Nistune Forums

In the never ending battle to get my car running right, I've come across something I wanted to ask about, well two things actually. One is about the O2 sensor. I've currently switched to a 1988 Z31 Non-Turbo ECU for my L28ET so I could use the larger style Zirconia 1-wire sensor with my ECU. Although I did upgrade to a heated 3-wire version to get O2 feedback to come on quicker. Anyway I'm not sure if the ECU is using the O2 sensor right or if it's due to a vacuum leak with the motor. Since using the O2 sensor, when warmed up and at idle/in general my car is running much much better actually almost normal. Anyway on the consult gauges I see my O2 sensor sticking around .86-.89 at least somewhere around there when running. If I unplug the O2 sensor I can hear the motor change a bit, and the voltage in the consult gauge will drop to I think .36 and not move. At least when plugged in I do see it fluctuating a little. Shouldn't the voltage be bouncing around a lot more? Or would this be an indicator of like I said a vacuum leak preventing the ECU to operate completely as it should in closed loop? I'm at least fairly certain this was a non-turbo ECU. The identification number on the cover shows a federal US non-turbo ECU. I don't believe the ECU was opened and switched around either. So this should be correct. I don't even know if O2 voltage would register with using the Turbo's Titania sensor as this board supposedly doesn't support it.

Also a quick question I had is that when the car starts from a cold start it seems almost as if it's hitting a rev limiter at 3500 RPM. I didn't hold or try to see if I could get it past, I'm not trying to wail on it or anything, but this sounds about the point where the car pretty much switches to open loop or I should say stops really using the sensors and just goes off the ECU maps. So I'm not sure why it's hitting a wall, or maybe if I held onto it and got it past there it would be fine. Any thoughts on this?

I'm mainly more interested in the O2 sensor portion. It kinda reminds me of when I had a bad vacuum leak on my L28ET when the motor was in my old car, the A/F gauge I had would never really reach rich. It seemed like it bounced alot less because it could never quite get to the rich point to drop off, almost as if the car is constantly trying to compensate for the extra air, and never getting to a point where is then gets the signal to back off for a moment, then start the enrichment process again.

Since using the O2 sensor, when warmed up and at idle/in general my car is running much much better actually almost normal. Anyway on the consult gauges I see my O2 sensor sticking around .86-.89 at least somewhere around there when running.

Means that its reaching richer than 14.7:1 on the sensor. What does your wideband say? Can you see it leaner than this when say reducing injection mulitplier?

If I unplug the O2 sensor I can hear the motor change a bit, and the voltage in the consult gauge will drop to I think .36 and not move.

So when you disconnect ECU uses default voltage. With .86 its thinking its reading rich and pulls out some fuel.

Shouldn't the voltage be bouncing around a lot more?

Yes it should but might not be running closed loop. What if you hold RPM @ 2000rpm when warm, does it fluctuate at all then?

Also a quick question I had is that when the car starts from a cold start it seems almost as if it's hitting a rev limiter at 3500 RPM.

What happens with your injection time and RPMs when it hits this? Anything in the consult logs we can see if you do some logging? Probably not O2 sensor related but something else

I'll grab some logs tomorrow or sometime soon when I can to see if you guys can give me any extra info. I wish I could hook up my wideband right now, but I don't really have a full exhaust, so I don't have an extra bung to have both the narrow and wideband sensors hooked up at the same time. I almost wonder if I could use my Zeitronix to supply the narrowband signal to the ECU and see if that makes any difference.

the bung sizes are probably different (wideband wider) but yes you can feed the narrow band signal if you have a 0-1 volt output

One more quick question I have about the ECU/O2 combination. The O2 sensors are supposed to be different between the the 86+ Z31 Turbos and Non-Turbos. I've heard that the O2 driver or whatever controls it/reads it in the ECU is separate and that you need the appropriate ECU to run the O2 sensor. I'm using what is supposed to be the non-turbo 88 ECU as well as the larger 3-wire non-turbo O2 sensor. It's the same bung size as the Wideband. At least I've been able to thread the wideband into the O2 bung and use it. Anyway as far as I'm aware the two different O2 sensors operate differently, I was wondering does changing the rom on the board cause a difference in what O2 sensor should be used, or would it still be ECU reliant? Also if I were to use a Z31 Turbo O2 with an N/A ECU and Vice Versa would it read the O2 sensor correctly? I assume it's also possible I could have a bad O2 sensor that is just sending a straight always rich signal? I have encountered this before where an O2 sensor got banged around and it seemed to just be stuck sending always rich. I didn't get a chance to go mess around with it more yet.

Its to do if its internally heated or requires 12V to heat the sensor which normally comes from the ignition signal via ECCS relay. Also the O2 lean/rich voltage levels change between the two O2 sensor types so these levels may need to be adjusted depending which image you have loaded in

Hm, this is really interesting that you can change the O2 feedback levels, so essentially with Nistune I can use a Turbo or Non-Turbo ECU with either type of O2 sensor? The way I currently have the larger 3-wire I believe it's called Zirconia sensor with I think it's an 18x1.5mm bung. I currently have the two heater wires wired up to one running off an ignition switched power, and the other going straight to a chassis ground. This is pretty much how the Turbo ECU has it wired, although the sensor is supposed to be wired slightly differently for the non-turbo with the ground for the heater running to pin 115 on the ECU.

Anyway I'm really interested in how I can go about changing the O2 voltages and what else needs to be changed to make sure I'm running this correctly. I'm running the stock image that came with the type 1 board, but I opened up an 87 Z31T map, and used copy image items to copy everything over, and then flashed it to the ECU. After that the only thing I've really only played with so far is idle timing with TPS on. There was very little difference between the 88 and 87 Z31T other than mainly idle timing, timing, and fuel maps. I noticed in Feedback Switch that Bit 2 is checked on the 87 map, but not the 88. When I look at the Feedback Switches on the 87 N/A map the only Feedback Switches that are checked are Bit 2, Bit 5, and Bit 7. Since I'm using the Non-turbo sensor, what do I need to switch to make sure I have the ECU set to use the voltages correctly for the N/A sensor. This could be the reason for why I wasn't seeing fluctuating readings on the gauge view in Nistune with my O2 sensor. Possibly just looking at the wrong voltage lookups? Also before I had installed the USB connector into my ECU I was using the stock LED lights, and I wouldn't even get it to flash at all in the Mixture Feedback mode or whatever it's called per the FSM. It says the light on the ECU is supposed to flash on when it detects lean and turn off when rich, but I never once saw the green light turn on.

At least I may be on to something in helping to get this thing running just a bit better.