Fix an ECU?

[DeanG]

I had a new ECU installed this past week. Is there anyone out there who can resurrect theses?

[Enright]

I guess you probably weren't going to anyway, but even if the answer isn't positive, DON'T THROW IT AWAY!

It links into something I was rather interested in - incorporating an oxygen sensor into my SE to turn the ignition/fueling into a closed loop system.

I have been suffering from poor power/economy (22mpg) from my Elan since I first got it, and know that others have noticed massive differences between apparently similar cars too. Having changed just about every sensor and gone through an exhaustive list of fault finding, I came to the conclusion that despite garages saying nothing obvious was wrong, my Elan just doesn't run efficiently at anything other than idle speed.

If it had a carburretor equipped engine then changing the jets and dyno-ing/rolling road tuning it might be the answer. It is certainly standard practice on motorbikes after fitting a performance air filter and exhaust to correct the air/fuel ratio.
Fitting a Power Commander to fuel injected bikes allows a person to select the appropriate parameters (exhaust make etc) and program the map for their individual bike.
For a fuel injected car engine the same result can be achieved by fitting a piggyback ECU which adjusts the map at small intervals throughout the rev range. But these are expensive (£400+), still require the use of a rolling road and costly specialist labour to set them up, and I've heard poor reports about them on here. Having the provision for an oxygen (O2) sensor may be the answer.

Usually the O2 sensor passes it's signal to the ECU, which then controls emissions so that they don't damage the catalytic converter. But if there isn't a cat there in the first place, then the O2 sensor could be used to optimise emissions throughout the entire rev range. This theoretically should mean the most efficient burn possible and so better economy and/or more power, without a cat strangling the result, and without risking an MOT failure (or even worse - a blow-up).

Combine this with an ESM chip to ramp up the boost, and the prospect starts to get quite exciting!

Only the Federal Elans and S2's had an O2 sensor. I spoke to ESM about this a while back. He had tried fitting an O2 sensor to one of his SE's but it ran worse and he then got a CO potentiometer error code. In theory the CO pot is no longer required, but unplugging it confused the ECU completely.

If we could find out the specific differences between the SE and Federal ECU from Lotus's Technical Dept, then that could be one way of cracking it. Utilising your fried ECU could be the other.

Would anyone else like to contribute?

[GeoffSmith]

When I have time, I'd like to have a good look at an ECU (preferably a duff one with the aim of fixing it) but Dean is the wrong side of the pond. I did offer to look at Sy's some time ago, but the chances are I wouldn't be able to get around to it before the Winter. Whatever, please don't scrap the ECU Dean.

Neil, I thought the only difference between all Elan ECU's was the MEMCAL that's plugged into it - can you confirm or enlighten Alan?

Geoff

[Enright]

I know that the chips have a sort of ID code that shows up in Elanscan, is this what highlights what version MEMCAL it is?

This makes me wonder if there's some sort of bridging plug used in Federals and S2's that replaces the CO pot, but still completes the circuit.

After all, the SE has a plug available to accept an O2 sensor - it just isn't used (the same as the obvious blanking plug sticking through the turbo heatshield). It suggests that Lotus designed a generic wiring harness that just had different bits added in or taken away to account for the various options.

I'm not sure if Alan has made chips for SE's, S2's AND Federals, and what the differences had to be.

Perhaps the answer is to see where the CO pot plugs into the wiring loom on an SE, and then find the same point on an S2 and see what's there. If I can find it on mine, would any S2 or Federal owners be prepared to have a look?

[Doug]

Neil- trying to figure out your signature -- sounds painful ??


There's only 2 ESM types of chips, the SE and the S2/Federal - I believe Alan said the S2 and the Federal 49-state Elan are identical. The California Federal Elan has a temp sensor on the EGR valve which adds a few code lines I guess?

Alan will answer eventually I guess, but yes I think there is some circuitry that bridges the CO pot circuit or something like that . . .

[Enright]

Neil- trying to figure out your signature -- sounds painful ??

Ah that's an easy one to answer:

"When you press the accelerator pedal it goes like a scalded cat!"

Admittedly, mine could be slightly better, but maybe this could be the solution.

[ESM]

I might have got the wires a bit crossed with you there Neil....

My red SE had a bit of a long term power issue and I fitted an oxygen sensor in a desperate attempt to improve matters. I had some initial issues (battery light on all the time) and I found that if I didn't leave the CO pot connected a CO pot error set, although it didn't put on the CEL. I suppose the catalyst equipped cars come with a fixed resistor rather than a potentiometer (it runs fine with it disconnected completely in spite of the code). Neither issue was a big problem, the battery light thing was odd but was related to a bad contact in a wire (supply for the heater in the sensor) and didn't actually have anything to do with the charging of the battery

These days I run my red SE with an oxygen sensor pretty much all the time. Its useful to be able to test SE and S2 proms myself. Initially I found no performance difference from open loop control and a decline in fuel economy! However, over time - without making any changes - fuel economy has returned to normal and so I wonder if the initial dip was just due to more use of the right foot when 'testing' it than anything else.

All you need to make an SE closed loop is:

1) fit an oxygen sensor
2) fit a 1499 chip
3) debug any minor issues that arise

The biggest problem here is removing the bung from the oxygen sensor mount - its been there a long time and doesn't want to come out!

I do five PROM ids these days 9929, 9930, 1499, 9949 & another one I can't remember that came from a car in Norway (5949 maybe??)

[ESM]

To go back on topic, I could look at the old ECU. If its the MEMCAL i can fix it, if not a spare memcal would be handy.

[Enright]

Thanks Alan for a very detailed and informative reply.

I've sent a quick email off to Lotus to see if there is a fixed resistor in catalyst equipped cars (and if so, what it's value is).

But just in case I don't get anything conclusive back from them, could somebody with an S2 have a quick look underneath their glovebox for me please?

Below are a couple of photos of what lurks below the passenger side of my dashboard. Sorry for the poor quality but I took them in pitch darkness with only the aid of a torch, so it really was a case of "point the camera and hope".

The silver thing to the left is the ECU, but I'm more interested in the blue thing with the yellow cap to the right - just above the pictures' date stamp. This is the CO potentiometer. S2's shouldn't have one, but they ARE likely to still have the black plug that goes into it. If they do, can anyone tell me what plugs into the plug (if anything)?

Thanks to anyone who can help.

[Enright]

Call off the search - I've had a very prompt update!

Dear Sir

Only open loop cars had the CO potentiometer, there is nothing in place of this on closed loop cars.
We would not recommend converting to closed loop, you should be able to get your car running properly after conventional diagnostic investigation.
Have you had the 1995 upgraded Mem-Cal fitted?, this was introduced to address retrospective MOT CO emission requirements. Ask your dealer to refer to Bulletin 1995/24
It may be that the fuel injectors are worn/leaky, the fuel pressure should also be checked.

John Hostler - Technical Service

This makes me wonder what the upgraded Mem-Cal did to address emissions. I've tried to do a bit more digging by sending back this:

Dear John,

Thanks for such a prompt and informative reply.
Unfortunately because I only bought the car last year I don't know if the upgraded Mem-Cal was ever fitted. However I will try to find out, and I will get the injectors and fuel pressure checked-out too.
Is it possible to find out how the parameters in the Mem-Cal changed to achieve the upgrade?

I'm surprised that you don't recommend converting to closed loop control. Utilising the features of the ECU to monitor the emissions and adjust the parameters automatically seems to offer the best option of controlling the emissions (and therefore power) throughout the rev range. I would have thought that for the cost of a chip and a sensor, this was a very worthwhile enhancement as it appears to turn it into a vastly superior system.
Would you mind my asking if your reasons for discouraging this are based upon cost, or are there other technical problems that I could face?

Tks&rgds,

M.Neil Wright

Alan, are you aware of the contents of the aforementioned technical bulletin, and if so, were you able to incorporate it's features into your chips?

[GeoffSmith]

Neil,

There is some more information here.

Geoff

[ESM]

Neil,

I am aware of the bulletin - its on my website! See it here.

Basically it describes the 9930 PROM which was designed purely to reduce CO emissions at idle in order to pass more stringent emissions testing in the MOT.