PaulS

I just failed my 2nd Maryland emissions test on the dyno for excessive hydrocarbons. They gave me a print-out of the tests which show the hydrocarbons spiking well above the emission limit each time the car is shifted or decelerated (M6). When the throttle is engaged, the hydrocarbon emissions are under the limit. I assume this means the car is very rich when decelerating.

State hydrocarbon limit: 0.70 GPM
1st test: 0.926 GPM
2nd test: 1.151 GPM

My engine mods are: FLP headers, lid, Whisper MAF ends, MAFT (set to 15%, -10 fist test, 10%, -10 second test), 180 thermostat, ASP crank pulley

I originally tuned the LTFTs to near 0 with the MAFT set at 15%, -10. After the car failed the first test, I Autotapped several runs and looked at what was happening during deceleration. LTFTs were going very rich, averaging -8, so I changed to 10% and the LTFTs averaged -1 during deceleration and +4 during aceleration. However, the car still failed the second emisions test.

Tuning experts -- what should I try next?

Your advice is appreciated.

BYE RICE

iTrader: (2)

Welcome to the board,Paul.
They have an IM/240 emission(dyno) test in M.D.?
That sucks.All counties? Nothing like that here in F.L. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> What kind of cats do you have on the car?

PaulS

I'm running the cats that came with the FLP headers. Not sure who made them.

Brother J

Random thoughts:

--How much oil is being sucked through into your intake under vacuum? Research PVC mods.

--Might want to go back to the stock t-stat. Hotter is better for emissions testing.

--Fresh oil changes are supposed to reduce concentrations of HC. I would guess that goes double if oil is being sucked past the rings.

--Last resort, try some "Guaranteed to Pass" gas additive from your local auto parts place.

--Almost forgot, new plugs?

<small>[ July 12, 2002, 07:41 PM: Message edited by: Brother J ]</small>

PaulS

Thanks for the ideas -- keep them coming.

My car has never used any oil. I changed the oil the night before the second test -- didn't make any difference.

The plugs are in good shape, about 7,000 miles.

I have no misfire codes.

ChrisB

If you don't have OEM cats see if you can install a set of those.

Ensure your car is HOT HOT HOT for the emissions test. If you have a cooler thermostat swap back in the stocker.

Try using some copper RTV to ensure a seal at your header collector.

Try reducing timing if you have LS1 edit (high timing will effect an increase in HC emission).

Finally try adding some alchohol (ethyl or isopropyl work best - no methyl) before the test - you can work with up to 20 percent.

Chris

BYE RICE

iTrader: (2)

What were the #'s like.CO's for example?
Do you have any exhaust leaks fwd of the O2's?Also
Try running a pint of methel ethel keytone.(MEK)available from a paint supply store.
What's strange is that they use decel data.Federal Test Proceedure doesn't use decel as a pass/fail,I don't believe.

PaulS

The CO emissions were 3.6027 GPM for the first test and 2.9598 GPM for the second test, well under the limit of 15.0 GPM.

Its wierd that the HCs spiked during shifts and deceleration. The test used the average value over the entire test, which pushed my reading slighly over the limit.

I'll check for exhaust leaks again, but as far as I can tell, I can't see any signs of leaking at the header flange or at the cats. Any ideas for finding exhaust leaks?

Ragtop 99

iTrader: (7)

chris:

Rather than swap T-Stats, couldn't you leave the 160 T-stat in, but switch back to the stock fan settings? Letting the car idle while waiting in the line should run the temp up.

how much timing retard would you suggested? Accross the board a 4 degree decrease, for example?

PaulS

Both tests were conducted when the outside temperature was around 85 degrees. I ran the 180 degree thermostat but put the fan settings back to stock. In this condition, AutoTap showed engine temp around 195-200 degrees. How much hotter would it be with the stock 195 degree (I think) thermostat?

Has anyone had sucess lowering HC emissions using additives?

Pro Stock John

iTrader: (34)

If you can run lower octane gas that will help.

I would not add fuel with the MAFT, if it was -10 it was taking OUT fuel.