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Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
Automotive Troubleshooting With An Oscilloscope.
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Automotive Troubleshooting With An Oscilloscope.

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A local auto repair shop made several bad guesses at a church van's intermittent ignition issue, with costs totally about $1,600. Volunteering to determine the cause of the problem, I instrumented …

A local auto repair shop made several bad guesses at a church van's intermittent ignition issue, with costs totally about $1,600. Volunteering to determine the cause of the problem, I instrumented engine ignition signals, set the oscilloscope to trigger on engine shutdown, and drove the van around town for about 3 months until the failure mechanism was revealed.

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  • 1. My Adventures With an Old Church Van by Jeffrey Bledsoe 4/24/2012 Amended 6/22/2012 Corrected 5/25/2013 Jeffrey Bledsoe, PE, MSEE
  • 2. WARNING Some of the images in this presentation are ‘graphic’ and may cause emotional distress to anyone who’s ever: • Paid a repair shop $1,000’s for repairs that didn’t fix their vehicle’s problem • Attempted to troubleshoot their vehicle after spending those $1,000’s Apologies to electrical engineers for the “bathtub” metaphor used in the Excel graph annotations. VIEWER DISCRETION IS ADVISED Jeffrey Bledsoe, 4/24/2012 Charts amended 6/22/2012 by adding the Christian Brothers Invoice dated 12/3/2010. Charts corrected 5/25/2013: (1) Corrected the date for the first visit to CBA in slide # 3. (2) Changed “inverter return” to “inverter safety ground” in one of the photo’s annotations. Jeffrey Bledsoe, PE, MSEE
  • 3. Background: A Church Van’s* Intermittent Ignition Failures •Random/intermittent engine shutdown • • • After shutdown, engine wouldn’t restart, usually restarted ~ 10 minutes later No correlation of failures with weather or driving habits No diagnostic codes were stored and Check Engine Light was never illuminated •Christian Brothers Automotive (CBA) Efforts • CBA attempted unsuccessfully to find the problem during 2 visits over a period of 6 months • 12/3/2010: CBA replaced crankshaft sensor, $392.97 charge • 5/27/2011: CBA replaced several other parts, ~ $1,230.76 charge* • $1,623.73 total paid to Christian Brothers Automotive in Weatherford TX *Included $70 fuel charge * Emmanuel Baptist Church’s Dodge Passenger Van, VIN = 2B5WB35Z6RK551308 Jeffrey Bledsoe, PE, MSEE
  • 4. Background: A Church Van’s* Intermittent Ignition Failures •Christian Brothers Automotive (CBA) Efforts, 12/3/2010 Invoice • • • • Diagnostics methods and results were ‘fuzzy’ $392.97 total parts and labor Replaced Crankshaft Sensor Result: Van exhibited same failure about five times over the next few months •Christian Brothers Automotive (CBA) Efforts, 5/27/2011 Invoice • • • • No engine failures while in possession of CBA (according to our youth minister) CBA did the following: • Ran engine performance diagnostics (no problems reported in receipt) • Replaced fuel pump • Replaced IAC Motor (Idle Air Control Motor) • Replaced ASD Relay (Automatic Shutdown Relay) • Inspected for damage caused by mice (LOL) • Refueled the van • Washed the van $1,230.76 total parts and labor cost to the church (including $70 for fuel) Van returned to church on 5/27/2011 • Van failed within a week while fetching children for Vacation Bible School • Same failure symptoms as usual; and same ones observed before both visits to CBA •I volunteered to troubleshoot the problem, starting 6/10/2011 * Emmanuel Baptist Church’s Dodge Passenger Van, VIN = 2B5WB35Z6RK551308 Jeffrey Bledsoe, PE, MSEE
  • 5. Jeffrey Bledsoe, PE, MSEE
  • 6. Most likely, engine was occasionally missing due to marginal coil drive What were the retest results? Did replacing the crank sensor fix it? I don’t think so. Jeffrey Bledsoe, PE, MSEE
  • 7. Jeffrey Bledsoe, PE, MSEE
  • 8. No charge for rodentia damage inspection.(LOL). Free wash! Jeffrey Bledsoe, PE, MSEE
  • 9. Jeffrey Bledsoe, PE, MSEE
  • 10. Background: A Church Van’s* Intermittent Ignition Failures (cont’d) •Fault Isolation and Repair by Jeffrey Bledsoe • • 6/10/11: Rigged timing light to a spark plug and bought alldatadiy.com account 6/23/11: Determined that spark was not present during failure to restart • From alldatadiy.com descriptions and schematics, 2 probable causes: • Probable cause #1: ASD dropout after loss of crank and/or cam signals • Probable cause #2: Intermittent coil driver (in PCM) or intermittent coil • • • • • 9/3/2011: Eliminated crank and cam position signals as cause of failures 9/10/2011: Discovered failed coil driver in the Powertrain Control Module (PCM) 11/4/2011: Replaced PCM 1,800 miles later, no failures (miles driven 11/6/2011 thru 04/15/2012) • Several trips to Fort Worth • One mission trip to Port Arthur, near Houston Jeff’s troubleshooting costs =~ $575 • $25 for alldatadiy.com account for the van • $70 for insulation-piercing probes • ~$250 for fuel for test drives (~ 700 miles driven over 5 months) • $230 for new PCM • ~ 40 hours of research, analysis, and study + ~30 hours of test drives • The experience: priceless * Emmanuel Baptist Church’s Dodge Passenger Van, VIN = 2B5WB35Z6RK551308 Jeffrey Bledsoe, PE, MSEE
  • 11. TROUBLESHOOTING TIMELINE FOR A 1994 DODGE B350 VAN*, JUN-NOV 2011 ACTIVITY Milestones Initial Data Gathering •Is spark present during failure? •Opened alldatadiy.com account Instrumentation JUNE Installed Timing Van Died, Light No Spark (6/10) (6/23) 06/10 JULY Set up scope and collected baseline data (7/21) AUG Van Died, Cam and Crk Sensors Are Good (9/3) 2 WK VACATION SEPT OCT NOV Install/Test Van Died, Bad Coil Tested Ordered PCM (11/4 Road Drive Signal new PCM & 11/5) Tested Wiring (9/10) PCM Vibe Good @ PCM (10/28) Tests (9/24) (11/6) (10/24) 06/23 06/24 07/21 •Schematics •Parts Procurement •Installation Sensor Tests 07/21 09/03 •Crank and Cam Sensors •8Vdc Pwr/Rtn (power to sensors) •ASD (Auto Shutdown Command) PCM Driver Tests 09/04 09/10 •Cam and Crank Sensors •PCM’s Coil Driver •PCM’s Fuel Injector #1 Driver Final Tests / Analyses 09/11 •Vibration and Wiring Tests •Data Analysis •Ordered Remanufactured PCM Resolution 10/28 11/04--11/06 •Installed new PCM •Test Drove to Fort Worth twice •Project End * VIN 2B5WB35Z6RK551308 Jeffrey Bledsoe, PE, MSEE
  • 12. Schematic With Key Signals •Key signals: based on research at alldatadiy.com •Van schematic only, i.e., no instrumentation •1 slide Jeffrey Bledsoe, PE, MSEE
  • 13. SCHEMATIC, KEY PCM AND SENSOR SIGNALS, 1994 DODGE B350 VAN PCM (Powertrain Control Module) Cam Sensor Cam Sense Crank Sense Crank Sensor 8 Vdc 8 Vdc Rtn 12 V from Ignition Sw 12 V from Battery ASD Relay Contact ASD Relay Coil ASD Driver* Coil Driver* Fuel Inj #1 Driver* Ignition Coil Primary Winding Fuel Injector #1 Solenoid 12 V from ASD • ASD == Automatic Shut Down • * Open/Ground drivers inside PCM Jeffrey Bledsoe, PE, MSEE
  • 14. Sensor Test Results •Instrumentation Schematic (1 slide) •Annotated Waveforms (3 slides) •Sensor Test Conclusions (1 slide) Jeffrey Bledsoe, PE, MSEE
  • 15. INSTRUMENTATION OF SENSORS, SENSOR POWER, AND ASD DRIVER PCM (Powertrain Control Module) Cam Sensor Cam Sense Crank Sense Crank Sensor 8 Vdc 8 Vdc Rtn 12 V from Ignition Sw 12 V from Battery ASD Relay Contact ASD Relay Coil Scope** 5 kΩ Ch 1 5 kΩ Ch 2 ASD Driver * Coil Driver * Fuel Inj #1 Driver * Ignition Coil Primary Winding 5 kΩ Fuel Injector #1 Solenoid 5 kΩ 12 V from ASD Ch 3 5 kΩ (At TB) 5 kΩ Ch 4 5 kΩ • ASD == Automatic Shut Down • * Open/Ground drivers inside PCM • ** Scope floated with an AC cheater plug Insulation-piercing probe Resistors built-in to harness Ext Trig Terminal Block (TB) Van Structure Jeffrey Bledsoe, PE, MSEE
  • 16. Here are the baseline waveforms with the van running okay Note: Because of the voltage divider made up of three 5 kΩ resistors, displayed voltages for 8V power (green scope trace above) are MSEE Jeffrey Bledsoe, PE, less than 8 V; voltage can be calculated at ~= 0.7 X the actual voltage. Q: Why the voltage divider? A: To detect either a defective 8V power source or a defective 8V power return. If the voltage went to ~8V during a failure, this would indicate a defective 8V return path in the PCM. If the voltage went much lower than ~6V during a failure, this would indicate a defective 8V power rail or open-circuited conductor inside the PCM. (The scope was “floated” and referenced to a local structure ground, thus allowing one scope channel to provide information on the health of two signals (8V power and 8V power return). Of course, in the unlikely event that both 8 V and 8 V return failed, the voltage at the scope would tend toward 0 V as well. Jeffrey Bledsoe, PE, MSEE
  • 17. After many days of test drives, the van died on 9/3/2011 Note: Because of the resistor divider, voltages for 8V power are approximately 0.7 X actual voltage ASD driver opens ~ 375 ms after last crank sensor pulse (maroon trace). Cam sensor (blue trace) is still at logic ‘1’ when ASD opens. Trigger at t = 0, PCM says “game over”, ASD driver opens, voltage transitions to 13 V as observed via the ASD relay coil. Jeffrey Bledsoe, PE, MSEE
  • 18. Crank and Cam Sensors Are Good During No-Restart (See blue(CAM) and maroon(CRANK) scope traces below) Scope trigger at t = 0……..ASD driver opens, ASD voltage transitions to ~ 11 V shortly after key  off Notes: 1. Because of the resistor divider, voltages for 8V power are approximately 0.7 X actual voltage. 2. Had to power the inverter from my truck battery via jumper cables because the van battery voltage was too low to run the inverter during engine cranking. Jeffrey Bledsoe, PE, MSEE
  • 19. Conclusions from Sensor Tests •The shutdown waveform shows active crank sensor pulses until ~375 milliseconds before ASD drops out; likely too short a time to have caused the ASD dropout. •The “No Restart” waveform shows conclusively that the cam and crank position sensors are functional during a “no restart” scenario; attempts at restarting the engine lasted 5 to 10 seconds, with cam and crank signals active during the entire period; the waveform shows only the last ~2 seconds of activity before key-off and ASD dropout, triggering the scope. •There was the possibility that, although I could see the cam and crank signals on the scope, one or both sensor signals were not observable by the PCM. However, if the PCM lost either of these inputs, it should have activated the Check Engine Light and flagged a sensor failure. (After failures, the check engine light never turned on and no failure codes were stored.) •The next logical step was to reconfigure the instrumentation to look at other high potential signal failures. The first signal on the list was the coil driver, i.e., monitoring a wire between the PCM and the ignition coil. {According to a Dodge service manual*, the PCM has no diagnostics on the output of this driver (most likely, newer vehicles detect failures in the coil driver(s)).} For information, I decided to also monitor one of the fuel injector drivers. *John Hagan’s Service Manual for his 1994 Dodge Dakota, i.e., not the fullsize van. Jeffrey Bledsoe, PE, MSEE
  • 20. PCM Coil Driver Test Results •Instrumentation Schematic (1 slide) •Annotated Waveforms (6 slides) •Coil Driver Test Conclusions (1 slide) Jeffrey Bledsoe, PE, MSEE
  • 21. INSTRUMENTATION OF SENSORS PLUS COIL AND FUEL INJECTOR DRIVERS PCM (Powertrain Control Module) Cam Sensor Cam Sense Crank Sense Crank Sensor 8 Vdc 8 Vdc Rtn 12 V from Ignition Sw 12 V from Battery ASD Relay Contact ASD Relay Coil Scope** 5 kΩ Ch 1 5 kΩ Ch 2 ASD Driver * Coil Driver * Fuel Inj #1 Driver * Ignition Coil Primary Winding 5 kΩ Fuel Injector #1 Solenoid 5 kΩ 12 V from ASD Ch 3 5 kΩ (At TB) 5 kΩ Ch 4 5 kΩ • ASD == Automatic Shut Down • * Open/Ground drivers inside PCM • ** Scope floated with an AC cheater plug Insulation-piercing probe Resistors built-in to harness Ext Trig Terminal Block Van Structure (TB) Jeffrey Bledsoe, PE, MSEE
  • 22. BASELINE DRIVER WAVEFORMS, SHOWING ON-TIMES AND OFF-TIMES, (THINK OF THE ON-TIMES AS LITTLE BATHTUBS STORING ENERGY TO BE RELEASED) Baseline coil and injector driver waveforms (van running normally), 9/8/2011 CAM (v) 195.00 CRK (v) COIL (V) INJ #1 (V) Note: The coil driver voltage data was corrected (multiplied by 3/2) to account for the voltage divider left over from the 8V power/return sense scheme. 185.00 175.00 165.00 ~ 200 V on coil primary, at beginning of off-time, produces several thousand volts on the coil secondary, which is routed to the spark plugs via the distributor. 155.00 145.00 135.00 Typical Injector #1 Driver Off-Time 125.00 105.00 Typical Coil Driver Off-Time 95.00 Typical Injector #1 Driver On-Time 85.00 (during this bathtub/on-time, fuel is delivered to cylinder #1) Typical Coil Driver On-Time 75.00 (during this bathtub/on-time, current saturates the coil primary winding.) 65.00 55.00 45.00 35.00 25.00 15.00 5.00 25 20 15 5 10 0 -5 -10 -15 -20 -25 -30 -35 -40 -45 -50 -55 -60 -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 -130 -135 -140 -145 -150 -155 -160 -165 -170 -175 -180 -185 -190 -195 -200 -205 -210 -215 -220 -5.00 -225 Voltage, V 115.00 Time, milliseconds Little green bathtubs: coil-driver on-times Jeffrey Bledsoe, PE, MSEE
  • 23. CAPTURED DRIVER WAVEFORMS DURING ENGINE SHUTDOWN ON 9/10/11 Engine Shutdown at home, 9/10/2011 Note: Last good coil pulse was at -713 ms; note annotations concerning pre-pulse voltage levels. CAM (v) 50 CRK (v) COIL (V) INJ #1 (V) Note: The coil driver voltage data was corrected (multiplied by 3/2) to account for the voltage divider left over from the 8V power/return sense scheme. 45 ABNORMAL COIL DRIVER VOLTAGES IN THIS PERIOD 40 •DRIVER OUPUT IS PRESENT BUT DEGRADED •DRIVER CAN’T SATURATE THE COIL PRIMARY (NO NICE SOLID BATHTUBS, NO SPARK TO SPARK PLUGS) •STRANGE RINGING ON THE SIGNAL •THE LOW LEVEL SHIFTED TO AS LOW AS -5V •EVEN BEFORE ENGINE SHUTDOWN, BATHTUBS ARE AT -3V •NOTICE THE INJECTOR #1 BATHTUBS NEAR 0 V 35 Voltage, V 30 25 ASD DROPS OUT, 12 V IS REMOVED FROM COIL AND INJECTOR, SCOPE TRIGGERS 20 15 COIL DRIVER RINGING 10 5 12 V 0 -5 -850 -750 -650 -550 -450 -350 -250 -150 -50 50 150 250 Time, milliseconds The last green bathtub before shutdown. Jeffrey Bledsoe, PE, MSEE
  • 24. ZOOM-IN ON DRIVER WAVEFORMS DURING ENGINE SHUTDOWN ON 9/10/11 Engine Shutdown at home (zoom-in), 9/10/2011 Note: Last good coil pulse was at -713 ms; note annotations concerning pre-pulse voltage levels. CAM (v) CRK (v) COIL (V) INJ #1 (V) Note: The coil driver voltage data was corrected (multiplied by 3/2) to account for the voltage divider left over from the 8V power/return sense scheme. 20 15 Voltage, V 10 5 12 V 0 -5 -850 -840 -830 -820 -810 -800 -790 -780 -770 -760 -750 -740 -730 -720 Time, milliseconds -710 -700 -690 -680 -670 -660 -650 -640 -630 -620 -610 -600 The last green bathtub before shutdown. Jeffrey Bledsoe, PE, MSEE
  • 25. CAPTURED DRIVER WAVEFORMS WHEN THE ENGINE WOULDN’T RESTART Notes: 1. The coil driver voltage data was corrected (multiplied by 3/2) to account for the voltage divider left over from the 8V power/return sense scheme. 2. Had to power the scope via an extension cord from the garage because the van battery voltage was too low to run the inverter during engine cranking. •NO COIL BATHTUBS AT ALL •COIL DC LEVEL AT 6 V, INJ #1 AT 10 V Jeffrey Bledsoe, PE, MSEE
  • 26. ZOOM-IN ON DRIVER WAVEFORMS WHEN THE ENGINE WOULDN’T RESTART Notes: 1. The coil driver voltage data was corrected (multiplied by 3/2) to account for the voltage divider left over from the 8V power/return sense scheme. 2. Had to power the scope via an extension cord from the garage because the van battery voltage was too low to run the inverter during engine cranking. •NO COIL BATHTUBS AT ALL •COIL DC LEVEL AT 6 V, INJ #1 AT 10 V 120-130 ms zoom-in on next page Jeffrey Bledsoe, PE, MSEE
  • 27. ZOOM-IN ON DRIVER WAVEFORMS AT 120-130 ms DURING NO-RESTART Notes: 1. The coil driver voltage data was corrected (multiplied by 3/2) to account for the voltage divider left over from the 8V power/return sense scheme. 2. Had to power the scope via an extension cord from the garage because the van battery voltage was too low to run the inverter during engine cranking. •NO COIL BATHTUBS AT ALL •COIL DC LEVEL AT 6 V, INJ #1 AT 10 V WAVEFORM TOO SPIKEY TO SATURATE TRANSFORMER’S PRIMARY Jeffrey Bledsoe, PE, MSEE
  • 28. Conclusion from Driver Tests •Shutdown waveform shows cessation of good coil driver pulses at about 713 ms before ASD dropout. •The “No Restart” waveform indicates a malfunctioning coil driver circuit; the sensor signals continue to look good. Several coil waveform abnormalities were noted on the prior charts; the most important one is lack of coil saturation, i.e., no “bathtubs, during restart attempts.” •I concluded that the PCM’s coil driver or the coil driver pin at the PCM was failing intermittently. •The engine failure remained intermittent and I was able to drive the van around town, risking a shutdown (as usual) in the middle of heavy main street traffic. I decided to try and induce the PCM failure with a source of vibration and to test/inspect the connector pins at the PCM and at the harness connector that mates with the PCM. Jeffrey Bledsoe, PE, MSEE
  • 29. Further Tests at the PCM •I tried to induce the PCM failure by running the engine with the scope ready to trigger while vibrating the PCM and firewall of the van with a large pneumatic chiseling tool*. The engine didn’t die, the scope didn’t trigger. •I removed the PCM connector and backshell and tested continuity of the coil driver wire to the coil driver mating pin while wiggling the wire in the connector backshell. Also tested the 3 returns (ground lines would provide a current path for the coil driver) at the PCM connector in the same way. No continuity problems at those 4 pins. All connector pins looked good on both the PCM and the mating connector: no corrosion, no bent pins. *Provided by John Hagan onsite at Moore Monuments Jeffrey Bledsoe, PE, MSEE
  • 30. Resolution •Based on the scope data, the PCM’s coil driver was failing intermittently. I didn’t understand the failure mechanism and had hoped the external vibration would induce the failure. •I ordered and installed a remanufactured A-1 Cardone PCM from O’Reilly’s Auto Parts •No “engine shutdown” incidents during the ~1,800 miles since replacing the PCM. Jeffrey Bledsoe, PE, MSEE
  • 31. Pictures of Instrumentation Jeffrey Bledsoe, PE, MSEE
  • 32. Tektronix TDS2024C Oscilloscope Bungee cords for scope restraint My Bent C-Clamp holding wood block to Ashtray Signal Wiring Wood Block Terminal Block mounted on wood block 4 Scope Probes Coax cable connected to Scope’s Ext Trigger Jeffrey Bledsoe, PE, MSEE
  • 33. Scope chassis isolated from inverter safety ground with cheater plug (orange) 100 W Inverter Scope chassis connected to the van’s structure Scope Power Cord/Plug My Bent Cam Crank 8V/Rtn ASD Thumb Drive for storing captured data Jeffrey Bledsoe, PE, MSEE
  • 34. Signal and Power Wiring Routed on Dashboard, secured with duct tape. My Bent Jeffrey Bledsoe, PE, MSEE
  • 35. Power Wiring Inside Convoluted Tubing EZ-HOOK Macro Probes (insulationpiercing probes) Signal Wiring Inside Convoluted Tubing Piece of wood trim supporting probes Battery Post Clamps: Power for the inverter. Jeffrey Bledsoe, PE, MSEE
  • 36. I “adjusted” the hood structure with a hammer to minimize pinching of cables as they exit the engine area. Signal and power wiring secured to outside of van with duct tape. Jeffrey Bledsoe, PE, MSEE
  • 37. Black Box: Powertrain Control Module (PCM) 60-pin connector that mates with PCM (removed by loosening this bolt) 40 wires in the bundle at the PCM connector (using the schematic and wire color data from alldatadiy.com, I hunted for the six signals of interest) Jeffrey Bledsoe, PE, MSEE

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