O/2 Sensor location

[art leong]

I have my O2 about 8 inches from the end of the collector. In order to get a proper reading at idle I have to put on a 24 inch extension made from flex pipe.
I can't reley on the O2 reading below 4,000 rpms without the extension on. After 4,000 or so it reads fine.
One thing I have noticed though is that the O2 reading is higher (leaner) in first and second gear, than in high at the same rpm's.
I've been tuning off of the high gear readings. And it seems to work.

[Alan Roehrich]

We locate ours right after or right before the minor diameter in the merge, preferably before, so it is as far from the end of the collector as possible. If not using a merge, 4-6" from the ends of the primaries. Also, between 10 and 2 o'clock, if possible, so as to prevent moisture from condensing in the sensor when it is off. The sensors aren't real happy lighting off with water in them. You may see some fluctuation at idle, or rolling along in the pits or staging lanes, due to fresh air being drawn back into the collector at low RPM, but when it really matters, going down the track, it will be fine.

[art leong]

Originally Posted by A56

I put them anywhere between 10" - 14" out on the primary tubes, try to find a good average for all eight and stick with that # of inches away from port. If you have a step in that area, put them right after the step, this helps because you just added some area to the primary tube, and if you do it just after a step the area change isnt as critical. Make sure you use a long O2 weldment, so the O2 dosent protrude into the tube excessively. In the collector I put them in the choke if the choke isnt excessively small, or just before the choke as to not change the area but get all the gasses. Though lots of people say not to put them in the collector, I dont agree, if your collector isnt short, they work fine there. I have not tried them on a straight collector, but can only assume you will get outside air at low RPM.

Mark Lelchook
F/SA

Mine shows excessively lean at low rpms. I once tried to tune the idle before I knew about the extension trick. And it was smoking black and still showing lean.

[art leong]

Originally Posted by A56

Well there you go then, at low RPM the pulses draw back outside air into the collector, especially on a 4 cyl with a 180 degree pulse.

Mark Lelchook
F/SA #764

That's it and it is just as bad on the 2 step. Shows real lean.
Over 4,000 rpms it seems to work fine.

[Ed Wright]

Problem with putting it in a primary tube is, if you get something in a jetborvinjector you won't see it in your run log. With it in the collectors, you will see a lean indication. You won't know which Cyl, but you will know which bank. If it develops a misfire for any reason you will see a lean indication, but a misfire from ignition, etc) you won't always hear it at high RPM) will cause an erratic reading. A misfire causes lean spikes. Only way I would want one in a primary would be having one in each tube.
I know I don't know everything, but have been tuning EFI cars for 23 years now, and have done it both ways. I much prefer them in the collectors, at least a foot from the end.

[Bill Bogues]

I thank everyone for their reply's. This is one of the nice things about the forum ; your just a keystroke away from finding out just about anything. Since I have a small diameter and relatively long collector I'm going to put the sensor just past the point that it merges. I think it will probably work out ok there.

[KRatcliff]

I think that is your best option at this point. That being said, I am in the process of putting one in each tube and in the collector for a total of 9 on my car. Surely, I should be able to figure this tuning thing out somewhat.

[art leong]

Originally Posted by Ed Wright

Problem with putting it in a primary tube is, if you get something in a jetborvinjector you won't see it in your run log. With it in the collectors, you will see a lean indication. You won't know which Cyl, but you will know which bank. If it develops a misfire for any reason you will see a lean indication, but a misfire from ignition, etc) you won't always hear it at high RPM) will cause an erratic reading. A misfire causes lean spikes. Only way I would want one in a primary would be having one in each tube.
I know I don't know everything, but have been tuning EFI cars for 23 years now, and have done it both ways. I much prefer them in the collectors, at least a foot from the end.

Hi Ed. Not to steal the thread. But can you tell me how I come out of the trailer. Warm the car up. Then make a run pops and bangs all the way down the track. Check A/F/R it looks fine everything in the data logger looks normal. Make zero changes go for another pass the car runs clean not a pop or bang Picks up 2 1/2 tenths. Datalogging looks the same as the first run?. Car runs clean the rest of the day.

[Ed Wright]

Art, is the coolant temp the same? Anytime I have had one pop & bang it has looked lean. If the engine is cooler I would guess it's a tad lean. My stuff always goes down the track quickest richer than the dyno liked. If your problem is at lower temps you might try adding a little fuel in your air/fuel coolant temp correction table, at the temp you are seeing first pass. That's providing you don't warm
It up to the same temp it runs at the rest of the day.

[Ian Hill]

Originally Posted by art leong

Hi Ed. Not to steal the thread. But can you tell me how I come out of the trailer. Warm the car up. Then make a run pops and bangs all the way down the track. Check A/F/R it looks fine everything in the data logger looks normal. Make zero changes go for another pass the car runs clean not a pop or bang Picks up 2 1/2 tenths. Datalogging looks the same as the first run?. Car runs clean the rest of the day.

Do you fog the engine after every race day? Next time you head to the track, do your warm up and pull the carb to check intake plenum, I bet some of the oil is present until you make a complete pass washes it out.

Ian