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I have a lean miss under light load conditions and I was wondering if my headers might cause this? I was reading on another forum that headers can cause a lean condition, but it wasn't clear at what rpm. If the headers can cause this, does the carb have to have the jets and metering rods changed? This is a CC Quadrajet.

Jim
 

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Jim, the CCC system will automatically adjust the carb for most any condition, so no need to consider changing jets, rods, etc. Headers per se should not cause a lean condition. If you had a radical cam with a lot of overlap, then it is possible to scavenge some of the fuel mixture from a cylinder that has not yet fired, but I don't think you have such a cam.

Most likely there is a small vacuum leak. Header bolts not tightened ( or re-tightened after a few heat cycles) can cause a lean condition. If you don't find loose header bolts, then I would also double check your TPS voltages. A TPS being off , or having a flat spot in it's resistance curve, can cause a lot of issues.

I've also had the check valves in the AIR system go bad, cause some funny running issues.
 

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Discussion Starter #5
Jim, the CCC system will automatically adjust the carb for most any condition, so no need to consider changing jets, rods, etc. Headers per se should not cause a lean condition. If you had a radical cam with a lot of overlap, then it is possible to scavenge some of the fuel mixture from a cylinder that has not yet fired, but I don't think you have such a cam.

Most likely there is a small vacuum leak. Header bolts not tightened ( or re-tightened after a few heat cycles) can cause a lean condition. If you don't find loose header bolts, then I would also double check your TPS voltages. A TPS being off , or having a flat spot in it's resistance curve, can cause a lot of issues.

I've also had the check valves in the AIR system go bad, cause some funny running issues.
Thank you, we'll check those things out. So far we have disconnected the EGR which smooth the motor out alot. We tried to restrict the EGR, but it didn't work and I'm going to run without it. I'm now trying to smooth the motor out completely.

Jim
 

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Do you get any check eng. lights. Also a rich running car will tell the computer to lean it out. Maybe you could find someone with a test meter that will show all the sensors while the car is running not just a code if a check lite is on. I was also going to say a overactive egr but you allready done that. Also on the carb there is a rectangle cover held in place with a cotter pin it's just in front of the whole that the air cleaner rod goes, pop that cover and turn the jet looking thing 1/8 turn in at a time to richen the mixture if you get a check lite you have gone to far. It's a fine tuning thing on the ccc carb.
 

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Discussion Starter #8
Do you get any check eng. lights. Also a rich running car will tell the computer to lean it out. Maybe you could find someone with a test meter that will show all the sensors while the car is running not just a code if a check lite is on. I was also going to say a overactive egr but you allready done that. Also on the carb there is a rectangle cover held in place with a cotter pin it's just in front of the whole that the air cleaner rod goes, pop that cover and turn the jet looking thing 1/8 turn in at a time to richen the mixture if you get a check lite you have gone to far. It's a fine tuning thing on the ccc carb.
It does get the servive engine soon light after a few miles on the highway (EGR code), but nothing else. i just got it back from the mechanic who adjusted the carb some more and reduced the gap on the plugs to .040. Its not running perfectly smooth, however, it is better than ever before. I'm going to drive it like this for a while and get a ZZ4 prom to eliminate the EGR function. I'm still thinking about a SMI stage 2 carb in the future.

Jim
 

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I have a lean miss under light load conditions and I was wondering if my headers might cause this? I was reading on another forum that headers can cause a lean condition, but it wasn't clear at what rpm. If the headers can cause this, does the carb have to have the jets and metering rods changed? This is a CC Quadrajet.

Jim
Can you please explain in detail what you mean by "lean miss under light load?"
 
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