Cranks & Cranks Unless Gas Pedal Is Depressed.

For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM.

Your symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal. The ECU will relearn the idle settings after a short period of driving and the engine will start and idle normally.

Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem. Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables and replace them as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body.

If the symptoms reoccur, you need to have your battery and/or the alternator load tested at a repair shop or auto parts store. This is usually a free service they offer to bring in potential customers. Even with low battery voltage, the engine will start, but the ECU can re-boot multiple times and a new battery may be required.

Cleaning the Idle Air Controller (IAC) with throttle body cleaner, regular tune-ups, and using fuel injector cleaner should be part of your routine preventative maintenance.
 
Alright job for tomorrow;

Start jeep up and let run for ~10 minutes. Turn off and read battery voltage. Let it sit for a few hours and read voltage again.

While i'm waiting that few hours i'll pull the TB off and inspect it and see if the IAC looked gummed up or something.

Tim, i just changed out all the charging wires and grounds about 3-4 months ago with all 4 gauge wire. Every single connect is properly crimped and tight. I will confirm this tomorrow again just to be sure though. Don't want to assume anything here.

Had another weird issue come up today. Before i elaborate on that i should mention i was driving through water today. Maybe a foot to about a foot and a half if that. Wasn't hammering down too hard, but i was maintaining momentum so i wouldn't get stuck.

About 4(?) hours after that i drove the jeep somewhere and shut it off. I came back about an hour later and there was NO power at all in the jeep (no power locks, window controls, radio, dash lights, etc. NOTHING at all) I suspected a loose connection or dead battery or something along those lines but was unsure how this was possible.

I went to pull the light switch out and push it back in to assure that i didn't leave the lights on or something and the second i pulled the light switch out all the power was restored like nothing happened. I'm thinking a short somewhere (have no clue where that would be) or something along those lines.

I should mention that when i drive with the lights on and turn the jeep off if i don't turn the lights off before i turn the jeep off the lights will not turn off even if i push in the switch. I have to turn the key back on, push in the headlights, and turn the key back off. This started occurring after i put in an upgraded light harness (putco) to run my headlights.

Anyways, when i did get power back tonight same problem. Crank crank crank no start. Gas pedal down fired right up.
 
should mention that when i drive with the lights on and turn the jeep off if i don't turn the lights off before i turn the jeep off the lights will not turn off even if i push in the switch. I have to turn the key back on, push in the headlights, and turn the key back off.
Click to expand...

Thats twilight sentinel. Standard on many XJs. They will turn off after about 2 mins IIRC.
 
Here's my IAC. How do I go upon cleaning it off and lubing it back up? Where do I even grease it?

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Clean the pointy end, and the housing, then re-install. There is no lubing needed, and I highly doubt you could spray enough cleaner on it to remove any of the original lube (if any was used).
 
Re: Cranks & Cranks Unless Gas Pedal Is Depressed.

Tim_MN said:
Clean the pointy end, and the housing, then re-install. There is no lubing needed, and I highly doubt you could spray enough cleaner on it to remove any of the original lube (if any was used).
Click to expand...

Got it. On that now.

DrMoab said:
I'm betting on low voltage. Had this issue so many times with my jeep I couldn't count them all.
Click to expand...

So you're betting on my alternator or battery going out?

Battery is new about a year ago and the alternator is unknown. It might be the original but i'm not sure.
 
Re: Cranks & Cranks Unless Gas Pedal Is Depressed.

DrMoab said:
Or abad connection somewhere.
Click to expand...

Cleaned it and put it back together.

Still having the same problem.

I have noticed recently though that my negative battery teminal is always loose or something along those lines. I'm going to go buy a different terminal and put that on and see if it helps.

If not i'll check all my connections over again.

My check engine light was on from pulling all the sensors out. The normal ones. MAP, IAC, and TPS. I reset them with my code reader with the TB still out, and then i installed everything again.

Started it up and my CEL was still on. Pulled the codes. Same codes except one of them dissapeared (i think the low volt tps disapeared) and a P0443 code showed up for "Evaporative Emission System Purge Control Valve Circuit".

Related? Unrelated? What the hell is that?

Just went out and took some readings under the hood. Battery sits at 13.72 volts while running. If i put the positive lead on the post on the alternator and leave the negative lead on the negative post on the battery it reads 13.75.
 
Last edited:
Tim_MN said:
Clean the pointy end, and the housing, then re-install. There is no lubing needed, and I highly doubt you could spray enough cleaner on it to remove any of the original lube (if any was used).
Click to expand...

I'm a curious sort of guy, I've taken one apart to see what makes it tick. A worm (screw shaft/jack shaft) gear driven by a tiny reversible motor. The worm gear is axial and runs through the center of the motor. They come with the worm gear covered in a lite synthetic grease. Over the years the grease collects grit and the grease gets about the consistency of partially dried toothpaste. That along with the sticky stuff that collects on the piston seat can cause sticking.

When I have the IAC out I let few drops of synthetic oil run down the sides and behind the piston. I figure it helps loosen up the stiff grease.

Might as well try cleaning it and lubing it before you buy a new one that may or may not help anything. Most times IMO it is a voltage issue anyway and not really a IAC issue. Even though, if the IAC is sticky it doesn't help it operate any better under low voltage.

Since I've learned how to clean them out, I've never had to buy a new one and am even still using one that is 25 years old.

Taking the piston out is not advised, when you try to get it back in you are in effect on the wrong end of a fulcrum and are likely to damage something. And don't try to plug it in and test it under power with IAC out of the TB. I launched a piston about 10-15 feet one day trying this. Though I did eventually find (on my gravel driveway) the pieces , reassembled it and it worked. :)
 
8Mud said:
I'm a curious sort of guy, I've taken one apart to see what makes it tick. A worm (screw shaft/jack shaft) gear driven by a tiny reversible motor. The worm gear is axial and runs through the center of the motor. They come with the worm gear covered in a lite synthetic grease. Over the years the grease collects grit and the grease gets about the consistency of partially dried toothpaste. That along with the sticky stuff that collects on the piston seat can cause sticking.

When I have the IAC out I let few drops of synthetic oil run down the sides and behind the piston. I figure it helps loosen up the stiff grease.

Might as well try cleaning it and lubing it before you buy a new one that may or may not help anything. Most times IMO it is a voltage issue anyway and not really a IAC issue. Even though, if the IAC is sticky it doesn't help it operate any better under low voltage.

Since I've learned how to clean them out, I've never had to buy a new one and am even still using one that is 25 years old.

Taking the piston out is not advised, when you try to get it back in you are in effect on the wrong end of a fulcrum and are likely to damage something. And don't try to plug it in and test it under power with IAC out of the TB. I launched a piston about 10-15 feet one day trying this. Though I did eventually find (on my gravel driveway) the pieces , reassembled it and it worked. :)
Click to expand...

LOL, that sounds like fun!!!!! You got me thinking it might be possible to take a 9 volt battery and let the motor run the piston out enough to be able to clean and relube that shaft!!! I just may try that some day!!!

Did you know the NOID light test kits have tester in the kit for the IAC wiring, that works just like NOID light testing the injector wiring?

http://www.harborfreight.com/11-piece-noid-light-and-iac-tester-set-97959.html

:party:
 
Ecomike said:
LOL, that sounds like fun!!!!! You got me thinking it might be possible to take a 9 volt battery and let the motor run the piston out enough to be able to clean and relube that shaft!!! I just may try that some day!!!

Did you know the NOID light test kits have tester in the kit for the IAC wiring, that works just like NOID light testing the injector wiring?

http://www.harborfreight.com/11-piece-noid-light-and-iac-tester-set-97959.html

:party:
Click to expand...
If you do try it, there is a spring behind that piston, when you run out of threads on the shaft it launches.:wow:
 
Ecomike said:
LOL, that sounds like fun!!!!! You got me thinking it might be possible to take a 9 volt battery and let the motor run the piston out enough to be able to clean and relube that shaft!!! I just may try that some day!!!

Did you know the NOID light test kits have tester in the kit for the IAC wiring, that works just like NOID light testing the injector wiring?

http://www.harborfreight.com/11-piece-noid-light-and-iac-tester-set-97959.html

:party:
Click to expand...
Use 5 volts max and be real careful. I tried to bag the old IAC exerciser from the dealership I used to work at but it was long gone.
 
Dragonslayer said:
My 1993 XJ did exactly this a few months ago. Turned out to be a bad MAP sensor.

The link (below) gives great, detailed, instructions on how to test it more thoroughly
than what is outlined in the FSM.

http://troubleshootmyvehicle.com/jeep/4.0L/how-to-test-the-map-sensor-1
Click to expand...

Good catch, the few failed MAP sensors I've seen, the motor started hard, ran like ----, full rich, with dark smokey exhaust that smelled like gas.

Really not all that different from a weak signal CPS, that works enough to give you a start, but not well enough for the engine to run right. Though the smoke out the exhaust and smell of gas seemed less.
 
From your video it sounds and acts like a classic IAC problem. If it were the MAP, starting is unlikely to be your only problem, keeping it running, no matter what you did with the gas pedal, would likely be the outcome. And dark clouds of unburnt fuel would bellow out the exhaust.
 
8Mud said:
If you do try it, there is a spring behind that piston, when you run out of threads on the shaft it launches.:wow:
Click to expand...

I had a brand new out of the box one that had a twisted, damaged spring in it.
 
cruiser54 said:
Use 5 volts max and be real careful. I tried to bag the old IAC exerciser from the dealership I used to work at but it was long gone.
Click to expand...
Good point, 9 V is too much for that circuit.
 
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