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PostPosted: Thu Aug 25, 2016 5:19 pm 
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Agreed Gilbert.

Does ring a bell that I've seen both types on XJ6's.

But - If 3 wires are ALL 0-1v and reading is 4.7v, what's going on there? If 0-1v 3 wire probes were factory, can't see a previous owner fitting 5-0v probes, changing looms to fit and removing one of the probes wires... You did say the probes had 3 wires, Glen?

In the unlikely event a previous owner did the above mod, that would cause the engine to go very lean.. At this point do we reckon more likely the probe is correct type(?) Glen not tested it after engine warm up, hopefully when functioning properly yet / fully diagnosed actually broken 5-0v sensors yet?

TBH I doubt the Jag's OBD system will have a full on limp home mode, so I think driving on petrol for a while would see lambda flick (in absence of any hardware or LPG system problem) regardless of battery disconnection as long as the engine is fully warmed up and trims given time to adapt... Which would be just as well if tests are to be done today as Glen txted to say he came out of work, vehicle started on LPG and engine cut out not far down the road..

Too low changeover temp could cause poor drive-ability when cold and also fuel trim issues, usually easily got around by manually changing between petrol and LPG. But I might have mentioned in earlier posts that some Stef systems don't have LPG vapour temp sensors (but use reducer temp as rough idea for gas vapour temp) - If this is the case then maybe changeover temp is set correctly (higher chanegover temp) in settings, but the reducer temp sensor is broken - in this scenario the incorrect reducer temp reading could cause incorrect fueling on LPG.. Interface would diagnose, but this test should come after getting lambda flick on petrol.

A good idea fitting Titania probes on a 4x4, they don't need an external oxygen/air reference, an external air reference on a 4x4 likely to become an external mud reference...

Simon

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PostPosted: Fri Aug 26, 2016 4:22 pm 
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Right chaps

They are 4 wire lambdas and I have just driven a fair old distance with a multimeter in the car connected to the signal wire of one of them and it stays around 4.7 volts all the time, fluctuating down to 4.6 at the lowest. Still reads 4.69 with the ignition off too.

Access to the wires and connectors is awful, I was kneeling on the cam cover - with both knees I might add - at one point and still couldn't get the multipin plugs disconnected.

I don't fancy the job of changing the sensors one little bit.

Glen.


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PostPosted: Fri Aug 26, 2016 8:40 pm 
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I think I mentioned I thought they might be 4 wire sensors.

Even if a pain, I'd be checking what the other probe is doing too.

As memory serves, better off working from the side of an XJ6 to access lambda connectors between the engine and firewall, sort of on top of the bell housing... but I might be confusing with XJ8's. Aren't the connectors just clipped in place, unclip to allow the blocks to be lifted a bit higher for access? To be fair, as I remember a bit of a reach to connectors... but very easy compared to some vehicles!

Anyway, you're seeing 4.7 volts... I don't remember if they'll be 0-5v or 5-0v (Gilbert's mentioned a website that has info). If 5-0v, which would seem likely, which would mean your probes are sending a lean mixture signal, you could try richening the mixture via the extra butane method I mentioned earlier. This would tell whether both probes are broken or something else, like maybe broke MAF sensor or unmetered air entering the engine.

I've made several different types of tool for changing probes, though a crow-foot is usually a good bet.

Simon

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PostPosted: Sat Aug 27, 2016 9:24 am 
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Gilbertd wrote:
According to http://www.lambdasensor.com/main/jaguar.htm the 3 wire sensor is a Zirconia which will be 0-1V. From 95 onwards it lists a 4 wire Titania which would be 5-0V with 5V meaning a weak mixture. However, as my Range Rover also uses 4 wire Titania sensors I know from experience that when they fail they will give almost 5V, so that would suggest a dead sensor. 4.7V would be telling the petrol ECU that it is running lean so would cause a rich mixture with the corresponding poor economy.


Hi Gilbert

Thanks for the info. I have scoured the website above, but can't see any reference to 5-0V, only 0-5V. I think mine are part number 250-24817.

It also says this "If the voltage is stuck high then the engine is probably running rich for some other reason. If stuck low then usually either a faulty Lambda Sensor, air leak or an engine running very weak for some reason." which stacks up for 0-5V.

I will try introducing an air leak and see if the reading comes down.

Glen.


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PostPosted: Sat Aug 27, 2016 9:38 am 
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It won't. 95% of cars use the 0-1V Zirconia sensors where 0V equals lean and 1V equals rich so that is a generic statement relating to 95% of cars. Titania sensors read the other way round, 0-5V or 5-0V it makes no difference how they are described but they read high for weak and low for rich. The Universal replacement on the lambdasensors website is the same one as listed for my Range Rover which is most definitely 5-0V with 5V being lean. So introducing an air leak will just make it leaner still.

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PostPosted: Sat Aug 27, 2016 9:40 am 
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Gilbertd wrote:
It won't. 95% of cars use the 0-1V Zirconia sensors where 0V equals lean and 1V equals rich so that is a generic statement relating to 95% of cars. Titania sensors read the other way round, 0-5V or 5-0V it makes no difference how they are described but they read high for weak and low for rich. The Universal replacement on the lambdasensors website is the same one as listed for my Range Rover which is most definitely 5-0V with 5V being lean. So introducing an air leak will just make it leaner still.


OK mate, thanks.


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PostPosted: Sat Aug 27, 2016 11:10 am 
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LPGC wrote:
Even if a pain, I'd be checking what the other probe is doing too.
Simon


So I did.

This one is more responsive fluctuating between 2V and 4.7V and slightly lower on LPG than petrol - maybe 0.2 - 0.4V lower.

Overrun = 4.7V, flooring it reduces the voltage, but never to zero. At idle after a run I was seeing 4.3V on LPG and introducing an air leak immediately increased it to 4.76V confirming that Gilbert is of course correct. Idling on petrol it's at 4.7V anyway.

Revving to 3000 at a standstill, I see about 4.3v too, I was expecting a lower figure.

So 1 dead and 1 half dead probe, or just 1 dead and something else preventing the other getting to zero?

I'm actually quite enjoying this even though it's a hot day and I'm leaning over a hot engine. I'm learning stuff thanks to you guys and that's always good.

Glen.


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PostPosted: Sat Aug 27, 2016 4:02 pm 
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it probably won't ever send 0v but would expect to go below 2v.

To test both probes you could introduce more gas to see if the probes read a rich mixture (low volts on basis of Gilbert's info).

When you're mentioning the readings under different conditions, are these constant readings? Lambda voltage should continuously flick if constant throttle (including idle) is maintained. It's doubtful but possible that with a failed component (maybe including one of the probes)the petrol ECU could ignore both probes (limp home / open loop mode). In that mode lambda won't flick as it should and voltages might be fairly constant, however since most lambdas (including your type) are only capable of reflecting a very narrow range of mixture, if mixture is very nearly correct one lambda might send a fairly constant extreme (of working range) signal while the other sends a fairly constant middle of range signal... If one lambda flicks and the other doesn't it's fairly clear that the none flicking probe is dead (provided there are no mechanical issues on the cylinders controlled by the none flicking probe), if neither probe flicks it isn't as clear cut.

Simon

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PostPosted: Sat Aug 27, 2016 9:34 pm 
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Just a thought here - are the two recessed cylinders (1 and 6 you mentioned i think) on the same branch of the exhaust as the sensor your looking at?


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PostPosted: Sat Aug 27, 2016 10:03 pm 
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I don't often Google stuff before commenting but found XJ6 firing order 153624.. Expecting every other number in firing order to be on same bank, I'd reckon 1, 3, 2 on same bank and 5,6,4 on the other.. or 123 on one bank and 456 on other. From memory now, I think that's how I remember the manifold design too.

Simon

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PostPosted: Sun Aug 28, 2016 7:59 am 
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LPGC wrote:
it probably won't ever send 0v but would expect to go below 2v.
Titania sensors on mine, when everything is working correctly, flip between about 0.2 and 4.8V, so you would expect them to go lower. The ECU is set to see 2.5V as the norm so anything either side of that will cause it to alter the fuel trims.

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PostPosted: Sun Aug 28, 2016 8:10 am 
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Bang on, 456 are on the bank where the lambda doesn't flick and 123 are on the one that does. So the answer to Brian's question is "no".

All of the inlet valves had recessed, but No1 and 6 to the point where it affected compression.

The 123 probe doesn't seem to flick as much as Simon is saying it should though. It is fairly constant at idle for example, maybe moving between 4.7 and 4.5V on petrol, slightly lower on gas.

Based on "If one lambda flicks and the other doesn't it's fairly clear that the none flicking probe is dead " I think the next step is to introduce more gas to see if the readings go down and if not, replace the 456 probe.

The MAF, coolant temperature sensor (not the dash gauge one) and crank position sensor were all replaced by the previous owner in a vain attempt to cure the misfire when the cause was in fact recessed valves. The MAF was second hand though.

A curve ball perhaps, but I did measure one tank of LPG before I replaced the head and it gave 19MPG - better than it does now. This. of course, was a one off reading so could be a red herring, but could I have damaged something? I have checked all wiring connections and inlet connections and all seems well.

Glen.


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PostPosted: Sun Aug 28, 2016 8:39 am 
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Sounds like a plan. I'd have a look once you replace at the other probe as you will have a known good one to compare to at that point.p


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PostPosted: Sun Aug 28, 2016 12:14 pm 
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Right

Butane test done using a canister from my portable camping stove with an aerosol button lashed to the top. I removed the air filter and squirted into the pipe leading to the MAF. The car didn't like it one bit, I had to keep the revs high to prevent it from cutting out.

456 probe (suspected as dead) stayed on 4.7V confirming suspicions
123 probe was flicking about a lot but seemed to rise in value slightly with butane poked at it when I was expecting it to fall.

Nothing is ever straight forward eh? Maybe the fact that the engine was trying to die each time had an effect.........

Off to a BBQ now, so no more from me until tomorrow. As always, I value your thoughts.

Glen.


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PostPosted: Sun Aug 28, 2016 5:18 pm 
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Wouldn't work with engine trying to die, can move pipe further away from air intake so engine gets less gas and won't try to die..

Simon

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PostPosted: Mon Aug 29, 2016 7:55 am 
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LPGC wrote:
Wouldn't work with engine trying to die, can move pipe further away from air intake so engine gets less gas and won't try to die..

Simon


Do you mean inject the butane closer to the inlet manifold?

I have a flash lube connection just engine side of the throttle body, whould that be a good spot?

Glen


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PostPosted: Mon Aug 29, 2016 8:06 am 
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The opposite - further away it is the more diluted it will be. Sounds like its going too rich hence it tries to die as not enough air left.you might find better control with an adjustable flow like a blowtorch or stove lighter. Just operate it without lighting it to allow a dribble of gas out


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PostPosted: Mon Aug 29, 2016 10:29 am 
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OK, can't get further away than the air cleaner box, so will try my blow torch.


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PostPosted: Mon Aug 29, 2016 4:08 pm 
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So, blow torch - (unlit!) into the airbox, engine now coping even with blow torch fully on and neither Lambda batted an eyelid.

Time to replace both I fear......


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PostPosted: Mon Aug 29, 2016 6:27 pm 
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Freebird wrote:
So, blow torch - (unlit!) into the airbox, engine now coping even with blow torch fully on and neither Lambda batted an eyelid.

Time to replace both I fear......


Certainly sounds that way, Glad to hear it was unlit too!


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