Ok so back story its a 1993 grand cherokee straight 6, got bad gas awhile back and had to have a new pump and filter by the PO who happens to be a good friend of mine. I bought it today and got it home fine, ran good and all. Changed the battery and fired it up and it wont run UNLESS you can get it over 1500 rpm and then you have to hold there and up to keep it running. If it drops under 1200 it runs like **** and will barely idle while spitting and sputtering. Added some heet and things improved very very little. So whats the groups opinion?

 

bad sparkplug or maybe one of the cylinders isn't getting fuel

 

One plug will cause all that?

 

If a cylinder or two isn't firing, it will make the jeep shake and run like crap. Well, At least mine did

 

When you say bad gas, what was wrong with it, was it dirty. It may have clogged fuel injector or somthin and a cylinder may not be firing cause no fuel. And then when u give it gas, fuel leaks by the clog and that's why it will run smoother.

 

You can also check spark plugs by unplugging one wire at a time to see if the engine changes in sound. If you unplug a wire and it sounds the same, it's that sparkplug, if it gets worse, then that plug is fine.

 

Ok so it sets an idles now but dies when. I try to move it. Put it in gear and try to move it and it goes to running like **** and dies.

Possibly fuel filter issue?

 

I had something like that going on, I checked the electric connector by the throttle body and cleaned it, fixed my problem. I try to keep a can of contact cleaner around. Go through all the connections and clean them, when I first started driving my 97 it would start spitting and sputtering under load mostly, but I just kept cleaning connections and checked by the computer for a screw that was put in by jeep/Chrysler that was to long or something like that. But it quit , not sure if I fixed it or I had bad gas but it didn't do it anymore. it had sat for a while before I got it I think.

 

Oh for the one that dies in gear , check bell housing bolts, if they are loose it moves when you put it in gear and kills the engine. CPS moves to wrong spot. Or it could be starving for fuel. Do you have a check engine light on? Mass air flow sensors can make a car not run unless you unplug it, that was on a ford though.

 

No check engine light at all. Didnt think about the connections at all. It seems to die under load regardless of if its in gear trying to move or in park/neutral. And once it dies it takes a few minutes to start again usually.

 

I'm in a hurry , not sure which year you have , but a coil breaking down could do that, bad plug wires , bad plugs, in fact the one I'm working on now was blown up from having bad plugs and the guy thought it was bad lifters and ran engine flush or off road diesel in it and wiped out a rod bearing, I say off road diesel because there seemed to be red dye in the oil, at least that's my hypothesis, or it was just bad also. Just take a day and check every connector , pull every plug, maybe look at your engine running in the dark for sparks from plug wires. Check your fuel rail for being stopped up with crud, that little valve on the fuel rail should spray fuel out if you carefully poke it in like letting the air out of a tire. Then you can look for vacuum leaks. If you have high miles , which im sure you do, give it a tune up, this money won't be wasted regardless of what the problem is if you plan on keeping your jeep. I run Enzyme fuel treatment at times and stabile sometimes. you could even pull the injectors but make sure you don't cause a future leak that could burn your jeep down.

 

I also want to say check the connections going back to your fuel pump and other stuff under your jeep. I somehow ran over some stuff once that cause some wiring to wrap around my driveshaft and it killed my entire electrical system. a loose or dirty connection would surely be a problem, in fact just a few months ago my arctic cat was doing just what your jeep is doing, turned out to be some goofy sterio system that was scabbed into my power wires to my key switch had made bad connections, I removed the scabbed in wires , fixed the connections and no more problem. That was in the main power before anything , I couldn't believe anything worked but it did just enough to throw me off for a while. It's good to go through everything anyway just to make sure you don't quit running way out somewhere that only your jeep can get to, lol

 

Ok I'm at my wits end here. I changed the fuel filter, changed the idle air control valve, flushed the fuel lines, new fuel pump, and it still won't run good enough to drive.

Start it and it idles rough as hell, play with the gas pedal till it revs up and it'll run at 3k rpm, let it set it goes back down to about 500 running rough as hell then shoots upto 2200 rpm for a minute then back down to 500 and rough as hell again.

Could it be the crankshaft position sensor?