misfire catalyst problem p38 4.6

hi guys
ive got abit of a problem couple of weeks ago i dicovered my cat had a leak (one of the welds had cracked) not wanting to take it off then take it to get rewelded i found a used stainless steel one on ebay for £45 so without hesitation i bought it.
its now been fited for a week or two and ive just developed a misfire/poor idleing (realy lumpy)and a massive loss of power, plus when i rev it its spiting bits of the catalyst out of the exaust.
i know the cat is f#@ked now but im reluctant to put my old one back on (ive had it rewelded) because i dont know if the stainless one was knakered when i bought it and thats whats causeing the missfire or i have a problem with the engine and thats whats done the cat in
any help or advice on how to diagnos the culprit is greatly appreciated

ps; someone told me if i take the cat off then knock all the material out of it then put it back on. then if the miss is still there its the engine.
but somone else told me that would cause it to run like crap anyway.

The cat is after all the electronics if its a gems setup so would suspect an engine issue. If its a thor setup then it may have an 02 sensor after the cat, so could be a problem. Need to know what type you have.

Uk spec Thors only have a pre cat O2 sensors. My money is on the cat you bought was shagged that's why it was on eBay and you have been ripped off. A blocked cat will give all the symptoms you have. My suggestion is to reset your fuelling adaptions as these will have been upset by the blocked cat, and then refit your old one. Better still buy a new pair. Sometimes you have to accept these cars are not cheap to look after and buying used parts can be a false economy.

sorry guys its a 1996 so would that be gems ?
also ive just looked at the old cat and it has no honeycomb inside the right side but it has in the left
ive only had the car 6 months so i dont know if this is because it has burnt up by the engine or it was knocked out by the previous owner.(cant think why unless this isnt a new problem)
it has always ideled abit rough but i put that down to its age but its alot worse now.

update
ive just checked all the plugs and leads and they seem to be sparking as they should and in fair to good condtion with a light dusty brown covering
could this be the early signs of the head gasket? as the cooling system seems to have abit of pressure in it even when cold
also anyone know what rpm it should idel at? its ideling at about 700-800 in neutral but around 500/600 when in gear

it is starting to sound like your maf is gone..

:frusty:
ok took the cats off again today and the right hand side cat is starting to break up with signs of it overheating (clumps of molton catalyst falling out of it)
so it appers the right hand bank is faulting
would the maf that j the range mentioned couse this on just one side?
ive put the old cat back on with NO catalyst in the right side and it runs alot better but still not great.
so as im not experianced with these engines im asking whats the common place to start ?
the plugs look ok as do the leads
im thinking timing/ecu ,faulty valve or the head gasket anyone got any better ideas cos its got its mot in 3 weeks and theres no chance it'll pass the emisions test
is there anyone in the leeds area that could take a look for me?

Gems have pre cat o2 sensors, I have a Gems and have had the cats removed, if the sensors are fekd it will make it run poorly. It may pass the emmissions test, but I would get the faults read if any, and pay attention to the o2 sensor readings, these will affect your emmisions and how smoothly the engine is running. What about cutting the cats out of the stainless ones you got from ebay or sending them back. The maf sensor would not effect one bank only. Also either take both cats out or have both in, not either / or.

as jonny said maf will do both sides, but its not just the cats. did you not say it is missing and loss of power, you need to get a print out of you codes, to find out what is happening when its running..

jonny427 said:

Gems have pre cat o2 sensors, I have a Gems and have had the cats removed, if the sensors are fekd it will make it run poorly. It may pass the emmissions test, but I would get the faults read if any, and pay attention to the o2 sensor readings, these will affect your emmisions and how smoothly the engine is running. What about cutting the cats out of the stainless ones you got from ebay or sending them back. The maf sensor would not effect one bank only. Also either take both cats out or have both in, not either / or.

Click to expand...

would it not fail the mot just for not haveing the cats fitted?
also where can i get a print out of the sensor redings or is it just a stealer that does that?

anybody with test book or the likes, could do a print out. you need live data reading, look for a good indy local to you, to find out whats going on. befor you start thowing any money at it..

Pretty sure it will fail the emissions test if you just remove the cats (unless you're running on lpg).

Mine had it's MOT on Friday and he had real trouble with the emisions until he realised how to get the lpg system running. I suspect both of my cats have had the contents knocked out. On petrol it was WAY higher than allowed.

I think you need to fix the running problem before you replace the cats or you run the risk of ruining the new ones.

Guy

agreed i think the stainless cats were ok when i bought them and its took little over a week to distroy one of them
so im gona have a good snoop around see if i can find a good mechanic and test the sensors before i do anything else
i still have two good cats (even though there on differant exausts) so once the problems found im gona see my mate see if he can cut and reweld them to make one good one.
im still gone check back heer regualy so if anyone thinks of anything else that might help i would be greatfull
and thankyou to everyone so far for there sugestions and help

update
it still has an intermitant problem somtimes it runs fine, somtimes not so
seams its worse when warm. not just running temp but after about 15-30 mins of driving.
it passed the mot. but only just failed the sniff test twice passed the third the guy said it seams abit rich.
ive had someone with test book look at it and when he came it was running fine so he coudnt find anything! cost me £50 to tell me that.

HI THERE. was wondering if yu got to the bottom of the fault. my 4.0 he has a similar fault, was running great but had a new s,s downpipes fitted to get it through mot , 600mls later was losing power then coughing and spluttering when warm, after an almighty backfire wont rev above 1500 rpm before going haywire, had it at barttec in airdrie , . ignition , maf , comp tests ect all show engine ok although fueling fault on left bank , lee said possibly the cat has melted causing back up into the plenum , old cats were empty , was also told to mot as a dual purpose vehicle and avoid the emmisions test . cheers......rab..

i was having simular issues with my p38 4.6 tirned out the leads to the coil pack were coroded and arcing causing it to misfire and dump excess petrol into the cats thus destroying them. 2 coil packs later i found the problem and traced the wires to under the air intake that lead in to the coil pack. try checking from there lads.

I wouldent mind betting you have disturbed or damaged a lambda while doing the cat work, they dont take too well to being disturbed, best thing to do is get it on a eobd scanner to check whats working and whats not...Gems Air flow meters are more reliable than thor ones I believe...

hi guys yes i did sort it
turned out it was the coil pack that was f"@Ked had an intermiten fault that only occured whan the engine bay got hot (loose connector inside?) causing it to not give a full current spark and that was causeing it to dump unburnt fuel onto the cat which eventualy melted it.got a used one on flebay £30 and well feck me it fixed it.
after that i got my mate to cut and shut the two cats together to make one good one and all seems good now! well except for a small leak on the exhaust manifold that i havent got round to fixing yet.

P38_Ireland said:

i was having simular issues with my p38 4.6 tirned out the leads to the coil pack were coroded and arcing causing it to misfire and dump excess petrol into the cats thus destroying them. 2 coil packs later i found the problem and traced the wires to under the air intake that lead in to the coil pack. try checking from there lads.

Click to expand...

gfromleeds said:

hi guys yes i did sort it
turned out it was the coil pack that was f"@Ked had an intermiten fault that only occured whan the engine bay got hot (loose connector inside?) causing it to not give a full current spark and that was causeing it to dump unburnt fuel onto the cat which eventualy melted it.got a used one on flebay £30 and well feck me it fixed it.
after that i got my mate to cut and shut the two cats together to make one good one and all seems good now! well except for a small leak on the exhaust manifold that i havent got round to fixing yet.

Click to expand...

wow i was actually right!! lol good man, glad it was a cheap enough fix. mine was worlds apart in performance when it changed them round.