Classic misfire/hesitation my99
 

At title says really, car has done 80k and had a recent service also fitted 4 ngk platinum plugs today, car had misfire previous to this too, Its not a bad missfire it only misses or pops once then clears, nearly always happens around 5000 rpm and more noticeable in 2nd and 3rd gears, car seems to drive fine too, if you keep a constant throttle postion the missfire doesnt happen, seems to happpen when you apply more throttle around 4000 - 5000 rpm, ie you can drive the car so it doesnt missfire its just when you squezze the power in at them revs it holds back you hear a pop then its fine again??car is virtually standard its just had the centre cat taken out and thats it?? any sugesstions very gratefuly recieved!!
Cheers

Anyne got any ideas what to try?

This sounds similar to a problem I had, I replaced the MAF sensor which done the trick, the car was a MY00.

Cool, was yours missin/hesitating at the same point in every gear mate? Mine is at 5000 rm every time?

Just been out again and reset the ecu, come back with no faults and stil misfiring, does it at exactly 5000rpm in 2nd and 3rd gear cant feel it in 4th. Very strange,any help with what to do next would be great!

Sounds like it could be fuel cut, you say you can drive round it, so does it 'always' happen with larger throttle inputs..?? but if you accelerate 'slowly' it's ok..???

I can drive it flat out with no problem right through the revs, its if your at say 4600 rpm with part throttle in, then apply full throttle progresivley it gives a hesitation or a mis for about half a second or so and a pop can be heard from the exhaust, it always pops at 5000 rpm, you can load it up at 4200 with full throttle and its fine?Steve

Mmm, odd one that then..... doesn;t sound like fuel cut in that case...... i'll think about it some more!!

Yeah its odd like, its more annoying and im worried about damaging car, its hard to explain aswell without you experiancing it. Cheers

Bump


I've been out in the car this evening, the problem is very specific and prominent at 5000rpm. The car has provided no error codes from the Black Plug diags. The boost solenoid sounds regular and healthy from the Green Plug diag. The problem is still apparent from an Black/Green Plug ECU reset.

This really has me puzzled - as Steve says when taken from 4000rpm'ish or above to 5000rpm with progressively applied throttle there is a definite yet faint 'miss' at the very same point near-enough every time the car is accelerated in this way. I don't think this is the result of ignition hardware or MAF failure as at all other loads/speeds/WOT to redline the car is absolutely perfect. The problem does not manifest itself anywhere else at other loads/speeds.

The only mod to the car is one cat which has been deleted - the problem was present before the de-cat however. The problem is definitely not fuel cut. Without a boost gauge it's difficult to ascertain exactly what's going on with the inlet manifold however it almost feels like the boost solenoid is being instructed to slow down at this point, increasing pressure on the wastegate actuator and dropping out the boost for a fraction of a second.

Any input/pointers massively appreciated - the MAF sensor suggestion is the closest so far. Are these checked as part of the Black Plug diag? If so are they known to report as 'OK' even when proven faulty?

SJ

edit to add:
The problem does not manifest itself in first gear - I suspect the loadings are too low. It is prominent in second and third - it may be present in fourth and fifth however the speeds involved at these RPM ranges are too high to be tested responsibly.

Ok so my plot thickens, chabged the leads yet again to no success. iIdid however notice that the car would still misfire if you loaded it up in the same was as described without driving it? So when more revs aplied near 5000 rpm still gives a missfire. Spoke to Steve Cotton at Cotcomp(big thanks to Steve for his help) who has sugessted to clean the cam and crank sensors? Ill do that tommorow and keep you all posted with it, as usual any more advice and comments would be great!!

I would try changing the plugs back to the standard NGK PFR6b's, i have heard about standard cars that have issues running 7b's (if thats what you have put in there)
If nothing else it will rule out dodgy plugs (they do exist, i know from experience!)

OK i think they are the plugs you mentioned, they were replacment plugs from the local motor factors, they were boxed as ngk platinum plugs, same as what were allready in it. Ill double check the make tommorow!! Jus really confused with it all!!

any news?

Plugs were the ones you said, also cleaned cam and crank sensors.Still no luck!!!