AFR off the meter...

[garetth]

Hey guys I'm not very new to this forum i have just been larking the forums for awhile finding others who had the same problems. But recently i have run into one that i can not seem to find much information on.
FIrst a little about the car.
1993 240sx
RB20DET Swap with 80,XXX km
5 speed manual
Walbro 225 fuel pump
Carbon Fibre Hood
3.5" Custom Exhaust & 4" Megan racing muffler
STANCE fully adjustable coilovers
Front Mount Intercooler
Greddy Type RS BOV
Greddy Profect B boost Controller
Boost Gauge

Now last night i just finished installing the AEM WIdeband AFR and when idling the sensor is showing 16-17 when I'm on the throttle it shows (---) And once i hit around 4000 RPM and start boosting it's at 12. Some times i am also getting a fuel cut of 2500-3000 rpm. So from what i have gathered it could be some sort of a leak? The fuel filter also looks old so i will try finding a 300z one tomorrow. Would upgrading to a z32 maf help any of this either?
Here is a picture of where it's mounted. The top one is the ECU afr and the bottom is the aem.

[Ramius83]

Now last night i just finished installing the AEM WIdeband AFR and when idling the sensor is showing 16-17 when I'm on the throttle it shows (---) And once i hit around 4000 RPM and start boosting it's at 12. Some times i am also getting a fuel cut of 2500-3000 rpm. So from what i have gathered it could be some sort of a leak? The fuel filter also looks old so i will try finding a 300z one tomorrow. Would upgrading to a z32 maf help any of this either?

First off, have you been having the 2500-3000RPM cut problem since you did the swap, or since you installed the AFR gauge? That RPM range limitation is usually due to a faulty mass air flow sensor, usually. Swapping one from a 300ZX will NOT work as your ECU is not tuned for that MAF. A boost/vacuum leak will also not limit your RPMs at that range either, just cause low boost, low vacuum readings. I would try swapping in another or a friends RB20 MAF to rule it out.

Second, The 16:1 and 17:1 you are seeing at idle with a "stock" engine is somewhat normal as it does not need to run rich when idling. 12.5:1 is a very good number when pouncing on the throttle. When it goes "----", that usually means that there is a loose connection with the wiring going to/from the ARF gauge or hook-up. I would double and triple check those connections, solder and tape all connections always, no scotch-locks.

Third, A/F sensor location is good and should not be a problem.

[garetth]

Thanks for the reply, from where i am from there are next to none RB20's. I didn't do the swap but the 3 weeks i have had the car i have got fuel cuts randomly when its cold. As the (---) it's not a loose connection its going off the charts the afr only reads up to 18 then after that it goes (---)

[Ramius83]

Your AEM AFR will only read between about 10:1 to 18:1 or so. Any lower is balls rich and any higher is balls lean. If it is going that high, then you have something going wrong. Lean conditions are caused by faulty Mafs, vacuum leaks, bad O2 sensors, lack or fuel, bad wiring, etc. Considering you have a 2500-3000 rpm cut, sounds like a bad MAF or faulty wiring to the MAF in my opinion.

[ST240]

This sounds very VERY suspicious of your factory narrow band O2 sensor being on the fritz.

The afrs during idle can vary like Ramius said, but cruising with light load, you should have bang on 14.5-15.5 due to the engine being in closed loop (ie using the O2 sensor voltages to meter your fuel). If you don't and its going off the chart, your O2 sensor is most likely screwed.

Trust me I know, because what I just described was happening to me and I replaced the O2 sensor and all was good again. Goto your autoparts store, and get the 1.6L sentra three wire O2; it will plug right in.

I have no idea what that "cut" is though. Check the O2 .

[Cjmartz2k]

I'm not really tracking with everything you are saying about what's wrong, but I will just throw this out there and maybe it applies. A missfire due to ignition will show up as super lean on your wide band, not super rich. An O2 sensor doesn't measure how much fuel is in the exhaust, it measures how much Oxygen there is, which is a lot if the cylinder didn't fire.