mobird

Hey guys, I finally got around to welding in my AEM Wideband 02 sensor and wiring it up. Took the car out for a drive last night to get some readings and see where my tune was at and this is what I Got.


At idle (once it idles down to 900 RPM or so) my A/F shows around 16.


At Cruise it fluctuates between 14 and 15.


At Wide Open Throttle it drops to about 11.5.


I'm running a stock Quadrajet that I rejetted with 74 main jets.


Little more info: I'm running Doug's side pipes and I welded in the 02 Bung about 12" behind the Collector.


I have a small exhaust leak where the Collector meets the Side Pipes (not sure if that affects anything).


Do I need to make any tuning changes?


I'm putting on a new top end next month (aluminum heads, 268 cam, Performer RPM intake), will that lean out the mixture a little I assume?


Also, I get some blackness around the end of my side pipes (and a little around the exhaust leak at the collector) which I always thought was a sign of running rich, however according to those 02 readings I'm only rich at WOT. Does this seem normal?

AirBusPilot

Your future mods WILL lean out your WOT readings, so get another reading when that happens.

Right now, your WOT AFR is rich.

mobird

Thanks, I'm planning on it.


Do you think my exhaust leak is affecting my readings at all?


And is it unsafe for it to idle at such a lean condition (16 A/f)?

MotorHead

If it was mine I would fix the leak, fatten up the idle, which in turn will bring the cruise down and the WOT should remain about the same

resdoggie

If that leak is sucking air in then you need to fix it because that will affect your readings. Is there a reason why you didn't put the bung in the collector? O2 sensors like heat so they recommend them about 36" from the exhaust port from what I've read. I wouldn't worry about too lean at idle but all you need to do is back out the mixture screws a tweak or so to richen it up. As ABP noted, a bit rich at wot if you are getting accurate readings. Aim for about 12.5, give or take.

mobird

When you say fatten the idle, do you mean just adjust the idle mixture screws on the quadrajet?

MotorHead

Yeah you want to richen up the idle to get to around 14:1 AF and that in turn will bring your cruise AF down a point or so.

mobird

Should I just use exhaust sealant on the pipe that slides into the collector? I know that would seal it, but I also need to be able to remove it in the future, possibly next month when I install new heads on the motor. Is there a less-permanent way to seal those side pipes?


There wasn't much room in the collector because the side pipe slides into it. I would have had to drill it right next to the welds where the individual cylinder pipes combine. It just made more sense to move it a little farther downstream where it wouldn't interfere with anything.

zwede

Idle and cruise readings are meaningless as long as you have an exhaust leak. Any leak at all will give you a false lean reading.

I had a 1/8" hole in the collector (used to have a rivet there that fell out). Fixed it and my EFI auto-adjusted 6% at idle and cruise. That's how big of a difference just a tiny leak made.

gkull

Like the other poster said. Put the bung on the collector and even wrap the collector area with thermotec header wrap tape so it heats up faster. To get correct readings you have to have it operate at a temperature range

zwede

GKull: I think you're mixing up narrow band and wide band. Wide bands have heaters and don't rely on the exhaust to heat them. You can stick them into the tail pipe and they will work.

To the contrary, It's possible to overheat a wide band. I had to add a heat sink to my collector-mounted sensor as it would overheat at idle (no airflow).

Belgian1979vette

Exhaust leak will play a game with you. Fix it first.

You need : at least 14 at idle, with a carb more likely 13-13.5.
Cruise, you can get away with constantly 14.

Accel and WOT is 12.5.

gkull

Thanks i goofed up on the wide band.

jaycenk

Fix the Leaks first.
As stated above they mess with readings on O2 sensors wide or narrow.

gerry72

The O2 sensor is great at revealing data. Telling you where you're going. Letting you know of bad news. But don't make the mistake of tuning your car to meet numbers on the sensor. You always tune the engine to what it likes. If, once you fix the exhaust leak, the sensor shows your idle A/F ratio at 14 and it starts and runs fine there and you lean it out to get to 14.7:1 and the idle goes unstable and the car is hard to start, would you call that better? Probably not and you'd put it back to where it ran better and log the data so you can always get back to what the engine likes.

Everyone will throw sensor values at you, and that's fine, but always, always, always pay attention to what the engine is telling you as the first and only reliable voice.

resdoggie

The O2 sensor is heated during warm ups also to get accurate readings quicker from a cold engine. They sensor heater may even heat to temps higher than the exhaust temps which then act to cool the sensor, from what I'm reading. Hence, placement in the exhaust stream may not be as critical. I stand corrected if this is in fact the case.

Swiftrider08

To fix your side pipe leak - the bolt that tightens down the side pipe to the collector, take a second nut of the same size and drill out the threads so it slides over the bolt, this will now act as a spacer. Slide that nut onto the bolt and then thread your good nut onto the bolt. The spacer moves the thread nut down away from the pipe and then you can get a socket and rachet on that nut and really get it tight. This stopped small leaks I had on both sides. No sealant necessary.

MotorHead

Tune to what your particular engine likes. Ball part AFR readings are a starting point.
In conversation with the inventor of the Innovate LM-1 he stated that small block chevy engines like it rich regardless of what the O2 meter says.

resdoggie

Good tip. I did the same thing a few weeks back.

mobird

I'll try this when I get home, however I seem to remember that my bolts are really short (doug's side pipes). As in, there's just enough thread to get the nut started, so I may not be able to do this.