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Old 12-17-2014, 06:12 PM   #1
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o2 sensor voltage...

So i have a 1998 black top sr20 and have read that the FAT o2 sensors should have a fluctuating voltage at idle, but for some reason mine isn't doing so.

On nissan data scan, it shows that the voltage gets stuck at .86 volts.... Weird thing though, is that sometimes the A/F ratio (on data scan) shows lean... even when its at .86, which is rich... My wideband always shows 13.3 at idle, so i know its not actually lean.


I replaced the o2 sensor thinking it was bad, but still does the same thing.

It fluctuates during cruising and my afrs stay between 14-15.2.

Also if i barely tap the gas in idle the afrs will start going between 14-15... as well as the o2 voltage fluctuating, but then gets stuck back at .86 volts and 13.3 afr.



Heres an example of the Nissan data scan reading for anyone not knowing what I'm talking about. Theres the voltage reading and then down below you'll see where it say A/F ratio.


http://www.dragtimes.com/img-videos-...TS-KFJo78g.jpg

Can anybody point me in the right direction...?
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Old 12-18-2014, 12:42 AM   #2
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You are lean! The ecu is just compensating for being far to lean. Retune! Or fix vacuum leaks or whatever as well.


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Old 12-18-2014, 08:06 AM   #3
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Even though it only does it sometimes? Sometimes, while it is stuck at .8 volts, it reads rich on the a/f ratio.

And its always ran within 14-15.2 afr on my wideband. Never too rich or too lean. While cruising anyways. Runs a little rich at idle, at roughly 13.3


I also boost on wot between 11.2-12. Depending on which gear I'm in
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Old 12-18-2014, 01:17 PM   #4
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its normal for these old engines. When you come to a stop at a light the ECU runs closed loop for a few seconds, then jumps back to open loop slightly rich and sits there until its time to go.

I noticed the same thing years ago. I took a video of it too, want to see...


I also made a thread asking "why, why?" and the only thing I can conclude is that either back in that day, narrowband sensors were unreliable at a stop (cold EGT?) Or, it had something to do with the longevity of the engine, perhaps running slightly rich at an idle helps keep the engine healthy long-term. Remember this is 90's technology so sometimes we have no real explanation for what we see.
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Old 12-18-2014, 07:07 PM   #5
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Based on your video though, mine is doing something different.

Say I'm cruising, AFR's are going between 14-15.5... And then roll to a stop. Whenever I'm stopped, the afr's will keep fluctuating between 14-15 for a few seconds.

Until they suddenly drop and stay at 13-13.3

Ive noticed that the o2 reading is related (obviously) to this, because as the afr's are fluctuating between 14 and 15... my o2 sensor voltage is too fluctuating. Between .1 and .9 volts.

But whenever the afr's drop to 13-13.3..... my o2 sensor is pegged at about .86 volts.
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Old 12-18-2014, 07:17 PM   #6
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Really the thing that gets me, is that even though the voltage is pegged at .86 volts (rich)

the A/F ratio sometimes reads lean and stays there.


Even if my wideband is showing that its not indeed running lean.
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Old 12-18-2014, 07:59 PM   #7
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Quote:
Originally Posted by Javi802 View Post
Based on your video though, mine is doing something different.

Say I'm cruising, AFR's are going between 14-15.5... And then roll to a stop. Whenever I'm stopped, the afr's will keep fluctuating between 14-15 for a few seconds.

Until they suddenly drop and stay at 13-13.3

Ive noticed that the o2 reading is related (obviously) to this, because as the afr's are fluctuating between 14 and 15... my o2 sensor voltage is too fluctuating. Between .1 and .9 volts.

But whenever the afr's drop to 13-13.3..... my o2 sensor is pegged at about .86 volts.
Its exactly the same. .83 is rich. 13:1 is rich. My wideband clearly shows the a/f bounce 14's for a few seconds then peg 13:1. Just like yours
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Old 12-18-2014, 09:52 PM   #8
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The ecu thinks you are lean based on what the o2 sensor. If your tune was on or close you could disconnect your o2 sensor and have a 14.5 afr. You have to understsnd, with the tools i think you have you could either fix this or find out exactly whats wrong.

Basic tuneup, set tps, set timing and base idle of course check for codes, after that clear self learn.
Your idle would need to be 850 or lower and timing needs to be 15deg btdc for me to help, fuel pressure needs to be 3bar or you have to let me know if its different.
It'll be helpful if you know if there are any vacuum/boost leaks. Do this when you dont have to be anywhere specific soon, because after cleaning self learn you need to drive and log.

If your ecu detects a lean or rich condition then richens up or leans out the mixture you are probably on the opposite of the extreme. If you think you are rich and not lean pull fuel and watch the wideband. I'll write my guess now as to what will happen. It will still richen up even if you pull out fuel until you have 14.7 afr. After a closed loop cycle, it will richen up again.

If you are stock then look for leaks if you have an safc, ask yourself why? If your ecu is chipped or stand alone we can fix it easily. Depending on the chip!

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Old 12-19-2014, 06:24 AM   #9
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Im on stock j4 ecu

I have checked timing, with both data scan and a timing light. In base idle mode my idle goes to about 850rpm, out of timing mode it goes to 900rpm. With timing at 15btdc

Im pulling -20 vacuum.

I did pull the o2 sensor yesterday while it was idling and nothing happened at idle with it pulled.

My fuel pressure is at 36psi with the vacuum plugged in. Unplugged it sits at 45psi.


Wouldn't a leak before the throttle body cause a rich condition, but after the throttle body, a lean condition?
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Old 12-19-2014, 08:47 PM   #10
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Well kind of. leaks after the maf at idle cause rich conditions throttle body or not, because if to much oxygen is detected the ecu will richen up the mixture. this is normal. if the oxygen sensor is working. a leak anywhere after the maf can cause an issue
the leak closer to the cylinders is either way. a leak on the exhaust side is usually lean. things change when boost is applied..

I think you should boost leak test and try clearing self learn if your stock.

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Old 12-20-2014, 05:14 PM   #11
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ill get around to doing a boost leak test.

And what exactly does Air/fuel base mean? When ever the o2 voltage is fluctuating my a/f base is at like 87

But when ever the o2 sensor stops fluctuating and stays pegged at .8 volts, the a/f base goes to about 95.
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Old 12-20-2014, 06:42 PM   #12
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Not sure if this is relevant at all, but I've also noticed that my temperature doesn't go above 155 degrees fahrenheit. Ever.

I drove 60 miles and it still stayed at about 150. I do have the ISIS "colder" thermostat which is apparently for high performance engines.

I dont intend on drifting my car, but i do plan on occasionally getting on it. Should i replace the thermostat with a standard oem one?
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Old 12-20-2014, 07:34 PM   #13
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A/F Base - is a percentage of a fuel map setting currently used to run engine in closed loop, also called Short Term Fuel Trim.

Which is why i suggested clearing self learn.

If you have electrical fans turn them off until 176f/80c or place a piece of cardboard in front of the radiator until 176f/80c.

Changing the tstat isn't gonna make the water any cooler or hotter it just opens at a certain temp. The fans, radiator and air do the cooling. So no!

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Old 12-20-2014, 08:26 PM   #14
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I clicked the "clear self learn" and wasn't sure it did anything. Im not even sure what it does to be honest.

So if my base a/f is at 87% while the o2 is oscillating, but then jumps up to 95 when the o2 stops oscillating, does that mean its running lean and richening up?

Will an o2 stop oscillating and peg rich if its sensing more air than fuel in a preferred a/f mixture, to keep the car from leaning out?


And I have the stock clutch fan and shroud.
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Old 12-21-2014, 12:20 AM   #15
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I clicked the "clear self learn" and wasn't sure it did anything. Im not even sure what it does to be honest.

So if my base a/f is at 87% while the o2 is oscillating, but then jumps up to 95 when the o2 stops oscillating, does that mean its running lean and richening up?

Will an o2 stop oscillating and peg rich if its sensing more air than fuel in a preferred a/f mixture, to keep the car from leaning out?


And I have the stock clutch fan and shroud.
Possibly, when i use to use nds, i would try to make the car idle with a base close to 100 with no big swings either way. 90 to 110 was my target, but later i could make it sit at 100.

You have to start from scratch to try to eliminate stupid things that make finding the problem impossible. Boost leak testing is just one of them, basic tune up is another step. What if its electrical? Me or anybody trying to explain how things work and why really doesnt help you. any if you still can't make it do what it do.

Come back with results positive or negative just remember what you did.
Therefore, boost leak test: torn coupler

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Old 12-21-2014, 09:08 AM   #16
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Alright, ill try and do a boost leak test later today.

How would you go about doing a leak test on the intake side, after the throttle body? Ive read that you can use starter fluid to spray around where you think it may be leaking, but i don't see that working if the leak is somewhere that cant exactly be sprayed.


Also, i saw a video with Eric the car guy about exhaust leaks and his method of finding one is putting a rag on the tip of the exhaust and finding the leak by listening for an apparent leak or seeing smoke from it. Would this method show me if i have a small leak at either the head/manifold ir the turbo/manifold...?


Is this ok practice? Or should i not stuff my exhaust to find a leak? lol
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Old 12-21-2014, 11:32 AM   #17
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For the intake side leak, you can try compressed air through the whole system. Or you can do it from the cylinders capping off iacv and the throttle body lines, i would leave the brake booster line connected to check it for leaks. But cap off the valve cover lines to crankcase.

Spraying starter fluid any flammable fluid works but it's hard to tell if you idle at 1100rpm you might not hear or see the change in idle. I dont use that method.

For the exhaust i prefer to listen and feel when the engine is first started, most leaks i find are at the cat/test pipe, and elbow to down pipe. Occasionally wideband and o2 bungs.

If you have a well ventilated area maybe,but carbon monoxide will kill you. Choose a different method if you can or just peek under the car while idling and feel around you might feel but you have to train yourself to hear exhaust leaks over normal engine and exhaust sounds. Compressed air works and so does a smoke machine.

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Old 12-21-2014, 06:08 PM   #18
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Could you give that a watch, Cotbu? And tell me your opinion?

Also, why does my exhaust sound like this? doesn't sound normal

http://www.youtube.com/watch?v=4gUOO...ature=youtu.be
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Old 12-21-2014, 07:05 PM   #19
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Your mafs voltage at idle looks high, tps i would adjust to .45v closed and verify voltage swings with throttle, check for dead spots and wot voltage about 4.xx volt but under 5v.

Your timing sounds off in the exhaust, but other than that can't tell. Part of that tune up should include syncing nds with the timing. And verify mechanical. Do you have a way to adjust fuel pressure? Or can you safely clamp the return line. I want to know if it changes anything.

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Old 12-21-2014, 08:11 PM   #20
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when i had the engine out, i made sure both of the dots on the cams lined up with the colored links with 9 links in between. As well as making sure the cas was lined up with the orange notch. And the engine being at the 0 mark on the crank pulley.

I have an adjustable aeromotive fpr, but its at 36psi at idle. I could try clamping the return line from the fpr. Im guessing the engine should start to bog?

At wot my tps goes to 4.04 volts
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Old 12-21-2014, 09:54 PM   #21
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So you've synced nds with the timing light on the crank? If you are plus or minus on the crank nds is wrong. You have to know this for certain.

Try idling with the mafs disconnected record a log for me.

If you have an adjustable fpr, disconnect the vacuum line and plug it. Base fuel pressure is 43.5psi or 3bar
Raise the fuel pressure a few psi clear self learn and log
See if it goes richer or leans out and how long it takes before a change is notice. Then try a few psi lower. If there's no significant change put it back to 3bar.

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Old 12-22-2014, 06:43 PM   #22
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What if my base fuel pressure is already a little higher? Its at 45, according to my aeromotive fuel pressure gauge. Its attached to the fpr itself.

Will 1.5psi make a difference, even if with the vacuum hooked up it goes to 36psi?

And when you say i should disconnect the vacuum and raise the pressure to see what it does, do you want me to reconnect the vacuum line after doing so, or am i doing all of this with vacuum disconnected the entire time?
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Old 12-22-2014, 07:55 PM   #23
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Yes, hook the vacuum back up. But now you should try turning it down.
What brand of injectors do you have? And why is the fuel pressure not set correctly. If your tuner or injector manufacturer told you to do so you should be consulting them.

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Old 12-22-2014, 08:14 PM   #24
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just the stock 370cc injectors. When ever i try adjusting the pressure to about 43.5 with the vacuum disconnected, the pressure always goes too low when reconnecting it. It goes to about 32psi.

But whenever i put the base pressure at 46 (i was wrong about it being at 45) and reconnect vacuum, i get 36psi.
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Old 12-22-2014, 08:22 PM   #25
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So based on some reading and testing. If the base a/f is above 100 it means that the o2 is reading lean and its adjusting the base a/f and adding fuel, to richen it up. If the base a/f is below 100, it means the o2 is sensing a rich condition. Not sure what is does to fix a rich condition. Injectors open slower or maf input is manipulated..?

I did the a/f base test in NDS and set it to 110, and it made my afrs go to 12.0. And when ever i set the base a/f to 90, my afrs stayed between 14.5-15.5
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Old 12-22-2014, 11:03 PM   #26
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Base fuel pressure should be 43.5psi or 3bar set everything to stock including tps timing etc. The vacuum should not effect fuel pressure that much, unless your fpr is faulty. Even if you were to idle at 2000rpm fuel pressure shouldn't go down that much.

Thats why we adjust base fuel pressue with the vacuum disconnected.

I need you to dump the stock tune on the ecu and send it to me, but first check to see if you have a daughter board fitted to the ecu. If not you have to do a boost vacuum leak test and fix it, also make sure you're setting ignition timing correctly. If the tune is stock and there are no problems elsewhere you might be ok. But the fuel pressure is clearly not right.

It could also be the gauge location or a crappy gauge, i like my readings from after the filter before the rail.

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Old 12-23-2014, 08:55 AM   #27
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Well, here is that log with the MAF unplugged. Are my injectors doing anything funny? You can see how high they go when i barely rev it.

http://www.youtube.com/watch?v=ovBiR...ature=youtu.be
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Old 12-23-2014, 09:34 AM   #28
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Quote:
Originally Posted by Kingtal0n View Post
its normal for these old engines. When you come to a stop at a light the ECU runs closed loop for a few seconds, then jumps back to open loop slightly rich and sits there until its time to go.

I noticed the same thing years ago. I took a video of it too, want to see...


I also made a thread asking "why, why?" and the only thing I can conclude is that either back in that day, narrowband sensors were unreliable at a stop (cold EGT?) Or, it had something to do with the longevity of the engine, perhaps running slightly rich at an idle helps keep the engine healthy long-term. Remember this is 90's technology so sometimes we have no real explanation for what we see.
Correct, the idle is supposed to be rich. The O2 sensor is too cold to read accurately after the car has been idling for more than a few seconds.

ECU wants to see .8v but the O2 sensor will start drifting down to .5v
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Not sure if this is relevant at all, but I've also noticed that my temperature doesn't go above 155 degrees fahrenheit. Ever.

I drove 60 miles and it still stayed at about 150. I do have the ISIS "colder" thermostat which is apparently for high performance engines.

I dont intend on drifting my car, but i do plan on occasionally getting on it. Should i replace the thermostat with a standard oem one?
Yes. You will stay in cold idle till you get above ~160. Cold thermostats are just a bandaid for "race car." I will assume your MPG is bad and you are rich all over the map.

Get a 176F/80C thermostat.
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Originally Posted by cotbu View Post
If you have electrical fans turn them off until 176f/80c or place a piece of cardboard in front of the radiator until 176f/80c.

Changing the tstat isn't gonna make the water any cooler or hotter it just opens at a certain temp. The fans, radiator and air do the cooling. So no!
That's not how it works. The thermostat keeps the engine at a fixed temperature by opening and closing incrementally. Bleeding the hot water into the cooling system as needed.

It is what keeps the hot water in the car. Regulates the temperature to a fixed amount. Changing the thermostat operating temperature will make the water stay hotter or cooler.
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Old 12-23-2014, 05:01 PM   #29
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If the tstat opens at 60deg does that mean the engine will stay at 60deg?

No it doesn't.

What it does mean is that that tstat will remain open untill the temp drops or wax gets cold. So if i have a 60deg thermostat how can i make the engine hotter? The engine produces heat, heat is transferred to the water and oil, the water and oil get cooled sent back to the engine. Lets focus on the water the water is cooled by the radiator it doesn't care what type or brand of thermostat you have. It will continue to do what it do, which is cool the water. The fan aids the cooling practice significantly, SO by adding a piece of card board in front of the radiator the fan (clutch or electric) will allow the water to reach a higher temperature before it is cooled. A thermostat will not make you car run cooler alone. It just allows the water to flow at a certain temp.

Thank you.

Ps A house's thermostat control a heater or burner.
A car thermostat in the cooling system only controls the flow of fluid. If it actual did any temperature control we would not have to worry about over heating. Because that 60deg thermostat would never ever let me overheat right?

Also he drove 60 miles, but thats a different indicator.

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Old 12-23-2014, 05:34 PM   #30
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The injectors are doing what their supposed to do when the mafs is unplugged. The most part its using the limp map correctly then it goes rich again which says theres a leak. It should be rich but it should be 100 percent using those values it added even more fuel which could indicate a leak. The 02sensor was still plugged in i assume.

Therea usually a stumble when the mafs is plugged back in unless there is a radically change when you do.
You either get a rev up or stall

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