power loss/misfire/petrol heamorage...

eyup, got a misfire and what seems to be a bigger fuel consumption than a RR Merlin...
Its a 3.9, switchedfrom lpg to petrol cos ran out of gas, ran fine for a mile mainly on over-run, put foot down, lost power, heater temp went up but not temp guage, oil pressure fine but gained a misfire and strong exhaust smell. Stopped; oil, water and fuel ok but got an intermitant mettalic rattle. think a CAT has broken up or poss a plug has shattered.
There looked to be a smoky haze from back as i pulled up. fuelled up on gas, running fair but with tinny rattle from LH bank.
Any Guesses?

could be the cat, I dont have them on mine so dont know the noise when they break but it sounds like your really over fueling on petrol so that could explain it if the lambda sensors are giving crazy reading and one bank is blocked off partially.

If you have been on gas for ages your efi could have been up the spout for a while and you only noticed it now your out of gas and have switched back

Cheers Fett, gonna try changing the plugs and try to take down pipes/cats off to see if theres loose in there.
Any idea what effect disconnecting lambda sensors would have when running on LPG? Its an open loop system.

nothing I dont think as its not using any of the efi system???? mind you I havent got gas so its just a guess.

When peeps on here have had cats collapse before they glow red hot with the gasses trying to get past the blockage somtimes , so give it a good run and have a look.

Eyup, that would probably be about reyt, got misfire, smoke and rattle at same time (as i shut it down, grabbed fire extinguisher and popped bonnet...)
The left Cat is black and jingles if you bang it. Running ok on lpg, changed plugs number 6 is a bit sooty but rest look fine. Shes a lot smoother for having new plugs in though.
Any idea if there is a cheap way of de-catting it short of open heart surgery on the cats?
Cheers.
Bushwwacker.

depends on the year, there have been a few debates on here but I would say if its 92 or earlier you can loose the cat altogether and fit a diferent tune select resistor in the loom after the ecu which is under the seat.

that means you dont have to fork out for new cats when they go this way. the rattle is good sign its fooked.

if your is 93 or newer its time for new cat I am afraid.

oh and to decat just buy non cat downpipes

bushwwacker said:

Any idea if there is a cheap way of de-catting it short of open heart surgery on the cats?
Cheers.
Bushwwacker.

Click to expand...

As far as I know the quickest way to de-cat is to change the tune select resistor and then disconnect the lambda sensors, trouble is you'll have difficulty passing the emission test at MOT time. I think you would also need to remove the cats completely if they are already breaking up. I'm pretty sure there are posts about this so try doing a search.

cheers Kev,
its a 96 disco running an open loop lpg system so the emissions test is a non-cat one anyway so im not too concerned about that. How would i determine the correct tune select resistor if i did de-cat it? done a search but as i dont know what it is or does i dont know what im looking for.

its to do with the colour, but I am not sure which you need. It might beige???

bushwwacker said:

cheers Kev,
its a 96 disco running an open loop lpg system so the emissions test is a non-cat one anyway so im not too concerned about that. How would i determine the correct tune select resistor if i did de-cat it? done a search but as i dont know what it is or does i dont know what im looking for.

Click to expand...

Try again!!

http://www.landyzone.co.uk/lz/f16/v8-ecu-help-59931.html?highlight=tune+select+resistor

Come again chief?
mechanicaly, ive got a fair knowledge but on electronice im in your hands!
am i after a small brown cylinder with different coloured bands round it the size of a tic-tac or summat different.
Sorry if this is a daft question but im after your advice.
Cheers

With regard to the resistor, I seem to remember this is listed as the tune select resistor, for EU and UK, non-cat you want the one with the green wire, 470 ohm.

Thanks Mad Hat Man,
it is as simple as that then!

bushwwacker said:

its a 96 disco running an open loop lpg system so the emissions test is a non-cat one anyway so im not too concerned about that.

Click to expand...

Are you sure about that?

Running dual fuel, both systems should be tested. LPG is a non cat test but on petrol, non cat test is for cars up to '92. Having said that, my '94 Disco, without cats used to pass the cat test with room to spare

On the earlier Q you asked, if you do have an open loop LPG system (manual 'power valve') then the lamda sensors don't have anything to do with the lpg side of things.

Cheers

Chris

Eyup Ragtag,
The Mot station ive used for past couple of years tests it on whichever fuel its presented on, any idea on the Tune Select Resistor question?

bushwwacker said:

Eyup Ragtag,
The Mot station ive used for past couple of years tests it on whichever fuel its presented on, any idea on the Tune Select Resistor question?

Click to expand...

Fair enough on the MOT. Last time I went to the place I have been going to for 20 years with my bobtail, I had to virtually prove I had disabled the petrol side cos the wanted to test both fuels. It wouldn't have mattered as its a '77 car.

On the Tune Select Resistor Q, I'm sorry I haven't a clue. I don't think my old Disco has one but I wouldn't know what to look for. There is a reason why I run SUs

Cheers

Chris

Got a 93 RR 3.9 efi in my 90 no cats and runs a green resistor.
Also check out BritishV8: the car magazine for enthusiasts of modified British sports cars an american site that has loads of usefull info on the 3.9. Really helped me out on a wireing problem

bushwwacker said:

Come again chief?
mechanicaly, ive got a fair knowledge but on electronice im in your hands!
am i after a small brown cylinder with different coloured bands round it the size of a tic-tac or summat different.
Sorry if this is a daft question but im after your advice.
Cheers

Click to expand...

Did you not look at the link I posted??

Also, if you do a search for TUNE SELECT RESISTOR you will get a number of threads where this is listed and they should pretty much give you all the info you need.