o2 voltage? stumbling

**sl0z28** · 12-11-2011, 06:23 AM

Hi, ive been having a problem with my car stumbling, richening/leaning quickly. Somes times while cruising it cuts out, loses power and wideband leans most of the time but sometimes will go way rich fluctuating quickly. Does this at wot as well as pt at times. Also Its not a constant issue just happens every now and then but atleast a few times during a trip. i noticed most of the time on cold start it says around where it needs to be 14.7-15.0 but has sometimes done it then as well. Also what controls the Iac as i think that may be sticking open causing a high idle at times untill i come to a complete stop for a minute or turn off for a second then it will come down. I dont think its tune related because it will run perfect at times. Ive changed tps, iac and cleaned maf. I dont notice anything jumping around on the little handheld scanner tho maybe its just slow tho the tps will 0 .4 0 .4 but dont think thats the issue. With the maf unplugged it idles but will not drive ( stumbling,cutting out gets worse). Its a turbo car tuned for a maf so maybe thats why it wont drive without it? ANyway on to my question for making the thread, o2s11 usualls reads around .600-.900 while o2s21 will stays between .05-.300 and sometimes flashes up to .600 or so. would that be bank 2 lean? could this cause the issues im having with the car losing power for a second and cutting out while accelarating and sometimes cruising? ALso will do it wot leaning me way from o2s, it doesnt really do it much at idle but more so under load. could it be an injector or something else?

**0rion** · 12-11-2011, 06:32 AM

have you pulled plugs and looked at them? I'm kinda having a tough time grasping exactly what your car is doing. Is it cutting out like a miss that lasts for a few seconds? What do your fuel trims look like? Also, the first thing I would do is check everything over to make sure you don't have a vac. or exhaust leak. Everything nice and sealed on your turbo piping? Front or rear turbo?

**pajeff02** · 12-11-2011, 06:37 AM

^^ This. Narrowband O2 sensor data is damn near useless -- you really need a wideband to see what is going on. I think that stoich is around 450 mV from what I remember reading. The data stream from the front sensors should rapidly cycle up and down if they are functioning properly.

**sl0z28** · 12-11-2011, 07:43 AM

im going off my aem wideband. o2 volts im referring to is off scanner. It looks like it just goes lean as the wideband will peg out when it cuts out but maybe thats unburned air? Other times when its not really cutting out but bogging the wideband will go 10.1. Im pretty sure its reading correct since the car runs right sometimes when the af is good. this is at part throttle and wot. Usually doesnt start till after its warm.

**sl0z28** · 12-11-2011, 07:45 AM

oh also pulled plugs last weekend and they just looked a little hot/lean. going to swap autolite 103s today if it warms up a little

**sl0z28** · 12-11-2011, 07:57 AM

front mount, boost gauge shows no vac leaks at the intake and still builds boost. one tiny exhaust leak i need to fix on the right side. It doesnt seem like one cylinder but all. Never dies just drops 400 or so rpms for a second sometimes idling and. Its not a constant issue but a few times a trip or sometimes the whole time ha. Im going off my aem wideband. Reads good af when the cars running right. Other times its fluctuating rapidly when the cars cutting out. SOmetimes 10.1 wot other times 15.1 wot or jumping and sometimes good af. maybe bad inj or maf?

**pajeff02** · 12-11-2011, 12:16 PM

Have you changed your fuel filter lately? Do you run a fuel pressure gauge?

If the exhaust leak is before the O2 sender, that could be an issue as it might result in a false lean condition being read by the PCM. Sounds like you might just have an engine sensor on its way out -- do you have a scanner?

**0rion** · 12-11-2011, 02:01 PM

like jeff said....I would probably look at that fuel pressure to make sure it's not dropping. Did you upgrade the fuel system and how much boost are you running? It sounds like it's doing it at cruising speed from your description so boost is probably not factoring into your issue. It's the same as trouble shooting any other engine though....check your fuel pressure, spark, vac. leaks, exhaust leaks, and things like that first. I take it you don't have access to a data logger to look at your fuel trims and things like that?

**sl0z28** · 12-12-2011, 12:54 AM

i dont have a logger just a handheld scanner to show me a few little things, nothing jumps around but maybe the scanner doesnt pick it up quick enough. It happens sometimes steady cruise, accelerating or wot. Usually when i first start the car it runs good and af is right where it should be 14.8 or so. The car doesnt even drive without the maf so im leaning away from it but maybe its dirty. Will happen at wot as well so im leaning away from o2s as well since it doesnt use them wot? The wideband will lean out when it cuts out so does seem like a fuel issue but fp is new. will check fp while cruising around to see what it does.

**pajeff02** · 12-12-2011, 03:44 AM

On cold startup, the PCM does not accept sensor data from the O2 senders, it runs off tables to adjust fueling. Once the engine temp warms up to a certain temp, the PCM switches over from open loop to closed loop and then utilizes the feedback from the O2 senders to adjust fueling. Can you see your fuel trims (short term - STFT and long term - LTFT)?

**sl0z28** · 12-13-2011, 05:16 AM

the scanner shows zero for ft tho not sure if it picks it up. would a bad map cause these issues? hesitation, high idle? car was running like it had a vacuum leak earlier reved up to like 2-3k on its own like on cruise control lol. DOesnt show a leak on the gauge but it shows the maf pulling that much air even when i would brake it down to 1krpm. I disconnected the map and the car seems to run better. real rich wot 11.1 but didnt notice any hesitation or a/f fluctuating like it has been. Going to drive with it disconnected a couple days see if it makes the difference.