greg92jeepxj
Official Supporter
Best of luck this Sunday , looking forward to positive reports . I'm certain all the labor entailed will be for the better.
Hesitates in 2nd gear and/or Sputters in 1st and 2nd
- Thread starter Bond--007
- Start date
Bond--007
New member
Update: Changed out the exhaust manifold gasket. Actually there wasn't a gasket there at all. Just a gasket on the intake manifold. Pulled the old gasket off and put the 1 piece gasket I got from Autozone. Bolted everything up tight and also changed out the O2 sensor since I already had it there. Fired up the jeep this morning and there was a slight "bucking" but it doesn't seem to be as bad as it was before. I'm going to run it all week and report back at week's end of any changes
also, ran some Seafoam through the vacuum lines. No leaks were in the lines but boy did that thing smoke out the neighborhood...lol
also, ran some Seafoam through the vacuum lines. No leaks were in the lines but boy did that thing smoke out the neighborhood...lol
greg92jeepxj
Official Supporter
Thank you for your update . It will also be interesting to note if the sea foam product is effective as claimed. I certainly hope it did a good job cleaning carbon from the jeeps combustion chamber especially around the intake/exhaust valves and hoping it cleans piston rings as well.
A word of caution regarding Sea Foam or any other (flammable) cleaner. I had to douse a carburetor fire last night after I sprayed carb cleaner on my (still warm) carburetor and then tried to start the engine. Guys in the parts store just laughed and pointed when I tried to get their attention for an extinguisher. I had a dry washcloth on the passenger seat to clean my hands with - smothered the flames and only scratched my hand on a bolt.
I'd suggest allowing the cleaner to evaporate before adding a spark!
:shock:
I'd suggest allowing the cleaner to evaporate before adding a spark!
:shock:
JPNinPA
Active member
Since doing this disconnect your battery for 15 min to reset the PCM air fuel trim levels back to stock settings. They will be relearned. This may help as a richer or leaner mix may have been being called for due to any leak.
Hopefully your intake pins lined up and the gasket sealed any leak.
Bond--007
New member
So.... fired the jeep up this morning and it did the same spit and sputter from take off. Cleared right up after I got 2 blocks from home and everything got warmed up. About at a loss at this point. Just seems like I'm chasing the rabbit down the hole
JPN: I'll pull the positive side tonight to do the reset and I'll report back tomorrow after the drive into work
Just wanted to take a min and thank everyone who has posted on here trying to help me figure this issue out
greg92jeepxj
Official Supporter
I'm not going to put any money on the stuck thermostat causing this glitch . I understand the point but a rich mixture shouldn't cause this . This jeep is fuel injected , not carburetored . Only bad injectors , bad spark or pcm or sensor glitch causes this kind of a miss. I believe you have already checked and cleaned all grounds including O2 and pcm ? O2 sensor swapped too. If wiring harness is trustworthy and not causing intermittant condition , it seems that another drive and scan will have to be performed paying attention to one sensor at a time to,rule in or out if any are operating out of range at any time. Process of illimination . Also curious if spark quality is consistant from idle through cruise to WOT. All kinds of things come to mind to check at this point but I know you have checked so many by now . Intermittant is the problem and that could be spark , fuel,pressure , sensor communication or even pcm . But I'm not ready to blame a pcm . Not so fast. The only way that stuck thermostat can even cause such a condition is if the CTS is faulty and causing erratic reading . Before swapping any more parts , the scan total has got to show values of sensors while driving . It seems to be a cold engine condition now ( open loop ) , so the problem is not present when warm ( closed loop ) ?
JPNinPA
Active member
Simply: No
More: You have this issue when the engine is cold. So it doesn't matter what the thermo is doing.
Bond--007
New member
Greg, Could a bad CPS be the culprit? That’s about the only sensor I haven’t changed yet
JPN, I figured the same, but figured it was worth a shot for someone else to confirm
greg92jeepxj
Official Supporter
In your first post , among the parts list you've changed you mentioned a CKS. Did you mean a crankshaft position sensor ( CPS) or a camshaft position sensor (CMP) ? Kind of confused , not familiar with that abbreviation. You can try to wiggle the harness of the crank shaft position sensor while the engine is idling to see if the engine stumbles or stalls . I did mean to ask if you changed or checked the cam shaft position sensor which does have an important role and can cause symptoms your having . I don't remember if a DTC popped up related but at this stage , yes , it should be checked . It can be checked with a volt meter by back probing the harness still connected . You should see 5 volts . But I think since this problem is intermittant you may not see this part showing irregular readings unless it actually does miss once and you'll see that better with the scan tool when driving. The bench test dosen't always yield results and causes you to chase your tail. That's why diagnostic shops like lab scopes $$. I,will however respect your thoughts and we shouldn't rule out anything but before you change any more parts ($$) , evidence is needed. But yes , a CMP is probable and should be properly checked. I still believe all sensors should be read but to find the one that misses at the crucial moment is tricky. For now , if at least the values can be checked to see if at least all sensors are in range , this is still helpful . But I know that you do not want to over look the problem by thinking you checked one and found it good but still intermittently causes the problem . Could be a ground issue with one or defect or poor quality. Getting the right parts seems to be getting tougher. I've read that even MOPAR O2 sensors take a back seat to NGK. Just makes it tougher , I know.
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Bond--007
New member
Greg, thanks again for the input and walking through this. I replaced the Crankshaft sensor (the one on drivers sideI believe it was located on the bell of the transmission or in about there). I'll have to check the Haynes manual to see where the CPS is located. I originally thought I was doing the CPS (mine failed on the truck before and it ran like crap) but it was the crankshaft. I'll pull the CPS and clean it. I know other write-ups said they collect shavings and can give misreadings
I guess the most interesting part is like you said, this appears to only happen in Closed Loop since it runs fine when wared up and in Open Loop
greg92jeepxj
Official Supporter
Hey Bond , your most welcome . Like to thank JPNinPA too since he's very diagnostically inclined . Sorry if I confused you , open loop is cold and closed loop is warm. Sorry . The coolant temp sensor will determine when the PCM will go into closed. Loop when engine warm and a richer mixture isn't needed to,warm up . That's a good call to clean the crankshaft position sensor since it a magnet and will attract metal shavings , especially from a clutch. If you still got the MOPAR CPS , have faith , might still be kickin' . Mine is the original and still good because I got an aw4 (auto) trans and less likely that metal shavings will collect on it. Yeah , the CPS on a 2.5 will be on the driver's side of the bell housing . Easier to get to than a 4.0 , not so close to the firewall.
Ok,, looking forward to your posts of progress . Wishing the best and will keep,at it until we find the gremlin.
P.S. - would like to thank everyone else for their participation in this thread too . Thanks !
Ok,, looking forward to your posts of progress . Wishing the best and will keep,at it until we find the gremlin.
P.S. - would like to thank everyone else for their participation in this thread too . Thanks !
greg92jeepxj
Official Supporter
Yes , what is referred to as the camshaft positioned sensor is the sync signal generator , or stator which is found in the distributor. See if your repair manual has a test procedure for this sensor . My 1992 chrysler service manual has a general procedure to check for voltage of 5 volts but since we know the engine starts and runs this procedure will show 5 volts leading U.S. To believe it is good. The real test will have to be done with the engine running . A good scan tool may be able to perform this but a lab scope will . That's the tough part. I'm hoping your buddies scan tool can show live data in terms of signal reference from the camshaft position sensor. Hate to ask you to keep grubbing his scanner , I know you feel the same.
Incidentally , where did you obtain the replacement crank sensor ? Do you still have the previous sensor and was it a factory part ? Was it confirmed to be bad or could a cleaning help ? The factory sensors were the best and MOPAR crank sensors and other sensors are usually the best to replace with since the parts store brands are often questionable .
Bond--007
New member
I still have the scan tool. I just need to research what data it will stream while driving. I got the sensor off of Ebay (cross referenced the part number, not application type). It was like the rest of the sensors I have replaced already (thought it was the issue). I still have the original CPS. Changing the CPS confirmed the issue was not CPS related...lol
I did find the below regarding the open loop vs closed loop operation of the PCM
Open Loop and Closed Loop.
Whenever the vehicle is first started, the PCM operates in "Open Loop" fuel control. When the Powertrain Control Module (PCM) determines that the engine coolant temperature (ECT) sensor has reached at least 20 degrees C (68 F), and the oxigen sensor has reached operating temperature of 318 degrees C (600 F), it will then go into Closed Loop fuel control operation.
Closed Loop fuel control operation will be maintained as long as certain parameters are met. In "Closed Loop" fuel control, the PCM varies the fuel to the engine according to signals received from the oxygen sensor, located in the exhaust manifold. The oxygen sensor varies a voltage signal to the PCM, indicating the oxygen content of the exhaust gases. If the oxygen sensor signals that the air/fuel mixture is lean, the PCM will increase the amount of fuel to the engine. If the oxygen sensor signals that the air/fuel mixture is rich, the PCM will decrease the amount of fuel to the engine.
During "Closed Loop" fuel contol operation, the PCM is constantly adjusting the amount of fuel to the engine, according to signals received from the oxygen sensor, to try and obtain a 14.7:1 air fuel ratio.
If there are any oxygen sensor related PCM/EC diagnostic trouble codes, or if the oxygen sensor does not switch between rich and lean, or if the ECT does not obtain 20 degrees (68 F), the PCM will not go into "Closed Loop" Fuel control operation.
Bond--007
New member
ENGINE WARM-UP MODE
This is the Open Loop mode. During engine warmup, the powertrain control module (PCM) receives inputs from:
† Battery voltage
† Crankshaft position sensor (REPLACED)
† Engine coolant temperature sensor
† Intake manifold air temperature sensor
† Manifold absolute pressure (MAP) sensor (REPLACED)
† Throttle position sensor (TPS) (REPLACED)
† Camshaft position sensor signal (in the distributor)
† Park/neutral switch (gear indicator signal—auto. trans. only) N/A
† Air conditioning select signal (if equipped) N/A
† Air conditioning request signal (if equipped) N/A
Based on these inputs the following occurs:
† Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
† The PCM adjusts engine idle speed through the idle air control (IAC) motor and adjusts ignition timing.
† The PCM operates the A/C compressor clutch through the A/C compressor clutch relay. This is done if A/C has been selected by the vehicle operator and specified pressures are met at the high and low–pressure A/C switches. Refer to Group 24, Heating and Air Conditioning for additional information.
† When engine has reached operating temperature, the PCM will begin monitoring O2S sensor input. The system will then leave the warm-up mode and go into closed loop operation.
After Reading the above and knowing what has already been replaced/changed, this really only leaves the temp sensors, Camshaft sensor, or battery causing my issues since it’s only present in the initial start-up and runs fine after everything is up to temperature.
This is the Open Loop mode. During engine warmup, the powertrain control module (PCM) receives inputs from:
† Battery voltage
† Crankshaft position sensor (REPLACED)
† Engine coolant temperature sensor
† Intake manifold air temperature sensor
† Manifold absolute pressure (MAP) sensor (REPLACED)
† Throttle position sensor (TPS) (REPLACED)
† Camshaft position sensor signal (in the distributor)
† Park/neutral switch (gear indicator signal—auto. trans. only) N/A
† Air conditioning select signal (if equipped) N/A
† Air conditioning request signal (if equipped) N/A
Based on these inputs the following occurs:
† Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.
† The PCM adjusts engine idle speed through the idle air control (IAC) motor and adjusts ignition timing.
† The PCM operates the A/C compressor clutch through the A/C compressor clutch relay. This is done if A/C has been selected by the vehicle operator and specified pressures are met at the high and low–pressure A/C switches. Refer to Group 24, Heating and Air Conditioning for additional information.
† When engine has reached operating temperature, the PCM will begin monitoring O2S sensor input. The system will then leave the warm-up mode and go into closed loop operation.
After Reading the above and knowing what has already been replaced/changed, this really only leaves the temp sensors, Camshaft sensor, or battery causing my issues since it’s only present in the initial start-up and runs fine after everything is up to temperature.
JPNinPA
Active member
Any of those may be bad and should be checked. Though before you spend any additional $$$ consider a few things
1.) A week or bad battery is a constant. You would be missing or stumbling longer than just warmup. Clean the terminals and the ends of the grounds. While the exterior of the battery with a damp cloth to remove any moisture, acid or oil. You could take it to be load tested for free.
2.) similar to the battery a bad temp sensor is bad all the time. You could measure the resistances as it warms up.
3.) cam sensors are referenced all the time during operation. The voltage should switch between 5 and zero as the engine is turned.
4.) generic sensors are known to fail right out of the box.
The issue is start up or open loop. This is where preset values are used for air fuel trim levels. If you were getting too much air you get detonation. Too little air you run rich and may get carboned plugs or stuttering. If the issue is a vac leak you get too much air until open loop. Then it will be compensated or closed up due to expansion.
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