1985 - Is 16:1 normal at idle?
 

I posted this over in Tech:
http://forums.corvetteforum.com/show....php?t=1149736

Very near stock setup. AFR in open loop = 12:1 -> 14:1.
Then in closed loop, at IDLE, climbs to a steady 16:1. Is this normal for an '85? Did GM tune for that much ECONOMY at idle?

Are you watching a wideband?

If so, often at a idle the o2 sensor isn't satisfied and gives false lean readings.

Especially if the sensor is placed in the tail pipe tip and not in a bung. Also verify that the AIR pump diverter valve isn't diverting air into the catalyst.

tjwong - The sensor is welded in a bung about 4 inches downstram of the stock O2....

They still have a hard time at a idle. Mine is adjacent to the O2 and I shoot for 18:1 due to the cam overlap. The widebands don't always work well at a idle. Tune the idle with a vaccum gauge

Alvin - Yes a wideband by TechEdge. On my Toyota, I see 14.7:1 easily at idle.

My jeep reads 14.7 at the tail pipe.

They just are not accurate enough to read at idle, whats the point anyway, tune for vaccum and be done with it.

There are so many things that can mess with that sensor especially at a idle... Like it going cold, air pump coming on, exhaust leaks, etc. We are here telling you that seeinga high AFR at a idle isn't out of the ordinary

Alvin, I think he has a stock cam. He has another thread going in the tech/perf forum as well.

Yes, I've switched to a '87 cam. Just got in from the garage and am dissapointed to say that at 2000-3000 rpm the afr is like 15.6 to 1.

..also at about 2500-3500 rpm the tach starts 'bouncing' back to like 2500 rpm. The engine is at about 3500 rpm bet the tach is going crazy.

Do you have a misfire?

Stock cam or not, I do not like them for no-load and idle tuning. one of my personal cars has a 210/220 114.5 duration cam and even it requires like a 17:1 or else its a stinker.

No misfire. When I dis start the motor poped once. I thought that was unusual.

Tomorrow I'll hook up a a scan tool to get a better look.

Do you get any popping while revving by anychance? Have you driven it yet?

Check to see where the BLM"s are. thats the key.

No poping that way. From idle, if I punch the accelerator the engine revs up wondefully. Ok, will check BLMs.

Ok, ran it on Diacom got: BLMs 108 after about 3 minutes. Stayed at 108 too. Integrator was at 128...
Had 3 control spark counts. Pulse width was about 1.4mS

Then hooked up EASE diagnostics and got some weird results. Had codes:

052 - calpak missing (nope, got a fresh GM version)
053 - over voltage
054 - Fuel pump voltage.
A/c request = on (big lie since it was off)

All this in Closed loop....

Did you have a 108 while observing a High AFR?

If so you may have some sort of O2 failure. Usually when I see them fail they go lean, but anything is possilbe.

Did you say that you have chip burning equipment?

Try clearing the codes and see what comes back.

Yes, during all this it was at approx. 16.6:1 The O2 is new. I have some old ones lying around I could swap in or I can just get another.

..as I remeber 108 is the low limit correct? ...and the ECM can't add any more fuel? Yes I do have the chip burning equipment.

actually 108 means that the car is very fat and it can't pull any more fuel out. 160 is very lean, can't add any more fuel.

I suspect either a bad O2, (your using delco right?)
Misfire (can do funky things with O2 sensors)
Valve adjustment

Try swapping the o2's and see what happens.. If your wideband was reading 16:1 and your BLMS where in the >140's I would say your definately lean, right now your just getting a false signal from somewhere.