Intake Manifold Gasket
Thread Starter
|
Mountain Pass
Joined: May 2018
Posts: 217
Likes: 12
Intake Manifold Gasket
All indications are that the intake manifold gasket on a 302 is blown creating an internal vacuum leak, so I took the air cleaner off yo provide more air and it runs fairly well before I can get to it. It started running rough again doen low and the engine goes into a vapor lock ehen trying yonstart, Can anyone explain this phenomenon? The gasket blew more and gas is crossing between cylinders?
Thanks
mjac
Thanks
mjac
Thread Starter
|
Mountain Pass
Joined: May 2018
Posts: 217
Likes: 12
Intake Manifolld
I am sorry p, ai was in a rush. It is a carbureted 302 and when you go to start it the engine acts like it wants to lock up, before it catches on a real slow revolution like a vapor lock. Iy finally occurred to me the intake manifold gasket may have blown more and might be causing it. The engine sometimes will barely turn, like a dead battery , then it will finally catch and start up, especially when cold, not as bad when hot. It is also starting to run rough again. Every check was made and everything pointed to an internal vacuum leak and I minimized the affects by pulling the air cleaner to give it more air.
Thanks
mjac
Thanks
mjac
More Turbo
Joined: Aug 2017
Posts: 508
Likes: 69
From: Tucson
Vapor lock keeps fuel from getting to the engine and usually happens when underhood temps are high.
Slow cranking is a battery/starting system problem.
A vacuum leak lets too much air in and changes the air/fuel mixture.
Not sure how removing the air cleaner to "let more air in" would help.
Sounds like you need to bite the bullet and change the intake gasket.
Slow cranking is a battery/starting system problem.
A vacuum leak lets too much air in and changes the air/fuel mixture.
Not sure how removing the air cleaner to "let more air in" would help.
Sounds like you need to bite the bullet and change the intake gasket.
Thread Starter
|
Mountain Pass
Joined: May 2018
Posts: 217
Likes: 12
I am just trying to feel my way through this and am learning as I go. From what I know, when the vacuum leak started, the engine ran very rough down low but cleared up pretty well on top at high rpm. My understanding of that was more air was being pulled in at high rpms so the air fuel mixture was a little better. I pulled the air cleaner and the rough low rpm running stopped. Now it is starting again and the engine is binding up, belching a little bit and not turning over when you go to start it. The battery, Odyssey, is at 13.4. I was wondering if further problems with the intake manifold gasket was causing this and importantly, why, so I could understand what was going on. I am heading out as we speak to change the intake gasket, Cometic, and see if everything clears up. Should have done it before.
Edit: You are 100% correct, it is not Vapor Lock, what I meant to say was, it was “acting” like a vapor lock but it wasn’t.
Thanks
mjac
Edit: You are 100% correct, it is not Vapor Lock, what I meant to say was, it was “acting” like a vapor lock but it wasn’t.
Thanks
mjac
Hotshot
Joined: Jul 2020
Posts: 10,461
Likes: 2,630
From: Near Salt Lake City
I am sorry p, ai was in a rush. It is a carbureted 302 and when you go to start it the engine acts like it wants to lock up, before it catches on a real slow revolution like a vapor lock. Iy finally occurred to me the intake manifold gasket may have blown more and might be causing it. The engine sometimes will barely turn, like a dead battery , then it will finally catch and start up, especially when cold, not as bad when hot. It is also starting to run rough again. Every check was made and everything pointed to an internal vacuum leak and I minimized the affects by pulling the air cleaner to give it more air.
Thanks
mjac
Thanks
mjac
Check for an intake leak with brakleen
Are all the intake bolts tight? Yes check those
Hotshot
Joined: Jul 2020
Posts: 10,461
Likes: 2,630
From: Near Salt Lake City
Pulling your air cleaner off should have "no" effect on the engine unless the air filter is plugged
Factory air filter?
What year of carbureted 302? Do you have points or a Duraspark?
"Vacuum leak started" you say, what makes you think your trouble "is" a vacuum leak?
Stumble? Misfire?
I would be looking at the cap, rotor, plugs and wires
Then on to vacuum leak testing
The breaker plate and the vacuum advance, I would test those too
Spray those plug wires at night, with a spray bottle of water with the engine running
You should see "no" lightning around the wires
Factory air filter?
What year of carbureted 302? Do you have points or a Duraspark?
"Vacuum leak started" you say, what makes you think your trouble "is" a vacuum leak?
Stumble? Misfire?
I would be looking at the cap, rotor, plugs and wires
Then on to vacuum leak testing
The breaker plate and the vacuum advance, I would test those too
Spray those plug wires at night, with a spray bottle of water with the engine running
You should see "no" lightning around the wires
Thread
Thread Starter
Forum
Replies
Last Post
Mjac167
Performance & General Engine Building
38
Mar 9, 2026 09:57 AM
jazqa87
Pre-Power Stroke Diesel (7.3L IDI & 6.9L)
1
May 22, 2022 09:35 AM
fordguy2100
1973 - 1979 F-100 & Larger F-Series Trucks
8
Sep 11, 2016 06:50 PM
ferryj1
1987 - 1996 F150 & Larger F-Series Trucks
7
Nov 10, 2004 07:29 AM
