I am having a low vacuum at idle on my new engine. at 1st I did have a leak at the intake manifold but I torqued down the bolts again and I think I fixed it, but maybe not.. I have looked everywhere for a leak and cant find any. I do notice at idle the vacuum will go from 12-15 while idling. Also I noticed when I rev the engine the vacuum goes up to 20+ around 1500 rpm and runs nice and smooth. If I had a vacuum leak I would think it wouldnt go up like that. Im using mr gasket runner gaskets, and Mr gasket utraseal manifold gaskets. with edelbrock manifold and ASM runners. My rockers have 1/2 turn of preload. Base timing is set at 6 deg. idles at 20deg.

 

I'll let someone a little more familiar with TPI comment on the possible leaks there.

You didn't mention what your idle speed is, in Park, or in gear? That can have an impact.

There are other places to have a vacuum leak....HVAC controls on our cars are semi-notorious for wearing out and leaking. Your brake booster can also be a source of a leak, not to mention all the rubber and hard line that feed these things. Just a couple of additional thought starters.

 

Thanks DynoDave43, I have a manual trans. Also I disconnected all my hvac from the plenum. At this point im guessing that my intake manifold gaskets are leaking somehow..

 

Have you tried the old trick of spraying around where the manifold meets the heads with carb cleaner while the engine is idling, to see if you find an area that makes the RPMs change?

Granted, this method is not by any means infallible, it won't find a manifold leak that's on the lifter valley side, for example, but if you DO find an area that when sprayed causes an RPM change, that's where the unwanted air is getting in

 

A smoke test would be another way of finding a vac leak, I just saw a Youtube video where a guy used a $5 harbor freight vac pump and a cheap cigar and it found it fast.


Credit to Alicempire who shared it the other day, it will be my go to if/when I need to track a vac leak on my TPI. On our TPI cars I figure it would best be used in the vacuum port in the plenum as long as you visually examine the rubber intake bellows first for holes/rips.

 

Advance the timing. See what happens. Make it run the best it can. Ignore whatever "number" you "think" the "timing" is set to.

 

Try advancing timing with est disconnected. Record setting and enter for your base timing. Advance a few degrees to see if vacuum rises depending on cam you could even be more than 10.

 

Just advance the timing. EFFFFFFFFF the "number". Make the engine ruin the best it can. EFFFFFFFFF the "number". The ENGINE knows what it wants, and doesn't pay the slightest bit of attention to what YOU think the "number" either IS, or SHOULD BE. Give THE ENGINE what it wants. It will tell you in no uncertain terms; if you get close to what it wants, it'll run better. Farther, it'll run worse. It's really too simple. Listen to THE ENGINE and do what IT tells you instead of thinking you know it all and can force your "number" on it.

 

Good point to bypass the EST for this diagnosis. The ECM could really confound you if it were allowed to adjust timing while doing that.