Replaced passenger cat and now I get check engine light - Defender Source
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  #1  
Old June 23rd, 2008, 11:00 PM
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Replaced passenger cat and now I get check engine light

I decided to replace the rattling cat on the 97 ST. Instead of buying the whole new Y-pipe, I went to the muffler shop and had them weld in a high flow magnaflow. I thought this would do the trick. Well, the rattling is gone, but I now have a reoccurring check engine light. I don't know the code right now, but I had a guy put a code reader on it and he told me it was being caused by the new cat.
I don't think it will pass emissions now.
What's happening to cause this and how do I fix it?
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  #2  
Old June 24th, 2008, 08:27 AM
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Question

Is the drivers side cat stock? Would a Y-pipe having a "high flow" cat and a stock cat create an unbalanced environment causing the check engine light status?


Good Luck...


Cheers...
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  #3  
Old June 24th, 2008, 09:08 AM
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Likely a "cat inefficiency" code. The GEMS system reads this when the upstream and downstream sensors are too close in value. You have to balance the free flow of the cat and what will keep the GEMS from blowing a code. We had a lot of issues with this in doing our own Y pipe design and it took a number of tries to get it right.
If you want to try and cheat it a little, run a clean and new 02 sensor in the front and a old one in the back, that can cheat the system in some cases, but not all.
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Old June 24th, 2008, 10:47 PM
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I assume if that doesn't do it, then I will need a whole new y pipe assembly?
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Old June 25th, 2008, 11:48 AM
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Run the rear O2 sensor in open air and plug the hole. This worked on my disco.
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Old June 25th, 2008, 05:28 PM
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Interesting...please explain why.
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Old June 25th, 2008, 06:10 PM
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I think because the rear one got enough O2 from the open air.

Don't ask why I tried it, but it did work.

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Old June 26th, 2008, 12:14 AM
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OK.... I will give it a shot.
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Old June 26th, 2008, 09:16 AM
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Yeah, the GEMS system will love trying to make the fuel trim work right with the rear sensors like that.
C'mon... WTF!
Lets take one bad choice (too free flow of a cat) and pile on another.
Then when the engine doesn't run right you can start changing all your other parts in order to try and make it run right, etc etc.
Seriously.... WTF.
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Old June 26th, 2008, 10:10 AM
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Okay. So I won't give it a shot.
Mike, what is the best option here?
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Old June 26th, 2008, 10:14 AM
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It sounds to me like your probably going to need to change that cat.
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Old June 26th, 2008, 10:22 AM
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Put a cat that works in.

I don't mean to be harsh, but if something you install causes a problem then it needs to come out. You can't band-aid fix around it, then band fix over that and then band aid fix over that.

If you want to go to silly costly lengths to save that new cat then you could buy a Tornado chip set for the GEMS as it ignores the rear 02 sensors, but it likely won't pass exhaust gas tests and it would cost 5 times more than just fixing the cat correctly.

Buy a used Y pipe. I've advertised many on this site and no one ever wants them so we end up giving them to the scrap guy.
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Old June 26th, 2008, 10:29 AM
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"Yeah, the GEMS system will love trying to make the fuel trim work right with the rear sensors like that. C'mon... WTF!"

My understanding is that the rear sensors just makes sure the cats are working and that fuel is all done by the front ones. edit: this is probably why the tornado chip can work as it does. This was per a fairly decent rover tech. The disco I had ran fine like that for at least a few thousand miles.
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Old June 26th, 2008, 10:38 AM
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Quote:
Originally Posted by ECR
Put a cat that works in.

I don't mean to be harsh, but if something you install causes a problem then it needs to come out. You can't band-aid fix around it, then band fix over that and then band aid fix over that.

If you want to go to silly costly lengths to save that new cat then you could buy a Tornado chip set for the GEMS as it ignores the rear 02 sensors, but it likely won't pass exhaust gas tests and it would cost 5 times more than just fixing the cat correctly.

Buy a used Y pipe. I've advertised many on this site and no one ever wants them so we end up giving them to the scrap guy.

So what higher flow replacement cats do you recommend? I remember talking with you about this a few years back when you didn't have your y-pipes done yet or they were out of stock. No offense but your y-pipes are expensive (especially if I need to replace O2 sensors as well) and I would rather just replace my cats as I assume many here would. Do you have O2 sensors you recommend as well?
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Old June 26th, 2008, 11:41 AM
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Quote:
Originally Posted by evilfij
My understanding is that the rear sensors just makes sure the cats are working and that fuel is all done by the front ones. edit: this is probably why the tornado chip can work as it does. This was per a fairly decent rover tech. The disco I had ran fine like that for at least a few thousand miles.

When Mark Adams was here he told us otherwise. I take his word for it.

Follow-up Post:

Quote:
Originally Posted by mdmccallum
So what higher flow replacement cats do you recommend? I remember talking with you about this a few years back when you didn't have your y-pipes done yet or they were out of stock. No offense but your y-pipes are expensive (especially if I need to replace O2 sensors as well) and I would rather just replace my cats as I assume many here would. Do you have O2 sensors you recommend as well?
We use Random Technology cats.
Not because they are cheap though.

How do you know what our ROX Y pipes costs considering we have never offered them via mail order and have never priced them outside of an entire system? In fact our Y pipes will not even work without our tail system so I'm a little curious as to how you know the retail price on something that I don't even know the retail price on. ????

We use Land Rover 02 sensors. You can use after-market. We use the factory ones due to our warranty, they aren't really any different.
In our ROX systems if you want to run your old 02 sensors you can. It is not required that you change them.

I feel kind of stupid talking about the ROX exhaust system like a sales pitch considering there are no current plans to mail order it.
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Old June 26th, 2008, 12:17 PM
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Overall, Mike has to be right. Philosophically speaking, a kluge solution should not beget another kludge solutuion - you should instead figure out how to solve it right and do that. If you have to pass an emissions check, and your inpector is stupid fuck who won't notice that the rear oxy sensors are unplugged, then by all means, use that method to get past an inspection.

But for the sake of god, apple pie, the environment, and all that is holy, get your emissions system squared away.
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  #17  
Old June 26th, 2008, 01:57 PM
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Can I use a Y-pipe off a disco 1?
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Old June 26th, 2008, 02:39 PM
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According to Morgan (who used the GEMS system in the plus eight, my tech is right and Mark Adams is not).

p.68

http://www.gomog.com/allmorgan/GEMS/GEMSbyPoole.pdf

Heated Oxygen Sensor (HO2S) (Lambda Probe)
 Part Number: ERR1834/AMR6244
 The oxygen sensors are located in the sections of exhaust pipe in front and behind the
catalytic converters, and form part of the closed loop operation of the engine
 The fuel injection pulse width is modulated by the feedback from front sensors to achieve
correct oxygen levels in the exhaust; the rear sensors are used to check correct catalytic
converter operation

Now I don't have my GEMS book with me, but this seems right. This is why O2 sensor eliminators work. They just trick the car into thinking a cat is there. Rear O2s don't have anything to do with fuel, just with making sure cats are in place.

Get a broken o2 and put it in the hole and up where the wires meet, strap the one that is plugged in and see what happens. Worst case you are out 15 minutes of your life.

Follow-up Post:

Also, Mike at Land Rover west chester had some attractively priced y-pipes when I was in the market.
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Old June 26th, 2008, 10:40 PM
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Mike, I take it the Y-pipe in this thread is long gone?

Follow-up Post:

You see, the problem here is that I already paid $300 for the local Meineke to fix my rattling cat problem. Now I am going to be putting more money into it. I don't want to half ass it, I want it fixed right. Can I put a different cat in and fix the issue, or do I have to buy the entire Y assembly?
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Old June 26th, 2008, 11:04 PM
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Quote:
Originally Posted by ECR
...
I feel kind of stupid talking about the ROX exhaust system like a sales pitch considering there are no current plans to mail order it.

...
Yeah, I was bummed after emailing you guys and not hearing back that that was the case and it was an in-house only product. The pics of your ROX exhaust look great and I would have loved to have run one. I ended up ordering a Rovers North/NRP Y-Pipe to replace the stock one that's been welded too many times. I am still waiting for the NRP piece to come in so I cannot comment on it's fit, finish and performance yet.
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