Failed smog at idle

[Don W.]

OK, I've done about all I can think of, or been told, to do.

New or replaced:
TB (ported) Old one had shaft play
New EGR
Dist. (High end shop, scope said it was bad, now scope says ign is "perfect.")
Connector from dist to coil
NGK Iridium plugs
Second o2 sensor (first one, Bosch, was bad, high end shop again

)
Early on the CAT was replaced by a 3" high flow.
Stock injectors were sent out for rebuild, balance, flow ect. Matched within 1.5%
No vac leaks
Turbo and DP are stock

Truck has an occasional very slight stumble if you come idle slowly. Otherwise truck runs very well.

Makes to much HC to pass idle smog test. Need 120 makes 130 - 150

Thinking:
Revert to a new stock style CAT.

$$
I've tried, but not since new o2, to revert to stock chip, no difference.
Stock, AC plugs.

All suggestions gratefully accepted.

TIA

 

[syclone1100]

Re: Failed smog at idle

ok I had the same prob.. Does the cat have a connection to attach a air pump?? If you do hook one up and that will get you to pass.. if you can look to open the exhaust up some where after the DP like a cut out.. Also see if the smog guy will let you apply a little gas while at idle to help smooth it out.. I had a similar prob and the smog tech owned a GN and he said by giving it a little gas to smooth out the idle during the idle portion of the test does the trick ( Ithink the idle has to between 800-1100) the stumble is probably what is causing the high HC...

 

[SY2455]

Re: Failed smog at idle

What setting is your Ultimate on? What is your Fuel pressure set at? To pass Ca smog I have to set fuel press to 34lbs and run the Valet mode or T1-15 setting. And the guy that runs the test, runs the idle test at 900rpm, He said if the test is done right after doing the 2500rpm test that 9 times out of 10 the truck being tested will fail the idle test because the tech drops the rpm too quick.

 

[Don W.]

Re: Failed smog at idle

The old cat didn't and the new one does not have the connection. I've heard of the gas trick. May go there next. Funny, my smog guy has a GN also.

Anyone else?

 

[91blazins10]

Re: Failed smog at idle

wow CA must be really strict, here in PA the limit on hc is 220 my ty had a 168 at idle and 56 at 2500rpm.

 

[JSM]

Re: Failed smog at idle

turn idle up to max allowed

lower fp

 

[SY2455]

Re: Failed smog at idle

Don my last test was showing 115 HC at idle and 24 HC at 2500rpm with a bad cat. I have to replace it next year before testing.

 

[Don W.]

Re: Failed smog at idle

OK, thanks. I'm not sure resetting the the Ultimate will help as long as it's on T1, easy to change of course. Fuel pressure for sure. Currently 42 with engine off. Last time, before the dest and o2 change, it didn't help. Maybe this time.

And I'll run the idle up.

Getting good at changing plugs , whadda think of putting a set of CR42TS' in just for the test?

Thanks all

 

[SY2932]

Re: Failed smog at idle

wow CA must be really strict, here in PA the limit on hc is 220 my ty had a 168 at idle and 56 at 2500rpm.

The first and only time that I had my truck tested after I bought it in July of 1999, my HC's were 8.9 PPM @ 2500 RPM (no reading is done at idle). The limit here in Ohio is 220 PPM.

Another thing to looking into is your thermostat. If you have a "cold" one like a 160, replace it with a stock one which is 195 degrees. The hotter the better since it will help burn off the offending gases.

Just remember the closer that you are to stock, the more likey you will be able to pass. So, putting the old AC Delco plugs in certainly shouldn't hurt. I put a fresh set in my truck before I got mine tested...

 

[4C FED]

Re: Failed smog at idle

Don,
You aren't still using the 160 deg. thermostat listed in your sig., are you?
The hotter you can get it the cleaner it will run.
I see Stant has a 205 deg. thermostat available. You might give it a try since it's relatively cheap compared to a cat.

Secondly, try to come in & get it smogged right after logging some highway miles. Try not to let it sit idling & cooling down.

 

[4C FED]

Re: Failed smog at idle

turn idle up to max allowed

lower fp

How would you crank up the idle speed?
I thought since it's running closed loop the IAC will compensate for throttle butterfly adjustment. And if you adjust butterflies to far won't it throw a code because the ECU can't command the correct idle speed?

 

[It's just a six]

Re: Failed smog at idle

How would you crank up the idle speed?
I thought since it's running closed loop the IAC will compensate for throttle butterfly adjustment. And if you adjust butterflies to far won't it throw a code because the ECU can't command the correct idle speed?

I have turned up my idle this way & set no codes, max RPM is 1100 , just get it a little below that, should help.
Good luck!

BTW, what size is your cat?
The larger it is = less restriction = less likely to heat as much.
You can put a 2" cat & it will get hotter (not good for performance ,,,but good to pass smog.)

 

[EcSy#2671]

Re: Failed smog at idle

I know a smog guy down here that could get to pass. In the two speed idle test after the 2500rpm does your guy just let the truck fall back to idle? It sounds dumb, but if you slowly down the engine speed back down to idle it will help. I'm sure you already know this, but I just thought I would throw it out there.

 

[Don W.]

Re: Failed smog at idle

It sounds dumb, but if you slowly down the engine speed back down to idle it will help. I'm sure you already know this, but I just thought I would throw it out there.

Had not heard that one before. Thanks. My next try will be Wed AM due to work. Planing on lowered FP, increased idle, and now your trick. Prolly revert to stock plugs as well. And maybe some of that "guaranteed to pass" stuff??:roll:

 

[Jimmy]

Re: Failed smog at idle

Had not heard that one before. Thanks. My next try will be Wed AM due to work. Planing on lowered FP, increased idle, and now your trick. Prolly revert to stock plugs as well. And maybe some of that "guaranteed to pass" stuff??:roll:

Test it with 87 octane in the tank too.Just stay out of boost untill it's used up.

 

[turbodig]

Re: Failed smog at idle

OK, I've done about all I can think of, or been told, to do.

I've tried, but not since new o2, to revert to stock chip, no difference.
Stock, AC plugs.

All suggestions gratefully accepted.

TIA

Put some alky in the tank, put a 195 thermostat in, disable your intercooler pump and get it *really* good and warm. The heat will get your HC numbers down at idle.

 

[Don W.]

Re: Failed smog at idle

Well I got the alky so will try that. Can do the t-stat fairly quick now also.

 

[Don W.]

Re: Failed smog at idle

Uh, how much? I was thinking 5 - 10%

 

[It's just a six]

Re: Failed smog at idle

So, what was the final outcome???

 

[Don W.]

Re: Failed smog at idle

Gonna throw in a new set of CR42TS plugs set to .35+ (just for the test) and the alky this week. Been driving on an extension. Will post as soon as I know. Thanks.