Topic: 1991 yj vacuum problems?

[SamsonJR]

Ok so wile working on my Fiances 93 yj, I picked up a new breather for my 91. installed it, and wile I was under the hood I thought I heard a hissing like a vacuum leak. its not constant but I can hear something almost like it pulsates . I wasnt sure if I was just being crazy and hearing things, but on my way home from dropping off a driveshaft to be balanced "for the 93" I noticed while I was in motion, my RPM would stay up in neutral around 1200. once I was at a complete stop, it would go back down to 800. I also had to bleed my coolent system, and wile doing so I had the heat on. ive noticed for a wile that my heat will blow very well, then suddenly drop and blow lower. I'm only saying all this b/c I feel it might be relative. anyway after the coolent bleed, I went to take it or a drive, and the check engine light came on. and its stalling out. I recently put in 19 yellow top injectors, and a wile back I put on a 4.0 thottle body. its a later model TB that had the MAF sensor attached, so I blocked the vacuum inlet where it would be. could this all be connected? I dont have a scanner to check the engine light, but it seems to go on and off when it feels like it. also at start up its taking longer for the RPM to drop down. any help would be appreciated!

[jfrabat]

Ok so wile working on my Fiances 93 yj, I picked up a new breather for my 91. installed it, and wile I was under the hood I thought I heard a hissing like a vacuum leak. its not constant but I can hear something almost like it pulsates . I wasnt sure if I was just being crazy and hearing things, but on my way home from dropping off a driveshaft to be balanced "for the 93" I noticed while I was in motion, my RPM would stay up in neutral around 1200. once I was at a complete stop, it would go back down to 800. I also had to bleed my coolent system, and wile doing so I had the heat on. ive noticed for a wile that my heat will blow very well, then suddenly drop and blow lower. I'm only saying all this b/c I feel it might be relative. anyway after the coolent bleed, I went to take it or a drive, and the check engine light came on. and its stalling out. I recently put in 19 yellow top injectors, and a wile back I put on a 4.0 thottle body. its a later model TB that had the MAF sensor attached, so I blocked the vacuum inlet where it would be. could this all be connected? I dont have a scanner to check the engine light, but it seems to go on and off when it feels like it. also at start up its taking longer for the RPM to drop down. any help would be appreciated!

I think it can.  I chased vacuum leaks all over my Jeep until I just got sick of it all and used silicone hoses instead.  The heat is just not well tolerated by the stock lines.  I also had issues when at WOT the HVAC system would go ballistic as a result of lack of vacuum, so I also installed a couple of vacuum reservoirs in the system, and since then, no more vacuum problems.  As for the idle, mine still stays at higher idle until I come to a stock then goes back down; I dont think that's vacuum related...

[SamsonJR]

Thanks Jfrabat, I was just messing with it a little more before I leave for work, I pulled the IAC wile it was running and no change, so I took it off and inspected. I cleaned it when I did my TB swap, so it wasnt dirty but I wiped it down anyway, I pulled it again after I re installed it and the RPM went up and stayed up. I noticed that when I start it up it idles pretty high, "going up to 2000 now" and slowly settles down. but when I apply gas at idle its choking and wants to stall. It's also running rich. I'm going to go to the parts store tomorrow and pick up some more vacuum block offs, it seems the one on the TB is't looking to good again, I'm hoping thats the issue. But as for you running Silicone hose and reservoirs, I think that might be a good idea for me as well. any pics of what you did? and where and how many reservoirs did you install? I'm tired of vacuum leaks, I considered just replacing all of them, but your idea sounds better. thanks!   

[sharpxmen]

when you roll it always stays up in revs a bit, it's by design on the MPFI, mine does the exact same thing (always did). you could  unplug the speed sensor and see if it doesnt do it anymore, never tested it that way.

the hissing could be from your t/b, it does that and if it oscillates it is something with the IAC control or valve, a vac leak can do that so if you want to find it take a piece of garden hose and put one end to your ear and the other move around where you hear the hissing to pinpoint it better.

[SamsonJR]

thanks sharpmen, that''s a good idea, funny you say that b/c out of habit I reached for a socket extension to use as a stethoscope then realized  this isn't going to work. I have some hose I'll cut up in the morning. I've been throwing the idea of replacing all of the lines though, I'd feel better knowing there new, but I still have to find the problem to correct it. I'm thinking.. High idle= vacuum leak, Fuel rich= air/ fuel ratio off? computer trying to compensate for to much air? and when I give it gas it bogs out and chokes. too much air.. I'll do better inspection in the morning and see what I come up with, I'm hoping its just a bad line

[jfrabat]

HAve you reset the computer lately?  Sometimes it takes a while for the ECU to learn the fuel curve...

[SamsonJR]

I reset the ECU when I swapped in the 5.0 Injectors. not since then. I've reset it 2 times before that after doing the TB swap too. I'm about to go outside and see what I can find

[SamsonJR]

Jfrabat, when you said you added vacuum reservoirs to your lines..I think I understand the concept, "the vacuum can build up and give a stronger pull when needed"? correct me if I'm wrong please! But where did you add them? I'm assuming the heater lines but anywhere else? I did a few searches but came up short. I decided once I figure out what my problem is, I'm going to run new lines anyway for the piece of mind   

[sharpxmen]

you don't need new lines,
unless your vac leak is at the map sensor line it will not cause the engine to bog down, i would look somewhere else for the reason (like catalytic converter, fuel pressure, bad injector or injector plug/connection, ignition components). you can start with the map sensor line to make sure there are no leaks on that. A bad map sensor would throw a code in 99% of the cases but it could have bad readings and cause some issues, if you have a spare to test could help eliminate it as a cause but it's unlikely to be it unless like i said you have a MAP sensor code.

[SamsonJR]

So the problems fixed. I checked the codes via the key, besides a/c and recent bat. disconnect, I got a MAP code, I pulled the line, and sure enough on the intake side it was caked up with carbon and crap. I scraped it out the best I could and it's running fine now. I'm not sure if I can run some acetone threw the lines "not connected to the jeep of course" to clean out the rest of the build up? I don't want to destroy the line ya know? I spoke to my Dad before too and he told me leave the lines alone too. "he was a mechanic at Chrysler for over 20 years, now has his own fab shop and build's motors all day long" so I'm just going to drive it. I'm going to replace the vacuum block off on my TB anyway just to be safe b/c it's not looking to great. Thanks for all the help!

[sharpxmen]

you can replace that line if it's got crap in it, most importantly make sure to clean the fitting on the intake manifold.

[SamsonJR]

already cleaned the fitting, have to pick up some parts for my Fiances 93 tomorrow from Mopar, I'll see about getting a factory line from there

[SamsonJR]

any idea why the line would get so badly clogged? I noticed that I had a burnt oil smell for a little wile, mainly when I would let off the gas wile in gear and coast. I replaced the breather, and cleaned out the CCV, now that the MAP line is clean I don't smell it nearly as bad. I assumed it was worn rings. my Motor is a little tired. "I plan to pick up another 2.5 to rebuild, and beef up soon" so I wasn't to concerned. Is there something I'm overlooking?

[sharpxmen]

maybe blowby, i don't know to be honest, how's the filter looking where the PCV hose goes in? with EGR systems you get a bunch of that crap in there but with Jeep MPFI that's not an issue other than the blowby - you can do a compression check. If it runs well now i wouldnt worry about it.

[SamsonJR]

the filter? do you mean the air filter or the metal shim in the valve cover? the air filters clean I maintain my jeeps the best I can, The shim is a little cruddy. I was thinking of pulling the valve cover and cleaning out some of the build up soon anyway