97 Discovery Burning too Rich on engine braking?

[x0054]

Hay there, this is my first post. I am used to working on Porsche, so this is my first time really digging in to Land Rover. I hope you guys can help me out.

Here is the problem. My 1997 Land Rover Discovery head its cats replaced twice in the past 3 years ( before it became mine ). Now it looks like it needs new cats again. They heat up to the point ware they start to burn carpet inside the car! This usually happens wile going down hill for a long time. I got a scan tool and tested the car with it. No fault codes were found but wile testing the O2 sensors I noticed that wile the car is driving everything is normal, but as soon as the car starts to engine brake ( like then going down hill ) the O2 sensor jumps to the rich side (.99v) and stays there till you give it some gas or shift to nutrual. It is normal at idle and normal during acceleration. However after 3500rpm the computer switches to open-loop mode and the O2 sensor gose rich again.

Any ideas on what could be doing this?

Thank you,

- Bogdan

 

[discomike]

You might want to look at your ECU for the problem. Past that I don't have an idea, wish I could be of more help[.
Mike J.

 

[x0054]

Any other Ideas. TPS sensor? ..... Something.

- Bogdan

 

[Sergei]

ECU is good place to check out.

How are yer spark plugs looks like? And what petrol you putting in?

 

[x0054]

I looked at the plugs today, only got around to looking at 3, and they were good (kind of ashy gray). I'll take a look at the rest of them tomorrow.

I am using the 91 gas (USA), that's the best I can get in California.

I looked at TPS sensor today, it was running at 10 degrees at idle (closed TB). I adjusted it to run at 1 degree now. Thought that would do the trick, but no such luck. In my other cars TPS has a microswitch that clicks on ant tells that car that I have let go of the throttle. Is there such thing on Land Rover? How does it know that I am not pressing gas?

Just to restate, the problem is, it maxes out the O2 sensor on the rich side and stays there wile I am engine braking, like then descending a hill or simply stopping for a stop light.

Any Ideas

- Bogdan

 

[Sergei]

Well if i will find me RaveCD i probably can find it...

In general i'd say if something causing that mixture to be way rich. Have you tried to play with
- fuel temp sensor
- coolant temp sensor

both of above playing some role in forming of mixture..

also can be fouled MAF sensor... Have someone drowned poor truck by any chance?

I also recall seeing somewhere some instructions on how to adjust mixture by hands, but it totally eludes me for the moment I'll try to check in bookmarks tomorrow..