O2 voltage bouncing around
Thread Starter
Burning Brakes
Joined: Oct 1999
Posts: 843
Likes: 2
From: Nashua New Hampshire
O2 voltage bouncing around
My '86 just barely failed the emissions test. I don't have the stock PROM, I have a good custom one. Everything was replaced 3-yrs/5,000 miles ago - O2 sensor, all EGR parts, plugs, wires, etc. etc. Didn't have problem passing before with this combo. Now, it's 3ppm over on CO.
I hooked up Diacom this morning. After it went into closed loop, I pressed the accelerator enough to bring it up to about 1000 rpm and tried to hold it steady. The O2 voltage is bouncing all over the place. I was expecting it to be fairly steady in the range of 700-800mv or so. But I haven't used Diacom or thought about engine tuning for a few years, and can't remember what's normal. Is bouncing O2 voltages (30mv to 800mv) normal with constant engine speed?
My PROM runs the engine rich most of the time. AFR is at 14.7:1, Integrator at 132, BLM at 108. Does it sound like the O2 is bad, even though it's fairly new?
TIA, Gregg
I hooked up Diacom this morning. After it went into closed loop, I pressed the accelerator enough to bring it up to about 1000 rpm and tried to hold it steady. The O2 voltage is bouncing all over the place. I was expecting it to be fairly steady in the range of 700-800mv or so. But I haven't used Diacom or thought about engine tuning for a few years, and can't remember what's normal. Is bouncing O2 voltages (30mv to 800mv) normal with constant engine speed?
My PROM runs the engine rich most of the time. AFR is at 14.7:1, Integrator at 132, BLM at 108. Does it sound like the O2 is bad, even though it's fairly new?
TIA, Gregg
Melting Slicks
Joined: Apr 2001
Posts: 2,094
Likes: 217
From: Ca.
Re: O2 voltage bouncing around (gh86E)
Closed loop, no PE (wot) the O2 sensor is supposed to swing back and forth.
The blm's....are they 108 as you drive around/at all loads/throttle positions? If so....it's rich! 108 is the max blm; after that it can't compensate and it's then outright rich...which equals the cat is more than likely fried due to the con't rich condition. You can just throw in a new cat for now to make it pass, but you do need to get the "custom" chip retuned to acheive blm's of 128 +/- 4 or so at all throttle/load....
The blm's....are they 108 as you drive around/at all loads/throttle positions? If so....it's rich! 108 is the max blm; after that it can't compensate and it's then outright rich...which equals the cat is more than likely fried due to the con't rich condition. You can just throw in a new cat for now to make it pass, but you do need to get the "custom" chip retuned to acheive blm's of 128 +/- 4 or so at all throttle/load....
Thread Starter
Burning Brakes
Joined: Oct 1999
Posts: 843
Likes: 2
From: Nashua New Hampshire
Re: O2 voltage bouncing around (drive it)
Closed loop, no PE (wot) the O2 sensor is supposed to swing back and forth.
I dropped the original PROM back in, and will try the emissions test again.
I was wondering if the O2 sensor should be replaced as well, but might as
well try it with just the original PROM first.
I knew the custom prom ran it rich, but there was only minor carbon deposits in the exhaust, and it performed well, so I wasn't worried about it (and it passed emissions easily before). I suspect there's something else wrong, but I'll see how the original PROM does. It did recently spring a coolant leak, and the engine got covered with coolant (which is now baked on everywhere). Guess I'll just have to push a new crate engine up on the priority list.
..gh
Melting Slicks
Joined: Apr 2001
Posts: 2,094
Likes: 217
From: Ca.
Re: O2 voltage bouncing around (gh86E)
Even from sub-100's to 800's, with a constant RPM (at ldle)?
Yes....you can try the original prom-check the blm's with it...but if the cat is gone, then it's gone.....
Racer
Joined: Oct 2002
Posts: 293
Likes: 0
From: Newnan Ga
Re: O2 voltage bouncing around (gh86E)
Sounds like you might need a new cat. The O2 sensor voltage is supposed to oscillate after it gets hot. You can speed up the idle to aournd 2000 for a short time to get it hot, it will then oscillate.
