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post #1 of (permalink) Old 11-08-2002, 08:37 AM Thread Starter
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4.0 failed emission test in VA, what to do?

'91 YJ w/4.0 failed test. Too high NO ppm. What does it mean and what could be causing it? Other values are perfect. Shop said it's running a bit lean. They think it could be the cat (original).

If I decide to retire it from road duty since I don't drive it on the road any more what do I need to do? Can I cancel all insurance, registration and the works if I only trailer it to the trails and keep it in my back yard? What are the possible issues with that?
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post #2 of (permalink) Old 11-08-2002, 08:55 AM
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Re: 4.0 failed emission test in VA, what to do?

High NO results form higher combustion temps

Causes:

1. Higher than normal compression
a. Carbon Buildup
2. Timing is advanced (though this is EFI a bad knock sensor or computer [img]images/graemlins/confused.gif[/img]).
3. low oil-level
4. Cooling system is on the edge.
a. Scale building in the engine cooling galleys.
b. Plugging radiator
c. Defective or incorrect thermostat
d. Flakey Water Pump
e. Elecric Fan Thermostat set too high?
f. Loose pump belt
5. Possible tank of bad fuel?
7. EGR system flakey
8. Spark Plug heat range incorrect.
9. Intake Manifold Vacuum Leak

Check with your insurance carrier as there are issues of liability when towing/trailering a vehicle.... Get this infomation from the horses mouth!
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post #3 of (permalink) Old 11-08-2002, 09:18 AM
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Re: 4.0 failed emission test in VA, what to do?

I wouldn't cancel the insurance and the registration. Lots of organized trail rides require these. Just get liability insurance at least.
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post #4 of (permalink) Old 11-08-2002, 10:45 AM
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Re: 4.0 failed emission test in VA, what to do?

Most insurance copanies have systems set up for just such situations. You can insure the jeep as a non road driver. A lot of people do that up here in the great northeast because they have summer and winter vehicals. The insurance is really really cheap and it covers you in the event of fire, wind, flood... what ever, dependine on where you live. I wouldn't compleately take it off, casue you know that if you do.... somthing strange will happen.
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post #5 of (permalink) Old 11-08-2002, 12:37 PM
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Re: 4.0 failed emission test in VA, what to do?

Wow LEVE - What a great list - you even included something
I never thought of - scaling - and I was a licensed smog
tech and smog instructor.
Good show!

NOx starts forming at about 2500 degrees combustion temperature.
Then as the temp goes up it makes even more. At about 3000
degrees it goes nuts, makes a ton of it.

The EGR system introduces a tad of inert gas (already burned,
no more oxygen or fuel in it - supposedly.) That spaces out
the molecules slightly, lowering temperatures considerably.

Essentially NOx, Oxides of Nitrogen, is oxygen that attaches,
or welds itself to Nitrogen. Just like welding steel,
if there isn't enough heat, it doesn't stick.

Anything that increases combustion temperature raises NOx.

And - to add something to that great list -
When getting a smog test, always change the oil and filter
previously, within a few days. And that day fill a near
empty tank with fresh gas - take it for a 50 mile or so drive
on the freeway to blow out any crud built up. The gas doesn't
go stale that fast, but the addatives do - like an open bottle
of Coke.
Just those 2 things can make a world of difference.

Insurance - I'm in a go-around with GMAC Insurance right
now. I was adding another vehicle to tow my off roaders.
The guy asked why I bought the Suburban.
I told him to haul my Jeeps and stuff.
He asked about my Tracker, I told him I'd added a roll bar.
He asked if I drive it on dirt.
He informed me since I added a roll bar and I sometimes drive
it on dirt it was now an off road vehicle, and they don't
insure off road vehicles! They are going to cancel it!
Guess I never had the insurance I was paying for - lawyer time!

I thought GMAC was an honest company with sense, but obviously
not!
I'm looking for an insurance company with at least some
intelligence.
No, an IQ of over 6 is not required (maybe impossible), but
an honest one.

Good to find out now instead of when I need it!

Any suggestions as to an honest one?
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post #6 of (permalink) Old 11-09-2002, 10:31 AM
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Re: 4.0 failed emission test in VA, what to do?

I always thought that the temp was lower ...around 1500. Hence our 1200 exhaust temps. I could be wrong. Although I learned EGR from the 70's ...I learned the science of it in boiler school where they've introduced FGR (flu gas recirculation) for use in boilers that fire oil.

Check this out: I can't interpret any of this data ..just note the temp scale in which they're examining NOX emmissions

Anyway .. I'm not sure if the 91 4.0 uses an EGR. My 92 Caravan doesn't have one ..and my 99 4.0 doesn't either. My good friend, "dorfs", told me that DC uses cam overlap to leave enough spent gas in the combustion chamber to "take up space" as you sorta put it. My 92 Caravan typically fails NOX tests until I retard the timing. It then passes with flying colors. All the "enhanced emissions centers" around here (dyno - load test) LOVE Mopars. They typically fail NOX and then are subject to routine and costly tune ups that are truly unnecessary to pass the test. It wouldn't be so bad if the test itself wasn't already $45.

Now admittedly my 92 3.0 Mitsubishi isn't a 4.0 .....but wouldn't the basic ignitions be comparable? That is, although timing is governed by the computer ...isn't there still a static/initial setting tthat you can manipulate with the distributor ...at least in that era Chrysler spark managment system? [img]images/graemlins/tongue.gif[/img]
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post #7 of (permalink) Old 11-09-2002, 11:11 AM
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Re: 4.0 failed emission test in VA, what to do?

1200, 1500, 2500 etc - NOx probably forms at all of those
temps, just at 2500 it becomes significant enough for the
greenies to get upset. At about 3000 it goes wild.

It's the peak combustion temp that counts the most.
Exhaust temps are considerably lower, partly because lots of
the heat energy was converted to mechanical energy after the
peak temp was reached,- hopefully anyway.
And all the metal surrounding it heat sinks the heat away.

Interesting - peak temps are way higher than the melting point
of aluminum pistons, but they survive.

Yes, some cams are built to "leave" a little exhaust in the
chamber, eliminating the need for external EGR systems.
(I don't like those though, you can't disconnect them!)
And they do it all the time, rather than only when it's
needed.

Notice an external EGR valve drops out, stops working, under
full acceleration, a cam can't.

Know what the biggest polluter of NOx is?
Not industry, not cars, not even barbeques or lawn mowers.
Taco Bell gas is different.

Seaweed! Man made NOx is less than 1% of the total.
So if you want to help the environment, burn some seaweed.

Oops, no don't burn it, it'll produce CO and CO2.
Don't just pile it up to rot anyplace, the rotting seaweed
will produce methane gas - Hydrocarbons.

Don't carry it anywhere to store it, you may breathe harder
from the extra work and produce more CO2 when you exhale.

I guess the best you can do with it is eat it - no wait,
it'll end up in the sewage system and ground water supply.

Don't bury it, it'll hurt the ground water too.

I guess the only safe way is to shove it up a greenies ---.

Changing the base timing on a computer system often wreaks
havoc.
First it changes the burning slightly, then the O2 sensor
detects the Oxygen isn't "normal," then the computer "thinks"
the mixture's wrong, so it adds or subtracts fuel.
Now you have 2 problems, timing's slightly off (no big deal in
in itself) AND fuel mixture is no longer right.

Most times when they say 14, they mean 14, not 13, not 15.
It's surprising how just one degree of base timing error can
introduce a world of drivability problems.
You have to follow the label instructions to the letter - if
they say open the trunk lid - do it - there's a reason.

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post #8 of (permalink) Old 11-09-2002, 08:49 PM Thread Starter
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Re: 4.0 failed emission test in VA, what to do?

Thanks. Lot of good advice here. Interestingly the shop said they think the cat is running too cold and not burning enough of something... [img]images/graemlins/confused.gif[/img] Than they said it's maybe the EGR valve. But it doesn't have an EGR valve per say. I guess it has an EGR system... of sorts...or something like that... more [img]images/graemlins/confused.gif[/img]

The engine never ran hot, if anything it's running on the cool side. Oil is fresh, Mobil-1 synthetic, new filter. There are a couple of small holes in the exhaust pipe but they didn't find those. There is a slight blow by. Otherwise they said the engine numbers were all very good. Wish I could somehow convert that darn NO to N2O and have some fun on the dunes... [img]images/graemlins/tongue.gif[/img]
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post #9 of (permalink) Old 11-09-2002, 11:11 PM
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Re: 4.0 failed emission test in VA, what to do?

now i am not telling you this as a cop :-) but...

if you know anyone who lives in fredericksburg or south of there emissions is not required if that is where it is registered [img]images/graemlins/grin.gif[/img]

just a hint

-web
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post #10 of (permalink) Old 11-10-2002, 12:42 AM
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Re: 4.0 failed emission test in VA, what to do?

By hot I meant inside the cylinder. The water temp can be
nice and low but the internal instantaneous combustion
temperature can be over 3000 degrees.

Try retarding the timing about 3 or 4 degrees or so, and
fill an empty tank with premium gas. Drive it around a little
before taking it to the test facility again - to get the cat hot.
Try to get them to test it right them while it's still hot.

You may need a cat, they eventually get tired. A replacement
usually is around $100 at a place that specializes in them -
NOT A DEALERSHIP!
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