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1995-2002 Range Rover P38A
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Discussion Starter #1
Been getting a bank 1 lean code but no other faults. Watching the Sensor 1 output graph it clearly goes lean after a few minutes at very high speed. Sensor 2 continues to oscillate. Slow down and the sensor starts to oscillate again. The other noticeable difference is that Sensor 2 goes rich for a few seconds if you floor it (as you would expect), but sensor 1 just oscillates. I'm pretty sure the fuel pump feeds bank 2 first and then there is a transfer pipe to the bank 1 manifold, so if the pump can't supply the required flow rate the pressure will drop on bank 1 before bank 2. I'd be interested if anyone can dispute this theory.
 

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1995-2002 Range Rover P38A
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And your car is a GEMS or a Thor John?
On the Thor the rail splits equally in the centre so you wouldn't get any differential in flow rates. Can't remember the GEMS layout.
Tested the system pressure? Checked the injectors for spray pattern?
 

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1995-2002 Range Rover P38A
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Discussion Starter #3
It's a Thor and you're right. I could have sworn it went in the back on one side and then across the front. Pressure sensor tap is at the back of bank 1 though. Maybe I assumed the feed was the same place on the other side. Bang goes that theory then. Think I'll try swapping the sensors next. I will dig out the pressure gauge if that doesn't find the culprit, but I'm not wild about blasting it up the motorway with the pressure gauge wedged under the windscreen wiper. A fuel leak from the connecting pipe could be nasty.

I have checked that all the injectors 'go click' when you put 12v across them but I suppose one of them could be giving low/no flow. The ECU might be able to make it run properly at low speed by trimming the other three up but maybe three injectors can't provide enough flow at high speed.
 

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1995-2002 Range Rover P38A
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Well, here I must agree with TH. Let us know what we are trying to diagnose?
If we knew what year and engine from the signature, or first post, we could ask about things like filters, which Late Thors do not have.........
 

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1995-2002 Range Rover P38A
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121 Posts
Discussion Starter #6
Apologies, it is a 2000 4.6 Vogue (without a fuel filter!). I use/ have used a number of different forums for the various cars I own / maintain for friends / family. Most require you to give the car details when you register and and automatically include them in your signature when you post. I forgot that this forum doesn't do this. Perhaps whoever runs this forum might like to consider doing this.

Trying to adopt a logical scientific approach to my problem:

There are two possibilities, either bank 1 is running lean at high speed or the ECU thinks it is running lean.

If it IS running lean then the fault must be between where the fuel rail divides and the fuel entering the cylinder(s) so possibilities are:
Block in bank 1 fuel rail,
Injector fault(s),
ECU not commanding enough fuel to bank 1 only.
I'm discounting ignition issues because I'm not seeing any misfire codes and misfires would give too rich faults.

If the reading is erroneous then:
Sensor failing (at high temperature?),
ECU sensor circuit fault,
ECU Diagnostic fault.

I'm discounting wiring because it works reliably at low speed. Ditto ECU for now at least.

Anybody think of any more?
Swapping sensors is easiest so I'll try that first. After that it looks like I'll need to take the injectors out to test their flow rates (while trying hard not to set the garage on fire!).
 

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1995-2002 Range Rover P38A
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121 Posts
Discussion Starter #8
Finally Solved

Finally after tearing my hair out and doubting my sanity due to all the conflicting test results and symptoms I was getting; it was indeed the O2 sensor failing (at high temperature?) The diagnosis wasn't helped by a combination of dodgy connections in the orange connectors and a brand new sensor that was mis-wired.
 
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