Intake Question
Thread Starter
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
Intake Question
While changing my T-Stat last night, I noticed that the inside of the intake manifold was dirty. By dirty I mean it looked like an oily mess coating it. The car is a 96 lt4 w/ 117K miles, daily driver. Hotcam, stock tune.
Questions
1. Is this normal?
2. If not, what is the cause?
3. What is the most effective way to clean w/o disassembly?
Car is running strong, no issues. I just noticed this and thought it odd. Obviously if there is problem, PCV or something like that I would like to correct it. Also, if not, i feel it would run stronger if it were clean.
Thanks for your input --Chris
Questions
1. Is this normal?
2. If not, what is the cause?
3. What is the most effective way to clean w/o disassembly?
Car is running strong, no issues. I just noticed this and thought it odd. Obviously if there is problem, PCV or something like that I would like to correct it. Also, if not, i feel it would run stronger if it were clean.
Thanks for your input --Chris
Race Director
Joined: Nov 2003
Posts: 12,220
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Maybe you're pulling (extra) oil past your valve seals and the PVC system is sucking it into the intake? Or maybe you're missing an oil baffle in the valve cover?
Once you cure the problem, I'm not sure cleaning would be necessary (or possible) w/o removing the intake. TB cleaning might be necessary but a link on how to do that was already posted above.
Once you cure the problem, I'm not sure cleaning would be necessary (or possible) w/o removing the intake. TB cleaning might be necessary but a link on how to do that was already posted above.
Race Director
Joined: Feb 2004
Posts: 12,517
Likes: 19
While changing my T-Stat last night, I noticed that the inside of the intake manifold was dirty. By dirty I mean it looked like an oily mess coating it. The car is a 96 lt4 w/ 117K miles, daily driver. Hotcam, stock tune.
Questions
1. Is this normal?
2. If not, what is the cause?
3. What is the most effective way to clean w/o disassembly?
Car is running strong, no issues. I just noticed this and thought it odd. Obviously if there is problem, PCV or something like that I would like to correct it. Also, if not, i feel it would run stronger if it were clean.
Thanks for your input --Chris
Questions
1. Is this normal?
2. If not, what is the cause?
3. What is the most effective way to clean w/o disassembly?
Car is running strong, no issues. I just noticed this and thought it odd. Obviously if there is problem, PCV or something like that I would like to correct it. Also, if not, i feel it would run stronger if it were clean.
Thanks for your input --Chris
Since the intake above the fule injectors is just an air chamber, there is no way to keep it clean via fuel.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Also when you accelerate , the lower engine vac does not pull crankcase fumes through the PCV valve so the fumes go back up the air supply pipe from pass side rocker cover to the TB
Race Director
Joined: Apr 2003
Posts: 17,698
Likes: 1,667
From: moraga ca
The intake gets crudded up from the pcv valve and from reversion. The pcv valve sucks oil out of the crankase and cam overlap pushes the intake charge back up through the runners and gunks up the plenum.
Thread Starter
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
It is called coking, and it is normal. When you shut down the engine, the warm oil vapors in the crankcase rise, then settle out in the intake. On a carbed car, the constant flow of fuel keeps the coking down.
Since the intake above the fule injectors is just an air chamber, there is no way to keep it clean via fuel.
Since the intake above the fule injectors is just an air chamber, there is no way to keep it clean via fuel.
I don't think it's the valve seals so much as I have had no indications of oil burning in combustion. No smoke, oil smell, or excessive usage. But at this mileage, I'm sure it will be neccessary in the not so distance future. Hopefully around the time when I have a second driver and I can just have the heads ported and valves done.
Tech Contributor
Joined: Oct 2008
Posts: 3,729
Likes: 190
From: Custer, WI
I think EGR contributes too, my stock runners were totally caked with black crap. I ran AS&M runners for a few thousand miles with an EGR blockoff plate, and they looked just as clean as when I installed them when I pulled them off. Could be because I didnt have as many miles on them, but there wasn't anything on them
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Thread Starter
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
I think PeteK, Rodj, and 383vet nailed it. The intake is coated but not caked. I'm pretty sure, by what I saw, that most of it was located just behind the TB, so that would lead me to believe it was from the air pipe from the valve cover.
I think my plan is to make sure that the air tube is cleaned out and baffled. Then hit it with some top end cleaner, then change the plugs.
Like I said, the engine is running strong. I don't think any valves are sticking or leaking. Throttle response is good, no smoke. It does run a little rich at idle but there's no black, blue, or white smoke, in fact none at all.
I think my plan is to make sure that the air tube is cleaned out and baffled. Then hit it with some top end cleaner, then change the plugs.
Like I said, the engine is running strong. I don't think any valves are sticking or leaking. Throttle response is good, no smoke. It does run a little rich at idle but there's no black, blue, or white smoke, in fact none at all.