O2 Sensor Issue

[nickperth]

Hi i got a r34 gtt and my cars is having issues starting were itll start after 3-5 sec after turning the key and it has a rough idle like as it has cams in it.

This weekend im going to do a service on it were ill also do the plugs and fuel filter and clean the AAC valve, but i believe i got a bad o2 sensor.

The car has a tune on it i got the typical high mount with a gt3582 with the gate going straight to atmosphere and got a plazemaman plenum. I haven't had this issue till recently were its started to run rough and take a while to start. But when i checked my power fc i noticed that once the car was warmed up and after a drive the o2 sensor reading was at 0.02v and when i reved it to about 3000rpm it would only go up to 0.04v.

Ive got a photo of my data reading from the power fc, but does anyone know what else could cause my issues as i got no vacuum leaks or anything, but i am pretty certain it is the o2 sensor it self, as i dont believe it has been disabled. I was planning on just replacing the o2 sensor with just a genuine nissan o2 sensor.

Thanks,
Nick

[89CAL]

The stock o2 sensor is a narrowband sensor. This means it reads a narrow range, cant remember off the top of my head the exact figure. When the car is idling (which it is in your photo) then the o2 sensor is pretty much reading nothing, it is outside its designed operating range. The o2 sensor only really does anything at cruise. With the Power FC you can turn it off in your settings/etc menu (from memory), its o2 feedback you want to change. FWIW I had mine disabled permanently and tuned the car to the cruise AFR's I wanted

It will not be the cause of your starting issues. The o2 sensor does nothing during startup. If you don't believe me, turn o2 feedback off and you will see no difference.

The problem is probably with the tune of the car. Without a wideband o2 sensor and gauge, its not so easy to diagnose, and by the sounds of it you would be better off taking it back to your tuner if you are not happy with the way it starts. Most tuners will happily fix starting issues for free, however if its a cold start problem it is a bit harder becasue the car has to be cold before they can look at it, which means if you drive it to the tuner it has to sit there for a while

[nickperth]

Okay then, well i dont think hell remember me i got it tuned like 2 years ago and thought it could be something else other then the tune. But alright then ill see how it goes

Thanks,

[blind_elk]

Try getting the injectors cleaned.

[nickperth]

Hi guys id like to update, the o2 sensor is working fine i didnt check it properly at the time, however i believe after looking at my car i must have a vaccum leak somewhere as the car mainly idles rough,but will stall when i turn the ac on, it drives fine around and you know you can trash it but i think it might be under boosting as when i set it 20psi on the power fc it only boosts to 15psi.

However im not too concerned about it not boosting to enough pressure i am more interested in why its running rough and it stalling when the ac comes on. Ive noticed on the fuel pressure regulator it running at 28psi and under load about 36psi, i read somewhere that the fuel pressure is usually around 34psi im not to sure if its not been set. I did have a while ago a fuel smell and some hoses on the plenum side had to be changed im wondering maybe ive got a loose or broken hose on that side, thats causing the issue. Also possibly im thinking i might have a fuel sock blocked or fuel filter.

Could someone tell me what could be the causes off a rough idle that will smooth out when reved but it will stall on idle once the ac is turned on. Note that the car also has no bov but has been tuned without a bov, dont know if this could cause issues.

[89CAL]

The tune is poor at idle. There are settings in the Power FC to iron out some issues with the A/C on

Go to where your rev limit is and there are settings there for A/C. From memory there will be F/C (fuel cut) with A/C on and off (half of its in Japanese so can't remember which is which) and also Idle with A/C on and off.

Havent played with a Power FC for a little while but you can up your idle with the A/C on a bit and do the same with the fuel cut (which means it will disable fuel cut at whatever RPM you set). Playing with these may help your idle, and you can't really stuff anything up playing with these so I would play around with them first, you will just have to work out which is which.

If you struggle to get any kind of change in idle or the figures are maxed out, then the IACV may be wound in or out too far. You can adjust this and then try messing with the idle again.

Other than that you can use map tracer to see which cells the tune are jumping to when the AC is switched on and off. But without a wideband it is harder to work out what is happening.

Honestly, if it was me, I'd take it back to the tuner and say I wasn't happy with the idle and get him to fix it (should be done free of charge)