Strange HC Problem
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Junior User
Joined: Feb 2008
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Strange HC Problem
I have a 77 ford f-100 with a 302. CA truck so I still have to smog :-( For the past few years, I have had to battle a problem with high HC at the 2500 RPM range. The strange part is that it involves the EGR valve.
With the engine at idle i have 67 ppm for HC with a max of 200 PPM. When we got it up to 2500 RPM my HC spiked to 850 PPM with a max allowable of 250 PPM. Once the EGR was disconnected my HC went down to 100 PPM at 2500 RPM.
Now I have rebuilt the carb so I don't believe that it is the issue. All new intake gaskets. I have gone through five EGR valves all while experimenting with different orifice sizes.
All of my vacuum routing is correct. I've tried everything I can think of. Just wondering if someone else has had this problem, or if someone can think of something that I haven't tried.
I now have two years to figure it out, but I would like to get it solved to I can fix it and forget about it.
I appreciate the help.
With the engine at idle i have 67 ppm for HC with a max of 200 PPM. When we got it up to 2500 RPM my HC spiked to 850 PPM with a max allowable of 250 PPM. Once the EGR was disconnected my HC went down to 100 PPM at 2500 RPM.
Now I have rebuilt the carb so I don't believe that it is the issue. All new intake gaskets. I have gone through five EGR valves all while experimenting with different orifice sizes.
All of my vacuum routing is correct. I've tried everything I can think of. Just wondering if someone else has had this problem, or if someone can think of something that I haven't tried.
I now have two years to figure it out, but I would like to get it solved to I can fix it and forget about it.
I appreciate the help.
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Joined: Feb 2008
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And the smog tech thinks the egr is working too well and the technician that I talked to at another shop thinks the egr isn't flowing enough or that I may have the wrong egr for the application, even though I have gone through so many set ups.
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
A spike in HC that comes on suddenly like that points to a carburation problem.. it's dumping a bit too much fuel at that rpm. You could spend hours or days trying many combinations of jets and needles to lean the motor out but the simple fix is to just block off the EGR. Put a stealthy block off plate between the valve and intake, or tap and plug the hole in the intake and put the valve back on.. problem fixed.
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