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Does PCV to intake runner cause a miss?

S

sigtauenus

Active Member
I finally figured out the vacuum leak I had was with the 1" spacer with PCV. I removed the spacer and set the carb directly on the intake (with a gasket of course), but that meant running the PCV to a port on the back of the intake on the runner to #7.

Intake is a C9OX, carb is a Holley 4150.

I have a miss in one of the cylinders. I will try to confirm tonight which cylinder it is and will get back to you, but since I just did this change-a-roo with the PCV, I'm suspecting that as the culprit until I figure out otherwise.
 
Try what Craig said but my thought process is this...and it could be way off. You just took excess gasses that were being distributed evenly throughout the intake (attached to carb spacer) and directed them directly to one cylinder (#7 runner).
 
"blue65coupe" said:
Try what Craig said but my thought process is this...and it could be way off. You just took excess gasses that were being distributed evenly throughout the intake (attached to carb spacer) and directed them directly to one cylinder (#7 runner).
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It's just some "fumes" unless there is a lot of blow-by, it shouldn't be enough to cause a miss IMO.
 
As soon as I can I'm going back to the carb spacer PCV fitting. 1" spacer design didn't work, as the vacuum leak was from the hollow underside and carb flange design of intake.

I'm going to get a Boss 302 style 3/8" spacer, which is solid (eliminates issue with vacuum leak) and also has PCV fitting.
 
But he's pulling those fumes. It may be way off but makes sense in my peabrain. What he's done, again-my peabrain thinking, is basically created "open air flow" to that cylinder. I may be overanalyzing though.
 
"sigtauenus" said:
As soon as I can I'm going back to the carb spacer PCV fitting. 1" spacer design didn't work, as the vacuum leak was from the hollow underside and carb flange design of intake.

I'm going to get a Boss 302 style 3/8" spacer, which is solid (eliminates issue with vacuum leak) and also has PCV fitting.
Click to expand...

Oh he[[ no. You go out there right now and block that thing off. I know Craig is sitting there right now wanting to know who is right. I've met him. That's how he rolls. (me too)
 
"blue65coupe" said:
Oh he[[ no. You go out there right now and block that thing off. I know Craig is sitting there right now wanting to know who is right. I've met him. That's how he rolls. (me too)
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:lol
I'm not saying your wrong. Your logic is good, I just don't think it would be enough to cause a miss. It would take a serious shift in the air/fuel ratio to cause a miss.
 
Not going to happen tonight. Will do so tomorrow after work. I also need to pull it out of the garage and go around the block again and get some pics to prove it since it was delinquent this afternoon.
 
Hooked up like it is to the one runner, it would create a lean mix to that one cylinder, but only when the PCV valve was in the open position. When engine vacuum is low, the lean mix should be back to normal. I have never seen this cause a miss but it will change the color of a plug to indicate a lean situation on that cylinder. Short term should be no problem, long term, I have never run one long enough.......
 
"sigtauenus" said:
Not going to happen tonight. Will do so tomorrow after work.
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Great. Like I didn't have anything else to do except wait for an answer. Want to wager a little bit Craig?
 
"blue65coupe" said:
Great. Like I didn't have anything else to do except wait for an answer. Want to wager a little bit Craig?
Click to expand...
I think Pete hit the nail on the head, I'll wager all my StangFix bucks!
 
On a new, tight engine it is more likely to cause a miss, IMO. Why? The fumes in question are hydrocarbons, which burn. Fewer hydrocarbons (from tight engine) = higher fuel/air ratio to that cylinder.
 
When I built the 65, I ran the PCV to the intake runner initially. Didn't really have a "miss", but did have a bit of a "skip" at idle. No problems at speed. I did changeover to plenum after the first plug change... The sparkplug from the cylinder where the PCV was plumbed showed it was VERY lean.
 
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