J4YPS Posted December 29, 2014 Posted December 29, 2014 Hi guys As above, I recently purchased and fitted my cat back cobra non res system. I turned the car on, sounded beautiful. I reset the ECU and the other bits but now the car is really overfueling and this is causing it to backfire a lot. It's also occasionally missing and I'm unsure where to start. The car goes just as well, sounds incredible but is using more fuel and it's really noticeable at low revs that it is over feeling as is pops a lot. Anyone come across this before or have any suggestions? Thanks. J4Y Quote
Pritchard Posted December 29, 2014 Posted December 29, 2014 When did you fit it... only you went past me on Saturday ( i think it was) when i was working on the drive and it sounded louder than just a pop charger the exhaust does pop with the Cobra. does it sound like this?: If you want to compare to mine matey let me know and i'll wander over. Quote
KyleR Posted December 30, 2014 Posted December 30, 2014 Popping and crackling from the exhaust is a symptom of running lean, i.e., higher air/fuel ratio, rather than running rich/over fueling. To be expected and perfectly acceptable when you change the exhaust 1 Quote
Richie94gts Posted December 30, 2014 Posted December 30, 2014 Ironically, I'm disappointed I'm in not popping and cracking on the overrun after i fitted a non res cobra! Not sure what I'm missing. I dont have the y-pipe, will that help me get a nice bit of popping and cracking? If so I'll happily swap my stock y-pipe! Quote
J4YPS Posted January 2, 2015 Author Posted January 2, 2015 (edited) It snap crackles and pops a lot lol. Sounds fantastic. Just weird how it decided to miss the other day, felt like it was running on 1 or 2 less cylinders upon acceleration, no codes have been thrown although the CEL did flicker once but never came on. Hmm. I've scanned it and got no codes. I have y-pipe centre pipe and back box. (cat back) The popping at low revs isn't normal. Edited January 2, 2015 by J4YPS Quote
Neilp Posted January 2, 2015 Posted January 2, 2015 Popping and crackling from the exhaust is a symptom of running lean, i.e., higher air/fuel ratio, rather than running rich/over fueling. To be expected and perfectly acceptable when you change the exhaust Thats not the case, what you're thinking about is something different. What your are talking about is det which destroys 350z engines. Overfuelling causes this, unburnt fuel hits the exhaust and basically catches fire in the exhaust. You can do this by retarding timing also. Quote
J4YPS Posted January 2, 2015 Author Posted January 2, 2015 I mean it drives like a dream, just that one occasion is was rough on acceleration. Do you know of any cures or anything I can do, I mean, surely UpRev isn't the only answer? Quote
StevoD Posted January 2, 2015 Posted January 2, 2015 The other answer is put it back to stock if your not happy You cant blame cobra for your ecu not liking it Quote
KyleR Posted January 2, 2015 Posted January 2, 2015 Popping and crackling from the exhaust is a symptom of running lean, i.e., higher air/fuel ratio, rather than running rich/over fueling. To be expected and perfectly acceptable when you change the exhaust Thats not the case, what you're thinking about is something different. What your are talking about is det which destroys 350z engines. Overfuelling causes this, unburnt fuel hits the exhaust and basically catches fire in the exhaust. You can do this by retarding timing also. No, I'm talking about the pops and cracks on the over run. Back firing is of course caused by over fueling, but I'm assuming the OP has used the incorrect term. Quote
Ekona Posted January 2, 2015 Posted January 2, 2015 Neil's right: When you close the throttle (i.e. the overrun) there is still fuel in the system. As there's no air being drawn in the engine cannot burn this, so it gets passed through the valves and ignites when it hits the very hot exhaust. It's running rich very briefly, not lean. The main time an OEM engine runs lean is on the part throttle cruise where it can get away with it for fuel consumption benefits, otherwise running rich is a MUCH safer place to be. Bore wash is less likely than pre-detonation. Quote
J4YPS Posted January 2, 2015 Author Posted January 2, 2015 Mine pops and crackles on the over run like the one on the video but maybe a little more! Quote
Neilp Posted January 2, 2015 Posted January 2, 2015 I understand what you're saying and he may not be using correct terminology however I doubt the car is detting from running lean. It will be over fuelling due to the ECU map adjusting to accommodate the new exhaust. My car over fuels on the nitrous and blows constant blue flames. Without nos it still bangs and flames from time to time. If the OP still has cats i'd say it's not normal and what he's referring to is just the exhaust choking when he lets off the juice and not an actual pop from fuel etc. the exhaust wil still be running in and getting "coked" up As with any modification to fuelling on exhausts a remap is always recommended to adjust the AFR's back within suitable parameters. Quote
J4YPS Posted January 2, 2015 Author Posted January 2, 2015 I understand what you're saying and he may not be using correct terminology however I doubt the car is detting from running lean. It will be over fuelling due to the ECU map adjusting to accommodate the new exhaust. My car over fuels on the nitrous and blows constant blue flames. Without nos it still bangs and flames from time to time. If the OP still has cats i'd say it's not normal and what he's referring to is just the exhaust choking when he lets off the juice and not an actual pop from fuel etc. the exhaust wil still be running in and getting "coked" up As with any modification to fuelling on exhausts a remap is always recommended to adjust the AFR's back within suitable parameters. Ok, I have stock cats, poor fuel consumption, power and everything is still there if not more so. Car will only pop, crackle off throttle. Based on what you are saying in the above comment, is this something to be worried about? The car is not my daily anymore. Quote
StevoD Posted January 2, 2015 Posted January 2, 2015 (edited) how many miles has the new exhuast done as my cobra popped and farted for the first 200-300 miles once it had the inside coated in carbon it was fine again Edited January 2, 2015 by StevoD Quote
J4YPS Posted January 2, 2015 Author Posted January 2, 2015 I'd say 100/150 miles. I'm hoping it will settle down. Quote
Neilp Posted January 3, 2015 Posted January 3, 2015 After the exhaust installation there's a good chance the car was running lean, the engine may be over fuelling to compensate. You really may have to go for a remap. Have you got an obd scanner so you can check your timing and AFR's? Quote
Pritchard Posted January 3, 2015 Posted January 3, 2015 Hey J4Y, just replied to your PM. sorry been out driving all night, playing Its probably nothing to worry about. All you've changed is a piece of pipe, after every mechanical moving part and electrical sensor. If there was a miss-fire, its going to be unrelated. Quote
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