JaggerX

Have to start from the beginning. I bought this jeep probably 10 years ago. Over the last few years it has started skipping a beat, as if you turned the engine off then back on, but only for 1/10th of a second. It would only do it every once in a while, usually when you were going up a hill with your foot into it (but not downshifting, 5th gear), as in a high speed low rpm (1500-2000) scenario where it had a high consistent engine load with low rpm. It never did it in a lower gear but possibly would have if you matched the engine load and rpm for a long enough time, but usually you just end up shifting to the next gear obviously.

So winter came, issue seemed to just go away or wasnt common enough for me to care about. At one point I changed the CPS but that didn't seem to change anything and the issue was just too small to care about. Was fine all winter. Now here we are in the dead of summer, and its back, and its 10x worse.

I'd say for the past month its been doing its little millisecond stalling more often, and then in the last few days it started completely screwing up. It idles fine but as you get up into the RPM it starts to stumble and have trouble building RPM. I give it more gas to try and get anywhere and it increases speed but its slow, and it smells like raw fuel. It is more pronounced in the higher RPM higher gear/engine load scenarios.

Heres what gets me. It is completely.......random. The stalling is too random to say its random but the gutless stumbling/raw fuel smell crap that happened the last few days...on the way to work it was doing it then all of a sudden it just stopped doing it and acted like normal for the rest of the 20 miles to work. It feels like a tire vibration when its doing it, almost like its giving every other cylinder gas or something.

Anyways I've researched a lot but I don't have a lot of money or access to a garage very often so I don't want to buy a bunch of new parts. I was hoping to get some help on narrowing down what it could be.

Oh and lately it has cranked longer and longer before it starts. Sometimes it acts like the battery is dead, cranking very slow the first crank, then spinning up normally, other times it doesn't.

Any help is much appreciated.

CurrySoSpicy

I would first and foremost make sure your battery connections are free of corrosion and tight. Next would be a fuel pressure test, you can rent a gauge from your local advanced auto. You didnt tell us your year or model. So I can't give you the fuel pressure specs. Let us know.

JaggerX

It's a 1994 Cherokee Sport 4.0 5 speed 4x4.

Battery connections are good. It's a dry cell battery.

I just don't get why it all of a sudden goes from barely running to running fine at the blink of an eye and what has happened over the past week that has made it go from the occasional blip to this half-running crap. It isn't backfiring when it does it, just smells like raw fuel. Makes me think the CPS is getting mixed readings or something, idk.

BlueRidgeMark

Sounds like spark, or the lack thereof. Check the connection going into the coil.

Also, see my sig, #1. It's time for a good general cleaning of grounds. Can't hurt.

That can also be an 02 sensor. Have you pulled any codes?

JaggerX

No codes. I think. Assuming the CEL woulda came on. I'll check it all.

dans98xj

It sounds like your TPS. You may have a dead spot in the sensor causing it stumble.

here is how to test the TPS

TPS TESTING

You may have one or more of these Physical Symptoms:

1) The engine loses power and is stalling.
2) The engine will idle, but may die as soon as you press the gas pedal. When driving, it seems as if all power is gone.
3) Sometimes it feels as if the transmission is failed or isn't shifting properly, if at all. If you quickly jump on the gas you might be able to get the transmission to shift, but it won’t shift properly by itself. Shifting manually, the transmission goes through all the gears.

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics. The TPS function should be verified early in the troubleshooting process, when a transmission issue is suspected.

TPS TEST

You should have 5 volts going into the Throttle Position Sensor (TPS). It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. At idle, TPS output voltage should be greater than .26 volts but less than .95 volts. Move the throttle and look for smooth meter response up to the 4.49 at WOT. The other wire will be the ground and should show no voltage.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.


The TPS is sensitive to heat, moisture, and vibration, leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following:

-Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".

- High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.

-Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.

-Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted accordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.

- Engine Misfire: A faulty TPS can report values outside the acceptable range causing the ECU to incorrectly fuel the engine. This is noticeable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessive misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.

BlueRidgeMark

That's a good possibility.

Jagger, not all coded faults throw a CEL.

JaggerX

It was the distributor/rotor. The contacts looked like a magnet you drug through welding spatter. Runs better than ever now.

cruiser54

Wow. Simple maintenance wins again.

ElMartillo

I'm noticing the faint beginnings of the OPs described symptoms with my '96 daily driver. Additionally, mine seems to occasionally need a bit longer crank time to start. CEL illuminated the other day but I don't know how to check codes. My first thought with my symptoms and the OP was classic faulty TPS. I'll go check/clean rotor/dist cap contacts this am, see if it helps.

BlueRidgeMark

Odd.... very odd.....

JaggerX

I got about 400 miles out of it. It was flawless for the first couple hundred, then the random hiccups came back, then the roughness, then it just kept getting worse and worse until it was back to the way it was, all in a matter of 2 days.

Rotor/Distributor is brand new now. Pulled it off, still looks fine. Not sure what the deal is. Spark plugs were changed out 6 months ago with iridium tipped ones.

I'm convinced it is the distributor or something to do with it as changing it sure did something until it wore in, I mean it ran better than ever.

But basically it runs fine for a minute then runs on 3 cylinders for a minute, or for a half hour, it is very random but the more you drive it the progressively worse it gets. It basically does it the entire time now. It did a weeks worth of going downhill over the last week, to doing it in a matter of 2 days. I'm guessing ignition coil at this point.

JaggerX

Changed the coil, runs perfect again. At this rate it will only get about 50 miles before being back where to running like crap. But we'll see. My theory is the coil was dieing and changing the cap/rotor out gave it the shiny low resistance to keep the spark going, but then as they broke in and got dull it let the weak coil show its ugly face again. We'll see if it lasts more than a day. Didn't hiccup once the entire 5 miles back from the parts store.

BlueRidgeMark

Your theory sounds reasonable to me. In the old days, "coil, cap, and rotor" were standard tune-up items, always done together.

ElMartillo

My symptoms included a few more cranks to start at any temperature, and an occasional hiccup while driving, once even causing a CEL. I removed my distributor cap and the contacts had some light corrosion on them, but otherwise everything looked fairly good and clean. I cleaned all contacts with emry cloth, and drove daily for a few weeks. The hiccups while driving seemed to go away, but the delayed starting remained. Decided to try a new coil, picked one up at the Crown retail location here in MA, cost around $20. The coil I took out is likely the original, the plastic housing is cracked extensively. I made sure to sand the paint off the new one where it contacts the mount bracket, and bracket to block to ensure a good ground. Starts perfectly now, and seems to run smoother!

The coil I removed: