Stainless exhaust, high co emissions, erratic lambard sensor, cats cut out.....

[Jonny Boaterboy]

I have a little dilemma.... earleyer this year I cut out both the cats on my 1994 3.9 v8, as they were rattling... one was OK and the other completely gone! I replaced them with some flexable exhaust pipe no problems..... until MOT I was excepting to fail on emissions and have saved up for a stainless exhaust. I was planing to use my local Powerflow outlet, the guys down there said they would build in a removeable section and come the MOT I could borrow a cat off them remove the removable section and fit the cat to bring the emissions down to pass the MOT..... anyway went for an MOT yesterday and...... It Passed  :shock: Well sort of anyway the MOT man said the co emissions were off the scale, the lambard sensor was up and down and would not settel, but he passed it because I told him I was going to get a Stainless fitted with cats!

This brings me on to my dilemma, the engine is running well and still giving me about 17-18 MPG the only problems that I am aware of is a water leak, (no idea where it is leaking from but it is running down from above the starter motor somewear?) and it sometimes has an eratic tic over i.e. it struggles to settel down cycling between 500rpm and 1500rpm and will stall sometimes. After what the MOT man has said, if I fit a stainless exhaust, do I have to fit two cats or can I get away with one, the reason I ask is because the mot man said that it was unstable because the cats had been removed and with them fitted it would settle down, I thought the exhaust gases just passed through the cat and had no effect on anything before them? Do they create some sort of back pressure which helps settle it down??

Or have I got a faulty lambard sensor which is creating the high c.o. emission and the eratic tickover? As I said it seems to be running fine apart from the occasional tic over problem

Not sure what to do now, should I fit the stainless exhaust with one removable section for a cat next MOT? Or two Removable sections to recreate the back pressures? Do I try and find out why the co emissions are high and the lambad sensors are all over the place?

Any bit of help would be greatly received as allways

Thanks

Jonny

[trecfive]

Change the resister under the drivers seat for the non cat one.It might help out with the high emissions and you can do away with the cat and lambda sensors.

[JIMBOBLY]

i have the same rangie as you,l reg 3.9,ive took the cats out,left the lamda's in,not changed anything else,it runs absolutly fine at idle.high revs,and its now gone through 2 mots on the imission tests,with quite alot of lee way,i was the same as you,hoping maybe it might go through,and it did,so i would look somewhere else for problems,like air flow metre,or even an ecu problem,the only other thing it could be,is you maybe right in a sense about the back pressure,as the bore of you pipe is bigger than mine.because i left the bore size of pipe the same,because of that problem i may of had,hope this helps anyway mate,jim :-k

[Devon-Rover]

Decat it and using the older RR exhaust system. This too will loose the Lambda sensors. Use a Green Tune resistor (PRC 8172) To Re calibrate the ECU and IIRC will make it run open loop all the time, in other words not use the Lambda sensors.


HTH.

[Range Rover Blues]

I disagree.  Fit the Rimmmer's SS exhaust (a double S I think) for the '94 RRC, it has holes for the lambdas but no cats (you can always retro fit cats, albeit further back where they don't work as well) and leave the TSR alone.

I you fit the green TSR then the ECU will no-longer be self-diagnosing/self tuning and will run a default fuel map that will be over-rich.  Not only does this effect your emissions but your economy to boot.

BTW I'd be over the moon with 18MPG 8-[.

Alternatively fit a pair of lamdas as it is and see how things go.  You can pick up new ones form £60 on e-bay.

[Skibum346]

From past experience... check the air intake hoses after the air flow sensor... we had idling, sputtering, stalling problems and finally found a small split letting un measured air into the system that was confusing the brains of the car... (not me!)

Skibum

[Jonny Boaterboy]

Well where to start! I like the idea of removing both the lambard sensors and re fitting the resistor but I'm not sure if it will pass the emissions next mot the engine is running sweet but it has done 168,000 miles now so things will be starting to wear. I am starting develop two lines of thoughts now, my first is that there is a fueling problem somewere, lambard sensors, air flow metre, split in hose (thanks Skibum will check). My second is the MOT man does not know what he's doing! in previous years the Range Rover has flow through emission with loads of emissions left to give out! I think I might take it down to my local Land Rover place and see if they can find a fueling issue..... which I find had to believe as it is running so well at the moment apart from the tic over problem!

I'll let you know what happens.

RRB does it matter what make the lamdars are? I usually try and stick with L.R. But they are £200 each  :shock:

Thanks all for you help, I thought it would be as simple as Jims but life never is!

[Range Rover Blues]

I doubt an aftermarket lambda will last another 14 years but if it has an equivelent part number then yes it should be ok.  The LR ones are 3 wire and if memory serves correclty are 5 volt types.

[Rossko]

My first thought for poor V8 emissions is look to the ignition - cap, rotor arm,  leads, plugs.   My second thought at that mileage is clapped out camshaft.

How dainty were you hacking out the old cats?  The lambda sensors are suprisingly fragile and will almost certainly be ruined if you hammered the exhaust with them in situ, or welded it.

You do have to use the right 3-wire part, but it doesn't have to come in Landrover box.  You can get genuine NTK parts from a decent motor factors.

cheers, Ross K