Hey, quick question, when tuning on the dyno my tuner put the O2 sensor in the exhaust (ie. in the muffler). I was thinking that since i have my stock cat and muffler, my O2 readings would have been off by a couple of points. My tuner's dynojet was not equipped with O2 datalogging, but i remmeber seeing ~11.5 as the leanest point.

I'm guessing the O2 sensor would have read leaner than the motor is actually running, should i be concerned at all? I know its hard to give a definate answer. I've heard readings can be up to .7 leaner than it is at the B pipe.

 

you do know 11.5 is pretty dam rich right?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by underpressure02 &raquo;</TD></TR><TR><TD CLASS="quote">you do know 11.5 is pretty dam rich right?</TD></TR></TABLE>

I don't think he has any idea.. the lower the number the richer.

 

oops.. sorry... lapse in thinking, I always get messed up with the A/F ratio. I asked to be tuned to 12.5, i meant to say i saw numbers creep into ~13

well my main concern is the O2 sensor in the stock exhaust.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lenn &raquo;</TD></TR><TR><TD CLASS="quote">
Hey, quick question, when tuning on the dyno my tuner put the O2 sensor in the exhaust (ie. in the muffler).</TD></TR></TABLE>

I think the long and short of it is your tuner is an idiot. You cannot use a sniffer as an accurate AFR measurement tool in a car equipped with a catalytic convertor. You must use a wideband O2 sensor mounted in the manifold.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by beepy &raquo;</TD></TR><TR><TD CLASS="quote">

I think the long and short of it is your tuner is an idiot. You cannot use a sniffer as an accurate AFR measurement tool in a car equipped with a catalytic convertor. You must use a wideband O2 sensor mounted in the manifold.</TD></TR></TABLE>

right, usually the sensor is mounted down the DP a bit for tempreature/accuracy reasons but ya, before the cat is pretty important to getting usable readings. 5min of welding and a $1 nut is no big deal to save a whole engine by tuning it properly IMO.

 

alright.. i had the real strong feeling he should've been putting it in the header (no DP, JRSC), but he's got a pretty good reputation as a tuner (ralphie from DRT in NY) and he's tuned many many many cars successfuly and safely.

He also never got around to checking my plugs after the runs. I brought it up, and he said it was not necessary, although i've read everywhere that you should. He said detonation would show instantly on the graph, however I am pretty sure minor/small scale detonation would not show.

Dont get me wrong though, the guys at DRT are a really great bunch, they were very helpful to me, even told me to call back in a couple of weeks to pick up misc parts i was looking for that they had lying around the garage for free.

But anyways, getting to my point.... so assuming he "tuned" to 12.5 at the sniffer, it means that the A/F at the header is richer than the "12.5" he tuned to. So it probably means that I am running richer than I think? I'm reasoning that since the stock cat filters out some of the exhaust, the probe would read leaner than it would have if it were reading the "unfiltered" exhaust at the header.

I'm asking all of this is because if the probe was somehow reading RICHER than the actual exhaust is, I may be running leaner than I would feel comfortable, which means its time to upgrade my fuel system and retune... which i would like to avoid ($ i dont have)....


Modified by lenn at 4:03 AM 2/13/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lenn &raquo;</TD></TR><TR><TD CLASS="quote">alright.. but he's got a pretty good reputation as a tuner (ralphie from DRT in NY) and he's tuned many many many cars successfuly and safely.

</TD></TR></TABLE>

hahaha

Sent you a pm

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by underpressure02 &raquo;</TD></TR><TR><TD CLASS="quote">

hahaha

Sent you a pm</TD></TR></TABLE>

hehehe... sorry about your bad run in, PM'd back... time to get retuned..... hopefully by boostedhybrid.... NJ isnt TOO far for me....

 

The oxygen sensor is reading OXYGEN, so unless the catalytic converter is releasing oxygen as part of the combustion process taking place inside of it, the oxygen readings at the tailpipe will be pretty close to what is coming from the combustion chambers.

There will be a delay in the results though that needs to be accounted for in the tuning, but any competent tuner should be able to account for this. The cat is there to burn off any hydrocarbons that the engine doesn't.

 

i have actually seen demonstartions, and tailpipe reading are the same except at low low low rpm when eddies and **** make it ack into the exhaust and touch the sensor.

Anyone who says otherwise is wrong. period

I wish i could site the article...