Topic Options
Rate This Topic
#92625 - 10/06/17 05:15 PM O2 carb tuning
intergrated j 78 Offline
Active BB Member
*****

Registered: 11/16/13
Posts: 448
Loc: chillicothe ohio
Ok here goes, I had a o2 sensor welded on the exhaust pipe about 1 1/2 inches below the manifold on the nova, so I could tune the Dual Jet 2bbl I put on. I used a narrow band one wire sensor not having the $$ for a wideband. After hooking up a voltmeter, I got some readings. Full throttle that I was worried about was about 880-904 mv which is about right according to what I can find on the subject. So is idle at about 780-850. The weird reading I get is at cruise. The voltmeter goes to almost 0. I get a reading of about 021mv. Waaaayyyy past lean. This ia at 60 mph plenty of heat for the sensor to be working. Push the gas down a little at that speed and it goes to 850+ pretty quick as power enrichment kicks in. I next took off the air cleaner and set the engine speed high enough to go to "0" which is main metering, as you close the choke the engine only speeds up about 50 rpm which means I'm close. The reading jumps from 0 to 700+ as I close the choke. What gives? Anyone else had this problem? Do I have a bad sensor? Any ideas would be welcome. Thanks Jay

Top
#92627 - 10/07/17 07:39 AM Re: O2 carb tuning [Re: intergrated j 78]
tlowe #1716 Offline
Active BB Member
****

Registered: 04/01/04
Posts: 3141
Loc: Dysart, Iowa
It may be the volt meter you are using. The response time is not quick enough to really see what the sensor is doing. Or it my average OUT the real measurements and give you a false reading.
A WBO2 should not be that expensive if you are willing to just use a volt meter.
_________________________
12 PORT ADVERTISER
Information and parts http://www.12bolt.com


Top
#92630 - 10/07/17 02:51 PM Re: O2 carb tuning [Re: tlowe #1716]
intergrated j 78 Offline
Active BB Member
*****

Registered: 11/16/13
Posts: 448
Loc: chillicothe ohio
TLowe thanks for responding. I forgot to mention that I used 2 different brand and style of voltmeters with the exact same result. I have a third kind of meter that I could try in a few days but to be honest I think the results will be the same. How much does just the wide band sensor cost? When the sensor in the car goes low after pulling away from a light or when closing the throttle some like at the top of a hill it doesn't just go to 0 instantly. It takes a few steps to get there. Same thing when cruising and the throttle is opened some. It takes 3-4 steps to get to 900mv then just hovers in a 50mv or so range. Jay

Top
#92632 - 10/07/17 07:55 PM Re: O2 carb tuning [Re: intergrated j 78]
70Nova Online   content
Active BB Member
****

Registered: 05/06/11
Posts: 363
Loc: Va
Hi Jay... been a while smile

It could be momentarily too rich, fouling the sensor with soot and then better mixture cleans it up. Or it could be a big lean spot like you suspect. I'd say thats much more common. If it was fouling from too rich mixture, I would expect it to take a while to recover. Too lean would return to showing voltage instantly as the mixture falls back in line

The progression from idle jets to mains sounds too lean, a larger idle jet might help provide fuel closer to where the main jet starts taking over. Idle jets don't only affect idle. So.... maybe try a larger idle jet and set idle mixture with the screw back to where it was.

Top
#92636 - 10/09/17 07:18 AM Re: O2 carb tuning [Re: 70Nova]
intergrated j 78 Offline
Active BB Member
*****

Registered: 11/16/13
Posts: 448
Loc: chillicothe ohio
70 Nova, it sure is good to hear from you! Sadly its been way too long. The Q-Jet, which I am running the front half (primary side) of goes into main metering very quickly off idle. To be honest I don't think I have a soot problem as the car runs good with no black smoke. When I take my foot off the gas suddenly I get a very short spike rich, which is expected. Then as you come to a stop, the numbers come up to around 800 (always moving around a little) as the engine slows down and the idle circuit takes over. On a normal take off from a stop without pushing the gas pedal hard enough to get into power enrichment the reverse happens. As main metering takes over the numbers fall off. The car drives very well except a slight lean nose over when the engine is not fully warmed up and it is cold outside. My next step is to try another voltmeter which I have. (fluke77). I suspect that the results will be the same. One thing that I noticed when I was running the engine at 2000 rpm in the driveway was how just a small difference with my hand would change it from 0 to over 700mv. I'll post up what I find out with the Fluke 77. Jay

Top
#92640 - 10/09/17 07:00 PM Re: O2 carb tuning [Re: intergrated j 78]
strokersix Offline
Active BB Member
*****

Registered: 05/23/09
Posts: 417
Loc: NW Illinois, USA
The narrow band o2 sensor has a large hysteresis loop. Is this what you are observing?

Top
#92648 - 10/11/17 03:05 PM Re: O2 carb tuning [Re: intergrated j 78]
Turbo-6 Offline
Active BB Member
*****

Registered: 12/04/05
Posts: 452
Loc: St. Louis Mo.
From what my small brain can figure a narrow band 02 can only read 14.0 to 15.0 a/f other than that it only shows that it's richer or leaner but not how much. stoich is .5 volts That is why you must use a wide band to read air fuel ratios

Also and this is a big ALSO all racing fuels as in gasoline have different stoic values so a gauge set for 14.7 is not accurate for other fuels because the 02 reads lambda 1.0 as 14.7 a/f ?

Correct me if i'm wrong.
_________________________
Turbo-6

Top
#92651 - 10/11/17 05:50 PM Re: O2 carb tuning [Re: intergrated j 78]
panic Offline
Active BB Member
**

Registered: 01/11/05
Posts: 1475
Loc: Hempstead, Long Island, NY
Vizard suggests that a close approximate can be had in some cases by looking at the relationship between the main jet flow area and the A/F.
If it shows 14.0 with a #72 (not .072"!) jet and you need 13.5, 14 / 13.5 = 1.037. 72 X 1.037 = 74.7.
Obviously, with a Holley the WOT fuel area is both the PVCR + MJ, etc.

Top
#92654 - 10/11/17 06:54 PM Re: O2 carb tuning [Re: panic]
intergrated j 78 Offline
Active BB Member
*****

Registered: 11/16/13
Posts: 448
Loc: chillicothe ohio
Stroker 6, if I understand you correctly I believe that you are talking about moving very quickly then yes the response is very quick and moves around a lot.
Turbo 6 , you are correct it works well in a very narrow range, I just don't stay there long!
Panic, I didnt know about any realishionship between metering area and sensor numbers. This is not a Holley carb but a Rochester Dual Jet, which is the primary half of a Q-Jet. The carb is listed for a 267/305 V8, so I am close.
An update: today with an outside air temp very close to the other tests that I have ran, I tried a different voltmeter, the best one that I own a Fluke 77. (yes I am stuck in the 80s like my kids tell me). The result: idle 750-875, full throttle:(which I was worried about) about 900mv. Cruise: it would read .018-.048 at a steady 60 mph. Tap down a little on the throttle and it jumps up very quickly back to the full throttle numbers as power enrichment kicks in. Gas mileage is good, runs smooth, power is good. No stumbles. I think I am going to call it close enough. If I ever have to take the top of the carb after writing down what I have I might move the APT 1/4 of a turn. Thoughts? Jay

Top
#92655 - 10/11/17 08:06 PM Re: O2 carb tuning [Re: intergrated j 78]
strokersix Offline
Active BB Member
*****

Registered: 05/23/09
Posts: 417
Loc: NW Illinois, USA
j 78, I googled a bit but could not find a plot of narrow band sensor hysteresis. So I may be wrong about that. Perhaps someone can confirm.

Hysteresis means that the sensor voltage versus oxygen partial pressure curve will have two different paths when you go from rich to lean versus lean to rich. Plotted together they form a loop, called "hysteresis loop"

Top
#92661 - 10/13/17 08:41 AM Re: O2 carb tuning [Re: strokersix]
intergrated j 78 Offline
Active BB Member
*****

Registered: 11/16/13
Posts: 448
Loc: chillicothe ohio
Ok, I learn something new every day! Thank you. I have looked too, all I can find is a graph showing voltage vs rich/lean. Forgive me if I don't quite understand, are you saying that the curve for lean vs voltage could be different than rich vs voltage? Like voltage could climb quickly slightly rich and take a lot of lean to fall off by the same amount? Jay

Top
#92665 - 10/13/17 03:53 PM Re: O2 carb tuning [Re: intergrated j 78]
strokersix Offline
Active BB Member
*****

Registered: 05/23/09
Posts: 417
Loc: NW Illinois, USA
Maybe just think about it as sensor response time. Exhaust gasses are constantly changing composition and the sensor has some lag time in response.

https://link.springer.com/article/10.1007/BF00941613

Here is an abstract discussing sensor hysteresis effects under non-equilibrium conditions. Maybe not my imagination after all.

Top

Moderator:  nln6pinto, will6er 
Who's Online
4 registered (70Nova, efi-diy, stock49, will6er), 38 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Newest Members
Thomas79, octane103, schwoch1, Gregory Sheets, Eric Matwey
6001 Registered Users