I just bought a 1983 f-150, it has a I-6 300 4.9L. I went to ge get it tested for emissions, and i failed misserably. ive talked to a few people about it, and i've heard that getting a tune up would help. adjusting the idle screw (it idles around 550 in park). check the catalitic converter. so does anybody have any experience with this issue or have any solutions?

 

what were the numbers? hydrocarbons nox co what?

 

Recarbco, a carb rebuilder, has compiled common emission failures in a chart that might be helpful. http://www.recarbco.com/technical/smog/smoginfo.html

 

My1982 f-150, I-6 300, failed miserably. Forget the numbers, but it failed every test. HC's were through the roof. Carb was a problem since the vehicle had just come out of deep storage, but the biggest contributer was a couple of major vacuum leaks and a stuck EGR valve.

 

these are the results i got:

HC @ cruise: 198 limit is 150
HC @ idle: 901 linit is 220

CO% @ cruise: .06 limit is 1
CO% @ idle: 2.33 limit is 1.2

so that seems really bad to me.

 

Had a similar problem with my 460. The previous owner had put a Road Demon carb on it but did not dial it in very well.

My first DEQ tests looked something like this:

_______HC PPM (350max) CO%(3.0max) CO+CO2%(6.0min)
Idle:_____106___________4.98_________16.0
2500:____109___________2.92_________15.3

After I went through the general process for setting the idle mixture outlined here: http://www.chevyhiperformance.com/howto/45638/
(ok...it's a Chevy site...deal with it)

My tests then came out (passing) like this:

_______HC PPM (350max) CO%(3.0max) CO+CO2%(6.0min)
Idle:_____20_____________.44_________13.3
2500:____20_____________.55_________14.5

This is assuming the engine is of course tuned well and has no mechanical issues (vacuum leaks, stuck EGR, stuck PCV, bad plugs/wires/cap/rotor, etc). Just about an hours tuning and a few tools was all it took. Now the vehicle also gets better milage (up about 1.5mpg!) and is snappier off the line.

I guess the point I'm trying to make (taking the long way around the barn, I know) is that it may not be as bad as you think, and that the idle mixture circuit does affect non-idle emissions.

Give her a good tune up, set the ignition timing perfect, go through the adjustment process, set the float level on the carb, replace any cracked hoses that may be causing a vacuum leak, and inspect all of your emissions related controls. If you have a catalytic converter, consider replacing it (that will help a lot if it's plugged or gummed up).

Good luck man...

 

thanks, i'll look into that this week, would you happen to know what the spark gap would be for my year and make of truck?

 

For that year engine, the spark plug gap is .042-.046".