Any Ideas, Fuel Trim Problem Bank 1?

Hi Folks,
Wonder if anyone can give me any suggestions,
Bought another Range Rover ('95 4.6 HSE) a couple of days ago, (hopefully it will be going to my father when im finished sorting it) it had EAS problems and the centre and rear silencers were shot, plus it needs an MOT.
Sorted the EAS, fitted new centre and rear silencers, also gave it a service today.
Started it up, and checked Rovacom for any codes, the codes were;

P1188, O2 Sensor heater circuit high resistance (upstream)

p1185, O2 Sensor heater circuit open circuit (upstream)

Cleared these, and then done an adaptive reset.
Checked the Fuelling inputs, and Bank 1 was getting no Voltage to o2 sensor, Bank 2s readings are fine.
So changed the o2 sensor for a fairly new one (less than 200mls old), checked again the inputs, im now getting positive Voltages, which fluctuate with RPM, but the Fuel Trim is still reading 38.5 and only rarely dips down when throttle is opened.
The trim readings on Bank 2 are ok (negative readings).

Worst thing is, its booked for its MOT in the morning (9am), i've a funny feeling it will come back as failed on emissions. As i stand typing just now, im soaked through as i've been lying in a big puddle:doh:, plus its dark, so can't really do much more to it tonight .
Anyone got any ideas, could a dodgy catalyst be the cause?

Sorry forgot to say, i've also driven it a few miles pottering about and the original fault codes havent come back up.

Nout to do with the the cat,the sensors are upstream of that - unless the cat is blocked.Your fuel trim readings dont make sense to me,Gems short term trims are normally expressed as -25% to +25%. The oxy sensor readings should cycle between 5v - lean, and down to 0v - rich when the engine is hot and running at a steady speed.Drop down rich under heavy boot and go up to 5v - lean on ovverun.Have you checked the heater circuits - both supply and earthing,they wont switch if the heaters dont work.Are the plugs/leads in good nick,not rubbish hotwire leads etc.

eightinavee said:

Nout to do with the the cat,the sensors are upstream of that - unless the cat is blocked.Your fuel trim readings dont make sense to me,Gems short term trims are normally expressed as -25% to +25%. The oxy sensor readings should cycle between 5v - lean, and down to 0v - rich when the engine is hot and running at a steady speed.Drop down rich under heavy boot and go up to 5v - lean on ovverun.Have you checked the heater circuits - both supply and earthing,they wont switch if the heaters dont work.Are the plugs/leads in good nick,not rubbish hotwire leads etc.

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Thanks for the quick reply Eightinavee! The readings are weird! The Oxy readings now, since swapping the lambda, seem ok. Im not sure how to test the heater circuit, (if im honest i don't even know what it is) is it a case of checking voltages at the plug (C0635) which goes to the ECM?
Is it the spark plugs and leads you are asking about? If so the plugs were changed today, it was the Bosch ones i fitted, leads look fairly new no splits anyway.
Realistically, if the car has this sort of short trims, then i take it, it will fail on CO?

The actual value of the fuel trims doesnt really matter - as long as Gems can keep the oxy sensors cycling with those trim values.So have you actually viewed the oxy sensors as live data? Do they cycle ?
To check the oxy sensor heater circuits you need to download the Rave manual from greenoval.com - the wiring diagrams for the whole car are in there.

eightinavee said:

The actual value of the fuel trims doesnt really matter - as long as Gems can keep the oxy sensors cycling with those trim values.So have you actually viewed the oxy sensors as live data? Do they cycle ?
To check the oxy sensor heater circuits you need to download the Rave manual from greenoval.com - the wiring diagrams for the whole car are in there.

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By Cycle are you asking if the Lambda Voltages go up and down whilst driving?
If so then both banks Voltages go up and down.
For the most part, bank 1s short term trim stays at 38.5 but if you give it heavy with the right foot then it can drop to 0, but won't go below, and quickly goes straight back up to 38.5. Fuel Trim on Bank 2 very rarely goes above 0.
I have the Rave Manual, and i quickly checked it to answer your first questions, but all i am getting when i search heater circuit, are the fault codes, and a bit about the pins for the plug which goes to the ECM.
Am i correct in thinking that the heater circuits job is to enable closed loop fueling? As both banks are coming up as closed when checking the Fueling Inputs?
Sorry for all the questions Eightinavee, i do try and research things before i need to ask anything, but this has me baffled, i much appreciate your help.

Yes the heater circuits enable the oxy sensors to get hot enough to switch,enabling closed loop fuelling.The Gems ecu controls power to the heaters as is not needed all the time.
If both sensors are switching thats really good,but the bank with the large positive trim is most likely due to a leak at the exhaust manifold joint or a split in the manifold itself.Can you hear any leaks ?

I forgot to mention, that there was a leak coming from the manifold to downpipe (on bank 1), but i took that apart and pasted it when i did the centre and rear silencers. I've been right along the exhaust system and can't find no signs of any leaks. Do you think i should still put it in for its test in morning and see what happens? I don't want to waste the testers time.

If you are confident there are NO leaks then it should be OK. If you are concerned why dont you ask them to do the emissions test on it without logging on for a full Mot - be worth a Tenner to find out.If you do that,get a print out if its going to fail as the results are a great help in diagnosing whats wrong.

eightinavee said:

If you are confident there are NO leaks then it should be OK. If you are concerned why dont you ask them to do the emissions test on it without logging on for a full Mot - be worth a Tenner to find out.If you do that,get a print out if its going to fail as the results are a great help in diagnosing whats wrong.

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Thanks eightinavee. I'll post the results tomorrow when i've found out how its done.

Kraig said:

Thanks eightinavee. I'll post the results tomorrow when i've found out how its done.

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Bit Late in posting my reply. Car ended up failing, the CO reading were off the scale 9.99%
Also failed on Upper & Lower Ball Joints (Nightmare!) and anti-roll bar bushes/links.
Been messing about with it the last couple of weeks, new leads etc, making sure all the connections were dry an clean e.t.c. New gaskets on etc, still nothing!
On Friday, (with 24 hours left to go on the 10 day grace), i noticed that the voltage reading for bank 2s lambda was a bit slow at cycling. So had another look underneath, and the wiring at the end of the lamda was sooted, (I take it lamdas do vent?) so bit of penetrating spray on lambda, unplugged the connector and cleaned that too. Jumped in the car, fired it up, BINGO!!

Now 4pm rushed to garage straight on ramps, probe up its arse, PASS.
Its always the small things isnt it?

Thanks again for all your help eightinavee.