Co Potentiometer

[tte200]

Took my car to the garage as suspect car has been running rich, the garage have confirmed this but are unable to adjust the mixture due to the Co Adj Potentiometer being faulty.
Could anyone tell me where I can get a replacement as this part is now obsolete?
Thanks
Terry

[John_W]

I'm afraid I don't follow the logic on this one.
Have you done an ElanScan log to verify that the CO pot is faulty?
Even if it is, I don't see why that prevents the mixture being adjusted.
Maybe a bit more information would ring bells, or somebody else might understand the problem. Usually somebody comes along to explain how to adjust the mixture (can't remember if it's Ray D or Texas - or maybe somebody completely different).
Jast hang about and they'll be here soon.
John

[GeoffSmith]

Careful, there are no end stops on the pot so you can turn away to your heart's content and nothing appears to happen (and it appears that it doesn't change anything that ElanScan reads ). I would suggest whipping it out and seeing if you can read ~270 ohms at one extreme and >10kohm at the other extreme (20 turns clockwise). If it doesn't check out, don't worry because I had Chris Wheldon's apart at Donington and it is just a 270R fixed resistor (a few pence each) and a 20 turn 10k potentiometer (like this one). See the Wiki for more information.

[John_W]

Terry,
When you say "running rich" do you mean that the idle emissions limit is the problem, like this thread?

As Geoff says, the pot can be turned forever, but the actual adjustment effect occurs over about half a turn. I didn't remember that the CO pot doesn't show on ElanScan, but you can use ElanScan to check which chip you have. To meet lower emissions targets, Lotus brought out a replacement chip (9930) to allow lower CO levels. If you still have the old chip (9929), you may not be able to achieve the necessary CO level, even with the CO pot on minimum adjustment (270 ohms, fully anticlockwise).

When I fitted one of the first mountain chips to test, the new chip was based on the 9930 whereas my old chip was 9929. This meant that the idle was very lumpy because the position of the CO pot was set such that the CO level was now too low for the new chip. A check with an ohm meter showed that my pot was set on minimum (no doubt to get through previous MOTs) so I adjusted it slowly clockwise while listening to how the engine idled. There was a marked change in the first half-turn or so, but after that I heard no further improvement, so half a turn clockwise is where I set it and where it still is (I counted twenty-one turns min to max).

It is quite possible that you don't need a new CO pot at all, but a new chip or maybe just mixture adjustment.

John

[tte200]

Update
The garage said my car was reading about 4% on the meter but should be around 2%, they were unable to bring it down using the Co potentiometer and have informed me that it is faulty.
John I have carried out an elan scan attached and checked the prom id as 9239 ????
Geoff Have removed the Co potentiometer to test it.
Put a meter on it across the terminals at either end got 270 ohms and at the other end of adjustment 11Kohms, returned pot back to 270 ohms before reinstalling.
Thank you both for your advice.
So looks like the potentiometer is not the cause of my car running rich, any suggestions?

Terry

[GeoffSmith]

You need a 9930 chip from ESM Terry. It's an old problem that Lotus fixed when needed but didn't recall all cars - read all about it here.

[tte200]

You need a 9930 chip from ESM Terry. It's an old problem that Lotus fixed when needed but didn't recall all cars - read all about it here.

Thanks for the information Geoff
Could you tell me who ESM are?
could you also tell me is this something lotus should change / could change if supplied with chip or is it a do it youreself job?

Thanks again Terry

[HJ2]

Click on 'mountain chips' at the top of this page, and a new world opens ...

[Pascal]

Hello,

i notice from the ElanScan that i have a 9239 chip , this means that the car may not reach the MOT control limits next time ...
Is it possible to find an updated 9930 somewhere ?

Is changing the chip easy enough to do it myself ( a 9930 or a Mountain) ?
Does it need engine adjustments by someone who has the knowledge ?

Pascal France