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240 Emissions, High idle HC

BassGuy

BassGuy

Active member
Joined
Aug 10, 2010
Location
Sarnia, ON
Went to e-test my car today, and failed on idle HC.

1990 240, LH2.4, K cam advanced 2*.
What would cause the difference? Our system does NOT test NOX anymore, so I do not have those numbers.

HC (ppm)
Idle (968rpm): -Limit: 200, Reading: 388, Result: Fail
2500rpm: -Limit: 200, Reading: 26, Result: Pass

CO(%)
Idle (968rpm): Limit: 1, Reading: 0.29, Result: Pass
2500rpm: Limit: 1, Reading: 0.19, Result: Pass
 
Lean Fuel Mixture???

Don't know...but a small vacuum leak is not a big issue with higher RPM. With time, brake boosters start leaking air.

Also, an injector might not be delivering full volume at idle.
 
Even a single misfire will lead to a fail on HC. Could be a little rich also, but the 2500rpm levels look good.

Turning up the idle speed a bit can help.

New spark plugs are cheap, and might help.

A small vaccum leak might solve your problem, particularly if they don't test for NOX.
 
Misfiring dude. Sticky injector, bad plugs, wires, coil... something along those lines.
 
Found a vacuum leak at the IAC nipple on the intake manifold. Going to grab a hose clamp tomorrow, as well as test the O2 sensor sometime this weekend (just for posterity). Think that would help?
 
It won't exactly idle without a light miss with a k cam at 14.7:1 afr that the lh tries to shoot for.

Having said this, it shouldn't be blowing 300 ppm either.

Miss of some manner leading to Unburned fuel is likely. Dirty oil will affect Hc a little compared to clean oil. But t is running poorly if it is blowing 300ppm...thats bad enough that even if it didn't have a cat, running right it shouldn't be blowing that much.

Find the source of the miss. Where did you set your valves?
 
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