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Dyber
Dodge Dakota
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8/02/2004
17:52:18
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 Subject: catalytic converter question
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Can anyone tell me what the stock catalytic converter for a 91 V6 3.9L is? Would it be a dual-bed three way converter? If so, what effect does it have on NOx? Besides failing California smog on high HC, I also failed on high NOx at about 1100 ppm with 300 being average (999 is max).
Do these numbers sound right for a worn-out converter? I know the EGR system is a common culprit, but I was sure I'd cleaned out the passages fairly well and the EGR valve *is* working. Also, could someone tell me the potential effect of a lazy O2 sensor on the HC readings (O2 sensor is not throwing code).
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UH
Dodge Dakota
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8/02/2004
19:38:29
| RE: catalytic converter question
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Lazy O2 sensor runs it rich therefore the high hydrocarbon reading, something else then a bad converter will cause high NOx,, ready for this? if you have changed to a cooler running thermostat in the cooling system NOx will rise. it needs to run at 192 to keep it down.
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Bob Lincoln
Dodge Dakota
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8/03/2004
09:01:53
| RE: catalytic converter question
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Really? Higher engine temps raise NOx levels.
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Lemmon714
Dodge Dakota
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8/03/2004
12:34:28
| RE: catalytic converter question
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What is the CO reading? Low and High CO indicate different issues.
I guess UH must have an aluminum radiator. Remember, we learned that aluminum conducts better than copper, that is why people switch from an aluminum cap and rotor to a brass cap and rotor. I've been in engineering for 10 years and I'm still amazed at how many "New" things I learn everyday.
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Dyber
Dodge Dakota
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8/03/2004
14:43:19
| RE: catalytic converter question
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So a lazy oxygen sensor, though not tripping a trouble code, could cause a rich condition (enough to fail emissions on a high HC reading)? But a worn catalytic converter generally won't cause a significant raising of the NOx levels?
Here are the numbers, by the way:
(15mph RPM=1768)C02=10.50, 02=5.93, HC=112 max=118, CO=.29 max=.68, NOx=1150 max=999
(25mph RPM=1213)CO2=10.56, O2=5.96, HC=144 max=98, CO=.21 max=.87, NOx=1112 max=859
As you probably know, this truck has an air pump. It's also got new ignition coil, distributor cap/rotor, wires, plugs, clean throttle body, new oil/filter. I cleaned out the EGR passages and the valve works.
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Bob Lincoln
Dodge Dakota
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8/03/2004
15:41:33
| RE: catalytic converter question
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Newer cats handle all 3 pollutants, but your vintage was strictly for HC, I believe.
I'll ask the obvious, are you sure the truck was fully warm (really warm) when they did the test? My car failed first time ever in January in the Northeast, probably because they let it cool down over 30 minutes before testing, though I brought it in fully warm.
Typically you want to drive it 10-15 miles before testing, and test right away. Idling for several minutes just before test will give rich readings, also.
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Dyber
Dodge Dakota
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8/04/2004
14:16:09
| RE: catalytic converter question
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I know the air pump has a line into the catalytic converter, so shouldn't that be a indicator that it's a three-way?
I find it impossible to get the smog immediately done after a good drive, no matter how hard I try. There's always been a damned delay caused by the 'gentleman' doing the job. To be honest, I hadn't pressed the issue too hard because I'd figured it should help the NOx situation at least.
Bob, how badly did you fail the first time and how did the numbers compare to your eventual passing numbers?
Also, if someone could answer about the air pump/cat relationship question (above) I'd appreciate it.
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Bob Lincolln
Dodge Dakota
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8/04/2004
19:01:48
| RE: catalytic converter question
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Well, it was my car that failed. In MA, cars that are pre-OBDII get run on a dyno; cars with working OBDII just get a diagnostic test and no sniffing. My 92 Daytona, which in the old emissions-at-idle test got only 2-20 ppm HC, and zero CO measured, was getting the following numbers on the dyno:
0.7 grams/mile HC (max 1.20)
3 to 9 grams/mile CO (max 20.00)
0.63 grams/mile NOx (max 2.50) -but once got 2.25
Last Jan, I got the following:
0.71 grams/mile HC (max 1.20)
6.05 grams/mile CO (max 20.00)
2.84 grams/mile NOx (max 2.50)
re-test next month (I did NOTHING to fix it, except come in at 7:15 am so they could test right away - but I had to lie on the form and say I fixed something):
1.11 grams/mile HC (max 1.20)
15.73 grams/mile CO (max 20.00)
2.48 grams/mile NOx (max 2.50)
Note the very high CO reading - I smelled a strong odor of aromatic HC in the car when I left. Obviously they sprayed some fluid in the TB to get it to pass. They're doing something wrong. There have been issues in MA where some garages pass vehicles that should fail and vice versa, due to software problems. This was my first and last test at that garage. I know my EGR, O2 and MAP sensor are all working great, and the car gets 35 mpg, so nothing has failed.
Can you re-test elsewhere?
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Bob Lincoln
Dodge Dakota
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8/04/2004
19:04:57
| RE: catalytic converter question
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My cat has air aspiration (suction tube and one-way check valve) from air cleaner, and it's strictly an HC cat. I haven't dealt with an air pump on a car, my Dak doesn't have one.
My Dak readings, first emissions test since I bought it in Dec:
0.69 grams/mile HC (max 2.40)
5.76 grams/mile CO (max 60.00)
0.65 grams/mile NOx (max 4.50)
354 grams/mile CO2 (no max)
This was before I fixed the thermostat and tuned it up.
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Dyber
Dodge Dakota
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8/07/2004
17:35:17
| RE: catalytic converter question
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What year of Dakota? I'm really surprised there are Daks out there without three-way cats. I thought they'd been universally used in the auto industry since the mid-80s. Can anyone help clear this up?
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Bob Lincoln
Dodge Dakota
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8/08/2004
19:31:34
| RE: catalytic converter question
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It's a 92. I won't swear it isn't a 3-way, but I don't think they had them then. The truck was not equipped with an air pump, and the car has the air aspiration tube.
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Dyber
Dodge Dakota
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8/09/2004
14:57:44
| RE: catalytic converter question
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I can't tell you how confused I am right now.
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