At 09:52 PM 8/28/01 +0000, you wrote:
>State Max allowance:
>HC: 120
>CO: .67
>NO: 848.0
>
>Reading were:
>HC 174.0 (Failed)
>CO 5.04 (Failed)
>NO 237.9 (Passed)
>
>Any ideas?????
Hydrocarbons (HC) is simply unburned fuel that escaped the combustion cycle and
is being sent out the tailpipe. Some common causes are spark plugs, spark
plug wires,
misadjusted timing or vacuum leaks. The garage owner who tests my vehicles
says
that the number one cause that he comes across for high HC readings is vacuum
leaks.
High (CO) is the result of one problem, a rich air/fuel mixture but there
may be several causes.
When you fail because your CO is too high, that means the fuel and air
ratio is way off and there
is evidence of incomplete combustion or burning of the air/fuel mixture. A
CO failure will always
be rooted in the fuel injection system (or carburetor). CO failures are
not fixed with spark plugs.
Here are some common causes for the high production of CO and HC.
CO Failures (fuel injected vehicles)
1. Ruptured or sticking canister purge valve.
2. PCV plugged or drawing in fuel contaminated oil vapors.
3. Malfunctioning computer inputs. Example: O2 sensor defective,
reading lean
all the time. MAP sensor vacuum hose being clogged or broken
(reading a heavy
load all the time). Coolant temperature sensor having high
resistance or open circuit
(reading "cold engine" all the time). Throttle position sensor
stuck or open ground,
(reading wide open throttle).
4. Contaminated, restricted or bad catalytic converter.
5. Leaking or bad injectors.
6. Fuel pressure too high (restricted fuel return line or stuck fuel
regulator)
7. Ruptured fuel regulator (fuel leaking directly into intake)
HC Failures (all vehicles)
1. Engine was not at normal operating temperature.
2. Ignition system malfunction. Spark failing to occur for any reason
will send unburned
hydrocarbons (HC) down the exhaust pipe. Example: bad plugs, plug
wires, distributor
cap, rotor, coil wire, coils, etc.
3. An extremely lean fuel mixture that causes misfiring. Examples include
disconnected, leaking or mis-routed vacuum hoses, intake gasket
leaks, EGR stuck
open, low fuel pressure.
4. Over advanced timing or insufficient spark duration.
5. Low compression or mechanical problems. Worn rings, burned valves,
bad or
mis-aligned timing gears.
6. Over rich fuel condition causing both HC and CO failures.
7. Contaminated, bad, or restricted catalytic converter.
I would test for vacuum leaks and defective O2 sensors.
Bob
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:02:36 EDT