotus to ask what the signal voltage should be, (still waiting for a reply).
The easiest way to increase the signal strength in this case is to reduce the air gap between magnet (CPS) and reluctor ring teeth. Hence the CPS butchery.
I tried to recreate the issue over the weekend and the only way I could do so was to fit a new CPS. So conclude it was the CPS that was causing the issue.
PS JDS - Iâm working on a more permanent engineering solution to the CPS issue, just waiting for a new CPS. Will let you know if the trials work, possibly next week.
Ah ok. Anyway, glad youâre moving forward, good luck getting info from Lotus! I tried recently to get info on the ECU and was unsuccessful. The company that they used to use for ECU repairs also folded during COVID, which might have been another useful source of info.
The sensor is used in Elises too, and should be close enough to generate a strong signal but not too strong that it gets chewed up - but I realise that answer may not satisfy you! . If itâs working now, just leave it - I would have thought that anything less than 1mm would definitely be ok.
The Exige/340R ECU is a bit of an outlier, in that itâs sort of a standalone ECU by EFi - a modified version from the V8 Esprit from memory - hence the resistor in the wiring for the CPS, rather than the native Rover ECU that was used in the S1 Elise, that was always designed to work with that CPS.
Add in a single track of teeth for the crank trigger on the EP flywheel, and to me itâs just enough, in some instances, to not generate a strong enough signal.
Think about how few Exigesâs/340Râs there are, less how many have been converted to non Rover engines, written off, different ECUâs fitted, itâs no wonder that there are so few issues with standard ECU/EP flywheel combination. Thereâs probably very few out there. I know of two, Logicâs wouldnât start at all, one would only rev to 4k. Moving the CPS on both appears to have resolved the issue.
Be interested where you get to with your alternative solution, as we may need it!
Hi JDS,
I have a provisional solution to our issue.
I will go into more detail later, but for now Iâm still testing the resolution.
From the video included, (cold engine, no air filter, dirty fuel injectors and 6 month old fuel) you may see the red part at the end of the CPS, hovering over the reluctor ring. Thatâs my solution.
I painted it red to make it easier for all to see.
The CPS is a stock Lucas SEB353 part, totally unchanged.
For those wondering about the additional bits - The red and black probes in the back of the connector are for the Oscilloscope to read the signal, the red and blue wires to the left of the reluctor ring are to connect the Oscilloscope to the CPS to check the signal without fitting the CPS connector (protecting the ECU).
SORRY - NOT AUTHORISED TO INCLUDE MP4 video in post, and donât currently have pictures.
I thought it was a simple solution, but if it makes me a fortune I will call it cunning!
I contacted Exedy on the 15th May, to ask for their input into why the flywheel does not work in my car. There reply was, verbatim.
âGood morning
Exedy Clutch Europe Ltd. neither manufacture nor supply any flywheel products for your vehicle.
Please consult Eliseparts on this matter.â
I sent this reply over to Eliseparts, who supplied me with the âK Series Exedy Clutch & Flywheel Kitâ for comment also on the 15th May.
So far no reply has been received, but I noticed Exedy parts including this kit have been removed from Eliseparts website. I removed them from my Christmas card list.
I checked out their âK Series AP Clutch & Flywheel Packageâ which is not available to buy online. I have not contacted AP to ask if they know why you have this starting issue.
Two actions, cutting the CPS and bending the CPS end are not an ideal solution, a hit and miss non engineering workaround at best, so I set out to investigate the possibility of manufacturing a better engineering resolution.
My CPS pin is 2.7mm diameter and 7mm long.
I selected a piece of 4mm round bright steel rod, drilled a 2.65mm hole slightly off centre, 7mm deep. As the drill bit has a cutting flute, the cap will only slide on the CPS end 6mm, extending the original CPS pin by 2mm. This overcomes the need to cut 2mm from the CPS plastic casing and lug mating surface.
The hole will need to be honed out slightly to produce a light interference fit onto the CPS. Because the hole is off centre, the cap can be turned on the CPS to adjust the air gap. This will overcome the need to bend the CPS pin.
Objective is to turn the cap to the optimal position, measure the cap wall facing the reluctor ring teeth and add twice that measurement to the 2.7mm (pin diameter) to find the desired diameter of the final cap design.
Finally a simple process of turning down the steel in a lathe to the desired diameter and drilling the 2.65mm hole in the centre of steel rod for the resolution. The YouTube video is the engine running with the prototype cap.
Hi Dave, thank you.
I sat down with a cuppa listening to that burbling sound thatâs an unmistakable Janspeed Exige exhaust relieved. Still perfecting the cap diameter, 4.23mm works with a cold and hot engine, but needs to be run on a track to test it under load and rev range.
Unfortunately the new Exedy clutch trilogy I fitted failed. It has less than 200 meters use. Yes it too was from Eliseparts!
Tried all the usual tricks. The Gearbox is on my list of things to do next week. Going to attempt to remove it with the engine in place. Might be a few choice words mumbled, and have to bench press a few weight first!
Why we are being sold spares for the Exige that are not the right configuration? Rhetorical question.
. If itâs working now, just leave it - I would have thought that anything less than 1mm would definitely be ok.
