Jump to content

Idle kickup question and AC blower speed question


Recommended Posts

First....I have been fighting a low idle for a while now..still have not fixed it. Does not stall although it will hover around 500 rpm which makes me a nervous in traffic.

Last recomendation was change the O2 since the rest of the components that would affect it are fine or have been changed.

But....there should be a sensor that kicks up the idle when an electrical load is sensed...such as the AC. When I kick on the AC the idle does not bump up and it should like....40o rpm or so.

Who knows where the sensor is and what it is called. I know i read it on here somewhere but now I can't find it.

 

Second question si related to Ac Fan motor. It has been stopping or slowing down randomly. No big deal..usually it is a resistor in the speed control...if I can find it.

The wierd thing is this. If I am tooling down the highway in 5th gear and start to accelerate the fan slows down and slowly stops...let of the gas and resume a normal speed the fan speed returns and ....it does this regularly....and only in 5th gear...which makes no sense. Does not do this in any other gear on a regular basis. Sometimes it will just slow down or stop and then a few seconds later it will speed back up but it is random. Not in 5th gear at say 60 mph. Slowly accelerate and the fan speed always slowly dies...let off the gas and resume a light accelerator pressure to stay at speed and the fan speed resumes.

That has me a little stumped and wondering if it is more voltage related...regulator...alternator....I have no clue. Anyone have a thought.

scott

Link to comment
Share on other sites

First -- what year MJ, and what engine and transmission?

 

Second - What makes you think "there should be a sensor that kicks up the idle when an electrical load is sensed...such as the AC"? The fact some Japanese car you once owned had such a thing, perhaps?

 

Third - I doubt the problem is your fan speed. The HVAC duct controls in the MJ are controlled by vacuum. The default position for the flappers is to send all air to the defrost outlets on the top of the dashboard. When there is a vacuum leak in the system, when the engine is pulling lots of vacuum (such as when coasting), there's plenty to hold the flappers where you have them set. When the engine vacuum drops (such as going up a long upgrade in 5th gear), the flappers shift and the air gets diverted to the defrost. Pay attention to what's happening next time you drive it and I think you may find that, rather than the fan speed dropping, you are noticing a reduction in airflow to your feet or the front of the dash because it's all going to the defrost.

Link to comment
Share on other sites

It is a 1989, 4.0, 5 speed.

 

I thought maybe vacuum but was not sure...and so kinda blew it off.

 

What may be happening is two issues and I am correlating them as one. First the fan does just randomly shut off...and if I tap the AC/Heater controls it will pop on. Come to thionk of it...when it does THAT it shuts off instantly.

 

With the 5th gear thing I though I could hear the motor running but could feel the air slowly dying. I never checked the defrost. Although..now that you mention THAT...I did try it with no AC in heat with the defrost running and it did not do it....so I guess that answers that.

SO I will assume the vacuum thing is to be expected ( as long as there is no Vac leaks)....and the fan suddenly stopping randomly ( which I can rap on the HVAC panel and make it come back) ...is still my only original issue. I just combined the two.

As for the IAC...I thought I read there was one on the 4.0...I could be wrong...and I could have it confused with my 87 Pathfinder.....it happens.

scott

Link to comment
Share on other sites

With the 5th gear thing I though I could hear the motor running but could feel the air slowly dying. I never checked the defrost. Although..now that you mention THAT...I did try it with no AC in heat with the defrost running and it did not do it....so I guess that answers that.

If you have it set in defrost mode, the flappers are already set to direct air to the defrost vents. You have to test it with the flappers set for either HEAT (feet only) or VENT (front of dash only). The fan is not slowly dying -- the flow of air is gradually being redirected from the foot or dash vents to the defrost vents. The overall flow of air is not being reduced.

Link to comment
Share on other sites

BTW -- THe loss of vacuum is not normal. When it does that, it means you have a vacuum leak. The usual place is where the vacuum lines run near the battery tray to the vacuum reserve cannister (also known as the blimp or the football) behind the front bumper).

Link to comment
Share on other sites

Yah that was my next question...I actually logged back on to ask that question as it would seem to NOT BE NORMAL....!! Maybe this leak is causing some of my other issues.

What is a good method of testing for a vacuum leak over there. it is easy in the CCV lines or anything near the TB as Tb cleaner sprayed on the lines will show a leak real quick.

Would the old soapy water thing work on vacuum lines?

scott

Link to comment
Share on other sites

yah kinda figured. If the leak is over by the footbal would it still affect the idle with TB sprayed on it?

Certainly no surprise if there are multiple leaks due to the age of the lines. I replaced a few in the TB and the CCV. I need to look at the brake booster...I think that is vacuum too and the gasket at the check valve was cracked.

Oh well...guess I have something to do now this weekend anyway. I wouldn't be surprised if the other idle issues are all related to vacuum.

scott

Link to comment
Share on other sites

...man....I got leaks EVERYWHERE....I fixed like...7 so far. Most are in what i guess i could call accesory vac lines. These are the hard plastic colored vac lines. The small hard plastic vac line coming from the football had 2. There is a small hard plastic red line that is T off the larger rubber line that comes INTO the football...that had a few leaks. The pink line going into the canister by the Distributor had a couple.

Still...it is loosing vac as the AC still changes over to defrost under hard acceleration...although it is somewhat better. There must be freakin leaks everyhwere in the small hard plastic lines but I can't trace em all. They either go through the firewall and behind the dash or some under the truck.

There are no leaks in the main engine lines as I replaced those...easy to get to.

Man what did I get myself into...?

scott

Link to comment
Share on other sites

..yah I know...I expected some...just caught a bit off gaurd as to how many and how big. I am surpised anything that ran off vac was even working...I had some monster holes...I am sure you guys have seen them for sure...I am just shocked at the amount. Especially when the PO kept telling how good of a Jeep guy he is...yah.....well....I think not.

Thanks for the help guys. I think I have half the leaks found....the rest are gonna be a bugger.

scott

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...