Super high H/C level again!
Thread Starter
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Tuned
Joined: Jul 2004
Posts: 476
Likes: 5
From: Delaware
Super high H/C level again!
I recently bought yet another F body, a 90 F150 with 5.0 and AOD trans. It had been sitting awhile and ran OK but a little rough. When I took it for emission testing it had a miserable reading of 2062 (max allowed is 220) for the low idle hydrocarbon level, CO was also high. When my 90 Bronco 5.0 failed with a high (2000+) reading it was a leaking intake gasket which after I changed it, it had a idle reading of 39 and high idle (2500rpm) reading of 19 on the HC level. So I figured a bad intake gasket on this F150. I have changed the head gaskets, intake and upper manifold gaskets, and left the PCV valve pulled out. It still failed with idle reading of 1600 HC and CO was still a little high. I changed the throttle body gasket and cleaned out the throttle body, put a solid gasket behind the EGR valve in case it was sucking a little air and went back again. HC still too high at 725 idle but passed high rpm HC and CO. Retarded the timing to 5 btdc instead of 10 and lowered the HC to 523. So I thought maybe the old gas may be hurting the reading. I drained the rear tank, put in a little over 7 gal of premium (Yow! $2.72 a gallon!) and added about 10 oz of alcohol, and left the timing at 5 degress. Ran it at 80mph for 5 miles down the interstate and went for another reading. Still passes the low and high CO, passes the high idle HC, but the idle HC level back up over 700. The only code I've got is for the TPS sensor. Can the TPS sensor affect the idle HC level. What else could I be overlooking? Any suggestions are welcome. Kemicalburns I could use your expertise.
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
The TPS sensor can definately cause problems with high HC readings. If it's telling the computer that you're giving it way more gas than you are, it will run lean. Same as if the intake gasket leaks.
