V8 High CO

[ballcock]

Help and advice wanted. My 3.9 V8 has emmisions problems, after sorting out the rattly tappet (thanks for advice) I'm still getting high CO readings just under 2.0%. I have replaced the lambda sensors, new plugs, new leads, timing spot on, tried a different AFM, exhaust sound. Cannot think of possible cause other than the cats. I have the problem running on both petrol & lpg. On lpg the CO is higher. The engine seems to run perfectly no more noises it shouldn't have and pulls well. What have I missed?

[Range Rover Blues]

Change the oil, it DOES make a difference.

[ballcock]

With reference to my earlier oil pressure post I have changed the oil twice recently. I am now waiting for a pair of replacement cats, having tried a replacement AIC and tested water temp sensor so hopefully this will cure it.

[Range Rover Blues]

If you thinnk the cats are faulty you can tell the ECU to ignore them by changing the tune select resistor for one from an older RRC. This will make the car run open loop, then you can tweak the MAF sensor to lower CO.

If everything else is ok it should get you close to a pass.

[ballcock]

You cannot make the ECU ignore the cats as they do not form part of the control system, you are confusing them with the Lambda sensors which I have replaced recently along with most of the ignition system.

[FridgeFreezer]

I'm sure there was a similar problem to this either here or in the freelander forum recently (it was *just* high CO, everything else fine) but I can't remember what the fix was. Could be worth a scan back through the last couple of pages on each just to see if it's still there or I'm imagining it.

[mickeyw]

I think what RRB means is that cat equipped cars have lambda sensors, and that by swapping the tune resistor you can tell it to run as if it had no lambda sensors and therefore no cats.

Sounds odd that the CO is high for both fuels, LPG normally emist next to b*gger all CO. Is this info from an MOT place? If both fuels read the same CO, which is very very unlikely, I may be inclined to question their emissions tester.

Is the LPG system open or closed loop, i.e. does it use a lambda sensor to control its fuelling?

[ballcock]

Lpg is closed loop, although only single point mixer, It was my thought that on lpg there should be no problem on co but it is reading higher on my gas tester than petrol,

Mot tester tested and is reading 1.7% app. but it needs to be below 0.3%. I have done a compression test all ok, all new plugs,leads, good distributor, swapped coil for spare, tested water temp sensor and IAC has new lambda sensors, swapped AFM still getting same readings. Started to fit replacement cats this evening and snapped manifold stud whilst trying to get the damned thing to seal (cheap new set off Ebay). Spotted some rust on chassis so might mothball it as a future project as my neighbour has offered me a 300 Tdi but I don't like the colour.

[ollyr]

Had similar problem with mine for MOT this year however luckily it flew through on LPG, on petrol CO was 17%! however, it had idle probs on petrol.

Turned out to be the fuel pump and pressure regulator.

Your problems with emissions on gas and petrol is strange though but it narrows the fault finding down.

Closed loop lpg runs lambdas - replaced

exhaust manifold gaskets - Maybe worth checking? They normally make a ticking sound similar to tappets

Distributor plugs leads - replaced/checked

Throttle position sensor - Definately worth checking, Can be checked with multimeter.

ECU - only real way to check is to substitute for known good'un

Cams worn out - Is the engine high mileage/ rocker covers sludged up?

General wiring fault - e.g chaffing

Good luck, if you need to borrow an ecu I have a spare known good one

Olly