CO too high on Hyundai, rich condition, failed emissions test.

Hello all,
I have a difficult problem at hand and hope somebody can help me in solving this. After some parts swapping I have bought a Hantek 1008 scope in order to do some more intelligent troubleshooting.
The car: Hyundai Getz 2005 1.1TB 63HP 212000 Km The problem: Emission test failed: CO 0,5%_CO2 15,5%_O2 0,2%_HC 80 @2500 rpm The limit here is 0.2% CO.
The car runs fine, good power, cold start always perfect, doesn't misfire or sputter ever, no engine codes stored. Plugs and wires are new, recently serviced.
I have swapped the MAP sensor, the cat and tried three (used original) pre cat oxygen sensors with no change in the exhaust gas analysis or driveability. Car keeps having CO around 0,5% @ 2500rpm and what seems a rich condition. Through all of this the car operates fine.
After removing the ECU I tested the wiring from pre cat O2 to the ECU and all is fine, no short to ground or connection between the 4 cables.
Now with the Hantek scope I have plotted the pre and post cat sensor. Pre cat sensor at idle has 0,3 - 0,6Hz and a range between 0,15 and 0,78V, at 2500 rpm it has 1,8 to 2Hz and ranges between 0,05 and 0,86V. This is a used sensor, it is switching as it should but is it too slow due to age perhaps? Not sure if 2 cycles per second is enough.
Post cat sensor stays on 0,68V at idle and 2500rpm, only when accelerating it drops suddenly to near zero volts and then goes back to 0.68 again. Not sure why it does this.
I don't have a gauge for measuring fuel pressure or a tool to read live ecu data, at this point I am not sure what to test or try next. It might be that the O2 sensor is not quite as good as it should anymore, but next to that something seems to be causing a rich condition so there might be two issues causing the problem?

I think the o2 dropping like it does is part of the oxygen storage ability but high co I think secondary air injection system but you don't hyave that do you

You Need a tool to check the fuel-trims. This can do also simple Tools for generic OBD-Diagnostic.

Further: check the air-filter and the fuel-pressure if it's in range. You can have a leaking injector too (not fully closing).

From where are you?

BR Matthias from switzerland

It's a pretty basic engine, no secondary air. I checked the exhaust and found a small exhaust leak on a flange near the O2 post cat sensor. Closed it up but still get same reading for the sensor, so it was not pulling in outside o2.

Hi Matthias, I'm from Holland. Air intake is all good, also cleaned air intake valve and area around the axle where it goes through the housing. Tomorrow my obd tool will arrive so will know more then. Have tried to put together a pressure gauge for fuel pressure today but still need one adapter so with a bit of luck tomorrow as well. Have measured some more with the Hantek but the volt readings are all over the place. Today the O2 sensor 2 would be at 0,34V on average, the multimeter gave a more credible 0,745V. Only the wave pattern is useable on this thing so I'm sending it back. Still the issue persists that the post cat sensor drops to 0,08V at acceleration, recovers to 0,81V and then settles back at a continuous 0,745V. Not sure why it would do that.

Tested the fuel pump, it primes the rail at 3,5 bar so spot on. Took the injectors out and primed the rail, nothing came out, no leakage so think I can rule out a fuel system problem then. Still puzzled about the post cat O2 sensor, why it can drop the voltage on acceleration?

--- I would agree reading the fuel trims and looking for the MAF airflow rate. Also a fuel filter flow issue should be considered.

Finally been able to read the fuel trim and other sensor values. At idle with warm engine it is alternating between -2% and +2%. At a constant 2500rpm it goes up and down between 3% and 9%. After throtteling down it takes a while for the values to return to the -2/+2 level. Seems like the engine is constantly enriching the mixture at rpm and it thinks there is a constant lean condition, but why??

I swapped the MAP sensor already with no effect on exhaust gas. Currently reads 27 Kpa at idle. Intake and cooling temp values are normal and rise gradually to operating temperature. Any fuel flow issues would cause lean condition or engine stutter? Engine is rich and runs like clockwork. When I took off the exhaust manifold everything was covered in black soot, cylinderhead ports, manifold pre and post cat and also the exhaust tip so it's been burning too much fuel for a while.
Had one strange occurance today when measuring; when the engine was hot and idling the fan came on, and immediately the post cat O2 sensor dove to less than one volt. It remained there until it turned off and then went back to 0,7V. The fan came on several times after that but then it stayed at 0,7V.

Does it have EGR valve?

You said pre cat frecuency is 0,3 - 0,6Hz. that means you have a period there like 3 - 1.8 seconds which is low for me. Next week i can check a hyundai getz 1.6 and look for pre cat o2 frecuency.

Do you have good emission readings at idle?

What happend with O2 pre cat sensor voltage when you acelerate? Post cat sensor looks like reflecting a lean condition.

Try to take ECT voltage a little bit down. That simulate a higher coolant temp. than normal and allows PCM to substract a little bit of fuel.

Are spark plug gaps ok? Past week i fixed a kia soul which according to manual spark gap should be 1.1 mm. I adjusted gap to 1.0 mm and HC decreased from 270 - 70 ppm.

chears.

P.S I don't know why my replies are posting eco´s

guafa wrote: P.S I don't know why my replies are posting eco´s

Don't worry, it happens to everyone. :silly: Some kind of bug in the forum.

Are spark plug gaps ok? Past week i fixed a kia soul which according to manual spark gap should be 1.1 mm. I adjusted gap to 1.0 mm and HC decreased from 270 - 70 ppm.

Really? :huh: Were they the correct plugs for the application? I'd love to hear more about what led you to check plug gap.

Actually it was good luck. The car belongs to a friend known since ten years before, then i can tell you he doesn´t take to much care of his car and he has driven it for three or four years without any maintenance (except oil and filters change) 96.000km at the dash.

He took the car for emission test and it was rejected. He told me that some hesitation was present also. then I started by changing oil, filters and then a visual inpection of spark plugs. I saw one of the gaps at 1.0 mm and the others at 1.2 - 1.1mm. I cleaned all and adjusted at 1.0mm (which is the same gap of an old car i have). The car stopped hesitation and HC went down.

Again, lucky me. but i have heard some spark plugs which make the engine out of emission ranges (gap, materials, etc).

What took me lots of time (and learning) is an updated i made to an old carburetor car. It´s an old mazda which i adapted a new renault clio injection system. In order to comply with emission test, i had to play around with ECT voltages, sensors, etc.

I have to clarify that at every change (oil, filters and spark plug gap) I tested for emissions.

Have swapped the cat and post cat O2 sensor for used units, this has brought down the CO to 0.28 at 2500rpm. This is a bit better, almost getting to below the 0.20 mark. Apparently the post cat sensor was bad, the current one does not drop to 0,1V on accelleration. Stays fixed on 0,7V almost perfectly. To bring down the CO more I tried a newer O2 sensor pre cat today, an original used one with 25K on it. On scope the amplitude is better, now reaching almost 0.9V and nice constant cycles at rpm. So this one looks better on the scope. The emissions test showed 0.32% CO at idle, 0.5 to 0.6 %CO at 2500rpm and when keeping revs at 4000 rpm it started dropping and ended up at 0.09% CO. So the bizarre result is now that the CO is perfect at high rpm, and worse than before at all other rpm levels. Now what could be the cause of this? Values for CO2, HC and O2 were fine at all rpm levels just like in previous measurements.

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Hi McFly1,

Have you checked oil, Evap system, fuel regulator, injectors?

Hi Guafa, yes oil and maintenance is always fine, new plugs - gap ok. Fuel pressure 3,5 bar spot on. Injectors are not leaking when pressurized (took them out). Values of temp sensors and map sensor are all fine. There is a small evap valve, it gets voltage, hoses are ok.

I would do.
1. Try with a brand new upstream o2 sensor (you have always tried with used ones)
2. Change ECT sensor (this according to my own experiments, affects so much emissions).
3. Connect a potenciometer in series with ECT and play until get correct CO levels (so that i can discard mechanical issues (for instance vacuum leakage or bad head gasket))

About evap system, you can have a small leakage, even if you have proper activation/deactivation. What about disconnect hose that take fuel gases into intake manifold and see what happend?

You said this engine doesn't have EGR system, didn't you?

Have you checked any carbon deposits inside chambers?

Yes I checked the chambers with endoscope and all looks normal, minimal deposits on pistons. Same as when I rebuilt the head 2 years ago. So now I hooked the evap valve up to the scope to see when it activates. Strangely enough there seems to be voltage on the wire to ecm continuously, Then after a while it starts to go up and down rapidly, more like measuring an ignition pulse. Thought I had interference first, but that was not the case. I pulled the hose from the canister off of the valve and then it went to constant battery voltage again. When it oscillates and I pull the hose, I hear the valve make a rapid puttering noise. Seems to open and close rapidly?! The oscillating increases when revving the engine. Tomorrow I'm pulling the valve out and will test it on the bench with a battery.