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  #16  
Old 01-12-2004, 07:21 PM
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checked the duty cycle do I need new O2 sensor?

Today it was relatively warm (high 30s) compared to least few days, I took the opportunity to do some work. Preparing the car for the next round of NJ emission inspection.
Changed the spark plugs (Bosch F8DC4) which were 6 months old looked OK.
Changed the air filters did not look too bad (2 year olds).
Checked the duty cycle (with Fluke automotive meter) when engine cold (open loop) it is rock solid at 50% when warmed up (closed loop) it varies from 50 to 60 % I would guess the average is ~ 54% at idle. The idle is very smooth, still the duty cycle varies quite a bit. Do you think I need to change the O2 sensor? it is 2 years old or ~30 k mi.

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  #17  
Old 01-12-2004, 07:59 PM
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No, there's nothing wrong with your car and nothing wrong with the parts you are removing. The 103 engine family has been identified by the California Air Resources Board as a "high emitter profile". Most are high on HC and many pass by a hair or fail marginally.

The key as I said in my previous post is to "manage" the test - make sure the converter is as hot as possible using the techniques I mentioned or any other techniques that you can think of. There's not much else you can do.

Even having to test the car in the winter is a disadvantage. Testing on a hot summer day will mean a hotter converter, which could be enough to make a difference between passing and failing.

Duke

Last edited by Duke2.6; 01-12-2004 at 08:04 PM.
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  #18  
Old 01-12-2004, 08:36 PM
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Duke2.6 thanks for your input. Actually mine is M119.975 anyway, I am not ignoring what you said previously. I am just trying to do everything I can. I undertand get the cat as hot as possible which it was when I got it tested, I drove about 15 mi to get to the inspection station. I am surprised that when it is cold it was not as rich as when its is hot I was expecting the duty cycle to be less than 50 as it was during warm up period. That is why I suspected the O2 sensor.

An idea poped in my head would it be benifical and not hertful to wrap the cat in fiberglass insulation material? just to maintain its temperature now the weather is cold so does loose a lot of heat.

Also what about directing the crancase ventelation to the outside instead of getting it into the intake manifold and pluging the manifold side. Some the oil vapours may not be easily combustible yest it is very low and the emission failed for 2 lousy PPM so every PPM counts. these mods would be just temporary for the testing benifit.
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  #19  
Old 01-12-2004, 08:43 PM
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folks, sorry for the fast typing errors, I am sued to relying on the spell checker.
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  #20  
Old 01-13-2004, 01:27 AM
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The converter has a radiation heat shield on it. I would be leary of wrapping the converter with anything - risk of fire.

Don't mess with the PCV system. It's part of the visual inspection, and modifying it will be an automatic failure.

I would recommend getting the car retested. Run it at 2500 revs until the tech is ready to take the car and run it through the test. If you have another marginal failure take your situation to the next higher level of management in the state emission test bureaucracy. Been there, done that with the CA BAR. More than once!

Duke
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  #21  
Old 01-13-2004, 08:26 AM
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Yea I was afraid of the cat getting too hot as well, so that is out.
Here in NJ there is no visual inspection of the engine comprtment they do not open the hood. They do the normal safety, lights, horn, wiper, etc. check as well as gas cap test for pressure leak. The rest is emission either on dyno or standing still and reving the engine.

So far the PCV is an option. I also though of disconnecting the intake manifold vacuum connection to the fuel pressure regulator to reduce the pressure and hopefully lean out the mixture. Another idea is to trick the intake air temperature sensor in thinking the air is hot in order to lean out the mixture. I wish I had an emmision tester to check out the effect of the temporary mods I came up with.

The NJ emission web site states that if after some work it does not pass emission a second time, they will give you a waver. But the that section is not clear and they do not wish people to rely on that, they do not also state how much money wasted is enough to put you over the limit to get a waver.
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  #22  
Old 01-13-2004, 11:16 AM
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Just to clarify.
Most fuelpressure regulators I've ever seen, will increase the pressure when there is no, or low vacuum !
When I went to school, the story was, for every 2 inches of vaccumdrop, the fuelpressure would increase by @ 1 pound.
Makes sense, when your cruising ( high manifold vacuum ) you need very little fuel, hence low pressure.
When you " get into it " there is low manifold vacuum & high fuelpressure.
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  #23  
Old 01-13-2004, 01:09 PM
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manny - I disagree with your explanation. I think you got it backwards. You need more fuel to maintain a car under a heavy load which results in high intake manifold vaccum. This is how the economy gage in some MB cars work. The economy gage measures the manifold vaccum. High vacuum translates to low MPG and high fuel consumption.
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  #24  
Old 01-13-2004, 04:12 PM
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Manny is right about the vacuum. Higher vacuum when cruising or at idle due tothe fact the throttle plate is closed or partly closed. At wide open throttle, the vacuum is less because the the throttle plate doesn't "restrict" as much air flow into the intake manifold hence less vacuum pressure. That's why the MB economy guage goes into the red when you get on the accelerator.
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  #25  
Old 01-13-2004, 04:53 PM
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OK, maybe there is disagreement in terms. If one step on the gas the vacuum increases in the intake manifold and thus the fuel pressure regulator increases the pressure in the rail to get more fuel through the injector. Agreed?

If there is less vacuum in intake manifold when you press the gas why would air flow into it? Vacuum or difference in pressure (atmospheric air pressure - vaccum) increases rate of air flow, if there is no difference in pressure there would be no air flow.

Just like saying if there is no voltage (difference in pressure) there is no current flow (air flow) in a circuit.
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  #26  
Old 01-13-2004, 05:35 PM
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The manifold pressure is higher when you apply throttle.

What is meant by the term vacuum is a lower pressure in the intake manifold. The manifold pressure will be low at idle typically below 12" hg and close to ambient at full throttle pushing towards 30" hg man pressure at sea level and a standard day.

So when you step on the gas, the man pressure increases and the vacuum decreases.

It is obviously not a difference of pressure in the manifold itself that makes air fill the cylinders.
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  #27  
Old 01-13-2004, 07:19 PM
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My last attempt at simplifying vacuum.
When the throttleplate(s) are closed, or near closed, such as when idling or cruising, the piston(s) still " suck " air through the engine.
Therefore = high vacuum ( negative pressure ) in the intake manifold.
When you open the throttle, all the air required by the engine goes " unrestricted ", and therefore low ( very little vacuum ) exists in the intake manifold.
I've never scrutinized the " economy gauge " on an M-B, but suspect it is nothing more than a vacuum gauge that reads " backwards ".
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  #28  
Old 01-14-2004, 07:15 AM
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sorry for my thick head

manny, DieselGuy, and Ali Al-Chalabi - Sorry, I see the error of my thinking. I understand what you are saying now, it takes some time to sink through my thick head. I need to apply vacuum to the FPR to reduce its pressure. Got it. The resoning that convinced me that I was wrong was that at idle the plate is near closed so there is a great restriction to air flow thus the high manifold vacuum.

I guess I should hook up the FPR to the car vacuum system (door locks etc) to acheive the low fuel pressure but most likely the O2 sensor with the ECU will ajust for it and I am back to square one.
I think FPR pressure reduction is out as a short term mod to make the car run much leaner.
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  #29  
Old 01-14-2004, 07:55 AM
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Looking at the numbers from your test, it looks like you are running just a hair rich and your cat is getting old. Most closed loop emission systems will try to run perfectly centered to slightly rich. If the engine runs slightly lean, NOX readings climb rapidly due to higher combustion temps. HC reading go up with a much gentler slope on the rich side and they figure the cat can clean them up. Harder to clean up NOX. Trouble is, as the cat gets old its efficiency starts to fall off. That's why all the comments about keeping it real hot before the test are correct. Keeping it hot like that keeps it operating at whatever its current peak is. 30k miles on an oxy sensor is enough for its response to fall off or for it to become a bit contaiminated. Changing it probably won't make a big difference in the numbers, but might be enough to pass. Those things commonly go for 100k. Personally, I'd find out how much you have to spend to get a waiver if it still fails, and then make sure you reach that number in counted repairs. In my area you have to spend $200 to get around the test. Oxy sensor, plugs and wires will put you there pretty easy and it's all stuff your car needs form time to time anyway. I'd probably adjust the system to run just a touch leaner since they don't seem to care about NOX.
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  #30  
Old 01-14-2004, 09:00 AM
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BobK - all valid points the trouble is I do not know or there is no easy way to adjust M119 system to be slightly leaner. I have to resort to fooling the ECU to make it it slightly leaner. So far I do not have a proven technique, just some ideas floating around.

With all the parts from Phil at FastLane I am not over $200 yet. I do not know what the NJ limit is. It is not eay to find out.

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