2001 LB7 Failed Emissions

[rpaoness]

I have a 2001 GMC K2500 with 151k miles that I bought in May.

It recently failed emissions testing here in CT. It's tested via a "snap" test which measures the opacity (thickness) of the smoke during wide open throttle acceleration in neutral. The test requries that the operator floor the accelerator and allow the engine to reach the rev limiter and hold for 1-4 seconds and release and repeat. The test is 3 practice revs and then the test revs. The truck failed at 47% opacity (vs. 40% allowed) after 9 "snaps".

Prior to the first test, I installed a new air filter. Since failing I've replaced the fuel filter and thermostats and cleaned the MAF. Testing in the driveway shows that the truck puffs a single puff of black smoke right as it reaches the rev limiter, which I'm guessing is the cause of failure. Other than the failed emissions test, I have no driveability problems other than a very minor idle variation.

I was wondering if anyone has any good suggestions to pass the emissions test on the next go around. I've already had a suggestion of a diesel fuel additive, so I'll try to run 1/2 a tank through with an additive before I go for a retest.

Thanks,
Rob

[Mark Rinker]

I wonder if you could push more air through the engine, relative to fuel, to improve the opacity?

Not sure how much boost you make sitting still at WOT, but if the boost feedback hose was removed temporarily from the wastegate actuator, you might make more boost sitting still and pass the test.

Just an idea - not sure if it will work or not. Don't forget to hook the hose back up after the test...

[YZF1R]

That doesn't seem to be a fair test for a light duty truck unless you're working it on a daily basis. I'm very easy with mine. Pull very little weight the few times a year I do pull and for short, slow distance. Maybe once a year it I open it up and let it go through the gears coming onto a four lane if no ones around. Boy does it blow out the smoke for a couple gears. But it's not smoke. I'm only blowing the soot off and out from inside the pipes. Do that a couple of times and I can no longer see anything if I open it up again. A class 8 truck, yea, maybe that test would tell you something because they are run hard all day. A picikup? If it hasn't been worked hard, I say it's just soot being blown out. Give her a couple good wide open runs in a safe area and take the test again.

BTW, I have stock fueling.

Steve

[rpaoness]

So I tried some fuel additive (diesel kleen from Walmart), drove as hard as I could for 100 mi or so and went for a retest. I scored a 34.4% out of the 40% allowed and passed.

Guess it was just routine maintenance stuff.

[YZF1R]

Glad you passed!

Steve

[rustyk]

Yeah, let's not emit carbon that drifts to the ground - let's get it into the ATMOSPHERE!