Wolf Posted January 4, 2006 Share Posted January 4, 2006 I seem to have developed a stutter or misfire at high speed - the wierd thing is it is only speed related not occuring when on full revs or full boost at lower speeds - basically when I get to around 145 it gets a hesitant and then by 155 its really noticable but will pull through and keep boosting, reving and accelerating right through to top speed (about 195) Running a single with the following spec Iridium IK24 plugs Full Boostlogic T61 kit FSE Fuel pressure regulator 650cc injectors Walbro fuel pump with 12v conversion HKS GT 50 Wastgate - Part of BL kit BL heat blanket for turbo. Full Blitz Nur Spec exhaust De-catted Apexi SAFC-2 Apexi AVC-R It just makes no sense to me that it only comes in at speed rather than rev or boost related and has just developed from nowhere - any ideas where to look?? Quote Link to comment Share on other sites More sharing options...
Alex Posted January 4, 2006 Share Posted January 4, 2006 Auto isn't it?? Just wondering if it could be the autobox and ecu retarding things at a certain point?? What RPM's do you hit 145-155? Quote Link to comment Share on other sites More sharing options...
Wolf Posted January 6, 2006 Author Share Posted January 6, 2006 I am at around 5000 rpm at this speed and I noticed last night the AF ratio gauge goes off the scale - below 11:1 - could it be it's stumbling a bit being too rich under load at that point?? Quote Link to comment Share on other sites More sharing options...
Alex Posted January 6, 2006 Share Posted January 6, 2006 Things get richer from 4-5000 rpm and then tail off again...I'd have the S-AFC setup to run 4500-5500 slightly leaner than >5600 or Quote Link to comment Share on other sites More sharing options...
Ian C Posted January 6, 2006 Share Posted January 6, 2006 Aha that extra bit of info helps, Mr Wolf You've probably got, as Alex says and your AFR gauge confirms, a rather rich spot in the map. It's probably borderline power-sapping, so in the lower gears you a) get through that spot faster and b) don't have as much load on the engine so it isn't quite rich enough to make a noticeable hesitation. Once you are in the high gears though, you sit in that zone long enough to go so rich it misses spark events. Dial out about 10% airflow in that area and see if that fixes it. -Ian Quote Link to comment Share on other sites More sharing options...
keron Posted January 6, 2006 Share Posted January 6, 2006 i had a similar problem on my old skyline....the problem turned out to be incorrect gapping on the spark plugs...so its worth having them set properly perhaps? Quote Link to comment Share on other sites More sharing options...
Ian C Posted January 6, 2006 Share Posted January 6, 2006 If it was a misfire when on full boost I'd agree, that or coil packs. But this is at a revs point in higher gears, not necessarily on boost (or at least, at low boost) -Ian Quote Link to comment Share on other sites More sharing options...
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