ok its on my m3, but i still need help and you lot are a lot more hands on than most bmw owners. lol



its an e36 3.0 gt
basically i fitted a decat pipe and backbox to the car last year, and this year it has rough running problems, i think its down to fitting these but wonder what you think.

the car is ok most of the time but occasionally it misfires, to stop the miss you have to let off the throttle completley and then reapply, usually this makes it ok.

i have had it on scanners and it never shows a fault with any sensors,
1 of the o2 sensors is new,

i plugged it in today and drove it down the road with the scanner attached, when it played up i help the figures on the screen for all sensors and nothing was abnormal.
the only thing that did show up as strange was that its charging 15.5v at any revs inc. idle,

do you think this could be the problem???

the car is std except for the decat and backbox, and its got a smaller front crank pulley, meaning the alternator is spinning at a different speed to normal, but this was fitted long before the decat and it was ok back then.

ive changed the coils, plugs, afm, tps, checked everything and still no joy, but my m8 whos a mechanic thinks it could be the 15.5v thats doing it.


thanks in advance

 

they have an oxygen sensor for the cat, what have you done with this?

the last car i decated, (evo4) i welded a boos in the decat to take the temp sensor, so the cat still thought the cat was attatched.

 

Nothing to do with the charge rate at all.
The pulleys don't work either as the alternator decreases voltage/amps as and when needed, it can produce enough power even at slower speeds.
You really need first to see what the fuelling is doing when it misses, If it can be made to fault easy I would be tempted in light of what you have replaced to get it on the rollers hooked up and it should be very apparant then what is at fault.
I would have guessed the TPS or AFM to start with.
The ecu is capable of handling this voltage easy enough, although it sounds a bit high.
It might be acheaper in the long run to do the R/R rather than replace bits, unfortunately I am not familiar with the beemers.
tabetha

 

i think its down to the decat and backbox, luckily my dad has an m3 to and this is where im getting all the other bits from to try so it doesnt cost me any money.

the o2 sensors are both still conected and the decat is a proper one, not just a pipe welded in place, its a supersprint system with resonating boxes to sort out the back pressure.

i think its going to need a map on the rollers to sort out but im selling the car so might just put the std zorst back on.

 

any1 else?

 

my mates 318 had rough running, gave it a service and was still the same, tuned out to be a small split in a rubber hose causing it to suck more air than it should

most likely not the cause but got to be worth getting under and checking everything it tight and in good condition so you can rule it out and move on.