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Randyj75 | So My Car Failed Emissions... | ||
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My car (1990 L98) recently failed it's emission test for high NOx. The is basically stock w/ 24lb injectors, true dual exhaust w/ cats, and a custom chip to delete the EGR, which has been removed. The car has a recent tune up, w/ new plugs, wires, cap, fuel filter. It had it's intake removed and resealed using FelPro gaskets last April. Other then that, the car runs great, w/ no problems at all. Mileage is about 102K.
The strange thing to me is that it was well within the limits of the other two categories. This what the test said; hydrocarbons 1.4000gpm -0.4612 pass carbon monoxide 30.0000gpm -5.1493 pass oxides of nitrogen 2.5000gpm -2.8883 fail Anyone have any ideas as to why it failed? BTW, I know that deleting the EGR is part of the problem. Thanks, Randy |
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Posted on: 2009/5/15 0:42
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bogus | Re: So My Car Failed Emissions... | ||
Grand Imperial Pooh-Bah
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Not to put too fine a point on it, but, you removed the damned EGR.
That is EXACTLY what the EGR is designed to do. And it is why it is not your enemy. As the engine heats, and the cats heat, the EGR comes into play to put a touch of exhaust gas back into the combustion chamber. That lowers the combustion temps, lowering the chance of detonation and the output of NOx. NOx is a component of acid rain, by the way. And guess what, removing EGR gained you exactly a zero HP improvement... How to fix it? You might get away with a gas additive... but I doubt it. I would reinstall the EGR and go from there. Seriously. |
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Posted on: 2009/5/15 1:38
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anesthes | Re: So My Car Failed Emissions... | ||
Master Guru
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You need a cam with more overlap.
-- Joe |
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Posted on: 2009/5/15 2:09
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'79 Z28. 412 CID, NP 833 transmission, 3.73 10.5" rear end. |
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Randyj75 | Re: So My Car Failed Emissions... | ||
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Quote:
Andy, The reason the EGR was deleted is because it set a code after the new exhaust system was installed. Everything was fine w/ it before the change, it seems that speed density cars need a certain amount of back pressure for the EGR to work correctly, so I really had no choice. That is the reason the car has a custom chip, to delete the EGR. Randy |
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Posted on: 2009/5/15 3:48
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bogus | Re: So My Car Failed Emissions... | ||
Grand Imperial Pooh-Bah
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I find that rather hard to believe, really.
You are still using the stock manifolds. If anything, I am wondering if the EGR solenoid failed. With the older Vette's, wiring and vacuum lines become real problems. I don't know exactly how much diagnosis you did, but, if the vacuum is being pulled, and the EGR is open, I don't see how it will set a code. The codes are set when the valve - a vacuum servo (dashpot) - is opened and indicated as such at the time the computer says so. It doesn't really care about what volume of gas is going in. Short of the EGR temp sensor, it's rather ignorant of the entire process. How did you deduce this to be the problem? |
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Posted on: 2009/5/15 5:42
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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CentralCoaster | Re: So My Car Failed Emissions... | ||
Senior Guru
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The exhaust backpressure is necessary to bleed off EGR vaccum to let it close. If the computer turns off vacuum to it but it still holds, then it will throw a code.
I can't help but wonder if putting a small hole in the diaphram would've solve that, yet still allow the engine vacuum to open the valve when the solenoid is on? The EGR temp sensor is used to detect flow (heat) passing through the EGR, basically acts a feedback to the computer if I recall correctly. I'm not sure how you can tweak the NOx without the EGR. Overlap could work, but I'm not sure how else you'd drop combustion temps. |
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Posted on: 2009/5/15 6:54
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1985 Z51, ZF6 |
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anesthes | Re: So My Car Failed Emissions... | ||
Master Guru
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Higher octane fuel + more spark advance. Lower operating temperature. If I can make a 500hp motor, with no EGR, a big cam, supercharger, No air injection, pass on an IM242 emissions dyno than Randy shouldn't have a problem making his stock L98 pass.. Mass uses the same 'standards' as California regarding the dyno and tailpipe test, although the visual is rather "laxed". They don't check ignition timing. They never even opened the hood on mine. Just ran it on the rollers simulating going up and down hills, slowing and accelerating. My car always passed with flying colors. A lot of you guys like to debate stupid shit like why guys like me run lower thermostats, lower fan temps, etc and I can't help but bang my head against the wall over it considering how much power my combos make and how they pass emissions compared to guys with stock motors. Hopefully the 20 year old I sold my Corvette to doesn't put it into a tree. -- Joe |
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Posted on: 2009/5/15 10:21
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Matatk | Re: So My Car Failed Emissions... | ||
Webmaster
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You running a heated 02 on your car? When's the last time it was changed. Non-heated 02s from out vintage are good for about 30,000 miles, the heated ones are longer but I can't remember off the top of my head.
When's the last time you checked the timing? Matthew |
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Posted on: 2009/5/15 12:27
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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Randyj75 | Re: So My Car Failed Emissions... | ||
Guru Newb
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The O2 was changed when the new exhaust was installed, May of '07, about 10K miles since then. I think the timing needs to be checked, as the last time it was set was by "ear", so I'll do that next. Thanks |
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Posted on: 2009/5/15 13:32
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bogus | Re: So My Car Failed Emissions... | ||
Grand Imperial Pooh-Bah
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oh... timing by ear is bad... very bad... get a light on that. If you are to advanced, and not running enough octane, you will have issues.
however, as the car sits in the test lane, waiting to reach that stage, the cats heat up and the NOx go up. Not a good mix. |
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Posted on: 2009/5/15 14:20
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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bogus | Re: So My Car Failed Emissions... | ||
Grand Imperial Pooh-Bah
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Joe - you are basically building from a net-zero basis. You have the skill to re-engineer the thing properly to deal with the output. I find fiddling with stock engines only pushes the settings out of range and compensating gets tricky. I do not recommend lower t-stats and fan settings on stock engines, they are not tuned nor built for that. Your engine, on the other hand, was. Hence forth the difference. |
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Posted on: 2009/5/15 14:23
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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anesthes | Re: So My Car Failed Emissions... | ||
Master Guru
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I was in a bad mood after speaking with the building inspector when I made my previous post. Please ignore. - Joe |
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Posted on: 2009/5/15 18:34
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Randyj75 | Re: So My Car Failed Emissions... | ||
Guru Newb
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OK guys, lets clear up a few things.
If I could reinstall the EGR, I would. But I can't, because I would then have to go back to the stock chip, which would then turn the EGR back on. Doing this will cause the car to set a code on the dash, which would then cause the car to fail the test again. The idea is to have the car pass emissions. Remember that I only drive this car 4 or 5K per year, it is not my DD. Finally, let me say that I don't appreciate people telling me I am misrepresenting the truth. My car is stock by choice, and it will continue to be that way. I have no interest in a 500HP engine in my car. The EGR and Air systems were removed because I had to do that for the dual exhaust system that I chose to installed. If I had known before hand what that would do, I would have just gone w/ a stock catback. Thanks to Joe and CC. Randy |
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Posted on: 2009/5/19 14:49
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bogus | Re: So My Car Failed Emissions... | ||
Grand Imperial Pooh-Bah
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Who is accusing you of misrepresenting the engine?
As for the EGR, I don't give a damn if you drive the car 1 mile or 10000 miles a year, it has to pass the test regardless. So that becomes rather moot. Is there an option to get the car tagged as a classic? It is nearly old enough. I would also consider a fuel additive like Smog Check. That stuff does help... never know. |
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Posted on: 2009/5/19 14:53
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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CentralCoaster | Re: So My Car Failed Emissions... | ||
Senior Guru
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Could retarding timing a few degrees help? Seems like it could reduce cylinder pressures and temps.
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Posted on: 2009/5/19 15:23
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1985 Z51, ZF6 |
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Randyj75 | Re: So My Car Failed Emissions... | ||
Guru Newb
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You did, Andy. |
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Posted on: 2009/5/20 4:09
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Randyj75 | Re: So My Car Failed Emissions... | ||
Guru Newb
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Yes CC, this is what I am going to try. Thanks |
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Posted on: 2009/5/20 4:10
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Randyj75 | Re: So My Car Failed Emissions... | ||
Guru Newb
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Quote:
First line, Andy. |
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Posted on: 2009/5/20 4:11
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bogus | Re: So My Car Failed Emissions... | ||
Grand Imperial Pooh-Bah
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No. You misread my meaning.
What I didn't believe was the nature of the EGR problem. Not whether the engine was stock or not. |
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Posted on: 2009/5/20 4:17
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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anesthes | Re: So My Car Failed Emissions... | ||
Master Guru
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Quote:
Retarding usually elevates HC #s.. Advancing timing typically reduces cylinder temperature to a point. I don't know what he is running for fuel though. A modern 3-way cat may fix it too. Like you guys, I don't understand what his EGR issue was with the true dual exhaust, however I also don't think the EGR cuts Nox down as much as you would think. I think with some really good fuel (93+), it should be fine. -- Joe |
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Posted on: 2009/5/20 10:49
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CentralCoaster | Re: So My Car Failed Emissions... | ||
Senior Guru
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I've seen the difference the EGR makes during the test when it opens. The NOx drops like a rock. Although even without EGR it still hovered around the high limit, so surely its possible to squeak by without it.
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Posted on: 2009/5/20 13:18
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1985 Z51, ZF6 |
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bogus | Re: So My Car Failed Emissions... | ||
Grand Imperial Pooh-Bah
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it's all about the heat. Even with a working EGR, the heat builds during extended idle. It's heat that creates NOx in the first place.
once the cats start to overheat, all bets are off. Even a three way cat, like those on my 92, won't kill NOx without the help of a working EGR... or, a cam with appropriate overlap. |
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Posted on: 2009/5/20 14:20
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_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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anesthes | Re: So My Car Failed Emissions... | ||
Master Guru
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Quote:
Andy.. They don't even put EGRs on cars now. Newer cars are more fuel efficient, make more power, have less emissions without an EGR or a smog pump. While the EGR does help on older cars, the L98 had a crap tune from the factory and I'd think a new cat and better tune would result in better emissions. -- Joe |
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Posted on: 2009/5/20 14:42
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bogus | Re: So My Car Failed Emissions... | ||
Grand Imperial Pooh-Bah
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he already has new cats on the dual exhaust.
The early LS1 was without EGR, but the later versions got the EGR back... somewhere around 2002 or 2003... |
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Posted on: 2009/5/20 14:49
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_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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CentralCoaster | Re: So My Car Failed Emissions... | ||
Senior Guru
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So then I guess we should just tell him to put an LS1 in there so he can pass smog. But until that happens the L98 isn't fuel efficient, makes less power, and has more emissions even with the EGR and smog pump. |
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Posted on: 2009/5/20 15:47
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1985 Z51, ZF6 |
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anesthes | Re: So My Car Failed Emissions... | ||
Master Guru
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Riight, but he still should be able to pass without the EGR. Nox gasses are created when combustion temperatures are above 2500 degrees. A higher octane fuel with a blend of alcohol should reduce combustion temps. I'm surprised anything running 10% ethanol even has Nox emissions. But even still, a good 3 way cat will reduce Nox emissions enough to pass. -- Joe -- Joe |
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Posted on: 2009/5/20 16:25
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bogus | Re: So My Car Failed Emissions... | ||
Grand Imperial Pooh-Bah
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Perhaps enough drygas...
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Posted on: 2009/5/20 17:00
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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