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PostPosted: Mon Dec 21, 2015 6:41 pm 
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evening people.

Having lowered the car this year and now after putting tiny winter tyres on it, my car now is about 3" above the ground and, as a result of such stupidity, has almost tore the oxygen sensor from the exhaust.

My question is, what will it mean if the sensor is removed? Does it effect the smooth running of the LPG system? Will it affect performance and/or mpg?

many thanks

Al


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PostPosted: Mon Dec 21, 2015 7:16 pm 
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Without knowing what LPG system you have, the answer will vary between probably to definitely. If you've got a lambda controlled single point then it will run very rich, if it runs at all. If you've got a multipoint, then it will be slaved off the petrol injection system so the petrol system will detect it is missing and go into a default, usually rich, fuel map. Depending on the car it may also put it into limp mode and bring on the MIL.

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PostPosted: Mon Dec 21, 2015 8:10 pm 
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Much as Gilbert said. Is this the pre or post cat probe? What car is it?

Simon

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PostPosted: Mon Dec 21, 2015 8:30 pm 
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Evening, thanks for taking an interest.

I have an 1985 4cyl 230e mercedes saloon with a multipoint ovml xxi-g code k901716 lpg system installed in 2005.

The car has just completed timing chain, head gasket, valves, radiator and exhaust replacements.

So, it will run, but be lumPY? Back fire? Loss of MPG & power? I guess the plan is then to put normal tyres back on, get the sensor repaired and after I replace the LPG filters, I'll get the LPG software checked over to steady things?

thanks again

Al


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PostPosted: Mon Dec 21, 2015 9:45 pm 
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It will run, shouldn't be lumpy but it will be down on power and thirsty. Your gas system slaves off the petrol system and simply adds a fiddle factor to the injector pulse duration to suit the different fuel. The petrol ECU has a pre-programmed map stored in it and adjusts the pulse length (to adjust the amount of fuel going in) depending on things like throttle position, intake air volume, engine load, temperature, etc. The lambda sensor checks that the combustion is complete and causes the petrol ECU to fine tune the pulse length. The petrol system is doing all of the fuelling calculations and adjustments, the LPG controller just modifies the pulse length for the LPG injectors.

Without a lambda sensor the petrol ECU will detect that it isn't there so will use a pre-programmed fail safe fuel map which will make it run rich (as rich running is far less likely to cause engine damage than running lean). So as the petrol system is running rich, it will make the LPG system run rich too. As LPG is less tolerant of an incorrect mixture, it will probably run better on petrol than on LPG.

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PostPosted: Tue Dec 22, 2015 12:34 am 
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I would suggest finding winter tyres with a higher aspect ratio to make the rolling radius the same as the summer tyres. Narrower tyres give better progress through snow but obviously if you reduce the width, you have to increase the aspect ratio to get the sidewall height back to where it should be. This link might help :

http://www.etyres.co.uk/how-to-change-your-tyre-size/

Scroll down on that page and you can put your summer tyre size in on the left hand part of the calculator and then play with the figures in the right hand part to get the nearest rolling radius for your winter tyres.

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PostPosted: Tue Dec 22, 2015 10:01 am 
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yeah cheers dave, I'm gonna do that.. put me summmer tyres back on and wait til it stops raining to hopefully repAIR the oxy sensor underneath.

I've bin talking with ebay seller 'lpg equipment' who's gonna sort me with filters ans software cable etc to tweak software post engine work. I'm sure I'll be back on here with ovml software questions...

thanks.


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PostPosted: Tue Dec 22, 2015 7:08 pm 
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Good luck with it - i'm not over familiar with the engine management on those Mercs (think they're Bosch/Motronic?) but you may need to reset it after to tell it that a new Lambda sensor has been fitted.

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PostPosted: Tue Dec 22, 2015 9:42 pm 
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if it helps, here's Benzos lpg setup :- http://carsinalbion.blogspot.co.uk/


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PostPosted: Fri Dec 25, 2015 11:34 am 
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Gilbertd wrote:
It will run, shouldn't be lumpy but it will be down on power and thirsty. Your gas system slaves off the petrol system and simply adds a fiddle factor to the injector pulse duration to suit the different fuel. The petrol ECU has a pre-programmed map stored in it and adjusts the pulse length (to adjust the amount of fuel going in) depending on things like throttle position, intake air volume, engine load, temperature, etc. The lambda sensor checks that the combustion is complete and causes the petrol ECU to fine tune the pulse length. The petrol system is doing all of the fuelling calculations and adjustments, the LPG controller just modifies the pulse length for the LPG injectors.

Without a lambda sensor the petrol ECU will detect that it isn't there so will use a pre-programmed fail safe fuel map which will make it run rich (as rich running is far less likely to cause engine damage than running lean). So as the petrol system is running rich, it will make the LPG system run rich too. As LPG is less tolerant of an incorrect mixture, it will probably run better on petrol than on LPG.


Sorry to threadjack but a quick Q. post cat O2 sensors on my BMW are for emissions control, if they are removed or fail only a light appears on the dash but the car would run fine, i 'believe' they play no part in fueling mixture. My failing pre cat O2 sensors certainly played a big part in some running issues i was having.

So my Q: On a BRC sequent system if a remove the cat, the cars post cat O2 sensors will trigger the dash light (not fussed about this).... but am I right in assuming there will be no impact on the LPG system?


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PostPosted: Sat Dec 26, 2015 12:45 am 
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oz striker wrote:
So my Q: On a BRC sequent system if a remove the cat, the cars post cat O2 sensors will trigger the dash light (not fussed about this).... but am I right in assuming there will be no impact on the LPG system?
The fuelling is controlled by the pre-cat sensors, the post cat sensors are only there as a check that the cats are doing their job so removal of the cat should have no affect to the running on LPG (or petrol for that matter). You may find that if the post cat sensors are left in place, the exhaust on LPG may even be clean enough that they won't flag a fault either. The only thing to bear in mind is that although you will still pass the emissions part of the MoT test without a cat, it is now an MoT requirement that if a car was originally fitted with cats they should still be there. Rather than removing them, gutting them is a better idea so they still appear to be there even though all you have is empty boxes.

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'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

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PostPosted: Sat Dec 26, 2015 1:28 am 
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I think cats should be removed when a vehicle reaches 20 years old and if it can still meet reasonable emissions criteria (regardless of fuel) then it should pass the MoT, on emissions at least. Line of thought here is despite the age, it has been well enough looked after to not present a danger from the emissions and besides, if the cat is still working, when running on petrol at least, maybe gas too, one of the by-products of the catalysation is H2S (Hydrogen Sulphide) which besides producing that characteristic "rotten egg smell" (Jeeeeez - i'd rather die of lead poisoning from petrol than suffer that smell!) is highly toxic and can in fact kill in sufficient doses. The governemnt doesn't bother telling us that though, i had to learn it managing a gas field to run generators from. Also a friend (sadly lost touch with him) who works for a very large oil company on the drilling rigs, informs me H2S can sometimes escape during drilling and this is enough to force evacuation of the entire oil (or gas) field they are operating until the H2S leak can be rendered safe.

Yet we are forced to produce it with catalytic converters??? It's the diesel thing all over again - in the early 80s they even had animated engines with green wings and halos flying round our tv screens to advertise the "green" credentials of diesel! Now they admit that diesel fumes are carcinogenic (something i've known many years) and not safe for us to inhale, even after going through a DPF on a modern diesel vehicle.

For the time being though, gutting cats is a brilliant idea. As soon as i've got mine converted, they will have either a genuine decat box (looks like the OE cat) or a gutted cat fitted. Bring on that 15% power and economy gain! Maybe not both at the same time though! :lol:

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PostPosted: Sat Dec 26, 2015 10:44 pm 
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Gilbertd wrote:
The only thing to bear in mind is that although you will still pass the emissions part of the MoT test without a cat, it is now an MoT requirement that if a car was originally fitted with cats they should still be there. Rather than removing them, gutting them is a better idea so they still appear to be there even though all you have is empty boxes.


The cat is only required to be fitted to cars which would need a full cat emissions test, if the car is presented running on lpg then it would not need a full cat emissions test so does not need a cat fitted.

See section 7.1.3 on page 157, 7.3.7 on page 162, also flow charts on pages 166-169 https://www.gov.uk/government/publicati ... 7-vehicles


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PostPosted: Sun Dec 27, 2015 12:05 am 
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..from the w123 pov I checked and it was apparently an optional extra in 1985.. Update and I've had the oxy sensor rewelded to the new downpipe and due it being lowered and the daft skinnny snow tyres fitted its snapped the sensor.. Pah, even at 2w8ish lpg mpg now at 50ppl I'm livin with Benzo. [reUpdate:- bought a £390 Punto as back up just in case]


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PostPosted: Sun Dec 27, 2015 1:05 am 
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mrLongstaff wrote:
..from the w123 pov I checked and it was apparently an optional extra in 1985.. Update and I've had the oxy sensor rewelded to the new downpipe and due it being lowered and the daft skinnny snow tyres fitted its snapped the sensor.. Pah, even at 2w8ish lpg mpg now at 50ppl I'm livin with Benzo. [reUpdate:- bought a £390 Punto as back up just in case]


Catalytic converters only became a legal requirement in 1992 (1st January i believe) so a 1985 Merc, Volvo, Rover, Saab, Vauxhall etc with a cat and a Lambda sensor is either an optional fit or a non-UK model from a country where it was mandatory in 1985 which weren't very many, certainly not RHD anyway. I think Japan was the only country at that time that drove on the correct side of the road and had cats as standard but i could well be wrong.

Have you thought about having a skid shield made up and fitted to protect your Lambda sensor? Might cost an extra few quid now but it should save future Lambda repair costs not to mention extra fuel used due to a "defective" Lambda.

As for the Punto - you wuz robbed! :wink: :lol: Joking aside, they're not bad little cars, just hope it doesn't need any repairs else you could find it's a money pit and a drain on your Merc funds. Many moons ago i bought a Clio 1.2 as a "back up/runabout" to save the miles on my 2.7 Rover. Firstly the insurance was about 3 times as much for the Clio, second it did no better on fuel than the Rover (unless i wanted to pootle about at 45mph all day), third it broke down every day - sometimes a free/cheap fix like the wiper fuses but others not, fourth it was incredibly uncomfortable even allowing for the fact it wasn't meant to be as comfy as the leather clad Rover and aside from a list of other criticisms i sold it in the end a few weeks later! In short it was a false economy!

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