Accelerator Position Sensor

Niall Owner/Technician Stirling, United Kingdom Posted   Latest   Edited  
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Driveability
2006 Jeep Grand Cherokee Limited Premium 5.7L 5-spd (45RFE)
Occasional Cutting Out At Junctions

Jeep in for MOT and service, noticed prior to doing any work that the engine would cut out occasionally when coming to a full stop at traffic lights or a junction. No fault codes are present, did a test run max 35mph during which the cutout/stall occured, recorded data on Launch, APP1, APP2, RPM, O2B1S1, O2B2S1, STFT11, STFT21, INJ1 Pulse, MAF, all looked good apart from APP2 which has lower voltage and what looks like dropouts (a post some where else thought this might be normal?). I have since done a test (engine not running) with the PICO at the APP connector and at the ECM which apart from the voltage difference seem to be good. Does anyone know if this looks OK. Following service including replacing sparkplugs and although the engine does sound much smoother the cutting out is still there.

Sorry should have said throttle body cleaned

Carried out checks on all 5v refs and grounds at APPS connector all good, still puzzled why the scope patterns show no dropouts its almost like the ECM is reporting the dropouts

To answer some questions, trans fluid was checked and is OK, the APPS I am concerned with is part of the gas pedal, I did do a throttle relearn (no change), spark plugs are NGK all 16 3.8k to 4.3k ohms, the PDF attached has test of APPS using OBDWiz software (same result as the Launch), the engine cuts out completely but restarts straight away (well as soon as you can get it in neutral)

Coil current for all coils and primary voltage #1, is the current and voltage high because these are waste spark coils. Also did a WOT test to check operation of throttle body its definately opening to 100%. Carried out road test to check for any gearbox glitches, although the Launch had within the Tranmission PIDS one for the TPS it was only showing zero, checked under ECM to see what throttle plate was doing as the engine stalled it did seem to try and open the throttle but too late.

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Gary Owner/Technician
Hydes, Maryland
Gary Default
 

I have seen some Jeeps stall as you mention if the battery is low or if the battery was disconnected during service and throttle body is dirty, usually after cleaning throttle, disconnect battery cables and perform hard reset, after installing cables, let idle for 5 minutes and drive.

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Todd Mobile Technician
Morinville, Alberta
Todd Default
 

Check the transmission fluid level.

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Tommy Owner/Technician
Holly Ridge, North Carolina
Tommy Default
   

Niall, If the battery has gone flat, or been disconnected, it will need an idle relearn. sometimes you'll have to drive it in closed loop above 45 mph for a while to relearn.

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Brian Diagnostician
Seneca, South Carolina
Brian Default
 

Check the APP theory of operation for APP 2 some Chrysler PCM use the app 2 circuit as an internal ground check and it will look exactly like what you have. Check your service info to be sure.

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Niall Owner/Technician
Stirling, United Kingdom
Niall Default
   

Hi Brian this information is not easily found in the UK, I would need to get a subscription to Alldata. The post on the other site seemed to say the same thing but the dropouts are so random, I have done a relearn but not road tested yet, scan data is just the same. If anyone has this info?

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Brian Diagnostician
Seneca, South Carolina
Brian Default
 

Upon further reflection the year model I was thinking of was a good bit newer than yours. I checked the D and O for your model and it doesn't say anything about the internal ground check. I would post the info but I am sure there is some copyright stuff involved.

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Grant Technician
Loves Park, Illinois
Grant Default
 

Got another scan tool to check rationality of the APP2 data? What do you mean by the phrase "the engine would cut out"? Stall? No throttle response? Plugs should be obtained from the dealership parts dept and should measure at 4-6KOhms. Aftermarket Champion with same Champion part number may measure at 20KOhms.

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Victor Owner/Technician
Doral, Florida
Victor Default
 

The TPS is still part of the throttle body​.​You probably need to perform an idle relearn procedure.

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Grant Technician
Loves Park, Illinois
Grant Default
 

Could have abnormal load on engine such as from locked up/dragging torque converter or no down shift. Abnormal load PID values can be a clue to this. Maybe look at TPS vs RPM to determine if downshift is happening. If there is a trans input shaft speed sensor PID for the output of the torque converter, you can compare it to RPM to determine TCC status. Also I know you stated you checked the…

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Niall Owner/Technician
Stirling, United Kingdom
Niall Default
 

Hi Grant I tend to agree that the APPS is not causing the stall (although I still think its faulty), good direction to check g/box shifts etc will try and do that this evening. The position of the ECM on a right hand drive is a PITA on the right side jammed down beside the brake booster (for wiring checks). I will see if the Pico paddle probe can pick-up a decent waveform from the coils.

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
   

Drops outs are normal, I've read about that numerous times. As mentioned this is the era known for a bad coil spiking the ECM brain-dead. You may notice the I/M monitors all resetting at each stall. A scope should pick-up the extra noise on any ground for the worst coil. The guerilla method is to just buy one new coil, and then try it in each cylinder until the stalling is gone. Also OE brand…

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Niall: You've got me confused with this statement. "Coil current for all coils and primary voltage #1, is the current and voltage high because these are waste spark coils." I fail to see what the one has to do with the other. These are saturation type coils and will charge until turned off unless the circuit has built-in protection to prevent overheating. 17 amps is a tad much. Usually, a…

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Victor Owner/Technician
Doral, Florida
Victor Default
 

Any coil amp draw over 8 - 9 amps points to an unhealthy coil.

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
   

Hi Victor: Perhaps. Since this isn't a current limiting coil, it can't charge if the circuit isn't on. While it is true that a coil can ruin a module, the inverse is also true. Guido

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Victor Owner/Technician
Doral, Florida
Victor Default
 

So true​.​Maybe it is a case of either the chicken or the egg.

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Niall Owner/Technician
Stirling, United Kingdom
Niall Default
   

The amp probe is connected at the main fuse for all 8 coils each coils fires 2 sparkplugs ie coil fires one of the plugs on #1 cylinder and one the plugs on #6, the primary voltage is connected to the #1 coil trigger at the coil but all primary voltages were similar. I was only wondering that if the coil was only firing one plug it might run at 8A twice that for two plugs?. All 8 coils seem to…

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
   

Hi Niall: I can't see 1 coil firing 2 plugs, at that current, at the same time. The primary is turned on by whatever module is in charge of ignition. Since this is not a current limiting coil, the current will continue to rise until the circuit is turned off. I really can't make out your time for current charging. It would be helpful to take some time out of your scope and just show one…

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Niall Owner/Technician
Stirling, United Kingdom
Niall Default
 

"I really can't make out your time for current charging. It would be helpful to take some time out of your scope and just show one event." I am not sure what you are looking for the Pico file should have everthing. The coils I think are original 140k, the motor runs very nicely apart from the cutting out (over here we would say stall when the engine stops while pulling away, cutting out when it…

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Ray Diagnostician
North York, Ontario
Ray Default
   

On this system, COP 1 will fire the spark plugs in cyl 1 and in cyl 6 at the same time as in a waste spark system. The 8 COP primary coil windings are grounded by the PCM. The hard to see photo is the plug wires from the 8 COPs.

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Ray: Your capture shows over 17 Amps. I'll sit corrected. Guido

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Niall Owner/Technician
Stirling, United Kingdom
Niall Default
   

Hi Ray thanks for looking, thats exactly what we have. I have an idea for a test will try it today. Ran the engine at idle with the #6 plug lead from cylinder 1 COP shorted to ground made no difference at all to either current or voltage. Single screen Pico attached. The coil resistance measured with Milliohm meter is 0.644ohm

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Victor Owner/Technician
Doral, Florida
Victor Default
 

By applying ohms law I presume total current draw should be: 18 amps. Wow!

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Niall Owner/Technician
Stirling, United Kingdom
Niall Default
 

Hi Victor I have taken out a subscription on Alldata coil specs are … Ohm which is close to my reading, it looks like the 17 Amps I was getting is correct but yes WOW

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Victor Owner/Technician
Doral, Florida
Victor Default
 

All Data or Some Data?

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Ray Diagnostician
North York, Ontario
Ray Default
 

This capture is from an 07 Jeep 3.8. The first primary coil winding shows the good, normal 4.3A draw and the 3ms dwell time. The second primary coil winding is the same coil but the winding is now drawing 11A because the PCM is holding the winding to ground for 6ms. The coil winding ohm resistance did not change. On this vehicle, when the PCM determines that there is a misfire, the PCM will…

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Victor Owner/Technician
Doral, Florida
Victor Default
 

Great find.

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Ray Diagnostician
North York, Ontario
Ray Default
 

The first capture is your good COP primary winding voltage and amps. The second capture shows a bad COP primary winding voltage, where some of the secondary winding voltage is arcing into the primary winding. The negative 85v can shut down a PCM. If you have an 8 channel scope, you could scope all 8 COP primary voltages in the firing order and when the engine stalls, you see which COP has any…

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Niall Owner/Technician
Stirling, United Kingdom
Niall Default
 

Thanks Ray I have the 4425 and a 4 channel 3000 series and some other probes I​.​ll see if the laptop will be happy running two scopes or it might be two laptops. I did initially scope all of the COP coils individually they were all identical. Niall

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Ray Diagnostician
North York, Ontario
Ray Default
 

Set the scope to 500 ms/div at a high Sample rate and don't use any filters on the channels. I would scope 4 COP primary winding voltages at the same time while driving, when the engine is stalling. Save the capture, then you can zoom in afterwards, to each COP's spark times, to see which COP is bad. Then drive it again while scoping the other 4 COPs, until it stalls again. This capture is…

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Niall Owner/Technician
Stirling, United Kingdom
Niall Default
 

Hi Ray decided just to use the AutoScope (I don't have 8 attenuators 2 x 10 2 x 20), I am not seeing any big problems? Niall

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Ray Diagnostician
North York, Ontario
Ray Default
 

I don't see any misfires and the best Sample interval for ignition is 1 us. The PSD file is from an 05 Ford 5.4 with misfires during 1500 rpm brake torques but no misfires at idle. The misfires were fixed with new plugs.

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Niall Owner/Technician
Stirling, United Kingdom
Niall Default
 

Hi Ray thanks again for your time, lookin at your PSD Channel Mins A -55.78 B -47.5 C -59.2 D -55.07 at what voltage would you start getting concerned, also because they are all dropping low would that lead you towards the plugs.

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Ray Diagnostician
North York, Ontario
Ray Default
 

On any ignition system you need to focus on the spark arcing across the spark plug's air gap between the plug's center electrode to the plug's ground terminal in order to ignite the air/fuel mixture in the cylinder, as in the first GIF In the second GIF, CH C shows no misfire and the spark is arcing across the spark plug's air gap to the plug's ground terminal. In CH A, there is no spark…

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Niall Owner/Technician
Stirling, United Kingdom
Niall Delay
 

I may have to give the Jeep back to the customer and see if the problem gets any worse.

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