Hi there,

I have a 2002 D2 V8 4.0, (Bosch). The SES came on mysteriously the day after I bought the vehicle and it's been on every since. I have the P0430 code. There are two questions I have:

1. Live O2 sensor readings: what do they tell those who know about these things? The attached video shows two sets; first the upstream readings, which flick between rich and lean and these look correct; the video then shows the downstream readings which to me look wrong, i.e. they should be stable but instead seem to be tracking the upstream readings. Does this mean the cats are shot?

2. In a hail Mary attempt at avoiding cutting out my cats I want to try the Liqui Moly cat cleaner I have sitting on my shelf. For this to work I need to spray it into the intake after the MAF. However - and noting this may be the daftest question asked here ever - when I disconnect the air intake pipe where it joins the throttle body to spray it in, I note that even at 2000 RPM the flip valve is closed. So, where do I spray the stuff?! (It states that it must not be sprayed in via the vacuum lines). Grateful for any advice.

 

I went thru this on my 2003 rig with the 4.6L. Was getting the PO420 (driver side cat). I have an Autel 619 ODB2 reader and was able to see the O2
readings pre/post cat showing that the cat was not doing it's job anymore hence the code.

I bought a new CAT on amazon (Magnaflow 51234)...had it installed and have not seen any codes since. Monitoring O2 pre/post confirmed the
proper readings for sensor output.

This video helped me to interpret the O2 sensor pre/post values:


skip to around the 8:30 timecode in the video to see where he is inspecting the O2 sensor after the CAT.

When I cut the old cat off, I contacted RRcats.com...sent them some info to confirm it was an original OEM Land Rover cat and got like 150 for it.

The money from the old cat nearly paid for the new cat.

 

Think of it this way....
Upstream O2 sensors will encounter rich and lean exhaust gas. They feed that back to the engine ECU to modulate A/F ratio. It is a constant game of the dog chasing its tail.

Downstream O2 sensors SHOULD be encountering 'scrubbed' exhaust gases if the cats are doing their job. What they sense should be fairly constant. Some variation is normal, but nothing like the upstream o2s.

If the downstream is encountering rich/lean/rich/lean conditions, that suggests the cats are not scrubbing the exhaust. That triggers the code.

 

@WaltNYC @mackendw Thank you both for your replies. I got under the vehicle the vehicle with an IR thermometer to check the temps upstream of the cat and the cat as I read online that the operating temperatures can also shed light on the condition of the cats. Those readings (averages of several readings) are as follows:

Right bank:
Upstream of cat: 175c/347f
Cat: 218c/424f
Delta: 43c/109f

Left bank:
Upstream of cat: 151c/303f
Cat: 170c/334f
Delta: 17c/64f

The significant difference between the banks would suggest that the cat on the left bank is inoperative.

Per my question above, I want to try a cat cleaner. I have a Liqui Moly product but it needs to be sprayed into the air system (not via a vacuum line) and upstream of the MAP. I found that when I disconnect the airbox behind the MAF (a) the engine wants to stall out but that's remedied by having someone keep the RPM up, but more challening is the fact that the butterfly valve is closed even with throttle applied. Can anyone advise where to spray or how to remedy? Thanks.