h4nsm0l3m4n Posted June 5, 2013 Share Posted June 5, 2013 (edited) I finally got my long tubes installed and had a shop weld up a full stainless exhaust. It all looks and sounds great but the car has seemed to develop a weird problem. Ever since installing the long tubes the car will stutter and lean pop. It only happens below 2000 rpm just at throttle tip in. Basically if youre cruising on the highway 55-70 mph and want to go a little bit faster the car will stumble. I've taken the car to a tuner and they have tried to tune it extensively both on MAF and speed density. We've also tried new o2 sensors. The problem is still there. The only time we can get it to go away is when we disconnect the o2 sensors entirely and dont allow it to go closed loop. I'm starting to run out of ideas as to what else to try. Is anyone else having any problems with their long tube headers? My best guess is that something is preventing the o2 sensors from getting accurate readings at low rpm, which can cause them to overcompensate and overly richen or lean out the car. At higher rpm this problem goes away. I've considered just tuning the car to run open loop but it seems like a poor solution, especially given the motor is completely stock. I've also wondered if switching to a more accurate wideband o2 sensor and using a simulated narrowband output will allow me to get more accurate afr readings to the ECU. Any one have any ideas? Edited June 5, 2013 by h4nsm0l3m4n Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted June 5, 2013 Share Posted June 5, 2013 SunnyZ mentioned a low rpm lean spot in his dyno tuning. He has long tubes. Maybe he can offer advice. Quote Link to comment Share on other sites More sharing options...
Domzs Posted June 6, 2013 Share Posted June 6, 2013 Location of your O2s , how far away from the collectors ? Quote Link to comment Share on other sites More sharing options...
SUNNY Z Posted June 6, 2013 Share Posted June 6, 2013 SunnyZ mentioned a low rpm lean spot in his dyno tuning. He has long tubes. Maybe he can offer advice. Thats just after the kit kicks in haha. 1000psi moves faster than 60 psi Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted June 6, 2013 Author Share Posted June 6, 2013 (edited) The o2 sensors are located right in the middle of the collector. This is drivers side, other side is similar Sorry the photo is so wierd, it was dark in there... Edited June 6, 2013 by h4nsm0l3m4n Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted June 6, 2013 Share Posted June 6, 2013 I'm studying your photo...Did you keep both O2 sensors for each side (the one before the catalytic converter, and the one behind it)? That's what it looks like... Since I have no converters, I had the rear set of O2 sensors removed from the wiring harness and from the tune. Could your computer be leaning it out because it thinks you are too rich on the downstream side of the (imaginary) catalytic converter? I'm not a tuning whiz - I'm just trying to help. Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted June 6, 2013 Author Share Posted June 6, 2013 (edited) I guess the picture isnt that great... My car has never had the rear o2 sensors, just the front ones. Edited June 6, 2013 by h4nsm0l3m4n Quote Link to comment Share on other sites More sharing options...
Zfan1 Posted June 6, 2013 Share Posted June 6, 2013 My friend had a similar issue with his LS1, he tried several fixes and it turned out his Mass air sensor was in need of cleaning. Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted June 6, 2013 Author Share Posted June 6, 2013 (edited) My friend had a similar issue with his LS1, he tried several fixes and it turned out his Mass air sensor was in need of cleaning. As part of this whole process my car was actually tuned to run on speed density alone. I believe this should ignore the MAF, so the dirtiness shouldnt be an issue. However, I will give this a try tonight just in case. I've been reading about LS1 o2 sensors and it seems like they arent all created equal. I know we tried putting new o2 sensors in the car before but I believe they were just stock replacement front o2s for the F-body. Some people have said that with long tubes you need to switch to Denso or Bosch corvette rear o2 sensors due to their higher sensitivity and higher wattage heating element. I may try switching to these in case it makes a difference... Edited June 6, 2013 by h4nsm0l3m4n Quote Link to comment Share on other sites More sharing options...
Domzs Posted June 6, 2013 Share Posted June 6, 2013 I'm studying your photo...Did you keep both O2 sensors for each side (the one before the catalytic converter, and the one behind it)? That's what it looks like... Since I have no converters, I had the rear set of O2 sensors removed from the wiring harness and from the tune. Could your computer be leaning it out because it thinks you are too rich on the downstream side of the (imaginary) catalytic converter? I'm not a tuning whiz - I'm just trying to help.Rear O2s only monitor CATs . Quote Link to comment Share on other sites More sharing options...
mattd428 Posted June 7, 2013 Share Posted June 7, 2013 Domz is right if the o2 sensors are too far back they will not read correctly. Try turning them off and using a speed density tune if that works theres your problem. Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted June 7, 2013 Author Share Posted June 7, 2013 (edited) Domz is right if the o2 sensors are too far back they will not read correctly. Try turning them off and using a speed density tune if that works theres your problem. I'm not sure how far back is too far back. If my o2 sensors were placed any closer they would be placed in the individual cylinder runners... I imagine thats not really desirable either. The car already is tuned on speed density and unplugging the o2s definitely cures the issue that I'm having. However, I really dont like the solution to just remove the o2s and run open loop all the time. Especially given that that the motor is completely stock... I tried the corvette rear o2s last night. No difference. My last attempt will be to install a wideband instead of one of the o2s and have it simulate a narrowband output for my ECU. If I dont get better o2 readings I'm not sure what else to do but force the car to run open loop. Edited June 7, 2013 by h4nsm0l3m4n Quote Link to comment Share on other sites More sharing options...
Domzs Posted June 7, 2013 Share Posted June 7, 2013 (edited) The O2 needs around 8" after the collector . Think you are too close . Any DTC ? Make sure you don't have any exh. leak upstream of O2s . Edited June 7, 2013 by Domzs Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted June 7, 2013 Author Share Posted June 7, 2013 The O2 needs around 8" after the collector . Think you are too close . Any DTC ? Make sure you don't have any exh. leak upstream of O2s . Right now that car has no DTCs. It was giving me the P0133 or P0153 (cant remember which) when I first had the exhaust made, before my tune. I'm not sure if the tuner disabled these codes or the sensors are working better but either way I'm not getting any more trouble codes Moving the sensor back 8" seems really far but I may be able to try it... I have a bung that is about 8-12" further down on one side of the exhaust that the tuner put in for their wideband. I will try putting one o2 sensor in the farther back position and comparing it to the closer positioned sensor on the opposite bank. Quote Link to comment Share on other sites More sharing options...
Domzs Posted June 7, 2013 Share Posted June 7, 2013 I would try the wideband location first to see if that bank is better before you relocate the O2s . It could be something else causes lean condition . Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted June 22, 2013 Author Share Posted June 22, 2013 (edited) Bit of a dissapointing update. We tried the wideband spot which was about 8 in farther back. It definitely cleaned up the narrowband waveform. Hoping for the best we moved the other bank's o2 sensor to similarly farther back position. Unfortunately there was no change. While the o2 sensor waveforms looks much smoother the car still exhibits the same symptoms. Some other observations: This problem is not load dependent - happens uphill, downhill, any gear always the same The problem is not throttle position dependent - it can happen at wot or minimal throttle the same The only thing that seems consistent is the rpm range that the problem occurs in - 1000-1800 Weve tried forever to fix it with the tune to the point that i have a hard time believing that this is a tuning issue.... but spark plugs? Wires? Coils? Injectors? Fuel pressure? It seems like if one of these was going wrong I'd feel it at high rpm too right? But the car runs awesome up top and only has issues 1000-18000 rpm so what the heck?? Edited June 22, 2013 by h4nsm0l3m4n Quote Link to comment Share on other sites More sharing options...
mattd428 Posted June 22, 2013 Share Posted June 22, 2013 (edited) vacuum leak? inconsistent fuel pressure? bad tuner maybe? no offence ive just seen a few "tuners" that couldnt tune a stock engine to save their life. Edited June 22, 2013 by mattd428 Quote Link to comment Share on other sites More sharing options...
casper9182 Posted June 23, 2013 Share Posted June 23, 2013 Sounds dumb but never hurt to check. Hows the voltage output at low rpm? Quote Link to comment Share on other sites More sharing options...
Domzs Posted June 23, 2013 Share Posted June 23, 2013 What's the O2 and longterm fuel trim reading at idle and 1k -1.8k rpm ? Quote Link to comment Share on other sites More sharing options...
ktm Posted June 23, 2013 Share Posted June 23, 2013 Go to ls1tech.com, search about lazy o2 sensors and headers and enjoy the reading. Quote Link to comment Share on other sites More sharing options...
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