DeckSmeck

I am trying to get a little more intelligent in the way I replace parts in my attempts to fix this stalling problem. I really do not know very much about engines but i am starting to learn.

The vehicle is a 2001 Grand Jeep Cherokee with a 4.0L, 6 cylinder. The jeep does not display any codes at this time. The problem has been occurring for 2 or 3 months.

The stalling appears to be as such. From a cold start the vehicle idles perfectly for about 10 minutes. It then stalls but it does so with out any struggle. It just stops running gracefully. I can then restart the jeep but I have to work the accelerator to keep it running. The jeep will also die while driving. It seems to operate well for 10 minutes or so and then dies. I can then restart the vehicle and continue. That is the normal way the jeep experiences the stalling problem. However, the stalling characteristics have been different at isolated times. Once the jeep was idling at a stop light after about 5 minutes of operation. The engine bogged down to almost a stall, revved up, then bogged down and finally died. There have been a few times when the vehicle had to sit from 2-10 minutes before it would restart. Restarting before this time would result in the engine turning over without any hesitation but it was if I had no fuel. The engine simply would not crank.

What i have done. I have been relying on advice from internet research and from other people who have experienced similar problems with jeeps. I have done these repairs. I have replaced the camshaft position sensor. I have replaced the fuel filter. I have replaced one upstream oxygen sensor. I have 4 of these. Two upstream and two downstream. i replaced the front upstream oxygen sensor.

I was just about to go out and buy the rear upstream oxygen sensor but i have to stop. I am basically just throwing parts at the jeep hoping to get lucky and i feel silly. Obviously this can't be the way to repair a hard to identify problem. i have learned more about the engines so I am starting to be able to use my brain now.

There are 4 basic things that the engine needs to operate correctly. Fire, oxygen, fuel, and electricity. I have also realized that when it is hard to identify what is broken, it is useful to identify what is not broken.

The jeep runs fine for 10 minutes before stalling. No hiccups. It purrs like a kitten. What does that tell me? All systems seem to work. The spark plugs are firing and at the right time. Fuel is being delivered. Air is being delivered. The electronics which operate the many sensors and other equipment is being delivered. All for about 10 minutes. At this time the engine ceases to operate because one of these systems fails. In order to repair this vehicle without spending more unnecessary money, I have decided that I should identify which system is failing. I know this is not easy.

I have spoken with several people and drawn some conclusions thus far. However, I am speaking with people like myself who are not professional mechanics and knowledge is very limited. Most people have a very cursory knowledge of the components of the engine and their suggestions are based on personal experience rather than analysis.

For now, i will assume that these parts are working.
Camshaft position sensor
fuel filter
Front upstream oxygen sensor.

The question: Which of these components fails? Electrical, oxygen, fuel, fire.

The clues: The problem is not consistent. The engine can idle perfectly for a duration. The engine can operate at speed for a duration. The vehicle can restart after a stall. The engine can keep running after a stall if i push the accelerator. The engine will stall again if I stop pushing the accelerator. Sometimes the engine will not restart after a stall unless it sits for a few minutes.

What happens after 10 minutes of idle time? There might be several things that happen in the engine after it has idled for a while but I lack the knowledge. I do know that the temperature of the engine has increased. But i do not know if the computer turns on or off certain systems after a time or makes adjustments. The 10 minute mark is pretty consistent for the initial stall. This leads me to believe that it is possible that the computer is doing something at that time. Alternatively, a part may fail when it gets hot.

Air
I am told that from an idle that the computer cannot do something that would cause the flow of air to cease. Apparently, if it were an air problem, such as a clogged air filter, I would experience problems consistently. I cannot verify this by myself. Can anyone eliminate the air flow based on the clues?

Fire
I am told the crankshaft position sensor is responsible for timing the spark plugs. i know something from personal experience. A vehicle can run with one spark plug not firing, although it is very noticeable. If the crankshaft position sensor were mistiming the spark plugs, it seems to me, that the engine would experience rough operation. As it is, the engine seems stall without any rough operation. Also, I can restart the engine and keep it running by pushing the accelerator. With the engine revved up a bit, the engine operates smoothly. If the sparks were timing incorrectly, it seems like it would be noticeable. If the crankshaft position sensor stopped operating completely, I can see how that would cause the engine to stall (based on my limited knowledge). But i do not think that if I restarted the engine that the sensor would be in such a state that it would be able to work if i stepped on the gas but fail if I let off it. At this time, i do not think it is a problem with the fire.

Fuel
Unfortunately, i do not know all the major systems responsible for delivering the fuel. I do know there is a fuel pump. Then the fuel lines. Fuel rails along the engine body. i know there is a throttle position sensor but I do not know how it works. From the clues, both the fuel pump and the throttle position sensor must be working for 10 minutes at an idle before the stall. Does it make sense that either of these components can operate normally then suddenly fail. Then on a restart, require me to push the gas to keep the engine running?

Electricity
This would probably be the hardest kind of problem to identify. It probably requires checking voltages or a scan tool that i can use for a long time to monitor voltages. i can see how there might be a problem with electricity being supplied to an important component such as a sensor. Maybe there is a short happening. Since it will consistently operate for 10 minutes or so before the initial stall then it seems that the computer would have to making an adjustment to something. Electricity would pass through a bad circuit and short out. However, if the problem were electrical, would it make sense that i could then restart the engine and keep it running by pushing the accelerator?

At this time, i think it is a problem with fuel delivery. i do not know how the fuel pump works. Can a fuel pump run normally but malfunction after a short period. Would it do this consistently?

I don't expect anyone to have a magic bullet for me but any help is appreciated. I will do my best to answer any questions. I may have left out vital information without knowing it. I really want to do a better job about picking the next part i replace. I know everyone has things to do, so thank you for your time and knowledge.

dave1123

Okay, here's a basic rundown on how the engine control system works. There are several key components;

PCM (powertrain control module, ie, computer)
ASD relay (auto-shutdown relay)
CPS (crankshaft position sensor)
Fuel pump relay
Cam sensor
Injector circuit
Ignition coil (pack, in your case)

Here's what happens when you start it;
Turning on the key energizes the PCM and all the sensor circuits, the fuel pump runs for about 10 seconds to bring up fuel pressure, then shuts off.

Then you start cranking the starter. The CPS sends a signal to the PCM telling it that the crankshaft is turning. When the PCM gets this signal, it turns on the ASD relay which supplies power to the ignition and injectors, and the fuel pump relay turns on. The cam sensor tells which cylinder to fire and the PCM times the spark and injectors. When the engine starts, the PCM monitors the throttle position, manifold pressure, air and engine temperature, and after it warms up, the 02 in the exhaust. All these sensors help the PCM adjust fuel trim and timing. These are just the basics. BTW, a bad 02 sensor shouldn't cause stalling.

Your problem sounds to me like a crankshaft position sensor that's on the verge of failure. It may also be a PCM that cuts out when it gets warm or looses the CPS signal due to poor connections. When this happens, the PCM shuts off the ASD relay killing the fuel pump, spark, and injectors.

This is just my opinion however and electrical diagnosis will determine if I'm right or not. The CPS and other sensors operate on a 5 volt supply so good, clean connections are important. The CPS signal can be checked with a multimeter before and after it stalls by back-probing the connector. Another thing you can try is after it starts, wiggle the wiring harnesses that plug into the PCM. If it stalls then, it's bad connections.

DeckSmeck

Thanks for the feedback. Sometimes the PCM is suggested as the culprit in these stalling problems from what I have gathered. This is why I don't think that is the problem in my case. The engine runs fine for a duration. If the PCM were experiencing a problem with lost input from an important sensor and shutdown the engine, I would expect a code. If the PCM itself were losing power or shorting out and the engine died as a result, it seems to me that when i cranked the engine back up and the circuit was restored, i would get the same behavior. The engine would run until that bad connection happened again and the engine would again die. Instead, when I restart the car, I have to use the accelerator to keep the engine running. I speculate if I had lightning reflexes and the patience to sit and wait for that initial stall, if i worked the accelerator I could keep the engine from stalling. This tells me that it needs more of something, like fuel or air, to avoid the stall. I don't know exactly which. That is unless, giving a vehicle with a faulty crankshaft position sensor more fuel and air would keep it from quitting. I lack the experience to know if that is the case. I was told that it was the crankshaft position sensor that was responsible for the timing of the spark plugs but if i understand you right, it is the camshaft position sensor. Or perhaps the two work together to accomplish this and other tasks such as air and fuel injection. Either way, could I expect the engine to operate roughly if one of these two sensors were malfunctioning and mistiming the spark plugs or air fuel injection? As it is, giving it more accelerator keeps the engine from stalling and the engine sounds smooth.

dave1123

Having to keep your foot on the throttle smells of a throttle position sensor or idle air control problem. Once the 02 sensor gets warm, the PCM starts reading the sensors to control mixtures. Before then, it runs on a pre-programmed mixture setting in the memory. Check the hose to the MAP sensor for leaks or cracks.

All this is just off the top of my head and my understanding of how the system functions. I wasn't aware that it runs smooth when you keep the throttle open with your foot. All the throttle body does is control the air flow, not the fuel.

CrisostamoSH90

I agree with the Crankshaft position sensor. It's a very common issue. When mine was going, it had no codes. I would be driving on the highway and she would shut off like a baby falling asleep mid stride. The jeep would start right up usually, but intermittently I'd have to wait for the sensor to stop its temper tantrum and start working again. It's about $60 from Jeep. Not too bad if you're trying to replace parts and pray. Side note about the electrical company's you've replaced, make sure you go with mopar parts from Jeep. Aftermarket parts seem to never work with Chrysler products, specifically jeeps.

Best of luck,
Nick

DeckSmeck

I am interested but I am still a little skeptical. When you say you had to deal with the sensor's temper tantrum, what does that mean? Was the engine running roughly when you tried to restart it? In my case the engine does not run roughly on a restart but I have to keep the engine revved up or it will stall? Can revving the engine up make a faulty crankshaft sensor perform correctly?

CrisostamoSH90

By temper tantrum I mean it just wouldn't start. The engine would run smooth as usual when it did restart, no rough idle at all. Revving would cause slightly longer run time for me, but would still die at 2,000rpms on the highway in gear. By any chance is your valve cover leaking? I ask because my sensor failed because oil covered the magnet on the sensor prohibiting it from getting the magnetic pulse from the flex plate

DeckSmeck

I don't know. I talked to another guy who had a bad seal, i think, and oil was causing his to malfunction as well. I guess, i could try the crankshaft position sensor next. I just wish there was a way to be sure.

dave1123

You guys just brought up a point I hadn't thought about. The CPS is a Hall-effect switch that has a magnet and coil in it that creates a magnetic field around it. When a metallic object passes close by, the magnetic field is disturbed which causes the signal to change or switch on&off. If it's covered with oil, as in a bad rear main seal, it can be like driving in fog for the sensor. After it sits awhile, the oil drains off and the sensor functions again. I just wonder if this scenario is fact. It would explain a lot.

CrisostamoSH90

Yes that's exactly what I was saying Dave, the oil prohibits the magnetic pulse from being sensed. In the case of mine I had already bought a new mopar sensor and had already pulled the old one out. So I just replaced. But, in a buddies wj his sensor failed and he was short on cash, so I said why not try mine. Sure enough over a year later he still has mine in his

Bustedback

I don't think oil is fouling the sensor. Most of the modern engines today have the crank and cam sensors in the side of the block with oil splashing on them the whole time.

CrisostamoSH90

Maybe not, but I can only tell you what I've experienced. I agree with sensors being inside the block, however the difference could be this particular sensor doesn't have a strong enough magnet or field to sense the crank pulse through oil. Just my idea