possible fuel starvation

[8Mud]

Note: I`ve used Idle Air Control (IAC) and Idle Speed Stepper Motor (ISS) and just Stepper Motor, kind of interchangeably, my terminology hasn´t evolved as far as the technology, sorry for messing up the acronyms. When I said IAC I was refering to the Idle speed Stepper Motor. Hope I didn´t confuse you any.

 

[HJ88]

Trying to run the plunger out with lectrical power, will spit the plunger across the driveway (ask me how I know this).

how do you know this? D lemme guess)

ok im gonna pull the TB off and clean it tommorow, since i lost my torx set (btw, anyone know what size bit is required to take off the TB?) so i'm gonna have to go buy a bit to get it off... when i toss out my air box and get my new cone filter in i think it'll help it breathe alot better (right now i have a paper filter which is black with oil from the valve cover vent (btw, will it hurt performance any by not routing the valce cover vent back into my intake? as said before i'd much prefer to have it on its own filter 1) so all that oil vapor isnt going into the intake and 2) so my nice new filter isnt soaked with oil after an hours drive... i've heard of other people using a seperate filter but i dont know if it has any effect on performance...

oh and will a paper gasket work ok under the TB, or some high temp rtv silicone gasket maker? just thought i could try and save myself from what im sure is a rediculously expensive pre-formed gasket .

 

[8Mud]

The oiled up paper filter will cause a rough idle. They are probably a better filter than the K&N, but get plugged pretty easy with oil, dust, pollen and moisture.
I haven´t found a paper gasket material thick and soft enough that I´ve felt comportable with, to use under the TB. I have put a thin coat of grease on the old TB gasket as a stop gap and made sure to realign the indentations from the TB on the old gasket, as a stopgap, until I could get a new gasket.
The crankcase ventilation system, is part of the emission system. In some areas, a serious thing to mess with. I´d make sure the 2.6MM (orifice) CCV tube is clear, blow through it, I´ve cleaned mine out with a very thin wire and solvent or buy a new one. And the CCV scavenger tube (the big one), is in good shape and hooked someplace above the TB.
There is a kit to hook up in the valve cover, to help keep fluid oil from being pulled into the scavenger tube. A plugged 2.6 MM CCV vent tube is most of the reason, the scavenger tube sucks oil into the filter box.
I guess theoretically, a filter mounted on the valve cover and a clean 2.6 mm line, will pull air through the filter on the valve cover (through the crankcase), through the 2.6 MM line with an oil vapor air mix, into the intake manifold to be burned. But at even mild throttle openings, the scavenger and the 2.6 MM CCV tube are both under vacuum, both probably help move oil vapor and moderate blowby into the intake system. I could be full of it, but have never bought the closed loop theory, that filtered air enters the large tube and exits the small tube at all throttle openings and vacuum. Maybe on a really fresh motor, not my old iron. IMO. At open throttle, manifold vacuum is pretty low, 2.6 MM doesn´t move much air, the engine generates just about max blowby, the vacuum goes up in the air box, the air voluum is higher and the so called cranckcase input air line (the big one hooked to the air cleaner) is probably sucking it´s share fumes out of the crankcase along with the 2.6 MM vent. IMO.
What I´m getting at, is on an old motor, when the throttle slams shut, cranlcase pressures, just may blow the filter off of your valve cover.

 

[HJ88]

ok..... that really made no sense to me what so ever... is the CCV vent tube the one ontop of the rocker cover in the front?and the ccv scavenger tube the one in the back? and what is the one that comes from on the lower ortion of the engine and hooks onto the front of the airbox (about 1.5" in diameter)... i always thought that was the crankcase vent tube... mine has a giant hole in it anyways... i dont have emissions checks where i live so i thought i could get away with using a different filter ontop of the rocker cover or atleast routing it over to its own filter... wouldnt the engine run better if it didnt have to burn all those oil fumes? just how important is it to the engines performance taht there be good air circulation in around the rockers?

 

[8Mud]

With the throttle closed (high vacuum in the intake manifold), air goes out the big tube in the rear of the air box, into the front of the valve cover, out the 2.6MM line in the rear of the valve cover, into the intake manifold and the oil fumes/blow-by is burnt.
This is oppinion. IMO, The 4.0 isn´t by nature a really tight motor. I think a seasoned motor, generates more crankcase pressure than will fit through a 2.6 MM line, especially at near wide open throttle, when manifold vacuum is at it´s lowest. Under certain throttle conditions/openings/manifold vacuum, the larger tube, that goes to the rear of the air box also scavenges crankcase vapors. If you put a filter on the front of the valve cover, it may spit quite a bit of oil, all over the top of your valve cover, under certain conditions (sudden wide open throttle or sudden closed throttle, at higher RPM´s). I´ve seen fairly new 4.0 motors, with a plugged 2.6MM line, push/or suck/or both oil into the air box. Even fairly fresh motors, generate some crankcase pressure. I may be talking through my exhaust opening, but I don´t think so.
Dumping the oil vapors and blow-by into the intake, has never seemed to hurt much. As long as the 2.6 MM tube is open (not plugged), crankcase pressures rarley push, sigificant amounts of oil into the air box.
As the throttle opens there is less vacuum in the manifold and more vacuum at the top of the TB. Got to remember the motor is an air pump, as well as being an internal combustion engine.
The large tube going to the front of the air box, is an air pre warmer (comes from the exhaust manifold), helps the motor run better, before the intake manifold heats up some. Also somewhat controls intake air temp. an emmision component.
Clear as Mud?

 

[HJ88]

Clear as Mud?

exactly :s

ok so i guess i'll route it over to its own filter instead of putting a filter ontop or routing it back over the the new filter... fk emissions...

 

[HJ88]

just in case anyone else was wondering, the bolts that hold the TB on are T-45 .. atleast on my 88' 4L... i'd imagine its probably the same on all the 4.0s up to 90' or 91'...

 

[8Mud]

Ok I dislike telling anybody what to do, favor passing out my experiences and some of what I´ve picked up over the years and letting someone make there own choices (who knows you may have the next better idea). The original (CCV) configuration, works (marginally), changing the configuration, will probably not work as well. I´m not saying stick with the original air box. Though I would, or at least, close to the original configuration. I live in a cold climate and the original air box, is designed to work in cold temps (though I do really dislike, the air box intake). The parameters of the sensor group, are designed with a few constants, in mind or at least predictable variables. The air box heater flap and the MAT (or IAT) seem to work in tandem. And The (OEM) CCV system seems to have a bit of redundancy, by design or accident, who knows.
On the other side I´m not beyond, trying something new or different, I just don´t throw away the original parts, until I´m certain it´s an improvement.

 

[Wiley Coyote]

HJ88, My XJ is a slightly newer ’91, but I’ve done what you are talking about. I put a Rock-It air tube and filter on it. It’s very similar to the K & N set up, but at half the price. I also put a small filter on the front CCV. All it did was blow oil all over my valve cover, absolutely no improvement in performance. I changed it back to the original configuration after a week. I relocated the IAT from the intake manifold to my intake air tube. That was a nice little improvement. All it does is trick the computer into thinking that the air is a little colder than it really is. The computer compensates by adding a little more fuel to make the engine run richer. The richer mixture gives you a little more power; not huge amounts but a noticeable difference. BTW When I redid my PCV/CCV system I ordered all new vacuum tubes and valves from the dealer. The original rear valve on my valve cover had a very small orifice like you were talking about. The replacement one is much larger, exactly like the front one. I asked the parts guy about it and he showed me the paperwork that shows the old valve is superseded by the new one. Jeep uses the exact same parts in the front and rear valves now. I’ve run mine that way now for a couple of weeks and I can’t tell a difference either way, so it must work.

 

[HJ88]

my main worry is that the bit of blowby that comes from the engine is get all over the new filter.... and from expierience i know that oil is really hard to clean out of filters... and i dont want to keep spending $80+ on filters... so maybe i could make some sort of oil trap to still get the same vaccum effect but without the oil going into the filter... i ddunno i'll start drawing out some ideas...

 

[Iansel]

Well thanks to all of you I managed to fix the problem with my Jeep. I read the title of the original post and realised that I had the same problem as HJ88. I moved ol' rusty out of the garage about a 2 months ago, and wasn't able to start it again, well it would start then shut off after about 10-15 seconds. Thanks to 8Mud's description of the system I was able to determine what was wrong. I found a corroded wire on the resistor. I replaced the end with a new crimp on terminal and voila RUSTY LIVES!!!!

Thanks to all of you

Ian