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Failed SMOG - high HC

B

btolenti

1/2 ton status
Joined
Sep 28, 2003
Posts
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Location
Gilroy, CA
Hey gents,

So, I just failed my latest SMOG test. Here are the results:

15MPH
HC Allowed - 121
HC Measured – 123
CO Allowed - .75
CO Measured - .54
NOX Allowed – 1050
NOX Measured – 28

25MPH
HC Allowed - 93
HC Measured – 92
CO Allowed - .95
CO Measured - .36
NOX Allowed – 1050
NOX Measured – 17

Any suggestions how to lower the HC levels?

I am thinking about checking the fuel pressure and changing the cat and maybe the O2 sensor….

Its an 87TBI motor with edelbrock cam and intake, MSD wires, MSD Coil, and MSD 6A.
 
Ugh....no one???

I did lower my fuel pressure from 14 to about 11.5 to 12... With WinALDL, my BLM's went down a tad across the board, but still are a bit rich for me. Any other suggestions???
 
do you have a aftermarket chip?, lowering your fuel pressure might make it worse by leaning it out to much, do you have a heated 02 sensor?
 
Yeah, put on a new cat. It now passes the 15mph test quite well, but it had no effect on the readings for 25mph....

I have no clue on this one. I am checking for vacuum leaks now, but winALDL says that at lower RPM it is pulling fuel already, so I am at a loss...
 
Was the truck nice and hot when it was tested, if not it will fail almost everytime.
 
truck was nice and hot....ran it while I was waiting for the test. What gets me is that after replacing the cat, only the 15mph test changed. The 25mph test was almost the exact same readings.

I have nothing else to do. So, I am going to change the plugs and oil and see what the heck happens.....

I did notice that at idle my IAC counts are 0. I have adjusted minimum air a few times and it still rests at 0 at idle....not sure what that means.
 
check your pcv valve and your smog pump filter, if you have one. you need to put more oxygen in the exhaust to burn the HCs. think as the CAT as another combustion chamber. it will burn everything that was not burned in the cylhd, it just needs more oxygen. that is the function of the smog pump. HC may be due to unburned gas or oil(blow-by).

also, did you just replace your cat?

ARQ.
 
My truck had the same problem, read some of the old post in this section and you'll see. My 90 didn't have air injection, not sure about your 86. Increased RPM has the same effect as air injection as I understand it. That's why the HC limit is lower at 25mph vs 15mph.

My truck shifted from 2nd to 3rd and failed "just barely" on the 25mph test. I found a tech that stuck it in 2nd and it passed with ease. Anything you can do to get your RPM's up will help. Maybe put on some smaller tires, stockers or anything and try again.

KM
 
I found that my EGR was not fully tightened down and could have been leaking. THe gasket was a bit black ...apparently leaking exhaust out of the EGR.

I just wonder if that was the problem all along.... Funny thing is that it never threw any codes...
 
That was great article Longbed!

Btolenti your truck should be able to pass. My truck has a 355,10.1compression,219/219 HR cam, CNC TF heads,ported intake,46mm TB,75# inj's,headers etc.... and it sqeaked out a pass in N.Cali.

I bet if you put's on some small azz wheels to bring the rpm's up, which in turn will get the cam into/closer to it's sweet spot. His emissions will drop some and he doesn't need much improvment to pass.

At one point, someone on the this board suggested that I jam the truck in 4wheel drive and tell the tech to deal with it. As funny as it sounds, it would produce lower HC emissions. I considered leaving my front hub's unlocked and taking it in.

Good Luck and keep us posted.

KM
 
Yeah, I figured smaller tires may help bring up the RPMs a bit. I was spinning about 1450rpm at 15mph.....and a bit over 1400rpm at 25mph. Unfortunately, I don't think I can get my hands on some smaller tires before my ref test on Tuesday....

I did torque down everything again, changed the EGR gasket, replaced the spark plugs cap and rotor, checked plug wire resistance, and changed the oil. Hopefully that will help.
 
Hows that work anyhow? REF testing, so if you fail they haul you in to a ref? Mine failed a test only, but the place told me I could bring it back for a free retest. So I'm curious how you ended up with a REF.

KM
 
I changed from a carburated 350 (stock in my 86) to a TBI setup from an 87. I needed to go to the ref for him to approve the engine change so I can smog it at any SMOG center.
 
woohoo! It passed!

all in all, here's what I did.

-lowered fuel pressure to 12psi
-changed TBI gasket, EGR gasket
-changed to delco plugs, opened gap up to .040
-changed cap/rotor w/delco stuff
-torqued down intake/exhaust manifolds.
-used a screw to keep the heat riser flap fully open
-changed cat and installed delco o2 sensor (non-heated)

HC's are at 85/56 for 15/25mph - max allowed is 121/93
CO at .05/.04 - max allowed is .75/.95
NOX at 193/67 - max allowed is 1050/1050
 
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