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Discussion Starter #1
Anyone know some quick tips for lowering the HC levels in the exhaust of the GA???

-HSentra
 

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bitter old man
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I presume you had trouble with an emissions test? If that's the case and you have room on your NOx number, advance the timing a couple of points. Arrange to test immediately after you arrive after driving several freeway miles, while the catalytic convert is still hot.

Make sure the ECU isn't throwing an O2 sensor code. A bad O2 sensor will make for a high HC number.

Excess fuel pressure will also lead to excess HC.

Replace the cat if all else fails.

And it's "hydrocarbon".
 

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if the timing trick doesn't work i'd really check the cat, it's common when the cat is rotted out or whatnot, do you have any rattling from the rear of the car underneath?
 

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bitter old man
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You missed one:
  • Excessive HC, no CO = misfires
  • Excessive HC, excessive CO = very rich
  • Low HC, excessive CO = slightly rich
  • Excessive NOx = high combustion temps. Could be overheating, inoperative EGR, advanced timing
 
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Discussion Starter #7
I forget what you get if you run too lean, but that can cause high HC too. Brother's car had this problem due to a leaking brake booster hose leaning out only one of his V8 cylinders due to the position of the tap in the intake runner.

Oh wait, I guess this is a misfire of sorts.


bahearn said:
You missed one:
  • Excessive HC, no CO = misfires
  • Excessive HC, excessive CO = very rich
  • Low HC, excessive CO = slightly rich
  • Excessive NOx = high combustion temps. Could be overheating, inoperative EGR, advanced timing
 

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A misfire is just when the plug fires at the wrong time or not at all, and leftover gasoline vapors and residue that isn't burned is dumped out the exhaust valve and out the exhaust.
 

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bitter old man
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If there is no spark, there is no combustion residue from that cylinder, just gasoline. Therefore excessive HC, no CO. However, exhaust sampling occurs at the tail pipe, so the firing cylinders will contribute CO, though HC will still be excessive.

Probedude reminded me to add to NOx:
  • Excessive HC, low CO = misfires
  • Excessive HC, excessive CO = very rich
  • Low HC, excessive CO = slightly rich
  • Excessive NOx = high combustion temps. Could be overheating, inoperative EGR, advanced timing, lean mixture, vacuum leak(s)
 

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Cone Dodger
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okay, misfires could also be caused by, here goes:
leaking valve cover gaskets...
messed up plug wire(s)....
worn rotor, and, or distributor cap....
altered timing....
leaking fuel injector(s).....
any vacuum, air intake, leak....unmetered...
insufficient fuel......
also insufficient air.......
insufficient spark......
wrong spark duration........not timing.....
fuel contamination.......which may sometimes leak to lock-up.....
crank sensor faults.......
knock sensor faults.....
maf sensor faults......
excessive heat, as aforementioned.......
and if i missed anything, please add...........
oh yeah......compression.......blown head gasket and such.....
warped cylinder head.........
blow-by......in extreme cases.......
 

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They have cat. convt. cleaner at some part stores that is supposed to lower your emissons.That may help it pass?
In some states there are exemption clauses that if your car is in certain yrs. and fails so many times they pass it.{my first car ,89 escort gt, failed 3 times and finally they passed it after i got the converter tested and it checked out ok}
 
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