96xj33

my 96 cherokee starts up most of the time and then wen i run it and shut if off sometimes it starts right up, then other times it starts but seems like its missing but after 10 seconds it clears out and it will run fine..i dont no what it could be, today it started and ran rough then died and i had to pump the gas to get it turned over then it was running fine..can it be cps or tps..help

96_xj

before you start changing out parts, give your throttle body a good cleaning and a new gasket (like $2). Then pull your plugs to check gap and the condition of the wires.

I had this a few days ago, i ran sea foam thru the brake booster and the rest in a tank of premium and it went away.

Also, whens the last time you replaced your fuel filter? it could be gunked up.

before you replace stuff, just clean stuff and see if it works =] its cheaper and its always good to clean =]


but if you are interested here is what i would do for a tune up (if your do for one):
new plugs
new wires (over 8mm)
new cap/rotor
new fuel filter
new air filter
oil change with extended oil filter
clean the throttle body
clean the injectors/fuel system with sea foam or injector cleaner


just trying to cover all the basics.

AKmudd

just curious what if the basics dont fix the problem?

96_xj

then try CPS (crank shaft position sensor), that seems to be a common culprit in our jeeps. i had the IAC go out on my throttle body to at one point. i forgot the symptoms it gave off when it went bad.... its been 2 years

AKmudd

my 89 is doing the ame thing one time it will run smooth another it will run rough almost not wanting to run sometimes it cranks over alot before it fires off

goalpost95

i had similar problems, i did a tune up, replaced the fuel filter, and some breather hoses and it was the cps, its "only" two bolts but they are a pain to get to but it solved my problem.

AKmudd

I can see the darn thing but it looks like a pain to replace how did you do it?

goalpost95

well i was told that you could do it with just a 12 and 3 inch extension put together but i could never get the socket flat on the bolt so i got a universal joint and i could never tell if it was on flat. Got a friend and the thing still would just not go flat maybe the bolt was stripped a little bit i forget really i was just happy it was off.

Anyway my neighbor came over with enough extensions to get it passed the tcase so it would be straight and flat on the bolt. basically about 3 people and 3ft of extension i'm not sure what your situation is but that was what mine was.

Its just hard to get to and make a decent turn with the lack of space.

funkle95xj

If it only misfires after it has been run for a bit, then shut off, and then restarted it could very well be the old cylinder #3 misfire situation. This situation will occur more often on hotter days, or in high heat environments (such as wheeling slowly on a warm day causing high underhood temps). The situation is due to the strange intake/exhaust manifold design on the 4.0, the exhaust manifold pipes are so close to the intake manifold runners that alot of heat soak can occur. Especially on hotter days.

Most of the fuel injectors seem to be located so that this does not affect how they operate, with the exception of the #3 injector. As the vehicle is running the injectore always has cool (relatively speaking) fuel running through it, but when you stop the engine the engines cooling systems are off and underhood temps rise. As the fuel injector just sits there right next to that extremely hot exhaust manifold pipe, plugged into an very heat soaked and hot intake manifold, with no "cool" fuel supply, the fuel that is in the injector can vaporize due to the high temps. When you start your truck up the #3 cylinder is trying to run on an injector full of vaporized fuel (which apparently doesn't flow all that well, lol). This causes the rough idle that often goes away in a few minutes once the vaporized fuel has cleared the injector and a new flow of cool fuel has been reestablished.

The best solution for this condition is to do all you can to improve cooling and reduce underhood temps first of all, but more specifically try to reduce heat soak to the injectors. Often times wrapping each injector with heat reflecting or insulation tape like this: http://www.summitracing.com/parts/SUM-350114/ will reduce their temps enough to solve the issue. To further reduce intake manifold temps you could use a product like this one: http://www.summitracing.com/parts/THE-13575/ and cut it to fit on the bottom of the intake manifold and up around the sides of the runners (where the intake manifold is closest to the exhaust manifold). This will help to reduce the heat soak of the intake manifold itself, therefore reducing temps at the injectors.

In addition to this there is all the accepted mods to increase cooling and reduce underhood temps. Such as adding a Taurus electric fan to replace the factory mechanical fan. Adding hood vents, wrapping the exhaust manifold (effective for heat reduction although it may cause cracking) etc... Good luck solving your misfire situation, hope this helps you out!

96xj33

thanks alot funkle95xj you seem to have the most logical explination on what my jeep is doing, i will deff take your advice and make it cooler under the hood, thanks alot.

AKmudd

me to! i know keeping the temp low is a must. living in Alaska it didnt seem that important but it still affects the rig. it dont like to get hot
Ill also try and replace the cps
thanks