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Discussion Starter #1
Hello again everyone,
The '92 LeBaron convertible I will soon be getting seems to have a climate control issue. I was told today that it will cycle through the different vents (defroster, AC vents, and lower heat vents) on its own, regardless of where the settings are on the control panel.
Is this a known issue?
Has anyone else experienced this, and maybe know what might be the cause of this?

Thanks, as always,

John
 

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Looking at the 1992 AJ-body parts list, I see that only MTC (no ATC) was offered.
The HVAC mode doors are vacuum operated and the most common issue is a failing vacuum check valve. It won't hold vacuum and allows the doors to change modes depending on intake manifold vacuum as you are driving. They will try to default air to defrost mode (for safety).
If this is what is happening, it is an easy fix.
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2012-06-29_214847_vacuum.jpg
 

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Discussion Starter #3
Cool, Thanks for the quick reply.
I'm going over to 'fiddle' with it later today, I will be looking for this check valve. Any ideas where it might be located? Under the hood most likely, I'm guessing, but possibly under the dash?

Thanks again!
 

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Probably under the hood. Fed off the power brake booster vacuum junction or right off the intake manifold. It will be a vacuum line going into the firewall near the heater hoses or A/C lines.
Underhood engine heat probably shortened the life of these check valves and they would have done better if placed under the dash.
 

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Check valve is on the power brake booster. It will look like one of these two canisters, and the larger one works better, reduces the chance of flipping to defrost on acceleration.



 

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Discussion Starter #6
Awesome guys, thanks for all the replies.
I went over to the car today (it's in my immediate family; I should take possession sometime in the next week), started it, ran the air,etc, but could not reproduce the problem. It may be in the heater, but it was so hot out today we didn't run the heater too long, maybe not long enough to trigger the problem. AC ran really cold in any setting: defrost, vent, and foot well, and stayed where it was set.

I did pick up the check valve from auto zone that was pictured, but since I could not reproduce the problem, I didn't change it out...... (Couldn't find it either). :blush:
But since I have pictures now, it should be no problem. Thanks again!


Car has been sitting for the better part of 3 or 4 years or so, but was started in the driveway/garage, and ran every couple of months or so.
 

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there is a whole thread on this a year ago by me.
None of that was bad on my car. It was the door that switches from the floor to vents.
The best way is to look under the dash by the gas peddle and see if the valve moves with the yellow hose to it. if it does and nothing switches over the door is broken. The dash has to come off to fix.
Pray its just that little air thing under the hood.
check the hoses to it. they crack due to the heat. I got my car for cheap because only worked on defrost. I fixed that hose and it was fine. Later the door broke under the dash.
 

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Did you drive the car on the 5th, or just let it idle? I ask because a vacuum problem of this nature will not manifest itself with the engine at a steady rpm. It needs to have varying rpm and loads to have the vacuum change.
 

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Discussion Starter #9
peterjon1 said:
Did you drive the car on the 5th, or just let it idle? I ask because a vacuum problem of this nature will not manifest itself with the engine at a steady rpm. It needs to have varying rpm and loads to have the vacuum change.
No, did not drive it. Only idled and revved some in the driveway. Interesting. I'll have to take it out and see what happens.
 

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Discussion Starter #10
Did you drive the car on the 5th, or just let it idle? I ask because a vacuum problem of this nature will not manifest itself with the engine at a steady rpm. It needs to have varying rpm and loads to have the vacuum change.
Ok, I know it's been awhile.....but I finally have the car now, and driving it home yesterday, with the AC on, the air constantly rotated from vents, to floor, to defrost, and back to vents....before I drove it, I replaced the check valve with a large one from the junkyard that seems to work (could only blow thru it one way). I will put the new check valve in today, (when I find it) but I have a feeling it will be no different.
 

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If the check valve is OK, the the problem is likely either a vacuum leak or insufficient vacuum being produced.
If the car runs OK it's probably making sufficient vacuum but it wouldn't hurt to verify with a gauge. Then it's time ti look under hood and under dash for leaks.
 

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Discussion Starter #12
If the check valve is OK, the the problem is likely either a vacuum leak or insufficient vacuum being produced.
If the car runs OK it's probably making sufficient vacuum but it wouldn't hurt to verify with a gauge. Then it's time ti look under hood and under dash for leaks.
Thanks Valiant. Actually it could be running better....(just a little of the car's recent history here)...over the past two years it has been driven very little; only to get it inspected and registration renewed, and only a couple hundred miles during the third years ago. It was started and ran/idled periodically during that time. Replacement battery a month ago. It's now developed a miss that was not there before the last time my Dad cranked it. I filled it with premium and added a bottle of injector cleaner; I've been counseled to drive it for a while with the additives and see if it will work itself out before spending money on plugs and plug wires, distributor cap, etc......probably a topic for another thread, but....is there a common 'go to' to try with the Mitsubishi 3.0 when it develops a miss?
 

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The first step in a misfire is to find out which cylinder is misfiring. This can be done easily by pulling the spark plug wires briefly one at a time on an idling engine and listening for which one doesn't cause a drop in engine speed. The sound of the engine won't change when the suspect 'dead' cylinder has it's plug wire removed.
Use caution to avoid an electric shock while handling plug wires on a running engine.
There are insulated 'chicken pliers' to pull the wire off the plug end by the boot. Pulling on the wire may pull the wire off and leave the terminal on the plug.
Date codes may be printed along the plug wire to indicate their age.
Locate and remove the suspect spark plug. Note the tip color. Black carbon indicates a fuel-fouled condition. Wet with fuel indicates that the mixture isn't igniting.
Plugs.jpg
They should be the correct Champion RN11YC4 or what spark plug the underhood sticker or owners manual calls for. It must be the correct heat-range and some engines don't tolerate platinum spark plugs well. Always use the specified plug for best results.
A misfire can make it run rich with raw, unburned oxygen going past the O2 sensor. The PCM sees this as a lean mixture and will lengthen the fuel injector pulsewidth to compensate. This opens Pandora's box and can lead to cat overheating and damage.
The underhood sticker may also show a vacuum hose map where you may see the vacuum check valve attachment point.
0900c152800a747e.gif
 

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Discussion Starter #14
The first step in a misfire is to find out which cylinder is misfiring. This can be done easily by pulling the spark plug wires briefly one at a time on an idling engine and listening for which one doesn't cause a drop in engine speed. The sound of the engine won't change when the suspect 'dead' cylinder has it's plug wire removed.
Use caution to avoid an electric shock while handling plug wires on a running engine.
There are insulated 'chicken pliers' to pull the wire off the plug end by the boot. Pulling on the wire may pull the wire off and leave the terminal on the plug.
Date codes may be printed along the plug wire to indicate their age.
Locate and remove the suspect spark plug. Note the tip color. Black carbon indicates a fuel-fouled condition. Wet with fuel indicates that the mixture isn't igniting.
Plugs.jpg
They should be the correct Champion RN11YC4 or what spark plug the underhood sticker or owners manual calls for. It must be the correct heat-range and some engines don't tolerate platinum spark plugs well. Always use the specified plug for best results.
A misfire can make it run rich with raw, unburned oxygen going past the O2 sensor. The PCM sees this as a lean mixture and will lengthen the fuel injector pulsewidth to compensate. This opens Pandora's box and can lead to cat overheating and damage.
The underhood sticker may also show a vacuum hose map where you may see the vacuum check valve attachment point.
0900c152800a747e.gif
Thanks for the reply.
I've driven it another 20 miles or so with no change in the miss....a neighbor I have who has a pretty good knowledge of cars in general thinks it's likely a fuel issue from sitting so long. That being said, I originally thought to run at least half the tank out containing the premium fuel and intake cleaner additives and monitor it, but I'm getting that feeling it's not going to go away in that fashion.

Sometime this week after work, I plan on getting the pliers you mentioned, and, as a neighbor suggested to me, a tool that once clamped to a plug wire, will flash when the plug fires. Not sure about that, but I'll look into it.
The plugs have been on the car for the last 50K (93,000 total), so it's probably time for new ones anyways.
I have a thing for yellow spark plug wires, so Ill probably grab some of those as well.

Any other suggestions would be greatly appreciated.
 

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A 'noid' light will indicate that the energy pulse is getting to the spark plug, but the spark plug still may not be firing well. A plug tip visual inspection is still important.
If this is a steady 'rhythmic' misfire that indicates a single cylinder is not contributing, then the plug with the misfire will probably appear different in appearance than the other 5. Then we can find out why. If it is a scattered unsteady misfire that jumps around various cylinders, that may be more difficult to locate.
 

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I have been fighting what i think is a misfire too. The engine runs fine but seems to jump . Say you hooked it to a heart monitor, the jump would probably spike downward. It kind of feels like i am driving a car with an oversized cam, but not that bad. Some may not even notice. I can feel it on the steering wheel. I have replaced the plugs with champions, bought a professional gap tool. Wires are new accel 8mm. Cap and rotor are matching brands and brass. hall pick up didnt fix it. Dielectric grease was used.
The only thing i can think of is the cap needs to be vented more. Cat is new too.

Never replaced the O2 sensor.
 

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Oh and an old trick for the guy above is . Look at your engine in the dark for sparks off your plug wires. This will let you know they are bad. I read that they should never X each other when touching ( 90 degree angles). I try not to let mine touch when possible.
 

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Discussion Starter #18
Okay....just got done installing new plugs (basic Champion Copper Plus), new plug wires (Borg-Warner), new distributor cap and rotor (Borg-Warner).....and the miss is GONE!!!:cool:
Not sure what it was, but the number 1 spark plug (the back side firewall, furthest left, under the alternator), came out cracked and broken about a half inch below the top. I originally thought I broke it while removing it, but the spark plug socket I used has a pretty stiff rubber boot in it that keeps the upper portion of the plug from hitting anything; and with that alternator bracket right there in the way.....I don't see how I could have had the socket angle off enough to break the top part of the plug off.

Anyways, it really doesn't matter, damn thing runs much stronger now, and now it can actually get out of it's own way.:)

That was bugging me, so yeah, I'm happy.

Now back to the original issue.....while fiddling with removing the airbox yesterday, I noticed the small plastic line that connects to the aforementioned check valve was severed. I cut the pinched part off, made sure there was an opening, and re connected it. Left it be, then did the stuff mentioned earlier...plugs, etc. Now it appears that regardless of which setting I choose, the air only comes out of the defroster (under the windshield). I didn't mess with it too long, cause it pissed me off; trying to kill my good vibe about the miss being gone.
I will find my new check valve tomorrow and put it on, but I feel it won't change anything. Hoping I don't have to take the dash apart, but it's not looking good. If it comes to that, I will damn sure put a new heater core in while I'm in there.

One more thing....on the factory air box, (the lower half), there are two ports on the passenger side. The upper one connects via a hose to the rear valve cover (PCV valve), but what about the other one under it? There is a hose connected to it, with a 90 degree elbow going down against the firewall, but not connected to anything. There is also a hose with a quick disconnect coming out of the firewall, that also leads to nowhere, just dangling there. I'm guessing these connect, but what the heck is it for? Service manuals mention nothing about it, and anyone who has put on an aftermarket intake is not connecting this that I know of. Just wondering what the hell it is?...and if it has anything to do with my vent problem.
 

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There is a hose on the airbox that goes to nothing. It's just a vent.
I'm not sure about the other hose you mention though.
 

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I am not familiar with the 3.0, but the 4-cylinders had two hoses from the lower portion of the airbox. One goes to the valve cover (breather, or air INTAKE for the PCV - so you should not find a PCV valve right there). The other was the air intake for the passive air injection line to the catalytic converter. From the airbox, there was a rubber hose that went to a metal check valve (disk-shaped, a few inches in diameter). From there, a metal line ran to the catcon. These were often removed when they rotted away, and I found that emissions tested exactly the same without it in my car, so I never replaced it. Does no harm if it's missing, as long as there is no leak at the catcon.

The hose dangling from the firewall - could that be the rubber elbow that is your A/C condensate drain? It attaches with a spring clamp to the drain pipe from the heater box, which exits the firewall near the passenger side about halfway down the firewall. (looks like the rubber hose behind the brake lines in this photo): http://i1225.photobucket.com/albums/ee385/RT_Rob/HeaterCore040.jpg

If you are in defrost mode all the time, there is a low-vacuum situation or leak from the hose that goes to the climate control, the one that you found severed.
 
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