I'm faced with trying to pass emissions in my 6E MAF equipped 350 and a cam change.

The new cam is slightly bigger than stock (it's a zz4 cam), so 474/510 LSA 112 as opposed to
415/430 LSA 117 in the stocker.

Last time I went in with the stock cam, I was way under in CO and in NOX. HC was at the limit in the off idle test. Cat was new.

What can be done, chip wise, to give me a better chance at passing first time?

Will changing the injector constant to run leaner overall help?

Thanks for any advice. I shudder going in!
*****forgot duration numbers:ZZ4 - 208/221 .474/.510
L98 - 207/213 .415/.430

 

I -think- there were a couple of posts that covered emissions and larger cams. If i remember correctly running leaner actually hurt the emissions. I'll see if i can find the posts.

 

Hopefully these help:

https://www.thirdgen.org/techbb2/sho...light=emission

https://www.thirdgen.org/techbb2/sho...light=emission

https://www.thirdgen.org/techbb2/sho...light=emission

https://www.thirdgen.org/techbb2/sho...light=emission

 

ZZ4 isn't what I'd call a big cam for a 350 IMHO, so you should be able to pass without much difficulty.

You didn't mention what state you live in, or what test procedure you're subject to...but in general with catalytic converters, just tune it for a 14.7:1 AFR, and let the cat do its thing.

A properly functioning ignition system, and a fresh oil change, will also help avoid problems with the HC. (HC problem at idle might be as simple as worn valve seals). Also, if you've lowered the fan activation temps much, you might put them back somewhere around stock.

 

Indeed, Dave the valve stem seals have been replaced since, so I'm figuring this will help.

Branz-
I'll read those links you provided.
Thanks to both

 

I was going through the links Branz supplied.

One poster said that removing the pcv valve from its grommet would help.

Comments?

 

In some cases, I can see how that might help, although I'd be more inclined to add some type of oil/vapor separator to the PCV line instead.

 

I agree 100% with dave_jones. that cam isn't big enough to worry about.

Fill it up with fresh gas, go for a half hour drive to get everything heated up (cats etc.) and take it for the test.

 

Shouldn't HURT, though, right, Dave?

Z28, the reason I didn't go with the hotcam was for potential problems with emission tuning. My only concern presently is with the higher HC readings even with the stock cam. Mind you, I've replaced leaky valve stem seals since, so.... I like your optimism

 

Well, unless they do a visual inspection and notice it....

Edit: But IMHO you really shouldn't need to do that, if the engine is running even halfway right.

 

High HC's are almost always misfire (at least that is where I would look first, and keep looking and keep looking, until I stumble on some other cause). Oil HC's aren't very significant if all else is working fine. If CO is way low, like you say, then your cat is probably ok, but not definitely (of course).

The misfire could just be a bad plug or wire, and check under the distributor cap for problems. Bad plugs don't always look bad either. New plugs aren't always good plugs either. Faulty EGR can cause a mis also. Vacuum leaks that aren't common (to all cylinders, i.e. just a single runner with a vacuum leak is not a common leak) can cause a misfire - especially at idle.

 

Thanks for the reply, the cat's new.

Wires have been changed since with top of the line Taylors. Just a test with an ohm meter showed 10X less resistance in some cases.

EGR- new.

I will look at the cap- changed everything else!

 

Just FYI, we have a dude here in SoCal (VincentZ28) who passes smog with a 226/234 Lunati cam in a 350 and the ZZ4 cam is nothing compared to that.

 

Encouraging!
I'll find out soon.

 

The ZZ4 cam is not a big cam. I have a ZZ4 equivalent engine with a ZZ4 cam and passed emission with no EGR. It took a few tries and a few chips. Take out A LOT of timing and do not run lean, that was my mistake.

 

How much did you end up taking out?
You ran the same initial (9*), right?

 

The stock base timing is 6 degrees, that's what I leave the distributor set at. I changed the base spark advance in the bin to 10 degrees and pulled about 3-6 degrees from different parts of the spark table so a total of up to about 10 degrees retard. I also was using the base AUJP SA table, which has less timing then what I run with my ZZ4 heads.