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Posted by: r_towle Aug 19 2008, 07:13 PM

Instead of drilling and welding in a bung for an O2 sensor prior to the muffler,(clients car) how accurate would a tailpipe extension tube with an O2 sensor be?

Im thinking of a 1 foot long tailpipe extension with the O2 sensor welded in as close to the muffler as possible, yet without touching the stock system.

I intend to clamp the pipe in place with a stainless sleeve clamp so its air tight.

Any thoughts?
Rich

Posted by: orange914 Aug 19 2008, 07:28 PM

1 for best acuracy it should be as up stream as possible

2 on a dead end it wont be acuate with out the constant exhaust flowing by

mike

Posted by: r_towle Aug 19 2008, 07:31 PM

I dont understand dead end..
Exhaust is always flowing by via the tailpipe when the car is running...yes???

Will it show lean or rich at the tailpipe?
By what average percentage??? I can do that math.

BTW, this is how the state emmission tests are done

Posted by: orange914 Aug 19 2008, 08:46 PM

maybe i didn't understand you. i think i see now your planning to bolt a section between the muffler and tip... no?

the o2 is different than the sniffer in operation. to create voltage the one wire o2 along with unburnt fuel relies on heat, the closer the hotter. it can be further downstream if it has "power wires" to self heat.

the sniffer has a pump to draw the sample across the bench to read the hc, co etc... and yes thats how ca. does the test. but it can have false readings if any air makes its way to it by a ex. leak, even huge tip pipes can influence it's readings. the c.o is what could be effected and be slow to respond and could have lean readings.

the closer the better as a rule, but not always practicle. also on a 914 system the exhaust doesn't mix until the muffler so you'd only get a single cylinder reading if very close.

Posted by: r_towle Aug 19 2008, 08:53 PM

This specific system is a modified bursch with a single muffler at the end...its really not doing to much. Its loud.

The only place I could get all four is just in front of the muffler and that would leave a mark...I would have to drill, weld, plug etc.

If it was mine, NP...but its not mine so I am going to sniff from the end.
Its a four wire O2 setup with an LED readout box...I assume the two heater wires would get power from batteries....dunno.

I borrowed the unit.

So, will the readings be diluted and read to lean?

Rich

Posted by: orange914 Aug 19 2008, 09:32 PM

as long as it's a heated o2 it should be fine, just keep it as far from the tip as possible

to lower c.o. readings, the sniffer close to the outlet trick was/is used on some shady smogs. but is hard to regulate and often gets too much oxygen. (did i say that?)

Posted by: TimT Aug 19 2008, 09:35 PM

At idle it may give a false reading if there is any reversion in the exhaust stream, (from lumpy cams, etc). At higher rpms it will be fine.

Posted by: r_towle Aug 19 2008, 09:57 PM

Thanx Tim...I am really concerned about part load and WOT....I feel its still to lean based upon the plugs.

So, this is a drive and tune session with the LM1, allen wrench for the MPS (its custom) a POT for the CHT circuit and lots of chinese firedrills till I get the part load and WOT perfect...should be fun...not.

I actually may have a chance to buy a floor dyno that is being retired from a state inspection station...
I am hoping to get that with the computer and just acquire some simple dyno software instead of the inspection software...

That will make it a bit easier to deal with.
He may sell me the sniffer, but he may keep it...its up in the air and depends upon the state regs.

Rich

Posted by: McMark Aug 20 2008, 12:27 AM

You'll have an issue with delayed readings since the exhaust will be 'mixing' in the muffler.

Posted by: Mark Henry Aug 20 2008, 09:25 AM

Tim is right and Mark is to a point as well, if you drive as you check or give it say 30sec to settle down you're OK.
If your adapter has leaks it will give false readings.

The floor dyno may not be a good deal as it's most likely just a method to load the drivetrain for testing and the sniffer reads emission levels not AFR. I'd know for sure before jumpping on that.

Posted by: r_towle Aug 20 2008, 09:41 AM

The floor dyno will require a bit more research.
Initially its an emmission testing rig.
In reality its a dyno that has been modified...
I need to find out the manufacturer and call them to see if I can adapt it to be just a dyno...software is easy to change...hardware needs to be correct...

The O2 rig I am using is your old rig Mark....you sold it to Drew...I think...

Rich

Posted by: Mark Henry Aug 20 2008, 03:51 PM

I know I sold one to someone here but can't remember who BUT I sold a Haltec 30 narrow band not a LM1.

I think it was "ottox" as he bought a SDS and matching WMS O2 off of me and he sold his LM1 (I believe).

Posted by: TimT Aug 21 2008, 12:36 AM

We looked into buying a surplus emissions dyno a few years ago. Here in NY the dynos follow a loading program folowing a program.. Dont know about the dynos in Mass though.

The dyno was made by Mustang, and we contacted Mustang to see if it could be retro fitted to be manually loading. Basically it was cost prohibitive to do so. In the end we bought The Racers Group old dyno when Kevin got out of the Unichip business.