I recently hooked up a narrow band A/F gauge (it's actually an Apexi turbo timer, which has an A/F gauge function) to my '82 Turbo. Instead of displaying lights bouncing back and forth, it displays the actual voltage from the O2 sensor, and also has the ability to display a theoretical A/F value based on it. The strange thing I am finding is that once it hits 3300rpms, the O2 voltage drops below measurable values, indicating a severely lean condition. However, once it gets above 3500rpms, the voltage comes back up to normal. It's very consistent, and does it regardless of throttle position or whether I'm cruising or on boost. It seems like such an odd block of the powerband to be showing a lean value so consistently. I don't offhand feel a power difference, but I also don't stay in the lean range for long, usually letting off the gas as the voltage quickly drops.

I have a fuel pressure gauge in the cockpit, and it's showing consistent pressure, so it's probably not the fuel pressure regulator or pump. The O2 sensor was changed, and made no difference. It's still the original turbo and ECU. The only aftermarket mods that might affect the combustion process are as follows:
K&N cone filter and 3" exhaust
Crane ignition/coil
Pallnet fuel rail

So are there any thoughts on what might be causing this apparent lean condition so consistently between 3300-3500rpms?

 

I had a somewhat similar prob... except mine would lean out at full throttle no matter what. I did a lot of trouble shooting & couldn't ever pinpoint the prob, but I think it was part ecu programming, part AFM. I swapped to the Z31T ecu & MAF and the prob went away.

 

I'm not sure if I'm leaning out or not, but that seems to be similar for me, I just suddenly start to lean out and pop at higher throttle or I should say right around the 3250 mark.

 

I remember reading about the turbo ECU in the factory manual. It mentions something about the engine going into open loop above 3000 rpm and at wide open throttle. The voltage drop may be the ECU turning off the O2 sensor or starting to ignore it. The factory turbo runs rich at that point (well, it should) and doesn't really pay attention to rpm or AFM position I guess. The more I read about the factory ECU the more I realize its very inefficent.

I'm starting to think I have an issue at WOT. I'm running the 3 position NA TPS right now and I may switch back to the 2 position turbo one just in case the WOT position actally puts my car into open loop.

also, don't you need a 3-wire O2 sensor to get an accurate reading on your wideband?

 

Did you change or mess with any vacuum lines lately?

 

Bleach is correct in that ecu begins to switch over around the 3000-3250 rpm area. It's nothing to cause concern, it's just the feedback mechanism is switching for ecu. If you get popping out your intake, then it's time for some concern. That, or the usual pinging.

 

See for me, I was getting popping, but at least from what I can tell it seems like I had vacuum lines mixed up on my end. At least from what I've read the EGR has a valve that limits vacuum at higher throttle positions, and I think that's what might have been causing me issues, was the valve was hooked up where it wasn't supposed to be and causing an issue. At least that's what it seems like, unless for some reason running the seafoam through my intake/exhaust helped to clean something out.

 

From my readings on O2 sensors, the 3 and 4 wire O2 sensors have that many wires because they are heated and 1 wire O2's are not heated and most 2 wire O2's are not heated, if any. I believe what makes it a wide band sensor is the actual sensor inside the O2 sensor housing and not the wires themselves.

 

Unplug the sensor and see if it still happens.

 

If I unplug the sensor, my meter wouldn't read anything at all then.

I did change all my vacuum lines out for silicone ones, but I did make sure to connect everything properly. I just want to reiterate that this lean reading happens at part-throttle too, so it's not just a WOT thing.

 

I think its fine as long as the engine still runs smooth in that rpm area. Its just a very primative fuel management system that you're running.

The 1988 Z31 upgrade will be very nice if I ever get around to installing it.

 

Man you sure are a pimp for that Z31 upgrade.....the more you talk about it the more I think about it...even though mine runs killer when I play with those wires on the ECU.

 

Z31 ecu & maf is the best upgrade for the 280zxt in my books...

 

When my wastegate sticks it runs really nice at 8-9psi. I think the richness that you see at 7psi just needs a little more air shoved in there. If the POV was modified, I think the stock ECU would run best at about 10-11psi.

anyway, the Z31 ECU will run at correct fuel mixture at any psi up to about 15. I'm gonna need about 32psi though before I'm happy.

 

32psi in yo tires! oh snaps!

 

That's my next plan is to upgrade to the Z31 ECU. You get the MAF, the ECU diagnostics, better fuel management, etc.

 

I found me a 88 Z31 Turbo ECU and MAF. I just need to get the distributor thingy. However, since I read the 88-89 ECU's use a 3-wire O2 sensor, I'm unclear how that would wire up using the original harness, or if I need to run extra wires. Among other things I've read, it seems like it'd be easier to get an earlier Z31 ECU to use, but then I'd have to track down a Turbo version of the earlier years.

 

true. It is easier to wire up the earlier ECUs. The 'better' ECU requires a little more work. You have to install a 3-wire O2 sensor (smaller diameter threads too) and run the wires to the ECU yourself. fun fun!

 

You can still use a one wire O2 sensor. The other wires are just for electrically heating the O2 sensor so it reaches its operating temp faster. It still only uses one of those wires to send a signal to the ECU and thats the only wire you reallly need. I'm not sure about the VG, but the L28 has its O2 sensor fairly close to the exhaust ports & all 6 cylinders feed directly into the one manifold so the O2 senso will heat fairly quickly on its own.

 

the VG30DE (dont know VG is being talked about im lazy) one on only one bank and its in the actual manifold as well, about teh same distance as teh L motors have it from the head and such, at least thats how i saw it on my Z32.

 

in this case we're talking about an L28et.
The turbo O2 is right after the turbo so it has a good mixture of all six cylinders' exhaust. Still pretty hot place I would imagine.

Maybe Snwy can touch the downpipe with his lips after eating some hot pizza to see how the temps compare.

 

hmmmm..... my lips you say, lol well j mentioned something about a VG motor so i just like threw in my 2 cents there. lol.... didnt care to read why or how it came up since i was in a hurry

 

I'm just sayin that the heated O2 sensor wouldnt be needed on the L. Even with the late Z31 ECU.

 

So if the Z31 ECU can get by with the heated O2 sensor, does that mean we could get away with using the original 280ZX O2 sensor? Or is the resistance/voltage/whatever output different between the 17mm and 22mm O2 sensors?

 

I think that's what he is saying although I'm not so sure he's right...

so you pay an extra $50 for an O2 that is more accurate during warmup? ...and that's all? I think I'm going to use the proper O2 that the ECU was made for.

even for a 1987 Z, the turbo and NA have different part numbers for the O2 sensor
The 280ZX turbo and NA use the same O2 sensor
That is a key component I'm not going to scrimp on. I'm getting the Turbo Z31 O2