ViperDude152

I think I tested the o2 sensor right. Using my multimeter I connected the ground wire of the meter to the chassis and the positive wire from the meter to the o2 sensor.

If I swapped the wires I would get 12.80 or so volts. I knew that was not right.

When testing the o2 sensor at idle on my S4 n/a I noticed it read .84 while at 800 rpm. I have the correction on my SAFC at -2 for 800. Even if I add more fuel with the AFC to near +11, the o2 sensor still only reads .90-.92v. I feel +11 is very rich.
My o2 sensor possibly bad?

A little background to why im checking my o2 sensor. I had to get into my front cover last friday (few days ago) to check the o-ring for the oil system. after checking everything under there I installed everything and im getting around 240-280 miles to a tank when I was getting 350-425 to a tank right before I removed everything to get to behind the front cover.

Did I miss something? What could possibly hurt my milage so bad that would be near the front of the engine? Water thermo sensor is plugged in and I installed the CAS 4 times to see if I could have installed it wrong.
No fuel leaks, brand new rubber lines and solid lines. Fuel pressure holds. I have an exhaust leak between the manifold and the down pipe but that has been there for a few weeks. Timing is on the mark.

So after this I started to think that maybe some how in some time frame the o2 sensor took a dump?

Im going to replace the o2 sensor but what else could cause my millage to disappear from one tank to the other after removing the front cover?

misterstyx69

iTrader: (142)

My guess is that if you have an Exhaust leak then your O2 is Not reading Correctly ..I would fix the exhaust leak since it would be a good thing to do,and just see if that clears it up.(no expert on this..just givin ya an opinion)

NZConvertible

The sensor only reads from zero to 1V, with richer mixtures causing higher voltages. Stoichiometric is 0.4-0.6V. The voltage is going up because you're making it richer. 0.9V is a very rich idle...

ViperDude152

I know the volts go up because its getting richer, I just thought the reading should be near 1v because thats what the FSM says it should be at.

NZConvertible

The FSM says the TPS should be at 1V, not the O2 sensor.

HAILERS

A NORMAL RX-7 with all the components that the engine came with, will have a very low 02 reading at idle. This is because the ACV feeds air to the EXAUST PORTS and the exaust ports are located prior to the 02 sensor.

If you pull the Relief Solenoids plug off, most of the ACV air will now be dumped into the right front fender instead of the EXAUST PORTS, therefore the 02 reading will go richer. It'll go into the 0.7-0.8 vdc range which is very rich.

And that's how it works. IF you removed the acv/airpump, then expect to see the .8 at idle. If you have a wideband expect to see mid 12afr to 13afr.

ViperDude152

In the specs for the Emmisions Control System it said , O2 Sensor , Approx 1v (idle). Then it gave you numbers for acceleration and decel.


Thanks hailers.

HAILERS

The 88 online FSM says below 1 vdc at idle .............................Accelereation 0.5 to 1 vdc...............deceleration 0- 0.4 vdc.

I don't have my 87 FSM so I can't repeat what it says.

NZConvertible

Like Hailers said, it says below 1.0V, which is a pretty pointless statement since the O2 sensor can only generate 0-1V anyway. You should be looking for 0.5-0.7V at idle.