Making my Renix a little simpler?

I am in the process of taking out whatever I possibly can to clean out the engine bay of clutter. Right now i'm trying to figure out if it's okay to pull the "football" (vaccum canister), and the charcoal canister. I pulled the football earlier and it's running fine. There is a line that runs to the intake manifold. I noticed that when that line is sucking air, the engine idles high, when it's capped off it idles slower and smoother.

I also have the NP231 with the vaccum front axle. I spaced the shift fork with washers, so I wanted to get rid of the lines running from the t-case to the front axle? Can I just cap these off.

I was just reading my FSM, and I saw that the charcoal canister is there to hold in the fuel vapors while the engine is off. Have any of you got rid of this thing? What did you cap off, or what lines did you change.

I took out the entire HVAC system from under the dash, and my cruise control has never worked. I'm not worried about that stuff not working, I just want my underhood mess free. Hope someone chimes in...



1987 XJ 4.0

The line that runs to the intake manifold goes to the MAP sensor. The MAP sensor regulates air pressure from start-up to when the engine is running. Thus making fuel and air mixture adjustments automatically as the pressure changes.

eace:

p.s. I'm pulling my hair out just to understand my 88 Limited. It's not like working on a '62 Falcon.

The football is a vacuum reservoir--it literally stores vacuum so that there is constant pull on the accessories even when you have the throttle wide open. You can remove it if you want to but you must cap the line or else you will suck unfiltered air into the intake and cause all kinds of problems short and long term. Honestly you are better off keeping it so that stuff like brakes work

88chry said:

The line that runs to the intake manifold goes to the MAP sensor. The MAP sensor regulates air pressure from start-up to when the engine is running.

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Just for clarity, the MAP does not regulate pressure, it measures it, Manifold Absolute Pressure sensor.

The Canister is an EPA required piece of hardware that inspectors look for during the emission gestapo annual inspections, if it will over the road use, versus off road.

I recommend keeping the vacuum bottle for brake safety. Jeep brakes are already scary enough!

Ecomike said:

I recommend keeping the vacuum bottle for brake safety. Jeep brakes are already scary enough!

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The vacuum canister isn't involved in the brakes at all. The power booster directly connects to the manifold. It does affect the AC/Heat vents staying in the correct position during acceleration. But that is about it. As someone says the line needs to be plugged if the reservoir is pulled.

lpennock said:

The vacuum canister isn't involved in the brakes at all. The power booster directly connects to the manifold. It does affect the AC/Heat vents staying in the correct position during acceleration. But that is about it. As someone says the line needs to be plugged if the reservoir is pulled.

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Now that you mention it, you are right.

lpennock said:

The vacuum canister isn't involved in the brakes at all. The power booster directly connects to the manifold. It does affect the AC/Heat vents staying in the correct position during acceleration. But that is about it. As someone says the line needs to be plugged if the reservoir is pulled.

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Yes and No. There is no check valve in the manifold so any changes to any of the ports will affect all of the others. However the stock setup has a check valve on the line that leads to the bottle, which does prevents vacuum pressure from being pulled back through the manifold. If the check valve is removed (or more likely if it's broken) then the bottle will act as a reservoir for the whole system. But as for the OP, the line in question serves the A/C and CC from what I remember so if that stuff is all dead weight then the line can be plugged off at the manifold and less risk of loss.

ehall said:

Yes and No. There is no check valve in the manifold so any changes to any of the ports will affect all of the others. However the stock setup has a check valve on the line that leads to the bottle, which does prevents vacuum pressure from being pulled back through the manifold. If the check valve is removed (or more likely if it's broken) then the bottle will act as a reservoir for the whole system. But as for the OP, the line in question serves the A/C and CC from what I remember so if that stuff is all dead weight then the line can be plugged off at the manifold and less risk of loss.

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Actually there is a check valve in the brake booster. It is required for the same reason the reservoir is required. Under acceleration or when the engine dies you wouldn't have any brakes if it wasn't there. But you are correct if the line to reservoir breaks or is disconnected you will have low vacuum which will result in hard brakes. You are also correct I forgot the Cruise control.

Also the heater will no longer work either unless the control valve is eliminated

lpennock said:

Actually there is a check valve in the brake booster. It is required for the same reason the reservoir is required. Under acceleration or when the engine dies you wouldn't have any brakes if it wasn't there. But you are correct if the line to reservoir breaks or is disconnected you will have low vacuum which will result in hard brakes. You are also correct I forgot the Cruise control.

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I still say you were right the first time. The check valve on the brake booster makes the vacuum bottle and other vacuum lines irrelevant, as they do not have anything in common except the intake manifold. If, you connected the vacuum bottle to the brake booster before the BB check valve, then the bottle would help the BB hold vacuum. Basically a working BB has its own internal vacuum reservoir. The real reason for the bottle and its own check valve seems to be to maintain constant vacuum on the AC/heat damper door operator valves, and AC control valve assy.

Also, one typically only brakes under high vacuum (not at WOT). A non-leaking BB has enough vacuum stored to work even after the engine dies.

ehall said:

Also the heater will no longer work either unless the control valve is eliminated

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The 87s did not have the heater hose / heater core control valves, if that is valve you meant, but it will lock the damper doors in a spring loaded default, fresh air vent mode, IIRC.

Well he did mention that he ripped out all the hvac stuff, so it's not an issue for him. The heater valve defaults to on with no vacumn.

Ecomike said:

I still say you were right the first time. The check valve on the brake booster makes the vacuum bottle and other vacuum lines irrelevant, as they do not have anything in common except the intake manifold.

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The check valve is a one-way valve that allows the intake to draw a vacuum on the booster. Any vacuum on the manifold side of that valve will suffice, potentially including vacuum that is stored in the canister. The reason the canister is irrelevant by default is that there is another check valve on the accessory line, which is what prevents the vacuum from flowing back.

ehall said:

The check valve is a one-way valve that allows the intake to draw a vacuum on the booster. Any vacuum on the manifold side of that valve will suffice, potentially including vacuum that is stored in the canister. The reason the canister is irrelevant by default is that there is another check valve on the accessory line, which is what prevents the vacuum from flowing back.

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Unless I miss understood what you are trying to say, I disagree with your statement "Any vacuum on the manifold side of that valve will suffice, potentially including vacuum that is stored in the canister." as the RATE of loss of Vacuum on the manifold side is way too rapid, and too large volume wise. With out the check valves the vacuum in the bottle and BB would drop to near zero in about 0.1 seconds at WOT. Why do you think they use the check valves? To stop that loss from happening.

Well the vacuum in the bottle is consumed pretty much immediately at WOT anyway so that it irrelevant. However it is probably enough to service one hit on the brakes if the CC and AC are not also in use. Since the check valve on the booster also keeps a charge in the drum then that is two hits on the brakes (one from the booster reservoir, and another from the theoretical canister)

Of course the correct way to run constant vacuum is a supplemental vacuum pump. My 85 cadillac has one and the harness on that is 20-25 hg all the time. There are aftermarket pumps for hotrod brakes too, eg this one

ehall said:

Well the vacuum in the bottle is consumed pretty much immediately at WOT anyway so that it irrelevant. However it is probably enough to service one hit on the brakes if the CC and AC are not also in use. Since the check valve on the booster also keeps a charge in the drum then that is two hits on the brakes (one from the booster reservoir, and another from the theoretical canister)

Of course the correct way to run constant vacuum is a supplemental vacuum pump. My 85 cadillac has one and the harness on that is 20-25 hg all the time. There are aftermarket pumps for hotrod brakes too, eg this one

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The bottle is irrelevant. It provides no benefit to the brakes as the brake check valve is where the hose enters the booster. It is only for AC and CC. They are not connected systems.

ehall said:

Well the vacuum in the bottle is consumed pretty much immediately at WOT anyway so that it irrelevant. However it is probably enough to service one hit on the brakes if the CC and AC are not also in use.

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In addition to the BB check valve, I know of at least one, if not 2 (second one hiden in the bumper near the bottle IIRC), check valves on the AC and Bottle lines. The AC only consumes vacuum when a control is moved, and the same for the CC when engaged or disengaged. Not sure how much is used by the CC (mine is still dead ), but I doubt it is very large during braking. But the vacuum bottle has a check valve that keeps the bottle vacuum at a peak vacuum, near the bottle IIRC, even when the manifold goes to zero. It will hold vacuum for hours after the engine is shut down if the hoses are tight and the CVs are good. There is another on my 89 near the firewall leading to the AC system, but I don't know if it is OEM, as it is missing on my 87. I have operated my AC damper controls long after the engine was off, and could here the vacuum valves still working the doors, long after manifold vacuum was gone.

I got to learn a lot about all this dealing with my Mutant Nissan Diesel XJ. It has an oil filled rotory vane vacuum pump that sits on a shaft coming out the back side of the Hitachi alternator. Seems diesels can not operate the Brake boosters off of intake vacuum. They also use a belt driven and electric vacuum pumps to operate the brake boosters, like the link you posted.

Long story short, it would be smart to tie the bottle and brake booster together on the back side of their check valves, and on the outside of a third check valve leading to the intake manifold, but that would cost Detroit an extra check valve.

lpennock said:

The bottle is irrelevant. It provides no benefit to the brakes as the brake check valve is where the hose enters the booster. It is only for AC and CC. They are not connected systems.

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The BB check valve does NOT limit vacuum from that side of the harness. The bottle is irrelevant to brakes (by default) because of the accessory check valve, not because of the BB check valve.

Ecomike said:

I got to learn a lot about all this dealing with my Mutant Nissan Diesel XJ. It has an oil filled rotory vane vacuum pump that sits on a shaft coming out the back side of the Hitachi alternator. Seems diesels can not operate the Brake boosters off of intake vacuum. They also use a belt driven and electric vacuum pumps to operate the brake boosters, like the link you posted.

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That is correct, most diesel vehicles have a supplemental vacuum pump. When I tell mechanics that I have one in my Cadillac they often ask if it's diesel.

Ecomike said:

I got to learn a lot about all this dealing with my Mutant Nissan Diesel XJ. It has an oil filled rotory vane vacuum pump that sits on a shaft coming out the back side of the Hitachi alternator. Seems diesels can not operate the Brake boosters off of intake vacuum. They also use a belt driven and electric vacuum pumps to operate the brake boosters, like the link you posted. :

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Diesels can't operate off intake vacuum because they have do not have any vacuum. They are wide open intake all the time and do not have a throttle body. No restriction equals no vacuum. Only time a diesel develops intake vacuum is when the air clearer is really clogged. Same thing happens with the gas motor at WOT which is why we are having the discussion about check valves.