Volvo 480 Club Europe

High, this is my first ever post,
My 1995 480 celebration will not pass MOT emissions due to high co2, i have tested and replaced everything, air intake temp sender, coolant temp sender, map sensor, plugs, coil pack, and o2 sensor, even tried a new ecu and cat.
I haven't found an air leak to the inlet system and i don't have any exhaust leaks before or after the o2 sensor, i have good cylinder compressions and the timing is spot on.
I have tested the wiring from all sensors to the ecu and they all check out as should, the heater side of the o2 sensor is good, have 12v. I have scoped the signal wire at the o2 sensor but only get upto 0.09v.
Can anyone help if seen this before
Thanks

What readings are you getting?

Have you changed the oil and filters recently?

Engine oil and filter will not cause 9% co2, its replaced every year, airfilter too, fuel filter is new also.

9% co2? what are the HC's like?

Lambda sensor replaced - Genuine? Good S/H? Universal one?

Hello KCantle and welcome to the forum ! I'm sure you will get lots of help with your problem on here, but can I just change the subject and ask for details of your car for the Celebration Register ? It's held in strict confidence and used to produce general information, like no left with a current mot, colour distribution and an indication of what the no of 480 should be for those with no dashboard plaque. I will send you a private message (top right corner of the page, only shows when you are logged in) You should get an email telling you one has arrived if the system is working properly.
Good luck with those emmissions.
cheers
Sylvia

Are you getting any error codes?

what brand of cat did you fit? I had problems on another car I had changed the cat for an after market and struggled with emissions, eventual sourced a bosal one and that did the trick.

Tried BOSCH and NGK o2 sensors, cat is a good make, not cheap one.
It seams to me with the scope readings that the o2 sensor is not getting hot enough and so not sending a high enough voltage to the ECU, no flash codes present in system

Do you have the print out from the test?

The Mot is only looking at CO, HC and Lamda.

CO max 0.30
HC max 200ppm
Lamda Min 0.970 - Max 1.030

My last test was CO 0.19, 49ppm and 1.006

The garage I used dont check or give the O2 or CO2 levels.

A good running engine will look something this

O2 -----------14.5 - 16%
O2--------------- 0 - 0.35%
CO -------------0.1 - 0.45%
HC-------------- 0 - 35 PPM
LAMBDA ----0.995 - 1.005

Hello and welcome KCantle - another Celebration Look forward to seeing some details and pictures.

A previous Celeb of mine had a similar problem and so wouldn't pass an MOT. We tracked the problem down in the end to the green wire that runs from the lambda sensor to the ECU. It is a shielded wire and that shielding was breaking down inside. If you checked the wire with the engine off it gave resistance readings that suggested it was fine, but when the engine was running the other wiring in the loom it runs in were affecting it - badly!

I got hold of another wire from a 440 loom and cutting out the old one and routing it through the replacement (keeping it on its own as it ran through) solved the problem.

Might be something to consider?

Good luck and best wishes

David

Thanks for that, i will give it a try if i can find another loom with the wire in

Sounds like you have a simialr issue to mine

link viewtopic.php?f=11&t=36091

although i was getting a voltage swinging around the 0.3 to 0.8 or 0.4 to 0.9V

0.09V is VERY low, almost open circuit?

I t should swing every second or so as the ECU 'hunts' the mixture.

mine was 'odd' as the HC was good, lambda OK after it got hot, but the CO was crazy high and then slowly fell into range.

I couldn't figure why CO was high if Lamda was 'pap-on', the only thing might be a dribbly injector, or some of the emissions valves letting fumes from fuel tank into engine at idle.

I still need to really fix it. This 95 model has TWO small pipes from the cannistor (fuel evap rubbbish) on the wing to inlet, one at throttle valve and one next to the take off for vacumm pressure. the 93 only has teh one at the throttle valve

I had a problem like this. Similarly as the dcwalker said, the shielded wire between lambda sensor and the ECU fails with time. In my case the insulation between the shield (which is grounded) and the signal wire was broken. Due to this, the signal at the ECU was close to zero all the time and the ECU was giving too much fuel to the mixture. I failed MOT and also my fuel consumption was ridiculously high.

The proper fix would be to route a new wire, but I couldn't find a suitable one, so the quick fix was to cut the connection between the shield and the ground (it's near the ECU plug). It's a temporary fix that can last for years

AleksanderHugo wrote: ↑

Sun May 24, 2020 4:16 pm

I had a problem like this. Similarly as the dcwalker said, the shielded wire between lambda sensor and the ECU fails with time. In my case the insulation between the shield (which is grounded) and the signal wire was broken. Due to this, the signal at the ECU was close to zero all the time and the ECU was giving too much fuel to the mixture. I failed MOT and also my fuel consumption was ridiculously high.

The proper fix would be to route a new wire, but I couldn't find a suitable one, so the quick fix was to cut the connection between the shield and the ground (it's near the ECU plug). It's a temporary fix that can last for years

this is useful, was the lamda 'OK'?

this is why I have a problem Lambda was OK, only the CO figure was 'daft'
I know when I replaced the sensor on the 93 car it was only a 'pig-tail' on the sensor and this was connected to the original wiring with some very neat 'twist' connectors. . . .

I'll need to check the voltage still swings from 0.3 to 0.8 ish when the car comes back from a longer run, maybe cable breaking down with heat?

Yes, actually... both lambda sensors were fine I had it replaced by a rather incompetent workshop that used to swap parts before properly diagnosing the problem.

You can check a couple of things:
- unplug the sensor and check the resistance between the signal wire towards the ECU and the ground,
- check if the voltages given by the sensor plugged and unplugged are similar — in my case unplugged sensor was nicely fluctuating, but while plugged it was nearly constant.

Thanks everyone i have now found the fault, it was as AleksanderHugo suggested, i have a faulty o2 sensor signal wire, the sheilding has broken down and is a constant short to earth, cut the sheild earth wire and it now runs as should. Will at somepoint run a new sheilded wire.
Thanks for all the helpfull sugestions

Wish mine was that easy

checked today
5 ohm to heater, when unplugged, 12-13V at start up
0.6 - 0.7Volts from lambda for first few minutes

water at 92/ 93
9 ohm to heater
0.13 to 0.8 V swinging every few seconds,

so all looks fine . . . ..

any other suggestions appreciated . ..

further comments I'll put into the 'engine' section