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POOR vaccum

xjintx

xjintx

NAXJA Forum User
Location
Eddy, TX
is there naything I can do to increase vaccum?

when under power I have low vaccum... not only messes with the vent controls but can affect breaks.

I can buy an inline pump that will keep it at like 15... but a few hundred bucks.

There is no leak... it's low at the TB :(

any suggestions appreciated.

I know the 2.5 is no powerhouse but ?????
 
Nobody???

Took it to muffler shop today to check cat and muffler for nay blockage... NONE.

Vaccum is good at idle and slow speeds... step on it and loose vaccum until let off again.
 
I'm running into a similar problem on my 97. The cruise doesn't work and half the air blows out the defrost, no matter where you have the selector. After searching on here, I thought I found the fix in the vacuum reservoir. I replaced it along with the lines to the intake.

Whenever I unplug a line, I hear a rush of air, so the system seems to be holding vacuum.
 
THat sucks! :rolleyes:

I had the same problem. Mine turned out to be a very tiny leak due to vacuum hose near the AC blower firewall that had an invisible leak. The leak was due to brand new vacuum hose that was not round on the inside of the hose. Only way I found it was I turned off the engine, and listened for a tiny leak till I finally found it. Seems a very tiny leak in the AC damper vacuum lines has a huge effect. Probably due to the very small feed tubing diameters.

During acceleration the replacement vacuum to the lines drops to near zero.

The only practical solution is to find the real leak. I found that sucking sound, with the engine cycled on and off the only way to find mine. Next time I will try a hand vacuum pump on isolated lines.
 
On my old jeep I would loose vacuum at WOT on hot days. Turned out for me that the heat softened a (non OEM) vacuum line. The line would collapse under vacuum presure and I would loose vaccum pressure to the vent system. Just one Idea.
 
Beached Bones said:
On my old jeep I would loose vacuum at WOT on hot days. Turned out for me that the heat softened a (non OEM) vacuum line. The line would collapse under vacuum presure and I would loose vaccum pressure to the vent system. Just one Idea.
Click to expand...

Another excellent idea, great suggestion for checking with these guys! Easy to grab cheap flimsy wall hose that collapses under vacuum and heat thus starving the others.
 
Get an inline vacuum check valve, and put it into the vacuum line running through the firewall to your HVAC control panel. It will let the vacuum get up to where it needs to be while idling, but when you accelerate it won't let it back out, and your problem will be fixed. I have done this on several jeeps, and dodge trucks as well. You can get one of those check valves at NAPA for about $5.
 
x2elite said:
Get an inline vacuum check valve, and put it into the vacuum line running through the firewall to your HVAC control panel. It will let the vacuum get up to where it needs to be while idling, but when you accelerate it won't let it back out, and your problem will be fixed. I have done this on several jeeps, and dodge trucks as well. You can get one of those check valves at NAPA for about $5.
Click to expand...

Thanks for the info. That sounds like a good idea.

I found this online:
Inline Check Valve - Autozone
Inline Check Valve - O'Reilly

Both have the same part number, so I'm assuming they're all made by the same company. I wonder if you could put several in the system. Say one at or near the intake, and another at or near the vacuum reservoir. As long as you had them facing the right direction, you could keep air from going back into the intake from lines and keep from getting a leak down situation at the reservoir.
 
Do not put check valves near the vacuum storage bottle, it will add to your problems, put them near, and into the AC lines at the firewall. Do not put them between the MAP and the intake manifold either!
 
Ecomike said:
Do not put check valves near the vacuum storage bottle, it will add to your problems, put them near, and into the AC lines at the firewall. Do not put them between the MAP and the intake manifold either!
Click to expand...


He is right, some of the items attached to the manifold, and the vacuum canister are not supposed to have constant vacuum.
 
x2elite said:
He is right, some of the items attached to the manifold, and the vacuum canister are not supposed to have constant vacuum.
Click to expand...

The brake booster for sure, and I think the vacuum bottle already have a check valve. The MAP needs to see instantaneous true intake vacuum pressure, from 0 to +20. I think the AC is suppose to have a check valve, but it may be missing over time, on older XJs.

I think my 87 has an OEM CV on the AC, but my mutant 85 XJ diesel was a hacked mess of vacuum lines, and I need to add one on the AC for it. Probably why it was so sensative the bad hose ID, on that bad batch of new hose.
 
dagr8tim said:
Thanks for the info. That sounds like a good idea.

I found this online:
Inline Check Valve - Autozone
Inline Check Valve - O'Reilly

Both have the same part number, so I'm assuming they're all made by the same company. I wonder if you could put several in the system. Say one at or near the intake, and another at or near the vacuum reservoir. As long as you had them facing the right direction, you could keep air from going back into the intake from lines and keep from getting a leak down situation at the reservoir.
Click to expand...


These are exactly what I was talking about. If that works its the simplest cheapest fix I know. Most of the time if that doesn't work then you have one of two other problems: a bad HVAC control panel, or a bad leak somewhere else in the system before the check valve.
 
Thanks for the info. On my 97, there's a line from the manifold that T's on the firewall and goes through the firewall for HVAC, then goes to the cruise, and then the vacuum bottle.

I've tested new lines back to the AC T at the firewall with no effect. I suspect my leak is in the firewall. If I could check valve it at the T, hopefully I could atleast restore my cruise.
 
IF the AC, and duck dampers only act up at heavy throttle (low vacuum), then it may just need that check valve added right before the T. Try that first. If the leak is a bad vacuum damper valve on the AC, or the AC dash controls, it probably would not work right at any time. The firewall vac lines are very small in diameter, and any loss of vacuum under the hood feeding that small line is quite noticeable.
 
Ecomike said:
IF the AC, and duck dampers only act up at heavy throttle (low vacuum), then it may just need that check valve added right before the T. Try that first. If the leak is a bad vacuum damper valve on the AC, or the AC dash controls, it probably would not work right at any time. The firewall vac lines are very small in diameter, and any loss of vacuum under the hood feeding that small line is quite noticeable.
Click to expand...

That's what I'm thinking. Depending on engine load I get about 25% of the air out the defrost, no matter where the selector is set. The rest comes out where the selector is set. I don't mind the selector as much as I'd like to get the cruise working.
 
dagr8tim said:
That's what I'm thinking. Depending on engine load I get about 25% of the air out the defrost, no matter where the selector is set. The rest comes out where the selector is set. I don't mind the selector as much as I'd like to get the cruise working.
Click to expand...

If it always leaks out the defrost, it may have trash in the way of the damper door, or a bent control rod.
 
dagr8tim said:
Then why doesn't the Cruise work? Also, how can I access the door/rod? Is that under the dash on the passenger side?
Click to expand...

Well the cruise could have other problems. Like the top side, second brake switch sticking, white plastic switch hidden up towards the dash, top part of the brake peddle arm. It has a vacuum line on it too IIRC (electric and pneumatic I think). Or the electrics in the column switch , or the yellow cruise control computer under the bottom dash, drivers side (what year is yours?).

By the way, I have yet to figure out why my cruise does not work. I know mine is not a vacuum problem.

The damper doors and actuators are under the dash, on both sides. I am not sure which damper door is where right now. It is in a recent thread under AC here somewhere, but probably hard to find in a search too.

I know the fresh air versus max inside air circulation door is on the far right passenger side near the door. Another is near your left knee while driving, near the ash tray. I think there is third one buried way up inside, but not sure. I have not had to go that deep on mine yet.
 
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