Hesitation

Tiny
LORJOR
  • MEMBER
Spoke to the garage today they by-passed the oil cooler & got much better results. I will keep you posted. Phil
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Tuesday, April 5th, 2011 AT 6:31 PM
Tiny
LORJOR
  • MEMBER
OK found some info Dogde Tech posted 3/11/2011 3.8l top hose collapsing when coolant temp is under 140deg and throttle is raised hose might collapse no futher repair required. If customer wants it fixed install after market hose with internal spring. My mechanic was not satisfied with that so he dug a litte deeper when he bypassed the oil cooler hose it did not collapse. The bypass cooling ( I might be saying this wrong but I will give it a shot )hose from the overflow goes to the oil cooler then to the water pump & the oil cooler passages were blocked. Hope this helps others Regards Phil
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Wednesday, April 6th, 2011 AT 5:47 PM
Tiny
LORJOR
  • MEMBER
This was done as a test not a fix they will either clean out the oil cooler or replace it.
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Wednesday, April 6th, 2011 AT 5:57 PM
Tiny
LORJOR
  • MEMBER
Ok just posting a follow up with a question. Car is running fine. Drove approx 350 miles local & 160 miles on a highway trip all OK. No more surging no stumbling. Just to go over parts replaced coolant, t-stat, rad cap, hoses, serp belt, plugs OEM champ dbl platinum, wires, fuel injection service, computer reprogramed for idle. At rest car does not seem to idle as smooth as it did before all the issues I had. If you put your had on top of engine I can feel a slight vibration and ideas? Regards Phil 97K
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Tuesday, May 10th, 2011 AT 9:19 PM
Tiny
CARADIODOC
  • EXPERT
All I can suggest is if there is a misfire, the Engine Computer will detect it. The reason you can feel a misfire is because the rotational speed of the crankshaft slows down a very tiny amount when one cylinder doesn't produce its power pulse. The computer detects that slow-down in crankshaft speed.

Also, with all the work done, certain characteristics will have changed and can take some time for the Engine Computer to relearn them.

If the engine originally called for standard spark plugs, a lot of them will not run properly with split-fire or platinum plugs. Usually misfires will be detected that can not be felt, but switching back to cheaper standard plugs will solve that. If the special spark plugs are specified on the sticker under the hood, that is not an issue as their location and angle in the engine is designed for them.
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Tuesday, May 10th, 2011 AT 10:55 PM
Tiny
LORJOR
  • MEMBER
OK got it. The Champ double Platinum are OEM plugs. Thanks again.
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Wednesday, May 11th, 2011 AT 12:09 AM
Tiny
MAMAE
  • MEMBER
Hello- lorjor- Can you tell me what was the end result in this issue. I've had this same issue since October, 2010. It's driving me crazy. I love this car and when I start out it hesitates, lurches and acts like it's going to stall. On the highway it's fine and never has any issue. My husband never noticed it, until it became a real nuisance. We've changed the O2 sensor, checked all of the wiring, done a million different tests. The dealer was no help. I just couldn't tell from these postings what actually fixed your car. We've been looking for monthes to even see a similar issue on the internet. If you could let me know, I would be grateful!
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Friday, August 12th, 2011 AT 11:53 AM
Tiny
LORJOR
  • MEMBER
Hey mamaE Yes my car is running fine now. 1st what engine do you have the 3.8l or the 3.5l. I have the 3.8l according to my mechanic alot of the problem was the cars computer needed to be updated with a new idle program which was a recall way back when. I did all the other stuff like coolant plugs hoses ect because it was time to do all that stuff. My O2 sensor went bad because the check engine light went on. Please contact me regarding your problem I will try & help in any way.
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Friday, August 12th, 2011 AT 11:21 PM
Tiny
CRYPAC
  • MEMBER
Hi, have the 2004 pacifica 3.5, took it to dealer, checked codes and said no computer update available for this car, charged 89.99, still hesitates and surges. Been acting up for a month now, only from a stop or idling in gear, fine on highway. Did anyone has a successful solution for this problem?
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+1
Monday, November 14th, 2011 AT 3:52 AM
Tiny
MAMAE
  • MEMBER
The Chrysler computers need a signal from the front O2 sensor to run correctly. What is happening is the O2 sensor is not putting out a signal until it is warmed. This happens after a few minutes of driving but until a correct signal is sent out by the O2 sensor, the PCM (engine computer) is on its own deciding how much fuel to inject into the engine based on your throttle position and water temperature. It has a special program to do that; it is called open loop. What is happening is the computer is going into closed loop and expecting a signal from the O2 sensor. Because of emission standards PCM’s go into closed loop as quickly as possible. To get the O2 sensor sending out a signal quickly, so it is working by the time the PCM goes into closed loop, engineers have added a heating circuit to the O2 sensor. The sensor must be above 600 degrees to output a signal and this is where the intermittent problem starts to happen. You can let the car idle in the driveway for half an hour and 90 seconds into your drive you lose your throttle. If it is the O2 heater circuit causing the problem, slide the shifter into neutral and push the throttle down. Eventually the engine RPM’s will raise (maybe 5 seconds; seems like forever) and then hold them at 2000rpm for 20 seconds. This will heat the sensor and the throttle will work correctly. If you stop at the store, or wait too long in traffic, you will need to do it again. If you notice a little hesitation the O2 sensor is too cold to work again.
There are 2 reasons for this problem.
One is your O2 heating element in the sensor is bad. To check it unplug the sensor and do an ohm reading across the 2 black wires. It should read 5 ohms. If not replace it.
Second problem; your PCM is not sending out 5 volts to the heater to heat it up. This could be a bad PCM or bad wiring. Checking the wiring harness from the PCM to the O2 sensor one will be ground and one should have 5 volts. The problem with checking it with the O2 sensor unplugged is that there is no load on the PCM and it could still read 5 volts without a load and zero with a load. Plug the sensor back in and check the voltage at the PCM. The factory manual says the heater voltage is supplied to the O2 sensor bank 1 sensor 1 through pin 18 (Black/Orange plug) C2 PCM. It is the second plug up from the bottom and has an orange strip on it. The wire is a brown wire with a tan strip. You have to pull the hood, that covers the back of the plug, off and insert a thin wire into the back of the PCM plug reaching in as far as you can. This is not as easy as it sounds so I recommend unplugging the plug and check using an ohm meter to make sure your wire has contacted the pin. Before you reinsert the plug back into the PCM check the continuity of the brown wire with tan strip to the O2 sensor plug. If the wire is good plug the plug back into the PCM. Start the car and check for 5 volts. If there is no voltage on this pin the manual say replace the PCM unit.
I wanted to make sure the PCM was causing the problem before I spent a lot of money on a new one. All you need to do is supply 5 volts to the heater so I bought a 25 watt DC/DC 12V/24V step down to 5V on Ebay for about $15 including shipping. (I think you could get by with just a 5 watt) I cut just the positive black heater wire about 8 from the sensor and connected the 5 volt wire from the step down power supply. The other 3 wires are still in place. Use an ohm meter to find which black wire is the ground and the other black wire will be the power. O2 sensors have 4 wires 1 blue, 1 white (O2 sensor voltage) and 2 black wires (power for the heater). We have not had any more problems with the throttle so why spend the money on a new PCM. Fixing it this way will keep an Check Engine light on all the time. I’ve thought about adding a resister to the dangling heater wire under the car but my wife has become so use to warning light on the dash (it took me a year to figure this all out) that I didn’t go to the trouble.
Before adding a different power supply make sure you remove and clean your ground wires. They are located under the battery box up front. There are 3 of them. I added an extra ground wire from the negative post to the body grounds. These cars use 5 volt for sensors and any grounding problems will cause sensor problems. A sensor problem causes the body/engine computers to do strange things.
For those who claim this is an EGR problem I have to disagree. If you have rough idle, misses on acceleration, and hesitation then EGR is your problem. Those of us who have problems with a loss of throttle, sometimes, will know exactly what I’m talking about. It is like your car is ignoring you! This is an O2 sensor problem.
What we don’t realize is that today’s cars are accelerated by computers and not us. We request to the computer to go faster by pushing on the gas pedal. The gas pedal opens up the air to the engine and by way of a Throttle Position Sensor tells the computer how fast you want to go. The computer then pulses the injectors to reach the RPM’s needed. The PCM then checks with the O2 sensor to see if there is too much or too little gasoline going into the engine. It then adjusts the fuel injector pulses to get maximum air/fuel ratio. When the O2 sensor is not outputting the correct voltage, when the PCM is in close loop, it understands the voltage to say Too Rich; Cut back Fuel and the short term fuel trim bank will pull back. My Short Term Fuel Trim Bank was at a -30% when I would lose my throttle.
I hope this helps.
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Thursday, November 24th, 2011 AT 11:35 AM
Tiny
LORJOR
  • MEMBER
Thanks MamaE will keep your reply for reference. There are 2 guys in this post I am the guy who started the post but my Pac is the 05 with the 3.8l do the same rules apply to my car my car has been running fine but it just seems that at idle it's not as smooth as it was before all the problems & parts were replaced any input from you would be helpfull. Thanks again for your help.
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Thursday, November 24th, 2011 AT 3:07 PM
Tiny
CARADIODOC
  • EXPERT
Interesting interpretation of how the system works but -30 is not normal under any circumstance. What you need to determine is whether way too much fuel is entering the engine due to a defect, and the computer is seeing that and trying to correct it, or whether the right amount of fuel is going in but the computer is getting incorrect information and mistakenly subtracting fuel that it shouldn't be. One clue is to compare the two banks to see if both oxygen sensors are responding the same. If they are, look for something both sides of the engine have in common such as fuel pressure or a vacuum leak. If only one bank is acting up, look for something that wouldn't affect the other side of the engine. That would include an injector, spark plug, individual ignition coil, etc. You can swap two ignition coils side-to-side to see if the problem goes to the other side. Injectors take a lot of time to switch but Chrysler has extremely little trouble with theirs so that should be left as a last resort.

The throttle-by-wire system is totally independent from the emissions system. It only affects engine speed, not other performance problems. What they DO have in common is injector pulse width. The length of the "on-time" for the injectors is varied to control fuel / air mixture and for engine speed. The pulse width is varied for engine speed based on the reading from the throttle position sensor on the throttle body, and the pulse width is further modified for emissions by the readings from the upstream oxygen sensors. The oxygen sensors' readings are inaccurate when the sensors are cold as you mentioned, but the computer ignores them in open loop. O2 sensor problems should not affect engine performance when it's still in open loop. O2 sensors also have no affect on idle speed. If engine speed doesn't pick up when the accelerator pedal is pressed, that is a problem with the throttle-by-wire system, not the emissions system. This insane throttle system is the same as the one that put Toyota in the news last year. Any service work on that system should be left to the dealer. Working on it yourself, and especially modifying it in any way will make you a party to any future lawsuit.

Being in tv / vcr repair for over 30 years, I know all about using power supplies to inject voltages but we did that to test and troubleshoot circuits, never to replace what the engineers designed in. To modify anything in any way left us open to a lawsuit if that product started a house fire. It's these things mechanics and other service people have to keep in mind when working on the products they service, and it's what most do-it-yourselfers aren't aware of. I was impressed with your grasp of system operation until you mentioned the Check Engine light staying on due to the modification of the oxygen sensor heater circuit. How will you ever know if a different, potentially serious problem occurs? You could have a minor problem such as a leak in the fuel vapor recovery system which wastes fuel through evaporation, and is fairly common, or you could have a leaking purge valve which will allow way too much fuel vapor to be drawn into the engine without the computer knowing about it. That will cause running problems and very poor fuel mileage. Remember, oxygen sensors don't measure or detect unburned fuel. They only detect unburned oxygen. As long as it detects the pulses of planned, unburned oxygen, the computer will be happy and will not know about that excessive fuel.

"I wanted to make sure the PCM was causing the problem before I spent a lot of money on a new one."

You don't need a fancy power supply to run the heaters. A simple resistor in series with the switched battery voltage would do the same thing. I've never checked the circuit with an ohm meter so using your 5 ohm observation, if you're starting with just under 15 volts system voltage and you want to drop two thirds of that voltage across the resistor leaving one third for the heaters, you'd need a 10 ohm resistor. Doing the math with Ohm's Law, it would need to be at least a 10 watt resistor.

" I’ve thought about adding a resister to the dangling heater wire under the car but my wife has become so use to warning light on the dash..."

If you can make the Check Engine light turn off by inserting a resistor to mimic the heater circuit, that proves the computer is supplying the 5 volts and is monitoring current flow in that circuit. Why use the computer to run an external resistor? Use it to run the O2 sensor heaters as designed. If the computer is not supplying 5 volts, what else isn't it supplying? Or is something grounded in that circuit and the computer is shutting the supply down to protect it?

The second problem is the computer is constantly performing many self-tests during engine operation. As an example, it knows that after the engine has been off for six hours, the intake air temperature sensor and the coolant temperature sensor had better be reading the same temperature. It also knows the coolant temperature sensor's readings should increase at a given rate based on engine speed, load, and time. Once it reaches around 180 degrees, it knows it can switch to "closed loop". All that means is it is still making fuel metering decisions based on many sensor readings and other criteria, AND it includes the oxygen sensors' readings to make minute fine tuning adjustments for lowest emissions. During prolonged idle periods, the exhaust gas temperature can drop below 600 degrees at which point the O2 sensors will stop responding. That became a problem many years ago with police cars that would sit idling for a long time at crash scenes. The heaters built into the sensors solved that problem. That hardly compares to a passenger car sitting at a red light. Even popping into a grocery store for 20 minutes would not affect engine performance related to the O2 sensors. The driver should never notice any change in engine operation whether it be from a cold start-up, warm restart, or prolonged idle. An engine speed problem for five seconds has nothing to do with the emissions system and you should never HAVE to hold the gas pedal down to warm the exhaust system to make the engine run right. No one would buy a car that had that requirement. If doing that works, that may be a valuable clue to the cause of the problem but it's not a cure.

Getting back to the computer comparing sensor readings and performing self-tests, there are some tests that will not run when there are related diagnostic fault codes stored in the computer. When the computer sees road speed, for example, and a closed throttle, it knows you're coasting and manifold vacuum should be considerably higher than when the engine is idling. It measures that manifold vacuum with the MAP sensor. If there is a code set related to the throttle position sensor or vehicle speed sensor, it will never perform some tests on the MAP sensor since it doesn't know what to expect. I'm generalizing here by talking about older cars without the throttle-by-wire system, but the concept is the same. When your Check Engine light is on many self-tests related to the fault code will not be run. You could have a sensor problem or a performance problem, along with the associated running problem, and no additional fault code will be set. The only way to let the computer tell you what's wrong is to fix the first problem, in your case, the O2 heater circuit, then drive the car until the next code sets.

Some people ignore the Check Engine light for so long until a different running problem occurs, then they take the car in for service. All the mechanic knows at first is there's a fault code for one problem. Some owners are so inept at describing other symptoms or the car's history that the mechanic has to discover all the problems on his own. He may provide an estimate to remedy the fault code currently being displayed, expecting to find a defective sensor or corroded wire to that sensor. After the repairs are completed, he might be surprised to find the Check Engine light is still on and a new fault code is set seemingly unrelated to the one he just repaired. Had he known the car's history, he could have planned for finding additional problems, or at least expected there was more wrong with the car than just the one fault code, and he could have explained that to the owner and prepared them for that possibility. Instead, the second problem might finally show up, either on his test drive or the day after the customer gets the car back. Of course the uninformed customer blames the mechanic for doing something to their car or for not fixing it right the first time. They don't understand the current problem existed many months ago when they ignored the Check Engine light.

Also, the fault code the mechanic is basing his diagnosis and estimate on would likely be the one that caused the Check Engine light to turn on many months ago. Imagine his dismay when he has a fault code to tell him which circuit to check, he does that, finds the cause of the problem, corrects it, erases the code, goes on a test drive, and the light turns on again with a new code requiring a totally different diagnosis that he didn't include in his estimate. This happens all the time and is just one of the many reasons mechanics have an unfairly deserved bad reputation. Without knowing the history, (some owners intentionally keep it secret, either due to shame at ignoring the light, ignorance, or in hopes of getting two repairs for the price of one), the mechanic will typically think he did something wrong and will set out double-checking his work and possibly replacing the same parts a second time. That results in a lot of wasted time and money. More experienced mechanics trust their work so they move on to the new problem sooner but it still leads to lots of arguments with customers. That can be avoided by having known problems repaired as soon as possible before a second, different problem has time to occur.

As a side note, those unrecorded codes are a big headache with the anti-lock brake systems on GM cars and possibly other brands. GM has a real big problem with front wheel bearings developing a little play, which is normal and acceptable, but with their flimsy built-in wheel speed sensors, it's enough to cause signal dropouts, a related diagnostic fault code to set in the ABS Computer, and the system to turn off. In typical GM fashion, they like owners to have to buy big assemblies to fix little problems. The only way to get a new wheel speed sensor is to buy the expensive wheel bearing. Doesn't matter though; in this case the bearing is cause of the problem. Since this problem can occur in as little as 15,000 miles, it is very possible for the second bearing to develop the same problem before the car is finally brought in for service. Since the computer has to compare the signals from one wheel speed sensor with the other ones, when one fault code is set, it stops performing self tests. The result is you will finally take the car in for service, have a fault code for only one wheel speed sensor, have the new bearing installed, then the fault code for the second wheel speed sensor shows up for the first time. Now the mechanic has to tell you a second bearing is needed to turn off the warning light. Nothing was done improperly during the repair but wouldn't it be better to know both bearings were needed right away? Mechanics hate having to keep telling customers that they found more and more things that are needed. They would rather give you one list right up front.

I have no problem with you using a power supply to diagnose the O2 sensor heater system. The reason for my story is I don't condone leaving it in place permanently. I suspect you understand that other problems will pop up on occasion, but it's the other people reading this thread who might think that is a legitimate fix. Those are the people who don't understand the ramifications of modifications and how they affect other systems on their cars.

The biggest confusion is in your last paragraph. The injector on-time has always been controlled by the computer. It remains unusually constant. As engine speed increases, the number of pulses per second increases accordingly, one pulse per intake valve opening. The amount of air was controlled, by of all things, an unbelievably simple and reliable throttle cable physically connecting the gas pedal to the throttle body. Idle speed was controlled by an air bleed passage around the throttle blade and a valve that was opened or closed by the computer. When a higher idle speed was needed, the computer opened the air valve, (automatic idle speed motor), and increased the number of milliseconds the injectors remained open during each pulse. The oxygen sensors have absolutely nothing to do with idle speed. Where it gets confusing is there can be a problem that affects idle speed AND the O2 sensor readings but other than that common cause, the two things don't affect each other. The most common example is a vacuum leak. The extra air causes idle speed to increase, (without a corresponding increase in power), and the extra oxygen will be detected by the O2 sensors. You can't say the oxygen sensor caused the higher idle speed, only that the two clues are related.

As for open loop vs. Closed loop, the computer uses a long list of variables to calculate how much fuel should enter the engine. Once the coolant temperature is high enough, the computer adds the oxygen sensor readings to that list. You should never know when that switch takes place while driving, and there isn't really anything you can do to control it.

To add one more dimension to the story that I am less familiar with, most Engine Computers today perform some tests when a very specific set of driving conditions is met and some are done after the engine has been off for a certain period of time. Modifying the O2 sensor heater circuit will cause some of those tests to fail. I know of two tests, both on GM products because they cause so many complaints. One test causes a severe stumble at highway speed, but it occurs very infrequently. Simply being aware it's normal satisfies most owners. I can't remember which system is being tested but it was mentioned in a few high-level classes I attended. The other problem occurred on older Corvettes. Twenty minutes after stopping the engine, the computer runs a real high current through the mass air flow sensor's sensing element to burn off any contaminants. Twenty minutes is about how long it takes to change the oil and filter. Slamming the hood closed at the end of the service produced enough shock to shatter the white-hot element. The defective sensor caused a no-start condition. A new sensor was needed to solve the problem, and guess who got blamed for causing the damage?

I can't say for sure if your computer runs a similar self-cleaning test on the O2 sensor, but at least be aware those are the types of things that are going on that we don't know about. That would not take place if you leave the heater circuit disconnected from the computer. Besides the liability issues, it's why modifying anything on newer cars is not recommended. The days of common sense in car design are long gone. Today we have computers doing all of the things computers weren't needed for before. Other than the emissions system, very little of this new technology actually benefits the owner.

Things get even worse in areas with emissions testing. No car will pass with the Check Engine light on. Instead of stuffing a probe up the tail pipe, newer cars pass the test if all of the "monitors" have run in the recent past. Those are the self-tests built into the car's computer, and they only run when those very specific sets of conditions are met. A Check Engine light, a failed sensor, or any number of other conditions that don't even turn the light on will prevent those monitors from running. Many people, including mechanics, complain that no matter what they do they can't get one or more monitors to run for the car to pass emissions testing. As frustrating as that can be, imagine how much worse it will be when something is modified.
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Friday, November 25th, 2011 AT 1:29 AM
Tiny
ADAMT56
  • MEMBER
My 2005 did the same thing until I cleaned out the throttle body. It is a common issue on this car. 5-6 bucks for a can of throttle body cleaner and my problem was solved.
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Saturday, July 14th, 2012 AT 7:29 PM
Tiny
LORJOR
  • MEMBER
Hey Thanks adamt56 do you have the 3.8l engine and that's all it took was cleaning out the TB what product did you use? I just recently had it inspected & told my mechanic that it does not idle as smooth as it did before all the work was done ( before it was so smooth you did not know the car was running ). He had a dodge mechanic look at it and he hooked it up to his mopar computer & he said he see no issues & he said it drives fine.
Any other input would be great that slight rough idle is driving me nuts. Regards Phil
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Saturday, July 14th, 2012 AT 10:14 PM
Tiny
ADAMT56
  • MEMBER
Actually, my '05 if the 3.5 liter engine.

My pacifica also runs as smooth as a sewing machine, until the throttle body started to get gummed up. The car would completely lose power (not shut off) when accelerating from a stop, then kick back in. My wife described it as a bucking bronco.

I'm surprised no one has recommended a nice throttle body cleansing. Sorry, I don't remember which brand I used, but any (caustic [harsh]) cleaner should do the trick. Definitely give it a try - can't hurt - and I would be interested to hear the result.
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Sunday, July 15th, 2012 AT 1:03 AM
Tiny
CARADIODOC
  • EXPERT
Keep in mind a lot of chemicals will destroy oxygen sensors. Even the fumes from a lot of older gasket sealers in tubes used to cause problems. Regular carburetor cleaners should do the trick.
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Monday, July 16th, 2012 AT 2:28 AM

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