Idle HC emissions limit exceeded

[AlaskaFestivaGuy]

My WA '88 just failed an emissions test, with these numbers

Me/LIMIT

HC(PPM) CO(%)

Cruise 149/220 0.07/1.6

Idle 367/220(FAIL) 0.00/1.2


The engine (but not the carb) was rebuilt 37,000 miles ago (new pistons, valves, etc.)

Other than some stumbling on acceleration which I always thought was a weak accelerator pump, the car idles and runs just fine.

Anybody have any ideas what the problem might be? I really don't want to pay some shop that doesn't know Festivas more than the car is worth to mess with it.

[mechanicaldj]

problem: it is running rich

solution: buy an injected festy

or

check timing
check for dirty air filter
check all tune up items

to start with

[AlaskaFestivaGuy]

Are there any "home model" (as in inexpensive) HC/CO measuring devices that I can pick up to know when I've solved the problem?

Yes, I'm trying to migrate over to only fuel-injected Festies (that explains part of my collection). This 88 is an LX and in practically new condition. Can I convert a carb'd car into a FI one?

[getnhi1]

How bout the idle mixture screw? can you lean it out?

[FestYboy]

read your plugs.... that's the cheapest way to figure out what's going on. it's best to start out with brand new ones (do not use platinum), set the gap and run them for about 2-3 min at idle. pull them and look at the ground electrode (the bar attached to the threads) if things are good, you should see a blue-ish burn mark about the middle of the bend, if not, you need to adjust your timing until you get that mark. if your plugs come out black/sooty, then you'll have to adjust your idle air mix screw (it's a PITA to get that cover off it). also look down the horn during idle and look for dripping fuel. you can also take a multimeter and read the O2 sensor. a reading of .5V DC is Stioch and a good reading. higher = rich, lower = lean.

hope this helps

[AlaskaFestivaGuy]

The plugs were brand new a few weeks ago, gapped to 0.44, as suggested suggested by the parts store. I pulled one just now -- clean and dry, light tan color.

Notice that it passed at cruise with 149ppm out of limit 220, compared to 367ppm at idle.

Interestingly, I had a new muffler installed on the way to the emission test. It had been idling roughly before that, which I attributed to the lack of full back pressure from the holes in the muffler. Or does that tell me something?

The air cleaner is fairly dirty, which could obviously drive the mixture up by restricting air flow, but wouldn't it also do that at cruise when so much more air is required?

I haven't checked the timing in quite some time; not sure where the timing light is hiding.

Is the O2 sensor the cylindrical device on the exhaust manifold pointing to the right and slightly up, just above the flange where the pipe to the catalytic converter bolts on? If so, I'm looking for 1/2 volt on the non-ground side of that?

[FestYboy]

The plugs were brand new a few weeks ago, gaped to 0.44, as suggested suggested by the parts store. I pulled one just now -- clean and dry, light tan color.

light tan is good, but where on the ground bar is the burn mark? that will tell you if the timing is off.

Notice that it passed at cruise with 149ppm out of limit 220, compared to 367ppm at idle.

with this information you may have a misfire at idle causing the HCs to go up. get new plugs and run at idle only (install new plugs after engine is warmed up). run for about 30 seconds and pull the plugs: look for blue-ish marks as stated above and compare between cylinders, they should be the same. the one with the least color is misfiring.

Interestingly, I had a new muffler installed on the way to the emission test. It had been idling roughly before that, which I attributed to the lack of full back pressure from the holes in the muffler. Or does that tell me something?

mufflers rarely have anything to do with emissions or idle quality. at this point you should look into how well your cat is working (how old is it, is it clogged, which end is hotter while running: it should be the back, is there a restriction in the A.I.R. tube to the cat, is there a malfunctioning solenoid for the A.I.R. valves on the filter housing?)

The air cleaner is fairly dirty, which could obviously drive the mixture up by restricting air flow, but wouldn't it also do that at cruise when so much more air is required?

yes, but remember that a carb uses the air volume going through it to determine fuel flow, unless you're in the throttle so much that you've uncovered the secondary jet and activated the power valve.

Is the O2 sensor the cylindrical device on the exhaust manifold pointing to the right and slightly up, just above the flange where the pipe to the catalytic converter bolts on? If so, I'm looking for 1/2 volt on the non-ground side of that?

yes and yes. (engine must be warm before testing)

**NOTE** If your car is running lean at idle you may also have a misfire that will cause high HCs. high HCs = unburnt fuel; running rich or having any kind of misfire will cause high HCs.

!!!!!!!Adjusting the idle mix screw should be your last recourse after everything else has failed!!!!!!!!!

[getnhi1]

The O2 signal looks much like a sine wave on a graph, lower limit is .1 V and upper is 1 volt, if you have a DVOM with a bar graph on it, or a graphing multimeter, you can see the signal much easier. If the O2 is very old, just go ahead and replace it, eliminate the possibilty.

I'm I reading right that the CO was zero at idle?

[FestYboy]

also consider this: you're using a carb to regulate A/F, granted it's a feedback carb. but my point is that in this case you should only see a solid voltage instead of a sine wave: the carb can't compensate fast enough to produce that lean-rich wave that you see in FI cars.

so, look for a solid voltage- you can use a regular digi or analog volt meter for this.

PS: a digi meter can't read/display fast enough to keep up with an O2 sensor out of a FI car, you need a graphing meter or O-scope to see it properly.

[getnhi1]

PS: a digi meter can't read/display fast enough to keep up with an O2 sensor out of a FI car

Mine does, it has a bar graph.

[AlaskaFestivaGuy]

Sorry, the tab characters didn't come through.

HC was 149 at cruise, 367(FAIL) at idle. Limit at all times is 220.
CO was 0.07 at cruise, ZERO at idle. Limit is 1.6 at cruise, 1.2 at idle.

I'm parking the 88LX for now since the registration is expiring, and switching to the less nice blue 93L until I have more time to attack the problem.

[getnhi1]

With a rich mix you should have a lot of CO and HC, it takes combustion to make CO, so they saying you have none? :lol:

[AlaskaFestivaGuy]

Makes you kind of wonder whether the testing station has an equipment problem, doesn't it? This car passed easily 2 years ago, and I haven't done anything to it. Maybe I should get it retested at another lane at the same station or another station before putting in a lot of effort. The first re-test is free, after that, it's only $15.