yo guys i was driving along the other day and gave her a little in 3rd, after a couple thousand revs she felt like she gave out and started to hold back and miss-fire a bit! also there was a major rattle coming from the backbox, when i looked inside there wass all the wirewool baffles and a massive piece of rusty metal which is too big to pull out!!
so i take her garage and they said the downpipe cat was gone. so i bought a new de-cat downpipe(closed neck) and got it fitted, now when im hitting around 5000 revs the car holds back and wont rev any further and when shes warmed up runs like an absolute pig at around 700 rpm just coughing and spluttering!! Even if i try accelerating hard she just holds back and splutters a bit so i have to ease the power on!

Do i need to reset the ECU or summin? i was thinking its similar to maybe a HT lead problem but it didnt happen untill my downpipe cat went.

cheers

 

What age car is it mate. Early classics get away without a re-map but later classics and especially newages get boost spikes which puts fuelling out and can blow engines. Get it looked at straight away.

 

Really? its a 96 on an N so pre-facelift. its got a Z4 ECU if thats any help?
cheers

 

oh yeah i have a boost gauge and it holds boost all the time, doesnt drop off a bit when the car is holding back

 

Same as mine then (mines a 1995 Z4). Shouldn't be a problem then. Sorry to panic you. The later ones det like hell with a de-cat and no re-map. Yours should deal with it ok. I ran a de-cat for a year with no problem. Have you checked your coil-packs? Sometimes the ends under the boot near the plugs start to break up. It may just be a bad luck that two things have happened at the same time.

 

cheers m8, yeah i did leave that bit out to see if any1 picked it up from the symptoms. but yeah my coil packs are on the way out i think, will change em and hopefully she'll be firing right again.
cheers

 

Have heard API are the best place to get coilpacks from. Have you upped the boost at all? When I did with a PP chip I had a stuttering / hesitating problem. Coilpacks were fine so moved onto plugs. Bought NGK PFR7B plugs and that sorted the problem out.

 

I may have missed some of the thread but if all that stuff as you say has come out of the backbox because of the old downpipe breaking up then surely there could still be rubbish blocking exhaust gases from escaping further down the system. Or worse, it could have damaged the internal baffling of the middle/backbox silencers so they would need cleaning out or changing as well?

 

I agree with cushti how would the cat get right down to the back box from the down pipe

 

Maybe a quick change of back box might help,if it is knackered and it certainly sounds like it,then this can restrict the gases coming out the exhaust like a choking effect.Have you got a standard backbox or an aftermarket 1?.

 

I was always led to believe this to be the other way round, the early ones needed mapping, later ones were ok until new age anyway. I suppose really they all should be mapped accordingly after de cat. Iv had my99 decatted for years with no remap only ever had one issue I thought was overboost turned out to be fuel starvation!

 

Newage ECU is very clever, it should always be remapped after decat downpipe is fitted.

Classic is not so bad.

But like you said, they all need a remap to run their best

 

I'd have a guess at it being the back box, I think the garage is talking rubbish, I've had this happen and it had similar symptoms and the car started to get hot. I'd get the backbox changed asap.

 

Wow cheers for all the suggestions every1. It has a HKS legal muffler but I do have a standard backbox so maybe I'll fit that but dunno if it's safe or good for her to be driven from Cambridge back 2 Essex to do it? I took her out earlier to see wots going on and it seems the warmer she gets the worse she starts to run! Is this summin u'd associate with coil packs or spark plugs etc? It's such a pain in the butt I only just got her back from gettin a new clutch and I've spent all my student loan haha. Does any1 have a number that works for Andy at special scoobys? I've got 2 but neither seem to work!