I need to pass inspection in a couple days and I was told that it's better to run rich than lean. Or is it best to run in closed loop at BLM 128? Is it a good idea to have the car run in open loop for only 15 seconds after a warm start or is it best to just leave it at 30, what kind of harm can be done? I have 3.73 gears and my speedo hasn't been corrected, is this going to hurt or help my emissions when they do the 40mph run on the rollers?
Thanks in advance

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, Jon (350 TBI!)
91 Red My website

 

One could argue running rich or lean depending on the type of emission gas you're looking at, but running at stoichiometric (14.7:1) will produce the best compromise for CO, NOX, and HC. If you have a good working cat and your engine is running decently, I'd just go get tested and know that you'll pass. Your car should be running for more than 30 seconds before they start testing, and having your speedo off shouldn't affect it enough (if at all) to make a difference.

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Greg Westphal
'87 IROC 355TPI/A4

 

Fresh oil,
clean filters.
Fuel additive.
Run hot, 190 thermostat.
BLs at 128
not too much timing

 

My advice .... run cats and don't be aggressive on the tune. Don't change anything unless you have a reason to change something. Do a search on this forum for a post made by me with regards to my emissions test. I failed and I did a whole bunch of stuff with regard to the calibration in order to try to pass. Moral of the story is to change only what needs to be changed. If you fail find out WHY you failed. Find out what levels were too high and then adjust accordingly. Too much NOx? Then run richer. Too much HC/CO? Run leaner. HOWEVER - keep in mind that helping one element usually hurts the other. Keep the timing moderate ... not aggressive, not low. Make sure your car is in a GREAT state of tune and make sure your fuel curve is tuned appropriately. If your O2 is bad then you will probably fail so make sure the O2 is good. Check your plugs to find out how the engine is really running. In tank help is also a good thing - "denatured alcohol" from your local Home Depot does wonders. However, don't run alcohol for ANY extended period of time as it attacks rubber components.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

I would also recommend having a scan tool running while you are having the emission test done. The last time I had to take my car through emission testing, I did capture my scan readings and reviewed them later.

Luckily, I passed, but I was surprised how quickly I went into open loop due to prolonged idling. And how long it took to return to closed loop.

When your car goes into open loop, it will show all the inaccuracies in your calibration. If your calibration is too rich, then you will be too rich (even though the my engine tends to go to 15.2:1 in open loop). Conversely, if your calibration is too lean, then you will be very lean.

So an accurate calibration will help, especially if you get thrown into open loop due to prolonged idling.

 

Jon-

I just ran mine thru NJ treadmill emissions last month, straight off the street with no special tuning, and passed easily. Biggest problem they had was with it climbing up the rollers under acceleration and nearly leaving the pit...gotta love low-end torque.

Engine specs are at the link in my sig, LT4-HOT cam and all. If you're in a good state of tune and running closed-loop you should have no problem.

------------------
1982 Z-28

See http://www.mycar.net/mafb/registry/detail.cfm?id=276 for details

 

For you guys that program eproms: Could it be a good idea to make minimum MAP 8Kpa for BLM enable? How bad could it be to have closed loop on at idle?
What octane should I run (high or low)?

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, Jon (350 TBI!)
91 Red My website

 

Not sure about the minimum MAP for BLM enable, although I'd have to ask if you've ever seen a MAP reading that low on your engine. Closed loop is generally better at idle than open loop since the air/fuel ratio would be right at stoichiometric. Run whatever octane gas that gives you the least amount of spark knock, ie: lowest that you can get by with.

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Greg Westphal
'87 IROC 355TPI/A4

 

I just failed. The Emissions reading for NO_x was 1168 and the limit was 970. What does this tell me? What do I need to do to fix this?
BTW, if you have Diacom I have included a link below of my testing.
Keep in mind my data points are slow (160 baud ecm).
My Hydrocarbon level was REALLY low at 22. The Standard was 128. My CO% was 0.08 and the standard was 0.71 so that passed no problem. I was running 87 octane and no detonation but if you look at my engine temp you can see I'm having cooling problems (yes my fan is on always and 160 thermo).
<a href="http://members.aol.com/cyberlax/temp/e-fail.gdf">Diacom-e-fail.gdf</a>
A vin number to use: 1G1FP23E3ML104515

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, Jon (350 TBI!)
91 Red My website

 

Jon, do you have a functioning EGR? Usually high NOx is due to a poorly functioning EGR.

However, your numbers are not that far off (not like Tim, eh?) and you are very good on your HC and CO.

It may have been caused by going into open loop. When my SD car goes open loop, it leans you at idle which does increase NOx.

If it is not an open loop issue, then you could try lowering your Stoich from 14.7:1 to 14.2:1 or even 13.7:1. It will raise your HC and CO, but should lower your NOx. You may find this time that NOx is tolerable but HC or CO is too high...so you may have to play with it and try a couple of shots. But your HC and CO looks so good, that you can risk 13.7:1 to just get the NOx to a "passable" level.

Once you pass, just set it back.

 

Thanks for the quick reply. I just finished searching about lowering Nox emissions and I think I found the reason...ENGINE TEMP WAY TOO HIGH. When they did the test my car was just under 240 degrees! My single fan and stock radiator aren't doing their job. Where do I lower my afr? The only afr table in Tunercat for my ecm (8746 TBI) is the WOT afr. Can I just increase the fuel injector constant by one or two BPWs?
BTW: I have vortec heads....no EGR provision so if I did get EGR I would have to plumb it from my beautiful SLP 4-2-1 tri-y old school stainless headers ...and I don't want to do that. Oh yeah, I don't have the smog pump hookedup but I don't think that is a problem looking at my other values. The cat seems to be working and I believe the air pump is to help burn off HC in the exhaust and heat up the cat but it's only a patch for crappy head design.

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, Jon (350 TBI!)
91 Red My website

 

Just a couple of observations:
Is this a treadmill test or just an idle test?
If you don't have egr is it disabled? I *believe* another reason for high NOx is high advance timing (high compression too?) and if the egr timing is on but no egr, well....
You say you have a properly functioning cat but is it a three way cat? A three way does CO, HC, and NOx. Since most aftermarket cats are two way cats that don't do NOx, I had to ask.

 

I don't know if it's a 2way or 3way but that's a good point. I think it's because my engine temp. I disabled EGR (on temp at -40C, backwards temp on the 7747 and 8746 ecms) so for sure I'm not getting any EGR advance. I think I'm just going to bump fuel a little and retard base timing a degree or 2. Car's kind of hard to start sometimes so I think the retarding will help.

------------------
, Jon (350 TBI!)
91 Red My website

 

As Glenn said - try changing the stoichiometric value lower to run richer. I will increase CO and HCs but lower your NOx.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

I have no idea how to change that with my 8746 ecm. It doesn't have a value for AFR in either open or closed loop! PLEASE HELP ME, I leave for school Sunday but need to pass tomorrow or the car doesn't go.

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, Jon (350 TBI!)
91 Red My website

 

Check out hex location 2AA. For the 747 calibration the stoichiometric AFR is located at that hex address. I would check that address in a 746 BIN to see if it holds 14.7

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

I just looked up the $61.TDF info at TunerCat's web site and I could not find the Stoich. AF ratio in the Constants. It is most definitely there as the basis of the ECM in closed loop is to maintain 14.7:1, but TunerCat has not defined it.

I would suggest contacting TunerCat and asking them to add the Constant to their $61.TDF.

 

Another alternative, is to use the AF ratio for based on coolant temp (this is defined in TunerCat) and then set the enable "closed loop" temp for Coolant temp to a very high temperature to ensure to you remain in this table.

If you calibration is VERY CLOSE to 128/128, then this could work. But if your calibration is off, then this will not work as your tables will be too far off.

I would still give TunerCat a call and ask to have the constant added.

Alternatively, you could look at using a cooler T-stat and making sure the engine is not quite as hot as it was while you were being tested. You really are not off that much and you should be able to "correct" around this. If your numbers were "double" (like Tim was when he tested without any cats), then it would be too far out to 'fix' with the ECM.

[This message has been edited by Glenn91L98GTA (edited September 14, 2001).]

 

All I did was go back through, didn't change anything and the car passed. The engine temp was down to 210 compared to 240 the day before. My NOx fumes were 960, 10 more and the car would be sitting in a barn for a good 6 months!
I'm still kind of pissed off that I can't change the closed loop AFR.
I looked up the hex location and that number isn't part of the actual eprom. It's part of the built on rom which I can't change.
Does anybody have any ideas? I've been looking through the 8746 hack document and editing my definition file but this AFR is unkown and whenever I DO find an AFR it's like 1.8 and I have a hard time believing the AFR is 1.8:1 . I know that some values need to be converted but I tried doing the 100/255 or something on that line (in some programming guide) and that didn't come out to anything even close to a normal AFR!!
Please help a guy out with this one or I'm going to run over my ecm and go to a 7747!

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, Jon (350 TBI!)
91 Red My website

 

Rarely is there a real reason to change the idle low cruise AFRs, in closed loop. You have to remember the ecms AVERAGES 14.7, so while you might want 15.1 during this toggling across stoi, you might go too lean, and then have a lope at idle and ocassional stalling on decleration.
If you want to run other the 14.7 at idle I'd suggest you try going Open/loop at idle.
It's kind of hard to appreciate how much goes into the C/L function. If you can watch a WB O2 sensor at idle on a scope you'd see how much they toggle things.