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Elusive R
05-03-2006, 01:26 PM
I've posted this on Lateral-G as well, but thought I should try here. I'm having a very tough time getting my car through emissions and I think it is O2 sensor related. Here's what I'm running:

ZZ4 w/TPI injection and 1.6 rockers
Accel DFI Gen 6 system
Long tube headers
O2 sensor (standard 3-wire narrowband) approx. 1.5 inches behind collector flange in passenger side header
Mallory Hyfire 6AL

And the problem: I went to get emission tested last weekend and failed (twice) in all areas - idle and loaded. I discovered after some computer logging that my O2 sensor is not reading at idle - it shows ~0.02 volts and this continues at low loads as well. I did have the computer setup to run closed loop at idle and the computer is adding fuel because it thinks it is lean. The sensor is also very slow to respond to load changes. When it does read, the highest reading I get is maybe 0.300 volts. I have occasionally seen it read on the rich side, but only briefly. I really don't trust the lean reading because just walking behind the car while idling will make your eyes water - it is very rich and friends who have driven behind me complain that it stinks.

At the time of the emissions test, I did not have the Mallory box hooked up. I tried last night to hook up a 4-wire narrowband I borrowed from a friend, but I got the same types of readings - nothing at idle and lean once loaded. The Mallory box allowed me to add some timing at idle and also pull 25% of the injector pulse, so it definitely ran better and I think I'm getting closer. The idle quality certainly improved, but I am now in open loop at idle to prevent the computer from adding fuel again.

So my big question is - what next? I think I need to get a wideband that I can monitor and also feed the narrowband signal into the computer. I have worked with the widebands a great deal in my past jobs, but not with my own car or with others, so I'm concerned that I'll run into the same issues that I have with the narrowband. However, I do strongly believe that a wideband should be able to keep itself hot enough to read (and be accurate) at idle. It just seems odd that the narrowbands - both heated - are not reading. Is it possible I have a giant exhaust leak that is tricking the sensor?

Open to all opinions and thanks in advance!
Ryan

Fuelie Fan
05-03-2006, 05:13 PM
I once helped a guy tune a Motec system. Before I got there, he had already been working on it. He was doing the same thing, "it shows lean, so I'm adding fuel, but it's not getting any better". Long story short, it was SO rich that it was misfiring, and this misfiring results in a lot of unburned air getting to the oxygen sensor and reads lean.

Note, the oxygen sensor itself was doing exactly what it was supposed to do: read oxygen. Also note that a wideband is susceptible to the same problem, so don't waste your money until you know what the problem is.

Finally, a 3 wire sensor should be heated. All the 4 wire adds is ground isolation. Moving to a 4 wire doesn't improve things.

Of course, you should have the answer right in front of you: what were the emissions results? If it was really lean under load, you would see very high NOx.

The other things that you describe (only 300mv max output and slow response) do suggest a damaged sensor. I've seen this happen to an overheated sensor. But, the fact that you've duplicated it with another sensor seems to dismiss this.

I will also say that I've been behind lean cars that were smellier than rich cars. My Nova is pretty smelly in closed loop at idle because it doesn't really tolerate 14.7 very well and misfires.

Bottom line, I would start by replacing your sensor just in case (because it's cheap) and then try to figure out where all the extra oxygen is coming from. It could be rich misfire. It could be an exhaust leak. (The emissions data would also help with this). It could actually be lean (but that sounds very unlikely given your 25% experiment). I wouldn't go straight to a wideband.

Elusive R
05-04-2006, 07:27 AM
Fuelie,

Thanks for all the ideas. I don't think I've ever added fuel to the tune, because the base tune was definitely rich. I pulled some fuel out and it's been running fine - and it passed emissions in November, but the tags came up this month so I had to go back. So something definitely broke between now and then.

The other problem is that I don't get NOx results for my year here in Arizona - so I can't tell if it truly is lean and misfiring. I only get CO and HC and I failed both. I think I may end up leaving it in open loop at idle as that seems to be working very well. I spoke with the guys at Arizona TPI a long time ago and they told me they always setup ZZ4's with TPI to idle open loop - probably for the same reason your Nova doesn't like it. I won't get a chance to work on it again until Saturday, so I'll see how it runs then.

The only reason I tried the 4 wire sensor was due to the fact that it was free from a friend, so I didn't have to buy a new sensor that I probably don't need *crosses fingers*. I'm trying to not spend too much money on this whole deal since I just got married and things are a bit tight. I'll try looking at the sensor wiring and see what the heater circuit is actually seeing and also double check the signal voltage to make sure it's not a problem in the computer (doubtful). Hopefully I can get this straightened out and go to a wideband later on once I have some spending money and then nail down the tune for good.

Thanks again,
Ryan

Fuelie Fan
05-04-2006, 10:44 AM
My nova has a TBI setup, and the pulsewidths are too small to idle on in closed loop, so I have to go open loop and rich just bring them into a reliable range. I've idled ZZ4s in closed loop before, they're pretty tame all things considered.

If your CO was high, you're definitely rich. So, you just need to determine whether the oxygen is from a leak or from misfire. If it was fine before and is now running poorly, I would look at your exhaust system to make sure you haven't blown a gasket.
It could also be possible that your regulator took a dump and has pegged the pressure. Has your fuel pump gotten any louder recently? Also, check your MAP sensor output, make sure a vacuum hose hasn't come off, that would also make it crazy rich.

Elusive R
05-04-2006, 11:21 AM
I'll probably give closed loop idle another try if I can get the O2 straightened out. I'm getting close to too low of a pulsewidth, though. I'll have to check out the header flange as well. Who knows....lots of variables. I know the MAP is ok, too, but I'll check fuel pressure just to make sure I cover all the variables.

Ryan

Elusive R
05-13-2006, 10:52 AM
Well it took me two weekends, but I think I'm finally getting closer. I found out that the O2 sensor was not receiving any heater voltage, so I took care of that and voila! I still failed the emissions test but I got quite a bit closer. Just this morning, I finally found the idle sweet spot, so it's idling in closed loop at more or less stoich - no wideband to confirm that, but a lot of the smell is gone. I was suprised at how touchy the injector pulsewidths are - .1 or .2 ms either way goes totally rich or lean/lean misfire. I just need to do some around the neighborhood tuning for the loaded side and hopefully I can get it through today. I did end up adding about 8% more fuel at idle than what I ran last weekend, so I am thinking that I went way too far lean. Oops. Wish me luck!

Ryan

trackrat79
05-23-2006, 10:57 AM
I was under the impression that was not possible or legal. My friend tryed that a number of years ago and the tec just laghed at him. When you look up a zz4 crate motor in the gm catalog it used to say not for use in polution controlled vehicles. Did they change something about the motor.

Fuelie Fan
05-23-2006, 11:10 AM
Not sure what the laws are like in AZ. You cannot "legally" put a ZZ4 in a pollution controlled vehicle in CA...I'm sure many have, however.

Elusive R
05-23-2006, 12:31 PM
I have to be emission tested, but there is no visual and the only equipment check is on the gas cap, so it's really not a 'smog' check. My car is technically a '72 (with '70 sheetmetal), so I have no idea what it should have (smog pump, AIR, etc), but I've never had any problems here (equipment-wise). I may be moving to CA soon, is there anything I'll need to get it through there? Without doing any research, I've heard that emissions testing is only required for '73 and up??

Also, I've gotten everything to pass now except for idle HC. It's been so hot here the last couple of weeks that I can't take enough fuel out at idle to lean it out. I'm going to try an early morning time this weekend to see if that helps. Boy it sucks going to work - getting up early, going home late = no time for the car.

Ryan

Fuelie Fan
05-24-2006, 07:53 AM
Your car will be exempt in CA, no smog check at all. In fact, I think it got moved up to pre-76 a few years back.

trackrat79
05-24-2006, 11:36 PM
Sorry to say but the 30 year rolling window got revoaked. As it stands right now 73 and older are smog exempt. I emphasize (as it stands right know) there is legislation beeing drawn up to abolish the hole classic vehicle exemption. California wants to be like Japan and require you to replace you're engine every 60,000 miles and have the entire suspension replaced every 100,000 or it gets scrapped no ifs ands or buts.Your every two year smog check will become an every year hole car safety inspection. You can thank all the frikin tree hugers and polution control people for this.

Fuelie Fan
05-25-2006, 06:46 AM
Not quite. They did revoke the moving 30 year window, but did NOT roll back the exemptions. It's still pre-76.

"Sacramento, CA - Today the California State Assembly passed with bi-partisan support Assembly Bill 2683 by Assemblywoman Sally Lieber (D-San Jose) that will improve air quality by keeping 1976 or later model year vehicles in the smog check program. Under the measure, all pre-1976 model year vehicles would remain exempt from California smog check requirements."

Fuelie Fan
05-25-2006, 06:56 AM
And you know what else? I don't have a big problem with it. Why NOT keep your emissions equipment in tact? EVAP systems don't hurt power. High flow catalysts are cheap and plentiful. A lot of high performance heads, cams, and intakes have EO numbers. The only issue I see is smog parts availability, but I'm hoping that the law will drive demand which keep manufacturers pumping out your parts.

Off-roaders have a saying, "tread lightly", and I think we as a community ought to have a similar mindset. IF we can make a ton of power AND be clean about it, why not? If I ever do an LS1 swap into my car, for example, I'm swapping in the catalysts and everything. There's absolutely no reason not to.

Elusive R
05-25-2006, 07:43 AM
What kills me is the guys in newer cars that gut their cats out to get more power. Absolutely irresponsible and worth what, 5-10 hp max? All they'd have to do is put a set of appropriate high-flow cats in. It's always the people who can afford those types of parts that won't buy them, too. Yikes! I feel like I did my part by putting the EFI and the 6 speed in mine (although I still have to nail down the tune) and I've considered adding cats, too. Once I got the O2 sensor working, my loaded emissions were cleaner than they ever were with my low power, low compression smog-era 350 that was in the car before.

Ryan

TD509EFI
05-25-2006, 10:32 AM
Ryan,

Couldn't ageee with you more!:twothumbs

John

68Formula
05-27-2006, 05:04 AM
Ryan,

If you've been running that rich for a long time, might be time for new plugs and the O2 sensor might be carboned-up too.

Elusive R
05-27-2006, 10:38 AM
Mike,

Thanks - it got new plugs not too long ago, but I'll check them again. I changed out the O2 sensor, too.

Ryan