Here is the emissions report information maybe this will hepl you all narrow this down. It has had a recent tune up also when I start the truck it doesn't seem to fire up sharp and strong like I think it should. It's more like a lazy fire up but it does start after a pump or two of the pedal. The truck has 61,700 origanal miles on it. 318, 2 barrel holly,
15MPH Test
HC ppm Limit 155 Reading 236 Fail
CO% Limit 1.31 Readind 2.74 Fail
25MPH Test
HC ppm Limit 1.51 Reading 219 Fail
CO% Limit 1.68 Reading 2.05 Fail
Speed Dragon
07-29-2007, 12:41 PM
What kind of tune-up? Just plugs and wires, or a full check-up?
Chump
07-30-2007, 03:01 AM
You have a rich fuel mixture or a weak spark. Givin the age of the vehicle I would try a carb rebuild first and also check the operation of the air valves/doors on the air cleaner assembly to make sure they are opening correctly.
CO too high = Car runs rich, burns too much gas.
Bad carburetor adjustment, float too high, carburetor flooding, sticking secondary throttle, leaking fuel injector, leaking fuel pressure regulator, feedback system malfunction (oxygen sensor, coolant sensor, throttle position sensor), emissions vapor system malfunction (purge valve, canister clogged) Be aware that NOX will RISE after you fix a CO problem. This must be checked after a successful CO repair.
HC too high = unburned fuel in exhaust; car runs very rich or very lean. This is the trickiest condition because there are different causes. If the car is running rich (high CO), the HC can be high also. If the CO is very low and HC is high then the vehicle has a lean misfire.
If The CO is high, fix that problem first. If CO is low and HC is high look for engine skipping, misfire due to vacuum leaks, ignition timing set too advanced, ignition misfire problem (plugs, wires, cap), low fuel pressure, carburetor adjusted too lean. If you can’t find a reason for the high HC then perform balance test then compression test to check for engine mechanical problem.
