Jeep dying when leaving stop lights.

I also posted this in Co chapter.

My Jeep is feeling old and is going to need some lovin' this weekend before she leaves me on the side of the road.

Lately, a few times a day, it dies when I leave the stop light leaving me in the middle of the intersection pushing. Once I get it over to the side and turn the key off for a few minutes, it starts again and is fine for a few hours until I get to another busy intersection. Yes, it only happens at busy intersections.
I checked the codes and it is throwing 11, 12 and 41

11 is faulty cps or wiring, 12 of course is telling me that the battery was disconnected recently (which it hasn't been so I need to check my cables) and 41 is an alternator field switch (whatever that is)

It also had a bit of a struggle starting when it was very cold recently.

I had an old Chevy once that had a dirty fuel pickup and would die when I left the light and then start after the sediment in the tank would settle. Not sure if this is the same thing or not.

I did a search but after sifting through thread after thread trying to find something on this I gave up.

My Jeep is a 1994 276k stock 4.0 auto. Oh yeah it's a GT model. (Glamour Turquois)

This weekend I have wide open and I am wanting to replace the fuel pump and filter before it craps out on the mountain somewhere and I am going to service everything, change some hoses and the belt.
Its a perfect time to repair whatever is causing these codes but I am not really sure what I am looking for.

Anybody run into this before?

Thanks in advance!!!

If your going to throw a fuel pump at it, you might as well throw a CPS at it too...

Ok, so here's a thought. There's a sensor called a Throttle position sensor. It's black, and has a pigtail. It sits right on the side of the intake manifold. It's more of a rounded square. The cylindrical sensor with the pigtail is the IAC (Idle air control) valve. Not that one.

This sensor detects where your pedal is and when it wears out can develop "dead spots" in its range of detection. mine was between 45-50mph on the freeway. The throttle would just cut out. That's why it might seem like the Jeep "waits" for you to be at an intersection. It's becuase during normal driving, your throttle position is never @ the same place it is when you're idling. Good thing to check anyways, and the sensor is cheap, if I remember. $30.00 or so?

You can test this sensor by using a multimeter to check for resistance. There's a more specific write-up that, I think, has you placing the electrodes through the back of the sensor while its hooked up to look for spikes up or down in resistance. This would be done with the car on, (not sure if it needs to be running or not) with the multimeter in view, as you move the accelerator through its range of motion. Multimeters are like $2.00 @ harbor frieght. I have the little red one, and it works very well.

I personally went and bought a new one on a hunch, and tested the new one compared to the old one while it was out of the car, and it was blaringly obvious that there was a ton more resistance in the old one. Swapped it out, and haven't had an issue in two years.

Also, before you throw a fuel pump at it, make sure you test the fuel pressure at the rail. Our fuel pressure is pretty high I think. 30-40psi. Search for that specific number.


Oh, and the alternator field code meant a new alternator for me. Do you have a check engine light for that one? Mine would come and go. I nursed it along for about 2 weeks, by tapping on the alternator to get the brushes to hit the slip ring. Once they were completely worn down, even tapping wouldn't work and I had to spring for a new setup. about $120.00. This was reiterated by several people I checked with. It's been about 4 months, and that code has been absent since the repair.

Cheers, bro. You'll figure it out. These rigs are getting older, but the system is fairly straightforward with a few simple sensors that control a lot of stuff.

McQue said:

If your going to throw a fuel pump at it, you might as well throw a CPS at it too...

Click to expand...

Crank position sensor, which I believe is the one that resides on the side of the tranny, usually results in a no-start situation when it goes bad.

Not sure if it starts it downward spiral/death throes by causing symptoms like the OP is having. I've only heard of "no-starts" in mexico, where someone had a spare CPS by chance, and the jeep fired right up.

IAC usally cause rough idle, but not "cutting out" symptoms.

Not enough fuel pressure really isn't effected by speed, but you never know on those. I've heard some funky stuff caused by fuel pumps and not enough fuel pressure.

The 11 can be the crank sensor, but your symptoms don't sound like classic crank sensor issues.

But if you continue to code for this, I would first try spraying the crank sensor connector with electrical contact cleaner, add a dab of dielectric grease and reconnect. If it continues, I'd replace this sensor. With one from JEEP. I have had mixed (poor) luck with aftermarket crank sensors.

The 41 is usually an alternator problem. What is the voltage reading on your dash gauge? A healthy charging system and a healthy battery should result in an approximately 14 volt reading. Verify with a voltmeter at the battery if necessary.

Life starts with electrical. I'd chase that 41 first. Be sure connections are tight, serpentine belt is tight, and if it continues, I'd consider replacing that alternator.

Update....

I traced all the wires, had the alternator tested, cleaned the electrical connections, and generally cleaned the engine compartment and checked the grounds.

I was excited because it didn't die all day until about an hour ago. Dammit!

I have a buddy with an extra CPS that I am going to try to swap out to see if that helps.

This weekend I will fix it somehow if I could just figure out what is going on.

I have nothing to add other than the code 12 is battery disconnected in the last 50 key cycles per the FSM I have. I remember because it pissed me off when I went to smog the jeep and the check engine light wouldn't go off until i turned the key on and off for what must have been 10 minutes.

sounds like a cps to me, does it run ok right up until it dies, then cuts right out? if so it's probably not the fuel pump, they tend to make the jeep sputter out as it uses up the fuel in the lines. try pulling your cps off and seeing if there is dirt built up on the end of it, or try using a long screwdriver and a mallet to give it a little love tap and push it just a hair closer to the flywheel.

Number of reasons it could be stalling.

The crank sensor (and coil) are prone to thermal failure--they work fine up to a certain temperature and then cut out. When the fault presents itself, if possible, check for spark. To do this carry a spare spark plug in the vehicle and when it dies pull a spark plug wire off one of the plugs in the engine, plug in the spare spark plug and ground the metal body of the plug to the engine. Crank the engine over and observe the plug for a spark across the gap. Yes, an extra pair of hands helps.

IF you have spark, but the engine won't fire, then your problem is more likely fuel related. Pump isn't operating, or won't provide enough pressure or volume, or the PCM isn't sending a firing impulse to the injectors, or the synch sensor located in the distributor isn't functioning correctly so the PCM isn't firing the injectors or isn't firing them at the right times.

So--fire or fuel? Once you answer that question the number of possible solutions is greatly reduced.

Good luck.

I'm voting for TPS, mine died and gave me all sorts of headaches from bad idles to dying when I coasted to a stop at lights and signs.

Check with 5-90, he is the alternator guru around here.
Somewhere between 91 and 96 the voltage regulator moved from the alternator to the PCM/ECU, so it could be the PCM/ECU. Also the alternator problem can be intermitent (brushes about to give out, or loose solder joints or internal junction in the diodes, etc), so it could still be an alternator problem, especially if it keeps re-throwing the alternator code!!!

The CPS code is enough to justify a new CPS. A dying CPS can cause the engine to die at take off from idle. That is how mine started before it became a no start bad cps.

You may have 2 problems!!! Recheck the wiring harness and wires to the alternator for damage, or loose contacts!!

flingshot said:

Update....

I traced all the wires, had the alternator tested, cleaned the electrical connections, and generally cleaned the engine compartment and checked the grounds.

I was excited because it didn't die all day until about an hour ago. Dammit!

I have a buddy with an extra CPS that I am going to try to swap out to see if that helps.

This weekend I will fix it somehow if I could just figure out what is going on.

Click to expand...

Just to throw this in the mix Fuel Press. should be 42 psi at the rail if im not mistaken

I had this same thing happen to me, it would die sometimes a stoplights when I would accelerate to leave from a stop. It turned out to be a CPS issue but the CPS was actually fine. Turns out the bell housing bolts came loose somehow and when I would accelerate the transmission would pull away from the engine to the point the CPS could not read the teeth going around. Mine was a 87 so it had no codes like yours, good luck!