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Vacuum line runs cause low reading?


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So I tried blocking off the lines that run to the evap canister, no increase/change in idle vacuum. I tried connecting the lines according to the non-federal manual diagram (just to see), again no change/increase in vacuum at idle.

 

The vacuum for the canister is from the same one for the distributor vacuum advance. It does not leak vacuum, everything is sealed. It's just to open a valve on the canister. This vacuum is not manifold vacuum, in that it's not from below the throttle plate. In fact at idle there should be no vacuum on that line at all.

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There's a purge line that is basically a constant vacuum "leak", as it pulls fuel vapors mixed with fresh air through the charcoal filter. Without the engine running I was able to pull air through the purge line per the FSM test (which is a stupid way to test it). Fuel vapors don't taste good. As far as I understand, the distributor line, when under vacuum, opens the purge valve and allows the vapors into the manifold to be burned off. I shouldn't be able to pull vapors w/o vacuum on the dizzy line.

 

Could the fact that I'm using stock lash pads with a regrind cause the low readings? I'm certain the rocker geometry is correct, but perhaps the valves aren't opening/closing fully, causing the constant low reading.

 

And it does idle well, Smoke. No real issues at idle as far as I can see. I'm going to try and find an fuel/air ratio gauge that I can use to see how the mix is at idle as well, just to see how it's running fuel-wise.

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I can't drive and enjoy it. It's running poor because of the low vacuum, and has a rough hesitation just off idle. It clears up past part-throttle, and I believe it may be due in part to the TPS adjustment.  It idles fine, but put a load on it and it runs like ass.

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I looked at an interesting article on Hot Rod Magazine, http://www.hotrod.com/techarticles/camshaft_test_review_comparison/, that shows a small-block 350 that has a cam with slightly less duration/lobe seperation at .050 lift as having around 14" vacuum at an idle speed of 750rpms. Motorsport Auto lists the same cam as having "moderate idle" (power/vacuum at idle?), and XenonS30 lists a cam from Web Cams that is similar in specifications to mine as "needs lash caps", so perhaps I need to recheck the valvetrain geometry again. 

 

I know that the L28E is much different from a Chevy small-block, but is it entirely possible that the cam I'm running is the reason I have stable but low vacuum? And is anyone here running a MSA ,Schneider, or other-than-stock cam that pulls higher vacuum. And if so what is your idle timing/rpm set at? 

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I might see if I can source a stock cam, the only difficulties I see is getting rocker arms and keeping them with the respective lobes. The rocker arms I have were resurfaced by Delta, but I'm afraid if I use them on a different cam that they might wipe a lobe/damage a lobe. Think that might be an issue? Also, since S30s are hard to come by, would I have any difficulty using a 280ZX cam?

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Just got a message from Schneider Cams, they said that the cam will probably make around 14" at idle and that they use .165" lash-pads as opposed to the stockers that I'm currently running. I might order the lash-pads and run with this cam grind, but I might also see about getting a stock cam/rockers from a junkyard and revert to a factory grind. I wish cam manufacturers would post the expected vacuum readings at the factory recommended idle speed, so there's an expected baseline to work from. I spent a good bit of time troubleshooting something that may just turn out to be "normal" due to the cam grind.  :no: Oh well, lesson learned. I can't be too upset as this is my first full-on engine rebuild/restoration. Thanks again to all for the help and advice!

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