Toby85 Posted May 20, 2014 Share Posted May 20, 2014 Evening All, I have been having a hugely frustrating problem with my Z for some time now and have been trying to resolve it when i can in between family / house purchase / work etc. I posted on here about it quite a while ago and got a lot of help which i have been working my way through but am back for more! What i'm getting is a car that sometimes appears to run fine, without fault, but other times the exhaust note changes and my MIL lamp starts blinking/comes on solid. It doesnt misfire (pulling each coil pack makes an obvious difference), but i am getting the code P0300 and occasionally P0420. The exhaust sometimes sounds normal but can become quieter, almost silent above about 1750rpm, and other times become much bassier - sounds as if some cylinders (potentially one bank) is firing differently, maybe cam or ignition timing? If i put my foot down when the exhaust sounds like this it bogs down and splutters. Other things i've noticed are that the rev counter bounces/jumps (never moves smoothly, always in pulses) and also when i dip the clutch, the revs drop too far momentarily before they jump back up to around 1200rpm and slowly settle back to idle. Does this reliably regardless of situation but never stalls. Throttle response also seems needlessly aggressive/snatchy on very light throttle openings from coasting. I've tried injectors, coil packs, spark plugs, cleaned throttle body, cleaned cam and crank position sensors, cleaned MAF, cleaned every electrical connection and earth in sight, tried an extra earth, compression tested all cylinders and monitored live parameters whilst driving (comparing between when it runs ok and when it isnt running right) - nothing seems to change. Things i haven't tried but suspect - IPDM, CPS, Lambda/s. I did look at the iPDM and it looked ok aside from some corrosion on one relay (ignition). I swapped this with another relay - nothing changed. Car is standard, HIGH miles (in excess of 200k), has good compression (over 165lb on all cylinders) and is always quick and reliable to start. Economy seems unaffected and part throttle, even when misbehaving, is fine despite the change in exhaust tone. Remains totally driveable and reliable returning over 30mpg when driven carefully on the work commute. Sorry for the long post - but - HELP!! It does my head in! I'm in the midlands so if anyone local has a stock of spares or an unused car they dont mind me trying parts from i'd appreciate it hugely! Thanks in advance, Toby Quote Link to comment Share on other sites More sharing options...
Toon Chris Posted May 20, 2014 Share Posted May 20, 2014 I'll be the first to mention it then - collapsed CAT? They can crumble and move around and block the exhaust. Whip the exhaust off and shine a torch up it's fundamentals and see if you spot anything odd. Not at all connected but I do happen to have some spares. I was going to put them in the for sale but haven't got around to it yet. Quote Link to comment Share on other sites More sharing options...
Toby85 Posted May 22, 2014 Author Share Posted May 22, 2014 Thanks for the response. I'm not convinced about the cat but I will, when I have time, have a look. The exhaust won't come apart without a fight I know that! Where abouts are you based? Thanks again Quote Link to comment Share on other sites More sharing options...
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