shooting sticks

Hokay, so. On New Years eve I was getting ready to go up in the hills with some pals and right before my turn my RPM's started to drop and when I would give it gas nothing would happen. I assumed it was running out of gas (my gas gauge is stuck) so I pulled into the gas station that was right next to me thankfully. Put $20 in and pulled out of the station and after 10 seconds it started to not want to go again so I pulled over onto the side of the road and shut it off. Sat for a few minutes and then tried to start it again. All it would do would crank and try to start but wouldn't. It would be really close to starting every second but never would fully combust. After I sat for maybe 20 or 30 minutes it started fine, and I drove it home with no problems..... I drove it nearly everyday since that night ,Dec 31 around 11:30pm, with no problems. Today I was on my way to Lowes to get another can of spray paint for my roof rack aannnd sure enough it did it again. Same scenario. Just started it and drove it home without doing anything to fix anything.....anyone have a clue what is going on? The first time it happened I thought it was from extremely gunky oil so I changed the oil and put Seafoam in my vacuum line and gas tank and it ran wonderfully after that until today. I don't have a clue what it could be. It has the symptoms of running out of gas, but it's not.

Halp

salad

This is the Earth, and you might say, wow, that is a real nice Earth.

Anyway.

I'm far from an expert but after reading here for a little while it sounds similar to a fuel pump or pressure regulator issue. Someone around here has a nice copypasta on checking fuel pressure at the rail, a quick search should turn something up in a recent thread.

Flowpro

If it happens again listen for the fuel pump to run for a few seconds when you turn the key to the on position.

cruiser54

Check your fuel pressure and your CPS output voltage.

DFlintstone

X2^.....if you swapped your first and third relay's, all you could have to loose is the AC, (fuel pump relay is the third one back) http://autorepair.about.com/library/images/bl347lib.htm

Also the ceramic fuel pump resistor is on the fender near the air cleaner. You can bypass it, ( I'm SURE that is OK), and see it that helps.

And this test can be done in less time than it takes to but on your boots to go out and do it!

AC voltage CPS test; Small clips on the meter leads really helps.

Unplug the connector at the back of the manifold with wires going down to the bell-housing/cps.
Probe the two wires to the cps with the meter set on AC volts. (a 200 scale on mine).
Crank the engine and note the voltage. (jump it if your battery is low)

Mine somehow works with only .3, my wiring/grounds must be pretty spiffy. .5 seems to be a good mark. One article talked of .5 to .8.

If it's low you can modify the cps. With the next largest bit that won't fit in the hole, enlarge the hole's in the bracket just a tad. Now when mounting it's crucial to maintain firm downward pressure on it while tightening the bolts. An assistant could help with that from above.

Random staling warm, then working later is one of it's tricks.

You might go ahead and change your fuel filter, (down by the tank). Something that needs done anyway now and then...

shooting sticks

Okay thanks for all the suggestions guys. I had a feeling it was something to do with the fuel pump.. I<3 cherokeeforum

shooting sticks

tjwalker

This definitely could be the start of a failing "crankshaft position sensor". It is the most common sensor failure on the Jeep 4.0 engine.

If you lose that input signal to the computer, you will not have spark and you won't have fuel going to the fuel injectors.

Testing it when symptomatic would be a good idea. Testing it when the engine runs fine would probably not be helpful here.

shooting sticks

Oh yea I forgot about that sucker. Failed on my 4.0L Ranger as well..I'll check it out next time!

J20jeepster

Did you ever solve this?
I have the same symptoms on my 96 country. Just started this week. I only have 106,000 mi. on it. My check engine light came on though and came up with a crankshaft position sensor code. I am just wondering if it is the sensor or a plug to the sensor.

cruiser54

Unplug the connector, spray it out with electronics cleaner and plug it back in. See what happens.

I do that to every connector in the engine bay when I get a "new to me" Jeep or do any driveability work on someone else's Jeep.

shooting sticks

I don't know if I really solved it but it hasn't happened lately....new plugs and filters and oil, cleaned TB and IAC and it seems to be running well..

cruiser54

Imagine that!! Normal maintenance is performed and problems go away. Good job sticks. Always start with known good tune-up parts and maintenance procedures.

shooting sticks

Hahah precisely.

Chickenfloss

Just wanted to put this out, but if you have some clogged lines some older vehicles can lock themselves if the vacuum in the gas tank gets too high. As a matter of fact a friend of mine has a '99 dodge ram with v8 magnum that dies, pull the gas cap off and release the vacuum and it starts right back up.