Intake Leak Solved - Just do it!

[LBEEMING]

First off, thanks to everyone on here for the 100's of topics I read through to educate myself.

I was chasing a low idle and an erratic cold start. Replacing mostly everything and not fixing any intake leaks. Why??? Well, I just couldnt find any. Used a home made smoke gun, sprayed starter fluid and used a stethoscope to try and hear leaks. Couldnt find anything.

I did have two clues however, that I was running some leaks. Firstly the vacuum reading was only 13 inches. *** Frans Garage, she actually has the same reading as I did, but this was before she rebuilt. From reading on this forum, I found an article that stated a very healthy and rebuilt engine should run ~ 17 inches.

Secondly when removing the oil cap, my engine rpm did not drop significantly or at all.

How did I fix this leak, I just rebuilt the entire intake system.... I had enough and just thought, stuff it, ill put the effort in.

All new intake gaskets, hoses and o rings.

Now I am reading 17 inches of vacuum and removing the oil cap yields a significant drop in rpm.

Now I have to adjust the idle and CO as she is running slightly richer now.

I believe most of the leakage was from the intake gaskets, and why its hard to diagnose this sometimes, is the air flow from the fan and engine shield. Just my thoughts.

Thanks again for everyone's help, and hope that someone might just take the plunge and rebuild the intake instead of pulling their hair out for months.

[Hx911]

Is that CIS? I am struggling with my '74 CIS 2.7 and totally suspect a leak 'somewhere'.
My mechanic repaired the airbox, spiders, etc but really no fic.
I have NO change in idle when opening the oil filler cap.

[Dpmulvan]

[fanaudical]

Hx911 - There is no change in RPM when opening the oil cap on a 2.7 with CIS.

It's probably best to start a new thread with your specific issues and wait for all the CIS gurus to chime in.

[Flat6pac]

Hx911. Pryor to 78 the oil system wasn’t sealed for vacuum. Your 77 and pryor years the short hose from the tank filler neck to the air box assumed the oil mist into the engine to be burned.
In 78-83 the filler neck hose was replaced with a long hose to the rubber boot on top of the TB and FD. This seals the oil tank fumes to stay in the injection area and burned
The 78 and later cars, removing the oil cap induces false, unmetered air into the injection system causing the stumble.
Bruce

[Hx911]

Originally Posted by Flat6pac

Hx911. Pryor to 78 the oil system wasn’t sealed for vacuum.

Bruce, thank you very much! I was not aware of that, and second guessing my mechanic's work.
One more thing I learned on this forum