Member Since: 07 Sep 2012
Location: Gateshead UK
Posts: 248
Decat pros and cons
Hi guys, just got tigger back from the garage as it had been in due to rough idling, after it was in for a day and a half with real time checks done on it at Team Valley Land Rover (Btw great guys did all these checks and didn't charge me as they hadn't cured it) anyway they said that the Cats were rattling and breaking up inside giving the Lambda sensors false info which in turn was sending false info to engine causing the rough idle. They first suggested new Cats but at around £1500 I said no and then they suggested getting it decatted elsewhere, just wondering whats peoples thoughts on the decat and having the engine remapped to take out the rear lambda sensors, oh and the car runs on LPGG4 D3 4.4 V8, "tigger" all year round toy
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1st Nov 2014 5:39 pm
robbo770
Member Since: 29 Jan 2013
Location: Aberdeenshire
Posts: 2294
Petrols love decatting but yes new map will be required to prevent yellow management light so fact that in and find someone who guarrentees the map.
Your pick up and acceleration will be better. But fuel economy may suffer with no back pressure as the engine will start breathing faster so gulps more FFRR SC 4.2
Member Since: 07 Sep 2012
Location: Gateshead UK
Posts: 248
cheers Robbo, what do you mean backpressure and how will it drink more, cant afford more fuel it only does 14 to gallon now G4 D3 4.4 V8, "tigger" all year round toy
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1st Nov 2014 6:04 pm
robbo770
Member Since: 29 Jan 2013
Location: Aberdeenshire
Posts: 2294
The cats on a petrol screen nasty fumes, but at the same time cause exhaust back pressure in the 4 stroke engine cycle. 1'of the cycles the cylinder doesn't burnt but the exhaust Cycle valves open and exhaust fume pressure helps push the Pistons back down on the bores.
Therefore if the engine can dump all exhaust pressure because the cats are gone it gains but losses.
The gains are. Heat removed faster from engine
Faster rotation acceleration
Nicer exhaust note
Remap to rise fuel pressure as about 15 bhp will have been gained on V8
The loss is the back pressure
So the mass air meter sees more flow so ramps up the rate of fuel
Need one weight less on the boots size in your feet
Member Since: 07 Sep 2012
Location: Gateshead UK
Posts: 248
Cheers again Robbo, I like the "takes off when done " part, and I could possible not press as hard well when family are in G4 D3 4.4 V8, "tigger" all year round toy
Evoque 2.2 SD4
AC Cobra 4.6 V8 seasonal weekend toy
1st Nov 2014 7:05 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
MOT fail if cat is removed from a petrol, ok for LPG but some testers are rejecting vehicle if originally fitted with a cat.Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 07 Sep 2012
Location: Gateshead UK
Posts: 248
But running on LPG it runs lean and emissions are low and our MOT station only does test on mine whilst on LPG so hopefully will passG4 D3 4.4 V8, "tigger" all year round toy
Evoque 2.2 SD4
AC Cobra 4.6 V8 seasonal weekend toy
1st Nov 2014 7:19 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
I think the phrase is 'as presented' when it comes to the fuel for the MoT; so if running on LPG when presented to the tester then that is what will be used. Some LPG conversions fail when the PEF is applied but some testers fail to do the maths and incorrectly pass vehicles that should fail. Some EGAs have a button to the PEF for them so that the ppm figure is correct.
It would be good to hear the experience of others regarding the probability of an LPG pass with no cat before you do the decat.Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
Has the cat failure been attributed to the dreaded valve seat recession?
Given the price of LPG these days and the problems with the valves I really do wonder if it is worth the effort.Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
My indie tells me that he has had a plague of VSR 4.4s, with failed cats being one of the symptoms.Land Rover - Turning Drivers into Mechanics Since 1948
Member Since: 03 Oct 2014
Location: Pwllheli
Posts: 3976
Disco_Mikey wrote:
The 4.4 doesn't seem to suffer from VSR, whereas the 4.2 SC engine does (when running on gas)
My 4.4 had new heads fitted because of this problem just before I brought it, after just over 80,000 miles. And I think it still has related problems as I am getting random injector malfunctions coupled with cat issues & O2 sensor fault coded (check engine light comes on) Think the cat may be less than perfect dues to past misfires.
Prins suggest that the heads on this engine will only last 60,000 miles on LPG I have been advised Valve lub will increase the life somewhat but not indefinitely.==================================
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4th Nov 2014 11:40 pm
rookhope
Member Since: 07 Sep 2012
Location: Gateshead UK
Posts: 248
Was wondering when the cats are removed and the ecu remapped could you not just remap the lamda sensors out of the system without removing the catsG4 D3 4.4 V8, "tigger" all year round toy
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it only does 14 to gallon now 
part, and I could possible not press as hard 
well when family are in 
