Super high HC reading
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Tuned
Joined: Jul 2004
Posts: 476
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From: Delaware
Super high HC reading
I just bought another F body, 1990 F150 4x4 with 5.0 FI and AOD transmission. I took it thru our state's emission testing and failed miserably. The max HC level allowed is 220. This reading was 2062 at idle and 311 at high (2500rpm) idle. Any suggestions? Last year when I had almost the same problem with my 90 Bronco same 5.0 engine I had about 300 HC at idle and 2000+ at high idle but that turned out to be a bad intake gasket. Now it's just the opposite, higher at idle and lower at high rpm, which it should get lower at higher rpm. But the idle reading is way, way too high.
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Tuned
Joined: Jul 2004
Posts: 476
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From: Delaware
I've not pulled it down yet but I'm going with the intake manifold gasket and upper plenum gasket as the problem. Today I took a look at it and noticed a few little wisps of smoke hanging around the coil area on the left side. I thought that it looked like a little mist like from the crankcase but the breather tube was OK, etc. I climbed up on top and looked down with a flashlight and found an intake manifold bolt was missing with the smoke coming out of the hole. I guess the last owner thought it had enough bolts and didn't need that one.
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Joined: Jan 2004
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the cheapest way to get that little sticker is with rubbing alcohol, the highest isopropyl content you can find (90% or more, preferably).
my truck didn't pass a texas inspection right after i got it, and i had already replaced all the spark and fuel items to clear up a bad miss. so, i put two or three of the 16oz size bottles in half a tank of gas, drove it to the inspection station, and it passed a retest with flying colors. less than 1/4 the original test's HC emissions. i think it raises your CO emissions slightly, though.
my truck didn't pass a texas inspection right after i got it, and i had already replaced all the spark and fuel items to clear up a bad miss. so, i put two or three of the 16oz size bottles in half a tank of gas, drove it to the inspection station, and it passed a retest with flying colors. less than 1/4 the original test's HC emissions. i think it raises your CO emissions slightly, though.
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Tuned
Joined: Jul 2004
Posts: 476
Likes: 5
From: Delaware
I know about the alcohol trick. But, with a reading of 2062, even if it lowered it by 3/4 it would still be about 500 and I need 220 to pass. Plus the CO was high also. I'm going to pull the intake and replace the gasket along with the upper plenum. When I had the problem with my 90 Bronco the reading when from over 2000 to just 19 after I changed the intake gasket.
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