Puzzled by emissions.

My mk1 VVC F has been off the road for just over 2 years.

When I put it in for an MOT in August it failed marginally on emissions.

First fast idle test
CO 0.54 % (max 0.30%) fail
HC 122ppm (max 200ppm) pass
Lambda 1.09 (0.95-1.09) pass

Second fast idle test
CO 0.52 % (max 0.30%) fail
HC 143ppm (max 200ppm) pass
Lambda 1.08 (0.95-1.09) pass

Natural Idle
CO 0.42 % (max 0.50%) pass

It also failed on a brake issue which was quickly sorted.

For a variety of non car reasons I didn't get back to retesting until a couple of weeks ago and as I hadn't touched the emissions I expected a similar fail. The plan was then to do the usual Italian tune up and get a super hot test.

However the CO was massively out of range.

First fast idle test
CO 3.52 % (max .030%) fail
HC 93 ppm (max 200ppm) pass
Lambda 0.92 (0.95-1.09) fail

First fast idle test
CO 2.95 % (max .030%) fail
HC 96 ppm (max 200ppm) pass
Lambda 0.92 (0.95-1.09) fail

Natural Idle
CO 0.49% (max 0.50%) pass

The brakes passed.
In the intervening 2 months between tests the car has run exactly 20 miles.

Puzzled I plugged in the pscan and looked at the action of the lambda probe (only 1 on a mk1 VVC).

It showed a steady 0.50v with no change.

OK I thought, probe has had it and I got a new one.

The new one showed a steady 0.49v, even when unplugged!
The O2 sensor heater showed on.
At natural tick over the probe is active.
At fast tickover it is not active.
Closed loop is active at natural tickover but not active at fast tickover.
It also says O2 sensor monitoring is not active.

When I read historic faults it says
"Fuel pump relay or purge valve or MIL lamp or comms circuit"

I clear faults but the same returns.

Obviously the fuel pump is working or the car wouldn't run.

I have done a TPS reset but couldn't hear the steeper motor moving at all.

I have checked all the relevant fuses and they seem ok.

I unplugged the black plug to the ECU and the sampling speed in pscan improved vastly but no difference to over readings. I unplugged the red one, through which the O2 probe wires pass, but no difference.

I am starting to think the ECU or the ECU relay box have failed.

I have access to another relay box and to a MEMS 1.9 (non VVC) ECU.

Will the ECU work on a VVC (obviously the VVC won't work).

What is going on.

talkingcars wrote: What is going on.

Anyone?

Can you swap in a known working O2 sensor? Steady voltage from the sensor is just wrong. So is the new sensor also faulty? It's happened to me before.

Is this the car where you have swapped sub frames ? My train of thought would be ...was it ok prior to all the work you have done . Not that you would have reason to check the emmisions when it last ran . Could you have a poor connection with unplugging various components during the swap ?
John

David Aiketgate wrote: Can you swap in a known working O2 sensor? Steady voltage from the sensor is just wrong. So is the new sensor also faulty? It's happened to me before.

Thing is that pscan shows the sensor at 0.49v even when the sensor isn't plugged in.

sworkscooper wrote: Is this the car where you have swapped sub frames ?

It is but the only electrics I disconnected was the gearbox to rear bulkhead earth and the alternator as I kept the engine in place to avoid disconnecting too much.

Yesterday I discovered that there is a feed to the ECU from the rear light circuit which I snipped when I separated the lighting circuits from the engine loom as part of my prep to move to MEMS 3. Reconnecting it made no difference.

I would be looking at first wiring to the sensor, including bad connection on the plugs, also back where it goes into the ECU, then ECU replacement, or at least swapping it with a known good unit to prove your original is the fault or not.
The O2 sensor is an analog unit and the voltage it gives back to the ECU is just a variable one, similar to the temperature sensor or fuel tank sensor. As the voltage signal should change from the probe as oxygen levels in the exhaust gasses change, your pscan should be pick up the probe output as changing also. As you have already replaced the probe, its looking like wiring or ECU.

With having a MEMS 3 TF I am not too clued up on the MK.1 F ECU system, but the O2 sensors all work in a similar way.
Have a look at the wiring diagram, if you have one, and see if there are any other devices on the same circuit as the O2 sensor which may be affecting the reading of the sensor, such as a short circuit on another device that feeds back to the ECU that may affect the ability of the ECU to read the Lambda sensors signals.
I am also thinking that the O2 sensor has four wires, two for the sensor output back to the ECU and two for an internal heating element so the sensor works correctly when the engine is cold. May be worth testing the two wires going to the element to see if there is a voltage present for the heating circuit.

Sundance

Tonight I tried another relay pack - no difference.

I guess the ECU is the next step, there is a possibility I spiked it when I was re-installing the alternator.

If it isn't the ECU I'll probably end up doing the MEMS3 conversion that I was saving for next year.

Another ECU arrived yesterday but last nights parish council meeting and tonight's late finish from work have prevented me trying it yet.