I've gotten some opinions on another site but would like to check it out here as well so I can pass on the first retry

Car:
'89 with 165 ecm L98 MAF and zz4 cam installed since last test

e-test type:
asm2525 test on rollers at 25mph

Results:
Just as suspected, I failed emissions because my HC ppm was 86 with a limit of 58.

Now, NOx was way down from previous test taken with stock cam at only 37 ppm with an allowed 652 ppm.

CO% allowed was .32 and I registered .19.

Idle is not an issue, although HC levels are close to limit

I believe I know what to do to get this situation looked after. I'm thinking of raising the timing in the test area (on the rollers, btw) to decrease HC. I know full well that this might adversely affect the other reading but it looks like I have a lot of "wiggle room" in the Nox department. Not that much in CO.

What do we think and most importantly, by how much do I advance to see a difference?

 

Nobody?

 

Uhh. A car with less than 1ppm HC is really good. I think you gave the wrong #'s/values.

Please check everything and retype it carefully.

 

Quite right. The technician's pen marks were the dots I was seeing. Relatively speaking, the results are the same.
Opinions?

 

I have an 88 vert with a few mods when i go up against the sniffer if the person testing lets the transmission shift into second it fails . If he holds the transmission in low gear and runs thru the whole test in low gear it passes with good numbers no problem. Not sure what the deal is but it works.

 

Sorry I chimed in so late on this, I've been neglecting keeping up with the forum while the Vette's in hibernation for the winter

Bumping the timing up to reduce HC... hmmm, I'm trying to figure out the science behind that. NOx is relatively easy because high cylinder pressure/heat cause it to form, and retarding the ignition timing drops that pressure pretty quick.

I'd search more for:

1) misfiring cylinder
2) too rich mix
3) bad cat

You've got an '89 like mine, so if you're running the original injectors, you may have some problems there. In my case, I had 2 bad injectors on the driver's side of the motor, which is the only side the O2 sensor monitors. What happened to me was the driver's side was running too rich because of the bad injectors, and the ECM was leaning the fuel mix to compensate. The problem was, the passenger side of the motor ended up running too lean, to the point I was getting lean surge. I could see your driver's side cylinders running a bit lean (clogged injector, whatever) which is making the passenger side run too rich. Can you read all the plugs to see if any cylinders look like they're running rich?

Also, is your air pump intact and the line running from the air pump to the cat intact? I believe one of the purposes of that line is to supply excess air to the cat for the oxidation stage of the cat--where HC gets converted to H2O and CO2.

Good luck!

Ben

 

try taking the air filter off and running it around the block, then test it


works for my frinds 72 c-15 but its carberated

 

yes, bumping the timing will most times decrease hc's if nox gets over the limits you can hide a small bottle of water with a small orfice and hose and hook it up to the intake to get the nox down, as this will lower the combustion chamber temps.