Random AFR hunting....what can cause this?

[macipusy]

So lately my 91 SS has been acting up. I will cruise and AFRs will be near 14.7. After 5-15 min of driving, it will start hunting in cruise and idle. It will bounce between 11.5 and 16.5 every few seconds. Usually when I turn off the car and then drive it later, it will be fine again for a short time. Once it starts hunting again, it will not stop till I turn it off. It only hunts in closed loop.

I am running a PP6 with a MAP for deflection as well as 550cc injectors on E85.

It started doing this right after I swapped over the new transmission and clutch...which should have nothing to do with the way the motor is running.

Any suggestions as to why it's hunting?

[gijonas]

Any reason to suspect damage to the o2 sensor or wires from removing the exhaust to do the tranny work?,I have had similar issues before for that reason

[macipusy]

I was pretty careful with it....but it was removed from the down pipe. I have an extra O2 sensorso I can swap it over and see if it goes away.

Anything else that could cause it?

I already cleaned the MAF, but still hunting.

[gijonas]

First thing I would do is go over any wiring/plugs that were
touched in the tyranny change process.

[beatersubi]

Isn't is supposed to oscillate between lean and rich in closed-loop?

[gijonas]

his readings are pretty dramatic,16.5:1 is the point where my car falls on its face lean.

[beatersubi]

his readings are pretty dramatic,16.5:1 is the point where my car falls on its face lean.

During cruise and idle conditions there is very little load on the engine.

[gijonas]

Oh sorry i forgot about the cruise/idle thing.

[Legacy777]

First question I have, is this O2 a wideband or narrow band? I didn't see it mentioned, so just want to confirm that.

If it's a narrow band, I wouldn't really worry about it. It's oscilating like it should. If it's a wide band reading, then yeah something may be up.

Other thing to note is that the stoichiometric value for E85 is not the same as gasoline or even E10. This table provides some more details.

http://en.wikipedia.org/wiki/E85_in_sta ... ines#Table

Have you tried resetting your ECU?

[macipusy]

I am reading the values off my Innovate LC1 Wideband O2.

The problem is, that I have run E85 for a while now (3 months) and this problem is very new....last 2-3 days.

I have reset the ECU multiple times.

Right now I have swapped another O2 for the stock narrowband, reset the ECU and will report later, after I drive it, if it is still hunting.

[macipusy]

Very happy to report back that the issue is gone. Seems like the narrow band O2 was the problem.

[Legacy777]

Are you running both wide band and narrow band O2?

[macipusy]

Yes, I am running both. The stock narrowband for the ECU in closed loop and the wideband for my eyes only...for tuning purposes hooked up to gauge only.

I will get rid of the narrowband when I go full standalone, but for now just with the PP6 I still need the stock O2.

[gijonas]

Told ya so

[Legacy777]

Does your WB have a narrown band simulator?

[macipusy]

I am not sure about the narrow band simulator.....I will look into that.