Any smog experts out there?
- Thread starter cudamark
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cudamark
Well-Known Member
This is what is puzzling to me. It's only the 25MPH Nox reading that is off. The 15MPH Nox reading is fine. The only difference running-wise is the RPM change of a little under 1000RPM, unless there is some component I'm not aware of that takes MPH into consideration and/or the computer does something weird at that speed. I was hoping there was something obvious that I've overlooked and that someone has run into that situation before who knows what it is.
cudamark
Well-Known Member
Ca approved replacement.
MOPAROFFICIAL
Oogliboogli
All true but if there's an exhaust leak before the cat you will see the post cat o2 reading jumping around. .100-.800. Or even zero... because the front 02 senses the oxygen as well and when it is bouncing bounces further to the rich. What you don't want to see is the pre and post mirroring themselves at the same time outside of wot.
TT5.9mag
Two atmospheres are better than one
Have you driven it? If you can, go out and drive it steady state for a little bit, then jump on it. Watch the mirror and see if a bunch of crap comes out of the exhaust. This may be a case of just getting the cat up to temp and cleaning it out a bit.
MOPAROFFICIAL
Oogliboogli
You say you have no codes like a p0441. Does it have evap? Is it four-wheel drive and could there be a crack in a vacuum line that goes down around the transmission to some hard lines into the front axle. EGR stuck open not closing all the way?
It would be a bummer if a crack on the exhaust seat made it to coolant that'll cause a misfire, otherwise it could be cracked into the intake seat as long as it doesn't have coolant leaking through keep running and not bring any cells
You're 100% wrong, and have no idea what NOx is & how it's generated. High COMBUSTION temps create it, & the primary causes are lean conditions or excessive cyl. pressures, but a hot chamber and lot's of carbon can make it easier to occur than normal.
TT5.9mag
Two atmospheres are better than one
Stolen from wiki;
In atmospheric chemistry, NOx is shorthand for nitric oxide (NO) and nitrogen dioxide (NO
2), the nitrogen oxides that are most relevant for air pollution.[1][2] These gases contribute to the formation of smog and acid rain, as well as affecting tropospheric ozone.
NOx gases are usually produced from the reaction between nitrogen and oxygen during combustion of fuels, such as hydrocarbons, in air; especially at high temperatures, such as in car engines.[1][2][3] In areas of high motor vehicle traffic, such as in large cities, the nitrogen oxides emitted can be a significant source of air pollution.
In atmospheric chemistry, NOx is shorthand for nitric oxide (NO) and nitrogen dioxide (NO
2), the nitrogen oxides that are most relevant for air pollution.[1][2] These gases contribute to the formation of smog and acid rain, as well as affecting tropospheric ozone.
NOx gases are usually produced from the reaction between nitrogen and oxygen during combustion of fuels, such as hydrocarbons, in air; especially at high temperatures, such as in car engines.[1][2][3] In areas of high motor vehicle traffic, such as in large cities, the nitrogen oxides emitted can be a significant source of air pollution.
There will be more load (= higher cyl pressure) @ 25mph, which must be triggering the cause, I'm going to say carbon and a cyl. or 2 running lean. I'm also going to guess this pre-OBDII Magnum may need an intake & plenum gasket set, may be sucking oil & un-controlled air into a couple of intake ports, the system will dump enough fuel in to prevent a lean code.
Check fuel pressure.
I would drop the cat off, do an induction cleaning, change the intake set, add Seafoam/BG/etc. to the fuel & run that thing hard up a couple of long hills.
Also remove & verify the EGR passages are CLEAR, carbon build-up can cause insufficient flow even tho' the passages aren't blocked.
Then toss new plugs & O2 sensor in, put the cat back on run it again & then have it retested.
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cudamark
Well-Known Member
No codes of any kind. It runs great....no misses (which should show in the HC and CO readings too) 5 speed manual 2 wheel drive. Coolant is clean and full, no overheating problems at all. We could probably throw in a brand new cat and get it to pass. I'd prefer to figure out exactly what' making it fail instead. We'd also like to keep the price down on this beater too. I plan on starting with decarbonizing the combustion chamber. That's cheap and easy to do. Maybe put in a new O2 sensor too since I think it's the original (and 150K on the odometer). Then the free retest to see if that does the trick. Thanks for all the ideas everyone.
MOPAROFFICIAL
Oogliboogli
Well O2 sensors do tend to break or designed to fail to the lean side, so that wouldnt be a bad idea.
Track part numbers and even though they don't list them on Amazon and places like that or eBay Buy application you can track that part number and search it there and find it for really cheap like 40 or 50 bucks
Track part numbers and even though they don't list them on Amazon and places like that or eBay Buy application you can track that part number and search it there and find it for really cheap like 40 or 50 bucks
MOPAROFFICIAL
Oogliboogli
Well I tend to go for Bosch, that same one on eBay is probably $52, I just bought one and it showed up in 2 days. The bonus with the parts stores you pay that little extra for a warranty most the time and that can come in handy
MinnesotaMopar
MinnesotaMopar
I'd try the simplest solution even tho it probably will cost you another inspection fee. Is there any chance taking it to a different inspection station would make a difference?
MOPAROFFICIAL
Oogliboogli
If the o2 can be read Live data..you'll know if it's bad.
But if it's cycling 0.1 - 0.9 it's normal and working fine.
maybe it's an exhaust leak 'would have to be a pretty substantial one though'.. or stuck open pcv maybe... typically something that is below the throttle plate and before the O2 sensor.
Because all it did was sit for years things like chewed vacuum lines and bad gas come to mind...
@cudamark
Wait a sec..the transducer could be bad, you vac tested the diaphragm of the egr but not the transducer?
See if its stuck or frozen.
Pull vac through it, is it switched off when the key is off?
But if it's cycling 0.1 - 0.9 it's normal and working fine.
maybe it's an exhaust leak 'would have to be a pretty substantial one though'.. or stuck open pcv maybe... typically something that is below the throttle plate and before the O2 sensor.
Because all it did was sit for years things like chewed vacuum lines and bad gas come to mind...
@cudamark
Wait a sec..the transducer could be bad, you vac tested the diaphragm of the egr but not the transducer?
See if its stuck or frozen.
Pull vac through it, is it switched off when the key is off?
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