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Intake Manafold Holes

Intake Manafold Holes
C

CFCA

Jeeper
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Location
North
Vehicle(s)
CJ7
This is my first post. I look forward to learning from all of you!

A quick question. I recently purchased a 86 CJ7 . The engine was running rough, is a pain to start (starter fluid gets it going) and you would need to keep a higher rpm otherwise it would putter out.

As i stared cleaning up the engine, it became very clear that there are 3 threaded holes in the intake manifold that were left WIDE open by the previous owner - clearly some sensor was removed, never replaced and is allowing air to flow in downstream of the carb.

Has anyone ever plugged these up? I can literally stick a screwdriver into the manafold. Could this be the cause of my issues?

Thanks
 
CFCA said:
I can literally stick a screwdriver into the manafold. Could this be the cause of my issues?

Thanks
Click to expand...
Not familiar with a 1987 Jeep but unplugged holes in the intake side of the manifold would definitely be a huge problem. It would make it run much to lean.
Are the holes threaded? If they are get some plugs and plug them up and see if that helps.
Pics would help identify the problem.
Welcome to the site!!
 
Could this be a model that used a water jacket to heat the underside of the carb? Maybe they are just holes for water hoses.
 
Here's a pic of the sensor holes.Don't understand why you don't have coolant flowing out as two of the sensor holes have coolant flowing through them. The knock sensor is dry and not needed if you aren't using the computer.The only switch you should run is the manifold heater sensor. It turns the manifold heater on/off when the engine is cold. Manifold heater is on the bottom of the intake under the carb. Warms the fuel/air as it flows past.

I used the coolant temp switch for a manual temp gauge.

The hole on the top of the intake that is circled is the input side of the coolant, coming from the water pump, there is a similar hole on the rear of the intake that is where the coolant exits the intake and goes to the heater core. The coolant then comes out the heater core and runs back to the water pump.

Intake Switches.webp
 
Last edited:
This is the old style manifold. You don't have any coolant leaks? Sorry I see Yellow 85 beat me to it

oldmanifold.webp
 
You are all so helpful. Thanks!

No I don’t have any coolant leaks. If you plug the holes wouldn’t that be similar to the old style of manifold. Could I just get a replacement manifold and be done with all of this junk?
 
CFCA said:
You are all so helpful. Thanks!

No I don’t have any coolant leaks. If you plug the holes wouldn’t that be similar to the old style of manifold. Could I just get a replacement manifold and be done with all of this junk?
Click to expand...

I wouldn't pull the trigger on a older style manifold due to having to change the exhaust manifold as well. I'd plug the holes for now cause it's easy and cheap and will eliminate that from being a cause.

I'd bet it's in your carb though. You should have the Carter BBD carb which is a notorious pain in the hind end. By the return spring and bracket in the pic though I see someone has already done some modifications. Are there wires plugged in the back of your carb? I know it's kind of a pain but take off the air cleaner and get pics of the carb from the sides and back. It will be helpful to know what you have.
 
Vacuum isn't really created by the intake itself. It is created in the carb. So, first look at the carb base and hose connections/condition for leaks.

Your fuel filter is on upside down. The offset hose tube should be on top, 12 o'clock position, not the 6 o'clock position. Where it is allows fuel to drain down.
May be causing hard starts as fuel has been siphoned away. Takes a little to get fuel back up and into the carb.

You could leave the intake as it is, without running coolant through it and not having a working manifold heater. But then the fuel will probably not vaporize properly, especially when you first start up. Will run very rich and blow black smoke (un-burned fuel) 'til warm.

Swapping to earlier style intake and exhaust would be more trouble and expense than plugging one wet hole and getting a couple hoses and setting things up the way they should be.

Leaving it the way it is the engine will run, just not the way it should.

Your vacuum leak really has nothing to do with the intake(unless it is not tight against the block). It is coming from the carb.

Petescj is probably the closest to figuring out the bulk of your problems, what carb are you running?
 
If you want to spend money on modifications I would suggest an MSD-6A ignition and a Weber carb.

I also wouldn't change the intake manifold. The older manifolds are heated by the exhaust manifold -they are bolted together- so you would have to replace that too. Now, on the other hand, I am putting a later model exhaust manifold on my early intake so they will not be bolted together and I do not have a heater now, but I do have the MSD ignition which really helps on those cold starts so I countered that measure.
 
CFCA said:
Here you go!
Click to expand...

Part of your hard start issue is the fuel filter is positioned wrong.
The return line(outboard)must be at the 12 o'clock position.
Also-That factory location for the fuel filter, was well known for engine fire issues from dripping fuel onto the exhaust.

LG
 
I just found an even better picture! This is from the underside / back of the intake and exhaust and shows both water points and the exhaust connection from the exhaust to the EGR. Make sure you have this pipe or that your EGR valve is staying closed.

https://i.ebayimg.com/images/g/cpMAAOSwrD9dlojK/s-l1600.jpg
 
Here is a picture of the carb!

You guys are so helpful! I will change the fuel filter position! I will try plugging the holes.

B8DDCF0E-F69E-4B5A-8DE1-B09CF87545B1.webp
 
Ok some one replaced your Carter BBD with a Motor craft 2100. That's a good thing , many people would recommend it if you still had the Carter. Go through the solutions that were already recommended and let's see where your at. The next step will be verifying the vaccum lines are hooked up correctly. Best to take things step by step.
 
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