Simple cone intake swap results in confusing vacuum problems

adj4x4

New Member
Joined
Aug 6, 2007
Location
Raleigh
First off, not a car newb, but considering how I managed to make a cone intake install problematic, I feel like one. I should have eliminated these things one by one to isolate the possible problems.

Recently got an 88 comanche and was somewhat disgusted by the abundance of vacuum lines. In one fell swoop I tore out the charcoal evaporator and installed a standard off-brand cone filter. In doing so, I eliminated:

-the air box (obviously)
-Duct to hot air (near exhaust manifold)
-Replaced valve cover breather with mini cone filter (was connected to air box obviously)
-Char evap canister (and 2 lines to tank and former air box)
-Capped vac line at manifold which lead to a pair of nipples on the back of the air box (the other of the pair went to the diaphram which opens the gate to the hot air duct on the dirty side of the box)

Also, I capped the vacuum line which went to the valve cover at the back of the engine on the manifold and cover sides. The rubber fittings over the nipple on the manifold and the valve cover were shot, and I was advised that it is an unnecessary line(?)

Now, the truck has become ridiculously stall prone, indicating a vacuum leak (I would think). I was advised that this was likely due to the increased amount of time for the engine to reach normal operating temperature. While skeptical, the stalling does seem to be somewhat mitigated by the engine reaching 210, but still present. Nightmare to drive.

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If your still reading, thank you, and feel free to answer any or all of these questions:

-Would low temperatures be responsible for more stalling if stock air box/related lines were removed?

-Is the vacuum line from the intake manifold to the valve cover necessary, why, and if this is necessary, why isnt it a problem to be taking vacuum from something with an open breather inches away?

-What is the deal with this pair of lines at the back of the air box!?!?
-How does the vacuum line from the engine interact with the second line (that controls the hot air gate on the low side). They seem to be connected on the inside of the box by a little metal disc which Ive seen before on other cars and thought nothing of.
-How is a vacuum leak not created by sending a vacuum line from the intake manifold to inside the air box?
-If I cannot leave this line capped at the manifold, what should I connect it to with the air box gone?

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I know people drop in these filters all the time, what big concept did I miss?
 
Filter

I'll reply,
I put one on my 88 XJ. I only removed the air box to install the filter to the end of the factory intake pipe. I didn't plug any of the vac lines ecept for the one going down at the exhaust I juess that is the hot line you were talking about. I had trouble with it not running untill I snuck a BB in the lower end where it hooked into the diaphram. I've no problem sence. Everything else is still there. All emitions components are still there just the airbox is gone.
 
adj4x4,
To answer some of your questions if you havent already had them answered:

-Would low temperatures be responsible for more stalling if stock air box/related lines were removed?

Most likely not, however without the stock airbox, it will run better at startup before its warm....but chances are its not going to cause it to stall


-Is the vacuum line from the intake manifold to the valve cover necessary, why, and if this is necessary, why isnt it a problem to be taking vacuum from something with an open breather inches away?

If there is a vacuum line that runs from the intake MANIFOLD to the valve cover, there has to be a one way check valve between them...otherwise the vacuum will be lost to the crankcase via the valve cover (which would cause idle to go crazy). The purpose this line serves is for excess pressure in the crankcase to be vented into the manifold. You also mentioned a line from the valve cover to the airbox....this is the more common line, that most vehicles have. It serves the same purpose (crankcase ventilation) but it allows air to flow both ways from the airbox to the valve cover and vice versa depending on whether or not the crankcase has positive or negative pressure (vacuum). In theory, you should be able to cap the line on the manifold and on the airbox....the valve cover however needs a vent (line to airbox or a little filter fitted, although I prefer leaving the line...im not a fan of the filters)


-How is a vacuum leak not created by sending a vacuum line from the intake manifold to inside the air box?

That WOULD create a vacuum leak...i suggest you check the factory diagram as stated....any line from the intake manifold should not be vented to the open atmosphere (which is what the airbox is)


Hope the couple questions i answered help, but im sure its likely youve already figured it out by now :beer:
 
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