Stalling problems

Most likely there was nothing wrong with the engine computer. That is what a lot of mechanics fall back on when they can't figure out the real cause. That is because General Motors does have a real lot of expensive computer trouble and that is what they are used to finding. Chrysler products, at least up to that time period had very little computer trouble.

this guide will help

https://www.2carpros.com/articles/car-cranks-but-wont-start

There are two sensors that commonly cause the problem you described. They are the camshaft position sensor and crankshaft position sensor. Normally a diagnostic fault code wll be set in memory to direct the mechanic to the right circuit, but if no code is being set, the Jeep dealer has the Chrysler DRB3 scanner that does the best job of displaying live data while driving the vehicle. Once the engine stalls, it will display "no" or "present" for the signals from each sensor while you crank the engine. Many independent shops also have that DRB3 because with a plug-in card it can be used on any brand of car sold in the U.S. starting with the 1996 models.

It is very common for those sensors to become heat-sensitive when they fail. Once they cool down, typically in a half hour to an hour, they will work again. This is so common, your mechanics should be aware of this as it happens a lot on all brands of cars and trucks.

I can tell you how to test it but that is the only way you are going to find your problem.

All "crank, no start" conditions are approached in the same way. Every engine requires certain functions to be able to run. Some of these functions rely on specific components to work and some components are part of more than one function so it is important to see the whole picture to be able to conclude anything about what may have failed. Also, these functions can only be tested during the failure. Any other time and they will simply test good because the problem is not present at the moment.
If you approach this in any other way, you are merely guessing and that only serves to replace unnecessary parts and wastes money.

Every engine requires spark, fuel and compression to run. That is what we have to look for.

These are the basics that need to be tested and will give us the information required to isolate a cause.

1) Test for spark at the plug end of the wire using a spark tester. If none found, check for power supply on the possitive terminal of the coil with the key on.

2) Test for injector pulse using a small bulb called a noid light. If none found, check for power supply at one side of the injector with the key on.

3) Use a fuel pressure gauge to test for correct fuel pressure, also noticing if the pressure holds when key is shut off.

4) If all of these things check good, then you would need to do a complete compression test.

Once you have determined which of these functions has dropped out,
you will know which system is having the problem.

I do not know why Doc has not come back yet.

I did some investigating for you.

Some people believe in only "Genuine" expensive parts.

I am not one of them! I have gotten a bad parts before (non working from the start genuine or not!), But I have not had any problems out of "cloned parts" that I have used.

As far as changing these puppies, the cam sensor really looks easy I do not know about the crankshaft sensor. It is sort of hidden, and looks like it may be a bit difficult to get to (see picture) Both may be easy and you could do this yourself! A repair manual is a real plus, I use them constantly.

As far as cheating the mechanic, there are other inexpensive routes. My favorite is the person who works at the self service, Ma and Pop, Small Auto Salvage Yard. He will slap them on for $20.00 and a cold soft drink! Another is the Technical School Auto Technology Department. If you can schedule it, around here there's a $15.00 to $20.00 charge on various things (visit the instructor and ask).

Here is the locations of both sensors and my second Jeep.

Hope this does help.

The Medic

Could be that maybe it came unplugged or the contacts are corroded.

Maybe no need to spend money.

You can get little condiment packets of "dielectric grease" at the auto parts store. Smear some on your contacts before you plug 'em back in.

Good luck, come back to this post and update us.

This is an on-going soap opera for us we like to hear the rest of the story!

Thanks for coming to 2carpros.

The Medic

Sorry to take so long to reply. This site has stopped working on my main computer.

Happy to hear you have a code related to the crankshaft position sensor. Usually that will cause the check engine light to turn on, but that only must turn on when the detected problem could have an adverse effect on tail pipe emissions. A non-running engine will not cause excessive emissions.

This sensor sits on the top driver's side of the transmission, right behind the engine block. It is very important to install it with the proper air gap. If that gap is too large, the engine will hesitate, stall intermittently, or not start at all. If the gap is too small, it is possible for it to be broken from being hit by the spinning flex plate.

New sensors from the dealer come with a thick paper spacer glued to the end to set that air gap. Some aftermarket sensors have a thin plastic rib molded onto the end to set the gap. As soon as the engine starts, the paper spacer will slide off. The plastic rib, if used, will wear down. In either case, its job is done. Anytime a used sensor is going to be reinstalled, a new paper spacer must be used. If there is a partial plastic rib remaining, it must be cut off, then a paper spacer is used to set the gap.

The reason for bringing up that story about the spacer is every once in a while I read where a sensor got broken because someone did not know how important that air gap is.

Here is a photo from rockauto. Com showing what the sensor looks like, and a drawing from the Chrysler web site that shows where it is located:

First of all, if you are close to a larger city, you will likely have a salvage yard where you pay your buck, then throw your tool box into one of their wheel barrows, and you can spend the whole day there looking for parts. That would be a dandy place to find a similar vehicle to practice on. If you are near Indianapolis or between Ohio and southern Georgia/Alabama, there is a real nice chain of yards called Pull-A-Part. Their yards are very clean and well-organized, and the people and customers are very friendly. You can search their inventory on the internet too. I have been to at least a dozen of their yards in Nashville, Memphis, Knoxville, Indianapolis, Montgomery, four in Georgia, etc. I think they have about two dozen yards altogether. I think all you'll need to remove a crankshaft position sensor is a 10mm wrench but there might be other stuff that is in the way and has to be removed as well. You might even consider buying the used sensor. Parts are real inexpensive there. I bought a rust-free sliding door and lift gate for my 1988 Grand Caravan about two years ago for less than a hundred bucks for the pair. A similar type of yard in St. Louis wanted $250.00 just for a rusty lift gate.

Do not start replacing more things than necessary. When you consider that new parts can be defective, that air gap is critical, and anything else that can go wrong, you are inserting another variable into the equation each time you change something. If the camshaft position sensor was intermittent, there would be a different fault code stored in the computer.

As for your oxygen sensors, there is a different explanation for that. The engine computer is constantly running tests on all of the sensors. Some of those tests involve comparing their readings to those of other sensors. Here are just a few examples:

1. After the engine has been off for more than six hours, the engine coolant temperature sensor and the outside air temperature sensor had better be reading the same temperature.

2. If the coolant temperature sensor says the engine is at forty degrees when you start it, it had better be reading considerably higher after the engine has been running for five minutes.

3. There will be no signal coming from the vehicle speed sensor when it is standing still. That is a normal condition. There can also be no signal coming from it if it is defective. That is not a normal condition. If the computer sees that the transmission shifted to a higher gear or there is a load on the engine, it knows the vehicle is moving and there had better be a signal coming from the speed sensor.

In all of those examples the computer knows what to expect from each sensor for a given set of conditions, but it has to also know that "given set of conditions". If there is a problem detected with one sensor and a code is set in memory, the computer knows it can not rely on that sensor's readings to compare to other sensors. With nothing reliable to compare to, it will not set a code for the second item. That is likely what happened with your oxygen sensors. You actually have four of them, two on each half of the engine. The front ones measure if the correct amount of fuel is entering the engine. When everything is working correctly, both sensors will report nearly the same readings. As they age, one of them can begin responding slowly. The computer watches that but as long as the readings stay within acceptable limits, no code will be set in memory. If both sensors start to respond slowly, the computer will make fuel delivery adjustments that are not the best but you might not notice that fuel mileage has dropped or tail pipe emissions have increased. Eventually one of the sensor's readings will be bad enough, or unbelievable enough to the computer, that it finally sets that first fault code and turns on the check engine light. The second sensor is just as old and just as tired but it has not quite failed yet. Also, since there is a problem that was detected for the first sensor, the computer has nothing reliable to compare to the second sensor so it will never set a code for that second one.

Eventually you get the sensor replaced to take care of the fault code in memory. Now the computer has a reliable signal to compare to the second sensor, and it realizes that second one is not performing properly. That is when it sets the second code a week later. Unfortunately that means two trips to the shop, but there was no way to know during the first visit that another problem was going to show up. That is one reason mechanics get the blame very often for causing new or additional problems. Even if they are sharp enough to catch the second problem after they make the first repair, they get accused of "finding more things wrong as long as you keep approving the additional repairs".

General Motors is real bad about that with their anti-lock brakes. It is real common for wheel speed sensors to give problems within 15,000 miles, but only one fault code will be set in memory. Fix that sensor, then a different code pops up. Fix that one, then a different code shows up again. That is more likely to happen when the first code was ignored for many months giving those other things time to fail. Smart mechanics will ask you how long that warning light has been on. If only a few days, you likely have just that one problem. If it has been on for months, they know to prepare you for multiple items and lots of diagnostic time.

To address the poor running and whether it could be related to the crankshaft position sensor, the answer is yes, but it is usually intermittent. The signal from that sensor is either zero volts or five volts and it switches instantly between those two states. Those are the only two conditions the computer recognizes. If the failing sensor starts producing one volt or four volts, the computer might understand that it meant zero and five volts, but at some point it is going to get confused.

Think of a “do not walk” sign. The work “walk” is always lit up, but the word “do not” turns on and off. Those are the only two acceptable conditions. If the word “do not” glows very dimly when it should be off, you would understand it is okay to walk. Same is true if it does not quite get full brightness when it is on. You know to not walk or you will get mowed over by a bus! But what do you do when “do not” is lit up half brightness? Some people will walk, some will not, and some will step off the curb, then change their minds. That is the confusion the computer sees when the signal does not turn fully on or fully off from a failing sensor. It cannot decide whether it should fire a spark plug or an injector, or if it is supposed to be waiting for a better pulse.

It is rare for the sensor to produce those confusing signals for very long. Typically they go from working properly to total failure very quickly, with perhaps a few minutes of producing confusing signals. That said, it is also possible for a different type of failure to take place where the signal never reaches the full five volts. That is usually aggravated by the slow engine speed during cranking so it is more common to cause a no-start condition, but it can cause a hard start/hesitation/sputtering problem too. There are two ways to verify if it is the sensor causing the running problem. The fastest way is to install a new sensor, then see if the problem is gone. Professionals are trained to avoid that method because it involves buying parts that might not be needed. The other way is to connect an oscilloscope that lets you view the waveform and see if it is correct. Most people do not have access to a “scope” and they can take a while to set up and connect. In this case, since this is a known commonly failed sensor, there is a good chance it will solve the problem so my recommendation is to stick it in. If it does not solve the problem, hang onto the old one for a spare.

Good information, but the alarm will shut off the engine after two seconds and the horn should be blowing and the lights will be flashing. A broken wire between the door hinges is much more common than a bad switch. In that case, the alarm will turn off by unlocking the front passenger door. The alarm will not cause stalling after you have been driving, and it will not magically reset after the vehicle has cooled down.

The stalling when hot is the classic way crankshaft position sensors fail. I appreciate the information about the violet/black wire. Going to add that to the memory banks.

I have never gotten involved with aftermarket alarms, just factory stuff. I have never heard of a vehicle stalling while driving but I guess that does not mean it is not a possibility. If that were to happen, that would be extremely rare and uncommon. In this case, the original comment, "But it always started back up after a few (fifteen to thirty) minutes", is real common. The common stuff should be checked first. If that can be eliminated from the list of potential causes, that is when we start looking at the unusual or uncommon things such as the VTSS.

Still good information to have.

Just to let you know we are still monitoring your situation.

I feel caradiodoc is probably your best source of information for this problem!

He really goes out of his way to research these things and he writes back with informative novels. Lol!

Most everyone here respects his judgement (especially me, I am still living in the 1980's on back, with fixing vehicles of the past!)

Doc know quite a few of the other fellers here too, and they will jump in from time to time and aid him or share their experiences.

Doc's also way out yonder in Wisconsin his sleep patterns are definitely different than other folks.

Most likely drinking a glass of milk or having a cheese sandwich right now!

He will be back soon!

The Medic

Okay people, I am back, but only now finally because my internet service was down last night, again!

Jessiesjeep, "whenever it idles for any length of time (ex. In the driveway, at a red light)", what does "ex" mean? Example or except? I seriously doubt the automatic idle speed motor is the problem. It used to be real common for the air passage around the throttle blade on the 3.0L engines to become plugged with carbon but we have not seen that in over ten years thanks to the newer additives in the fuels today. I drive an old rusty trusty 1988 Grand Caravan 3.0L with 379,000 miles and have never had to clean that passage, and I always buy the cheapest gas I can find.

A real easy way to tell if the automatic idle speed motor is working is to observe engine speed at start-up. It should immediately give you an "idle flare-up" to 1500 rpm, then drop down to 800 rpm. If it does that, the AIS motor is working. If you do not get that idle flare-up and/or the engine idles too low when warm, suspect the engine computer has not yet relearned "minimum throttle" after the battery was disconnected during other service. Most mechanics will take your vehicle on a test drive at the completion of any service when the computer may have lost its memory to perform this procedure but many of them ignore it because it is so simple on Chrysler products that they leave it to the owner. It is probably the single biggest, although minor complaint after other service work was done. To relearn minimum throttle, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals. That will meet the conditions needed to signal the computer to take a voltage reading from the throttle position sensor. From then on it knows that whenever it sees that same voltage, your foot is off the gas pedal and it has to be in control of idle speed. Once that relearn is done, you will definitely get the nice idle flare-up at start-up. If you do not, that is the time to start looking at the automatic idle speed motor. It has four coils of wire that can be monitored by the computer for integrity, and a problem there will set a fault code and turn on the check engine light, but a stuck motor armature or plugged air passage are not monitored in any way so those failures will not set a code.

"Re-flashing" a computer simply means reinstalling the software, just like on your home computer. In the past, engine computers were relatively basic and performed simple functions. Chrysler's in particular were uncommonly reliable and rarely caused a problem. They get more complex every year, and starting with the newer "on-board-diagnostics version 2 (OBD2) emissions systems mandated in 1996, they also monitor the efficiency of the catalytic converter.

Two things can happen that require a change in the computer's software. One could be the discovery that under a specific set of conditions, (road speed, altitude, engine load and temperature, etc.), Tail pipe emissions might exceed legal limits. The engineers will design a fix for that in the software, then issue an emissions recall to re-flash all of the affected computers in those vehicles. That is less expensive than replacing the entire computer which is what they would have had to do in the earlier models. GM vehicles used their famous "PROM's. That was a plug-in integrated circuit that contained all of the programming specific to that vehicle and engine, and it set the "personality" of the computer. Those were fairly easy to replace too, after they sat down to redesign it and send out to have them manufactured, tested, then shipped to the dealers.

The second reason to reflash a computer is when the software is suspected to have been corrupted. This again is very common on GM vehicles due to the huge voltage spikes their generators produce. The problems usually start when the battery gets old and loses its ability to dampen and absorb those spikes. Welding on the car can also damage computers and the software.

A third reason to reinstall software has to do with simple economics for the manufacturer. In the past they had to have a different part number computer for every possible combination of engine size, power rating, vehicle weight, vehicle options, California vs. Federal emissions, etc. That could mean a few dozen different computer choices for each car model for each year. No dealer would want to stock hundreds of computers so when you needed a new one, they had to order the correct one and wait a day or two for it to arrive. Today they only have a few different computers and it is easy and inexpensive to keep them in stock. Once installed, they connect it to the internet and download the software specific to that vehicle. You can be on the road in an hour or less.

Today, with downloading the software over an internet connection directly into the computer, there is no need to redesign any computer chips or have them manufactured. Of course with any new technology there are drawbacks. General Motors is the master at separating owners from their money after the sale. One of their many customer-unfriendly business practices is that re-flashing computers can only be done by the dealer. Independent shops are allowed to re-flash three computers, as mandated by the government, because they can affect emissions. For all of the other dozens of computers, GM refuses to release the information to anyone else, so you are tied to the dealer and that very expensive repair bill you are worried about. These business practices are one reason why so many people are saying "never again" when considering which brand of new car to buy, and GM has been losing repeat customers.

Hyundai is at the exact opposite extreme. Any independent repair shop with a laptop computer can connect those cars to the internet and the Hyundai web site, and install any software into any computer for free. Look who is putting their customers' interests ahead of profits. Chrysler and Toyota are in the middle of that range. Any independent shop can download the software for any computer except the security system. For that one, the car must go back to the dealer so they can verify it is not stolen. The only time that software download would be needed is if that computer had to be replaced. Chrysler charges $40.00 per download, and the shop must purchase a one-day, one-week, or one-year subscription to their web site, but for that subscription you get access to all their service bulletins, service manuals, diagnostic fault code descriptions, and most of the things the dealer's mechanics get to use. The point is, even though there is a charge for the service, the information is available to everyone, and it costs way less than the aftermarket service information providers charge.

Okay, getting back to your intermittent stalling problem, the code 320 is the monster clue staring at you that is proof the AIS motor is not the problem. That code has to do with an intermittently missing signal from the crankshaft position sensor or camshaft position sensor which was commonly inside the distributor. It is common for mechanics to read the code and just throw in a new sensor, and ninety nine percent of the time the vehicle is fixed, but in reality, the codes do not specify a defective sensor. All fault codes get you into the circuit or system with the problem that needs further diagnosis.

This is no different than troubleshooting cars decades ago. There were no such things as fault codes. We checked to see if fuel was squirting in, then we checked to see if we had spark. Whichever one was missing, that is the system we diagnosed. Today we can have all kinds of problems besides the simple no-start conditions. There can be a dozen sensor circuits and it would be extremely inefficient to make the mechanic look at each one every time the car came in the shop. Instead, we let the computer detect the circuit that has a problem, then the mechanic diagnoses just that one. Most of the time the sensor at the end of the line is the cause of the problem, but there could also be a corroded terminal in a connector, a wire could be rubbed through and grounding out, or a terminal could just be stretched to the point of not making good contact with the mating terminal. To add to the confusion, some of the terminology can be misleading. An engine computer may use a "distributor reference signal" for an engine that does not use a distributor. The signal provides the same information but it comes from a different source or different type of sensor. On your engine, there is indeed a distributor, and code 320 refers to the camshaft position sensor that lives in it. You said your mechanic replaced the crankshaft position sensor which provides the same type of signal but it is actually in a different place and develops its signal from a different source. Either one of those sensors can become heat-sensitive and fail intermittently. They will often work again once they cool down in about an hour.

Another problem to be aware of when a new crankshaft position sensor is installed is they require the use of a thick paper spacer on the end to set the critical air gap. That spacer slides off when the engine is started but by then its job is done. Many aftermarket sensors have a thin plastic rib molded to the end to set the gap. It wears away when the engine is running so if that type is removed and reinstalled, it is supposed to have the remaining part of the rib cut off and you use a paper spacer. I had to reinstall that sensor after replacing transmissions. After doing a half dozen of them, I got so "good" at setting the air gap on those sensors that I didn't need the spacer. I learned later that on the thirteenth one, the owner developed intermittent stalling two weeks after I replaced his transmission, and a different shop read the fault code for that sensor, replaced it, and it solved the problem. Now I suppose it is entirely possible the sensor did become heat-sensitive and decide to fail, but I suspect it was due to my not setting the gap properly. I was going to suggest that is what happened on your Jeep, except the fault code is related to a different sensor. I suspect you have a failing camshaft position sensor. That is a bolt-in item, but I never replaced one so I am not certain, but I do not think there are any special procedures to follow or air gap to set.

Now, if you will excuse me, I have not eaten in over an hour! I am going to grab a slice of cheese and wash it down with some milk.