Difference between S2 and Fed ECU

[MPx]

Eleanor is in for its annual fettle and MOT and a couple of fixes. Amazingly (given how well it was running generally) it turns out the ECU had failed. I have a Switcher Mountain chip installed, but apparently it was the original mother board that had failed. Phil didn't have an S2 ECU (though has plenty for the SE) but eventually found a Fed one. That is now in with my Switcher on top and is working. Looking at the parts list there is only one closed loop ECU ... except for a separate one for California. Is the Fed ECU actually the Californian ECU? But my real question is ... what differences are there between the Fed ECU that I've now got and the S2 ECU that I used to have?

[dapinky]

Mike,

apart from the part number (and probably price!), the only difference between any of the Turbo ECUs is the memcal prom.

The NA had a much simpler item (as it doesn't have very much to control), but all the rest are the same. That said, there may have been the odd component change during their lifetime, but the actual "workings" are all the same and only the chip differs.

[MPx]

Thanks Dave ... but I don't really get it - way outside my comfort zone. You say they are all the same except the memcal (I don't really know what that is other than a "chip"). But its those differences that I was asking about - what does the S2 memcal do that the Fed one wouldn't...or would!?! Also if my old ECU is broken as reported, then presumably is the memcal that's wrong, otherwise my old memcal could presumably have been put on one of the many SE ECUs that Phil says he has??? Is the memcal retained with the mountain switcher or is that the bit that the mountain chip replaces? Assuming not is anyone aware of any way of getting a new S2 memcal??

[Fredjohn]

Electronics are somewhat alien to me too. However, if you read the Mountain Chips info on the tab at the top, it really helps to explain it all.

The memcal is removable and can be replaced by any memcal. Any Mountain Chip then piggy backs onto the memcal. Running Elanscan will tell you what memcal you have.

My UK SE started out as 9929, then had an Everest chip added, then I returned the Everest chip to have it re-programmed to equate to the 1499. I can now run closed loop with an O² sensor fitted.

Descriptions of all the different memcals are in above mentioned Mountain Chips tab.

Hope this helps.

[dapinky]

Mike,

In the absence of a 'proper' electronics guy (Geoff? Phil? Joao?) standing up and explaining it all a bit better, let me try this:-

The ECU is a box of tricks, which has 2 basic versions - NA & Turbo.

Lets ignore the NA one, because they are so few and far between that we can ignore them!

Inside the 'box' are 2 sets of electronics (probably more, but I will break it into 2) - 1 set, we can call the 'basic' bit. This collects information from all the sensors and processes it...... It is this bit which then sends out a signal to the injectors etc on how much fuel to squirt, and when to squirt it.

In between the bit where the inputs arrive, and the outputs leave, a series of complex calculations are worked out...... this is the Memcal area of expertise.

In the Elan, there are 2 basic 'versions' of the software used in the Memcal - "Open Loop" & "Closed Loop" - the first uses an input from the CO potentiometer, the second uses an input from the Oxygen sensor - but then they decide on how much fuel to squirt from that information. (Okay, I know that Lotus used 2 different 'open' chips - 9929 & 9930 - but they are the same in operation - but with adjusted parameters)

So, On to the 'Closed Loop' system as used in the Fed & S2 cars....... these both use the same (1499) chip - and the units are identical. Certainly, they are interchangeable, if not exactly the same internally, as the chip electronics are the same (1499).

There is a separate 'chip' for other applications (California cars, Japan cars and others with 'odd' requirements) - but actually, the 'chip' is the same, but the flash program which is burned in the chip is what is different.

So, to answer part of your question, there is no reason why your switcher chip couldn't have been put into ANY turbo ECU - including from an SE...... that is exactly what I have in my car (SE) - a switcher chip in the original (SE) ECU.

Then it gets a little more complicated..... but not really.

Did you fit your chip yourself? If so, you may remember that you had to add a piggy-back board, then use the old chip as well as the new chip (further complicated by the switching plug/wire/gubbins).... if not, then you won't remember it!!!!

I'll assume (for the education of anyone else who is reading this and wonders how it all works/fits/does anything) that you didn't do it, or had forgotten how it was done (mine was so long ago that I wouldn't have remembered if I hadn't done a few more since then).

Okay, so basically, the 'new' chip - whether switcher or single prom - takes over some of the calculations from the 'old' chip - lets ignore the fact that the switcher uses a couple of extra pins, because that doesn't matter to the end user - it was designed to work, and it does, so I leave it alone!

As such, the 'inputs' to the ECU still arrive at the same part and get processed...... then the "numbers" get sent to the 'new' chip for processing according to the programming, then sent back to the ECU for onward transmission to the injectors/wastegate etc.

The reason that we need to still have the 'old' chip installed is (If Im Not Mistaken.... but I could be) that if the inputs don't give a computable output, the car will drop into "Limp Home" mode, bring up a yellow light and drop revs to 4K max (or whatever it does).

My understanding is that the 'Limp' mode isn't controlled by the actual prom burned into the Memcal, but by a different part of the original chip/ECU/Board/Magic Box, and so that is why it needs to be retained and fitted in 'tandem' with the new one.

I think I've covered the whole set of queries, but to summarise:-

'All' Turbo ECUs are basically the same - it is only the chip (Memcal programming) which differs.
Phil *could* have used an SE ECU to do the job.... but may have thought that he still needed to have a '1499' closed-loop chip in the 'back-up' position for limping home.
The 'Limp home' mode is exactly the same in every version - after all, the whole point is to ignore inputs, and get you somewhere safely.

As for why your old ECU failed - I have no idea! There are people who understand these things who still have no idea, and there are companies who will offer to 'repair' it who have no idea!

Most "repairs" rely on someone seeing a burned component, or dry joint on a circuit board.... they don't tend to go much further than that, as it just isn't worth it.

[MPx]

Many thanks both. Very much appreciate you taking so much trouble with your replies. I think I'm "there" now. Yes I did fit my switcher myself (in about 2008) but since it was more than an hour ago most of the detail has been lost to history. Indeed, while the prompt helps me remember fitting the piggy back board, I would have been following Alan's instructions pretty much by rote and not particularly understanding exactly what each part was doing.

Given the apparant lack of closed loop memcal chips that does sound like a potential disaster for S2/Fed and closed loop SE owners. Maybe we'll all be converting back to open loop eventually and in consequence having to fake our MoTs - or stay off the road until 40 years old and exempt.

The bit I'm mightily reassured about is that there is no difference in how my car should act/react/perform with its new ECU and old Switcher compared to before.

Thanks again