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O2 sensor question
https://www.slantsix.org/forum/viewtopic.php?t=19251		 Page 1 of 2
Author:  ceej [ Sat Aug 19, 2006 9:23 am ]
Post subject:  O2 sensor question
What effect on reading should occur as the O2 sensor is moved further down the pipe from the manifold? Will it change the reading?
My O2 sensor is mounted about six inches beneath the manifold on
a 2 1/4" Head pipe.

CJ
Author:  Eric(Shivadart) [ Sat Aug 19, 2006 10:08 am ]
Post subject: 
You're readings will be less accurate, you can combat this with a heated o2 sensor. Try to stay near the manifold if you can though.
Author:  sandy in BC [ Sat Aug 19, 2006 10:29 am ]
Post subject: 
Eric is right.

However ,I run an unheated O2 sensor on a collector at the end of long tube headers and have no problems....takes about 1 block to warm the sensor on cold Canadian winter mornings.
Author:  ceej [ Sat Aug 19, 2006 11:01 am ]
Post subject: 
The sensor seems to be heating up just fine. Does running it in a slightly cooler spot in the exhaust flow shift the reading one way or the other, as an offset to rich?
The reading is stable enough, and I get a reading right away. Getting the idle mixture stable is going to be a chore. The moment the idle smooths out, the idle bumps up and I go rich on the meter. If I dial them down to a midscale or slight lean idle, the engine runs rough. Knife edge.

I've got the A/F reading a bar or two rich of peak at cruise and in the transition. One jet size smaller, and I drop off scale lean at cruise. This is with the Black spring in the secondaries to hold them out.

I'm working through Holley's instructions for the secondaries right now. Still no bog with the short yellow. It goes like a scalded cat. I'm going to install the white spring when the engine compartment cools off a bit to see if I get a bog, then play with the shooters again.

Running 52 primaries, and if memory serves, I think DusterIdiot stuffed 52's or 53's in the secondaries.

The Power Valve is now a 9.5
I was experiencing a dead spot with the 8.5 PV. No more.

Last tank delivered 18.5 MPG with the secondaries locked out, but I had the dead spot and the lean cruise situation. We'll see with the bigger primaries.

I'm cruising with just a hint of pedal, and the vacuum is holding around 12" HG on the flat at 60 mph. The vacuum cruises a little higher in the 65 mph range. Tall gears. If I drop back to 55 mph, I get a very nice 16" HG cruise. That'll get me killed on the freeway though...

This has been an interesting process. I just got back from a 20 Mile cruise at 60ish speeds, so I'm going to get another plug read. Hopefully a hint more color. It's really tough keeping my foot out of it. The car creeps up to 70-75 if I don't keep my mind on the speedo instead of the nifty growl coming out the tail pipe.

I'm going to try dropping back to a 28 shooter. That should extend my pump shot a bit. If it falters, then back to the 31. Here's hoping!

Any input appreciated!

CJ
Author:  Pierre [ Sat Aug 19, 2006 3:28 pm ]
Post subject: 
If you get any steady reading then its fine. If its too cool or too far from engine, then you either will get an intermittent reading or no reading at all, not an inaccurate reading.

If you have exhaust leaks upstream of the o2 sensor, then you will get erroneously lean readings.

Remember narrow bands aren't made for precision tuning. One or two bars above stoich is close enough. If you want more accuracy wideband is the ticket.
Author:  MitchB [ Sat Aug 19, 2006 3:54 pm ]
Post subject:  Re: O2 sensor question
Quote:
What effect on reading should occur as the O2 sensor is moved further down the pipe from the manifold? Will it change the reading?
My O2 sensor is mounted about six inches beneath the manifold on
a 2 1/4" Head pipe.

CJ
As long as the sensor does not take a very long time to heat up or if it does not cool off and stop working during periods of extended idle or slow speed driving, there will not be any downside to how far away you mount it from the cylinder head. Computer controlled cars are need to calibrate the exhaust pulse delay - which is the time it takes for each cylinder's exhaust pulse to reach the oxygen sensor, so it knows how to make fueling corrections. With a nonfeedback carb, this obviously is not a concern.

Mitch
Author:  ceej [ Sat Aug 19, 2006 7:24 pm ]
Post subject: 
Excellent. Thanks for the info.

I installed the white secondary spring. No bog. Hmmm. It really scoots.

I'm running right around Stoich on the narrow band, so I guess I'm fine. It really gets with the program now.

My pal Speedy and I were on a test drive south of town when our fire pagers started screaming, so I made a quick U'ey and mashed it. Got a grin out of my engineer! She's really starting to scoot!
Made it back to the Fire Hall in short order, and made the first out truck.

Thanks again!

CJ
Author:  Sam Powell [ Sun Aug 20, 2006 7:24 am ]
Post subject: 
What carb are you running? This all sounds very cool.
Sam
Author:  Joshie225 [ Sun Aug 20, 2006 7:46 am ]
Post subject: 
Sounds like you've got the primaries very close. I wouldn't be afraid to let the meter show lean under cruise as long as it goes rich when the power valve opens. Chances are if you lean out the primaries and get the cruise A/F around 16:1, or leaner if it will stand it, you'll need to open up the PVCR a little to get best power. The only problem is you may loose a little cruise vacuum, but that's ok. More lean mixture is more economical than less of a richer mixture. Pumping losses are lower and the dynamic compression ratio goes up. This has been proven over and over on piston engine aircraft.

The idle will almost always be rich. You must have excellent fuel distribution and a very mild cam to idle at lambda. The mixture shows lean before it idles cleanly as misfires have excess oxygen as not all the fuel and oxygen burned so the meter shows lean. Don't worry about it. Just set it up so it starts and runs nice and smooth and the choke opens as fast as the engine can stand. A heated intake helps a lot with getting the chioke open fast. That's why all desmogged engines have hot air intakes. But you probably knew that. ;-)
Author:  ceej [ Sun Aug 20, 2006 1:46 pm ]
Post subject: 
This is a Holley 390 on an Offy intake.

I think I'm going to leave it alone for a bit. It's running pretty close to Stoich. One primary step down, and it leans off the guage. Seems to run OK, but makes me nervous. I may experiment with dropping a heat range on the plugs.

Still not getting much color to them.

Well, back to working on the F163 in the fork lift. Darn up-draft carburation anyway! :D

CJ
Author:  Pierre [ Sun Aug 20, 2006 3:27 pm ]
Post subject: 
Your not going to get much color on plugs when you run close to stoich, thats normal.
Author:  Avenger2040 [ Sun Aug 20, 2006 5:22 pm ]
Post subject: 
Dang!, my plugs are black that means I´m running too rich? or lean?, I will try to get a A/F gauge and 02 sensor to get a good reading of the mixture trying to keep it stoich.
Author:  DusterIdiot [ Sun Aug 20, 2006 6:04 pm ]
Post subject:  Yuck...
Black plugs mean too rich...Black and sticky means you have an oil control issue...

-D.Idiot
Author:  Pierre [ Sun Aug 20, 2006 6:10 pm ]
Post subject: 
If you pull a plug and its black doesn't mean you've been continually running rich. If you just recently did a full WOT blast or put high load on the engine the plugs will take a few miles to turn back to their regular color again.
Author:  Avenger2040 [ Sun Aug 20, 2006 7:57 pm ]
Post subject:  Re: Yuck...
Quote:
Black plugs mean too rich...Black and sticky means you have an oil control issue...

-D.Idiot
Okay, now I know that I´m running too rich, for luck they are not sticky. I will clean my plugs and try to adjust the mixture tomorrow morning..... you got plenty of time while you are unemployed......
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