High CO on my S2... Again! (still)

[HJ2]

Begging for some help here!

Last week I drove my S2 to my friendly MOT station. Just a 'quicky' i thought, as I spent weeks and weeks optimising and perfectioning the Elan.
Unfortunately we were ready after a couple of minutes as the CO level at idle was a fail

Usually with my car the idle CO% is somewhere between 0.45 - 0.48. In the Netherlands for my car the maxium idle % is 0.5, so close but still good the last couple of years.
at the MOT station, idle % was now 0.65 (heavily fluctuating) and rising and rising when applying the throttle. I made sure the engine was HOT and did the CO test as the first test.


Some car facts:
Car = S2 (1995)
Mileage is 111.000 Km.
No Cat
Empty Pre-Cat
2.25" SS Exhaust (PECO)
Everest Chipped
Wastegate ported
No faults stored in the ECU
Engine hot during measurement
Everything in mint condition (besides whatever it is that is causing this problem)


Problems occurred a couple of months after headgasket job.
Problems occurred a couple of weeks after a HES failure (i repaired the sensor though)

Symptoms:
* Low maximum boost (slowly dropped from 0.96 to stock-ish levels over 3 weeks or so)
* When setting the base timing it looks as if occasionally there is a spark missing (well, at least the strobe misses a flash once in a while... could the strobe be faulty?)
* When coming to a full stop at a traffic light, sometimes Idle gets very low, engine barely keeps running, Only for a brief moment though, then everything is back to normal
* Engine appears to run a little rich
* The real bite(HP!) from the engine at WOT is missing (no wonder with low boost)
* I could be my mind playing up, but it looks as if the engine runs a little hotter than it used to
* There is a slight increase in revs when switching between normal operation and service mode


What have I done so far:
1. Reset Base timing
2. Exchange CAS
3. New Plugleads
4. New Oxygen Sensor
5. New CTS
6. Playing with CAS adjustment, with no results (so base timing appears to be okay)

Things left to do (well, what i can come up with anyway )is change plugs (although these look good and evenly coloured) and change Coils (these are MSD and approx. 6 month old, but i still got the old ones)

In the Netherlands a fine follows automatically if i don't show up for an MOT test soon. This is no use if I can't tackle this problem. If i delay MOT (legally) then i cannot testdrive it anymore as it is not insured! And i need to drive it to test it... Aaahhrg!

So: All technical assistance to lower my CO is welcome as I am running out of options...
Would an Elanscan be of any help?
Please help!

[Brit-Car-Nut]

Something probably redundant:

Re-check all vacuum lines and electrical connectors, especially the grounds (earths).

Is it possible the O2 sensor is wrong or contaminated?

Someone recently reported the air gap for the HES had to be adjusted after a rebuild, maybe revisit that?

Best of luck.

[HJ2]

Thanks, but vacuum lines appear to be OK (but i'll check again)
O2 sensor is new and gave same results as the old
I tried with 2 CAS assemblies, both in OEM condition, same results as well
I'l check the ground straps as well...

There is a slight increase in revs when switching between normal operation and service mode (thanks Ray)
Can I adjust tick-over on a Closed loop S2? http://wikilec.9600.org/index.php/Tickover

[norman lovie]

the ex manifold has a leak somewhere ? =
you draw in some air at idle to low load driving condition
the additional air tells the lambda that it thinks the mixture is lean
Lambda - closed loop - signals ECU to up the injection to get it AFR back to where it thinks it should be - but it was actually ok - so now its rich ( mind the AFR in Elanscan could now be wrong becvause of this)
seen this on another turbo engine type - but the symptom / conssequence is the same
High CO2
edge off the top of performance ( via ECU negative adation)
can get a bit of burble change in ex note - just not as crisp as it was

look for any signs of soot around the manifold area upstream of the sensor

[madbilly]

My car is an SE and I don't know if the S2 controls idle combustion open or closed loop, but either way - try winding open your throttle butterfly idle position, this worked for me. The ECU controls revs to the correct value using the idle air control (IAC) valve, and in normal mode it closes this more if the throttle idle position is more open as the latter has more air passing through it. In service mode the IAC is held at 20 counts (I think) so my idle revs in service are ~1500. As the MOT is in normal mode not service the high revs aren't an issue, and I got my emissions down from ~4%+ to ~2%. I think this means there's something wrong with the IAC valve (it's more closed than it thinks it is), or potentially the injector driver circuits ageing (longer pulse width and letting more fuel in than they should). Plenty of investigation yet to do, but this fix might work for an S2 and save you swapping all the ignition bits unfruitfully.

[HJ2]

Well, i found a CO meter for an acceptable price so i can measue what i'm doing without leaving the garage (no fines!)
I'll check for leaks in the exhaust manifold first. Can a leak further downstream of the O2 sensor cause these problems as well? For example recirculating air in the empty pre-cat housing, letting air (oxygen) in through a leaky joint between pre cat housing and exhaust (flexible part) ???

[HJ2]

Finally I found some time to get the Elan on the bridge to have a closer look and follow some of the leads as posted above.

First thing I noticed from below is that the flex section of the exhaust has quite some damage and is no longer gas tight... The skid plate is a goner as well
So, time to remove the heat shields on the turbo and exhaust manifold.

Cracked manifold in 3 places...


So... I will order a new Cybox flex part (PECO in my example)
But the manifold... Can this be welded and will this hold? Or is a replacement (new or used) the way forward)?


Grrr! Still no driving!
Let's hope that this is the root cause of all my nasty CO2 troubles then !

[HJ2]

The saga continues here:
viewtopic.php?f=8&t=21081

[Giniw]

I suppose you know that article in the Wiki, but just in case: http://wikilec.9600.org/index.php/CO_adjustment
I don't know whether that could address the issue though.

[HJ2]

Hi Ginwin,

Yes, i found it, thanks, and was pointed to that one by several people.
The exhaust manifold needs to be solved first anyway.

What i am not sure of is if this procedure is only for the SE, ofr or the S2 as well?

[Giniw]

I don't know, they write at the end "With the S2, the acceptable CO levels drop to a lot less!" so I suppose it applies to the S2 as well but it's just a guess.
Maybe you should check the "engine management" PDF? (but I think that PDF has been written for the SE ... :/) As for the engine, are the S2 any different from the catalyst equipped SE?

[Brit-Car-Nut]

As far as I understand, the CO Pot was used in the early SE (S1) model (with open loop) to adjust the exhaust output. There was a warranty replacement that allowed for more adjustment, but that system was never used on the S2 which has the O2 sensor to do that task.

[HJ2]

Thanks for aknowledging my gut feeling

[HJ2]

As a bonus, Peter showed up a week ago for some jobs to be done on his car (Gear Cables and shortshift... again!) and some quality time amongst Elan found friends.
He brought a new MAT sensor amongst other things that he lend to me so I could see if there are still things to improve (thanks man!)

I just now removed the MAT sensor of my car. It was liquid black, and the sensor part in the cage was bent to one side... not good ...
I Swapped it for the new part and took the car for a spin... Transformation!

I learned yet once again that troubles never travel alone. So besides the cracked manifold, cracked pre-cat housing, ripped flex section and not so gas-tightness of the rest of the exhaust (all sorted now ) it turns out the MAT sensor was on it's way out as well!.

The car runs absolutely beautifully now


Let's make things better!

[norman lovie]

nice one: your wow's are not wasted - makes for good reading and helps points me in directions to check for, whilst i,m in garage mod.

[HJ2]

Hmmzzz.. Judged by the (slight) Popping in the exhaust, things are still not perfect in Co land...
I think the next thing to do is clean the injectors. Perhaps one hangs a little and allowing a small leak when it's supposed to be closed....

Do the S2's have some sort of equivalent to the CO pot?

[ESM]

If you get the popping on lifting off the throttle don't worry about it, it's quite normal. I think it's something to do with overrun fuel cut.

[HJ2]

Dear all,

Last week it was MOT time, again
As the car is in perfect shape, i did not worry, however the ongoing high CO2 gave me a bit of a bad feeling prior to the MOT (as every year)

During the exhaust gas test, CO2 was approx 0.7% at idle and even 0.9% at 2000 rpm. It used to be 0.46% at idle a couple of years ago. just after I emptied the pre-cat housing (no main cat present anyway)

At first this was a fail as the garage thought the limit was 0.5%.
After reading the regulations carefully again, it turned out that the 0.5% was for a car with BOTH a cat AND a O2 sensor. Since my car has ONLY the O2 sensor + no notes on the paperwork that it has a cat, we could test it as a car without O2 sensor or cat!
So max. 3,5% CO2 @ idle after unplugging the O2 sensor.

Now: unplugging the O2 sensor made the CO2 DROP instantly from 0.7%to 0.35%
Does this mean that my O2 sensor is at fault? Or that I still have an air leak somewhere that the O2 sensor picks up and tries to compensate with injecting more fuel?

[Fredjohn]

HJ

Which Everest chip do you have fitted? If it's the closed loop (O2 sensor) version (and as it is an S2 I would expect this), then surely the ECU will not function correctly if you disconnect the sensor. Similarly the open loop chip will only work without the O2 sensor. If you want to alternate between closed or open loop then surely you need to fit the switcher version of the chip, or is this the one you have?

This may account for the unexpected readings.

John

[HJ2]

Hi John,

Yes,I have the switcher, closed loop off course (S2)
But it just contains a bunch of boost target maps, right?
So when i pull the plug from the O2 sensor, the car should just go into open loop mode as far as I recall. But it is strange that the CO2 level drops when it goes to open loop

Hmmmzzz....