CO Pot resistance values

Out of curiosity... when Lee did all the work on my car recently it was discovered that I didn't have a CO pot fitted (and therefore had not since 18 months at least)... what effect if any would that have on the running of the car? What's the point in having one, is it just emission control? Is performance better without?

The CO pot "trims" the injection duration & timing at idle speeds (up to appox 950rpm) to maintain the correct exhaust emissions due to variations in production tolences & ageing of components over time.

Thanks for the explanation Richard... would that explain my 'lumpy' idle then?

Thanks for the explanation Richard... would that explain my 'lumpy' idle then?

Possibly?

I've been looking into this for the same reasons as Jon_V

Tested mine today. The car hasn't been driven for about 6 weeks, hence after discovering the battery was flat, I ended up improvising a bit of hot wiring to power up the circuits to get access - normal route via power to the chassis and starter motor. This never happens to Tony Stark

Anyway result was mine only goes down to 355 Ohms (max 10500 or so). Lower resistance = less fueling = less CO.

I've got a variable pot from Maplins which testing that really only goes to about 80 Ohms min. Beyond this you're basically at zero.

So two questions....

A) Does anyone have a spare plug I of the same type used on the CO pot, temp sender and various other components I could grab?

B) Any ideas (Mr Faulks?) on how much of a drop a lower resistance may gain? Obviously we can't go lower than zero and as has already been pointed out, it's probably best to keep above that anyway so the ECU sees a 'sensible' reading.

You cannot get the grey connector from Renault but you can get black ones which may fit without modification.
7701996002
7701997018 X 2
7701999021 X 2
7701996007
Or you can try these.
http://www.simtekuk.co.uk/index.php/aut ... :12:359918:

Interesting your pot also only went as low as the 350's. You'll need to get hooked up to a has analyser to find out the amount of change.

I'll try to do mine next week and report back to you if you don't beat me to it!

Well I managed to get a black connector (Delphi) to attach to the variable resistor.

Interesting thing is that the ECU definitely has a range that it works within and it's relatively narrow - anything too low or two high triggers the ECU light to come on and the ECU defaults to over-fuelling 'limp-home' style mode.

I may try again with a fixed 100 ohm resistor from school-boy electronics kit and see where that gets me.

The wider range variable resistor just doesn't have the sensitivity required and unfortunately low resistance = low fuelling. But close to zero the ECU detects a fault as has previously been mentioned.

Back to the drawing board....

Hi Darren,

Did you buy the variable resistor JohnC suggested?

I find it almost too sensative! Havent got my car on a CO meter yet but have managed to lose the fault light and it defeinietly doesnt smell rich anymore.

One other thing I run my car on a set idle from a manual idle control valve which seems to work better at the moment although I know Martin is looking at the Renix to see if things can be changed there....

Will try to get it on a machine asap and get some figures for you.

Cheers

Jon

Interesting your pot also only went as low as the 350's.

A couple of points that might help. I have just looked up the idle speed "potentiometer" in the cct diagram, but it appears that only two wires of the three on the potentiometer, are being used, so in fact, the potentiometer is actually being used as a rheostat or variable resistor.
Usually, when designing a cct, pot or rheostat full range values are chosen so when correctly adjusted, the wiper is somewhere around the center of the track allowing for adjustment up or down. The track resistance of the one fitted is 10k ohms, therefore as a percentage of the full travel, 350 ohms at the minimum end is quite academic and has little or no effect on its normal operation.
If you want sensitive adjustment below 350 ohms, then try with a lower pot track value, say 1k pot where the minimum track value will be very much closer to your zero ohm as a percentage of its travel. As long as the "pot" is not being used as a potentiometer but as a rheostat, the full track resistance is not important as long as you do not have, as in this case, a need to go above 1k ohms.
Worth a try, but as said before, you don`t want to go much lower than say 100 ohms...... before fitting, with a meter, set the rheostat to 100 ohms, mark position of spindle, and only turn to increase the resistance. By doing this, you can always return to the 100 ohm position even if you experiment by going a wee bit lower.

Thanks.

Mine seems so sensitive that even getting it to 100ohms is quite a mission. Hadn't thought of marking it though

Very clever you people, very clever

Yes - too sensitive really at that end of the scale, hence why I wonder whether a fixed test with simple standard resistors would work as an experiment.

I don't think it will go low enough though.

My cold idle / start-up is very very rich. Hot running is better, but still too rich: 3.5 to 4% CO.

I was wondering about buying a few eprom chips of the type Martin's used and ask him to knock up a few variants with very low starting numbers for idle injection duration so I can try them out. Then being able to go up on the CO pot to increase the richness would be a more practical option.

I know when Martin and I looked at it before he wasn't sure whether there was another bit of code or restriction that was stopping the adjustments at idle, as fairly significant changes didn't seem to be reflected in the CO levels (and fuelling).

Bit confusing

Either that, or fit a wide band lambda and gauge - something like this....

http://www.ebay.co.uk/itm/AEM-Wideband- ... 737wt_1068

And then an adjustable fuel pressure regulator so that it can all be balanced and fine tuned....

Thoughts gentlemen please?

.
Hi all, nice work chaps . Great to see you all having a go.

Darren, I wouldn't advise start doing it on the fuel regulation pressure as you will mess with the top end fueling as well, which rather negates mapping it in the first place. The Renix 1 has limitations, and we are all hitting them in different ways. There are some more tables to adjust, but it's all time and experimentation, and time I don't have that much of at the moment. If you want to try some different bins, and get some test bed time in for me then I'm more than happy to do that, test and report style. There is another immediate solution in your case - fit smaller injectors as you are running a very low duty cycle on yours given the mass airflow demands of the engine in it's current spec, or indeed, fit a higher spec turbo and increase the relative airflow and balance the size of the injectors you have. Teglen is running fine on CO for the same cams and turbo, difference he has the smaller injectors, and this keeps it inside the working range. So options there, I don't think the C0 pot is going to get you low enough by itself, but may be wrong on that.

Talking experiements, I have tasked Jon with one to test and report back to me, so the more experiementers the more options we can cover in quick time.

Smiles,
Martin

Hi Martin,

I thought you might say that.

I think the mapping is probably pretty good mid range and at WOT (judging from our trips up and down the motorway nr Sunbury) - it's idle and start up that appear heavily overfuelled and as you say may be the limit of the ECU.

I've no issue trying out different maps though if you can burn a few experimental eproms. Let me know if you need me to buy or cover the costs of a few extra chips.

Alternative as you say is to try to go for smaller injectors. Original plan was the 214s as you know, then I upped that as with the cams / turbo they would have been maxxed out.

Do you know approx how much duty they're running at the top end? Or to put it another way what size / how much smaller would I need to go?

The issue is probably finding some low impendance ones that match up for the needs.

The reason I said variable reg and lambda was really whether a small tweak in base pressure might make enough of a change at the bottom end without underfuelling the top too much. But yep I accept it might end up a case of chasing my tail and changing more than one variable at a time is never good.

I'm in the same situation with work. No time to play with at the moment.