Stock '01 Failed Emissions

rpaoness · 07-21-2008, 09:15 AM

I have a 2001 GMC K2500HD w/ 6.6Dmax / Allison that I purchased in May - 151k mi, all 8 injectors replaced in '04 at about 90k mi according to GM service history.

CT emissions require a "snap" test, which is a test that accelerates the engine (in park) at full throttle until it reaches the speed governor, holds for 1-4 sec, and then releases. This is to be repeated 3 times before a "real" test, and then it can be tested several times after. According to my last test, they performed 9 "snaps", and the truck scored 47% opacity which is above the 40% permitted.

I've only put about 1000 mi on the truck since purchasing (stupid fuel prices), and installed a new air filter on the truck before the emissions test. Since the failure, I've replaced the fuel filter, cleaned the MAF, and replaced the thermostats (it was slow to warm up in May, but that may just be the way the Dmax's are).

Typically driving the truck I really don't see any smoke at all in almost all driving conditions, nor do I have any driveability problems aside from a very minor idle variation. I've tried to duplicate the emissions test (as much as I hate to see an engine run to redline unloaded), and don't see any smoke on accceleration until the truck reaches the rev limiter, and then issues a puff of very black thick smoke. I believe this puff is what is causing the test failure.

I was hoping someone might have experience with a similar problem. It appears as though CT is one of VERY few states with emissions requirements, and I have yet to find anyone with experience troubleshooting this. I will probably take it back for a restest shortly to see if mainly the change of the fuel filter has any impact on the test.

Thanks,
Rob

**BigRedChevy** · 07-21-2008, 10:28 AM

I do not know how you would do it, but i am sure with efi live you could change the fueling tables and rev limiter to make it pass and then after the test put the setting back where ever you want it. You might want to PM IdahoRob he is very good with efi live and i am sure he could help you out.

Hook'em_Horns! · 07-21-2008, 11:01 AM

Have you tried/thought of running a Diesel fuel additive?

gr8shot · 07-21-2008, 12:07 PM

Oh yeah, with EFI man, you could do some fun stuff and drive those emission people crazy. Set the rev limiter at like 2000 rpm's or somethin crazy like that lol. What a good no GREAT idea!!!!

rpaoness · 07-21-2008, 12:10 PM

I thought GM was steadfast in their recommendation to not need additives. I'd certainly be happy to try one if someone has experience that it reduces smoke.

Hook'em_Horns! · 07-21-2008, 12:13 PM

Quote:

Originally Posted by rpaoness

I thought GM was steadfast in their recommendation to not need additives. I'd certainly be happy to try one if someone has experience that it reduces smoke.

Could be...of course they LIKE selling parts.

Many testimonials here on this site on the use of additives to check, it just might clean it up some for the test.

Thankfully, they are not testing Diesels down here, though they DO have 'Fart Sniffers' at the on ramps for Gasser emissions checks.

delong_1 · 07-22-2008, 06:28 PM

i think the older models should be exempt from emission testing, of course its not going to look good during their test, it doesnt have a cat on it, so naturally it wont read as clean as newer models. i think that is b.s.

rpaoness · 07-23-2008, 06:36 AM

So I tried some fuel additive (diesel power - diesel kleen from Walmart) and found that the idle variation seems to have gotten quite a bit better. I also tried to really lay into the accelerator on a commute to work (usually the truck sits and I drive my Escort).

Went back for a test today and scored a 34.4% out of the 40% permitted, so I passed on the second time around.

Thanks for the input.

Hook'em_Horns! · 07-23-2008, 10:57 AM

Cool,

Glad to hear it worked out, I thought maybe several tanks would be needed to show improvement. IMO, that testing station’s methods are way off base for normal operations.

The GM recommendation of non-need of Diesel Additives is based on consuming fuel that is no longer produced, with only ULSD available now. And with claims of poor fuel on the market, use of an additive (even every other tank) may indeed be needed. Cheap insurance, I believe.