Emissions testing
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Senior User
Joined: Mar 2003
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From: Houston, TEXAS
Emissions testing
Do any of you know why my 85 is reading high HC(ppm) on my truck? I have changed the plugs, O2 sensor and set timing. What else is there that makes a engine burn rich at high rpm? Low rpm is fine. Does a egr valve or airpump have anything to do with this problem.
Last edited by RickDill1; Jun 16, 2007 at 05:43 PM.
Fleet Mechanic
Joined: May 2005
Posts: 1,575
Likes: 11
From: Puyallup, WA
How clean is your air filter? A dirty one will progressivly richen the engine as more airflow is required and the restricion increases.
Airpump has a effect on this as well, you need to dilute / promote futher burning of the unburned fuel particals that exist in the exhaust.
EGR serves mainly to reduce combustion chamber temps, which reduces NOx formation.
The big thing to remember is that the whole system works together as one to meet the targeted standards. Like a 4 legged table, you can remove one leg, and things might be fine or required a shifting of the load on the table, but take away two legs and things get real dicey, a real balancing act you might say, take away three and it will topple!
David
Airpump has a effect on this as well, you need to dilute / promote futher burning of the unburned fuel particals that exist in the exhaust.
EGR serves mainly to reduce combustion chamber temps, which reduces NOx formation.
The big thing to remember is that the whole system works together as one to meet the targeted standards. Like a 4 legged table, you can remove one leg, and things might be fine or required a shifting of the load on the table, but take away two legs and things get real dicey, a real balancing act you might say, take away three and it will topple!
David
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Senior User
Joined: Mar 2003
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From: Houston, TEXAS
I changed my oil. I bought a air filter and ran the truck a 1 1/2 hours. I still get burning eyes can a O2 sensor burn out in 7K? The air pump is quiet. The cat is original. I think the EGR is original too. I unplugged the wires to the Egr nothing happened no change in rpm. If I change all these things price is about $350. Being its a 85 no diagnostic input that I know of.
Post Fiend
Joined: Jun 2001
Posts: 5,228
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From: Running Springs CA
If the airpump is not pumping, the cat will not have enough air to oxidize the unburned hydrocarbons. If the cat is worn out, then, well, the cat is worn out. What is the total mileage? There is also the possiblilty of lean-misfire, which will also elevate the HC reading, but with a good O2 sensor and no error codes, it should not be running too rich or lean. The air filter wont matter, either. One trick we use to get the '87 Dodge to pass is retard the spark a few degrees.
Jim
Jim
