PicoScope 7 Automotive
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A problem shared…….
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Steve Smith
- Pico Staff Member
- Posts: 1587
- Joined: Sun Aug 25, 2013 7:22 am
A problem shared…….
A problem shared…….
We often receive several support requests where there is no logic behind how the vehicle is cured. (i.e., replace part “X” cured the problem)
The fact that replacing a component resolved the issue is great from a customer point of view but what about our perspective?
Can we learn something from the “fix” using post capture data or deep analysis of the failed component?
Most certainly we can but post fix data is a luxury and the time required to dismantle and further analyze failed parts is virtually non-existent
Below is one such example from our colleagues in the US; having chewed the fat for some days now we still cannot draw a conclusion as to why this vehicle demonstrated such symptoms:
Before I go on, a brief outline of how the engine management system is configured will help with interpretation of the included waveform
The vehicle below utilizes a PCM, Ignition control module (ICM), Crank sensor and Port injection
• The crank sensor reports engine speed to the ICM
• The ICM relays the engine speed signal to the PCM (@ twice the frequency of the original crank signal)
• The PCM then drives the injectors
• The ICM also incorporates an Ignition Diagnostic Monitor (IDM) signal and serves as a failure signal to the PCM in the event of an ignition fault (Similar to IGF signal for those that are familiar with Toyota)
I will lay the sequence of events out in bullet point form so as not to introduce any assumptions
Vehicle:
1994 Ford Ranger 2.3L, (4-Cylinder Petrol) Auto trans, Federal emissions, Dual-plug ignition system.
• Vehicle recovered to workshop as crank non-start
• Diagnosis confirmed loss of injector signal (i.e., no injector drive)
• Conclusion of diagnosis; Ignition control module (ICM) required (No engine speed signal to PCM)
• Customer authorized the replacement of ICM and a Timing belt (due to mileage)
• With the timing belt and ICM replaced (aftermarket ICM) the vehicle started and ran fine (N.B vehicle partially reassembled as alternator was not connected)
• Vehicle then fully reassembled and now starts and stalls
• Further diagnosis confirmed the stalling to be linked to battery voltage/charging
• Without charging, the ICM engine speed signal switched from approx. 0 - 6.5 V & engine runs OK
• With charging, the ICM engine speed signal switched from approx. 0 - 7.5 V & engine fails to run (no injector drive)
• With the alternator disconnected, engine runs fine, apply an external charger to the 12 V battery and the vehicle stalls (no injector drive)
• Replace the ICM for a genuine unit and the vehicle runs fine when charging (problem solved)
• The genuine ICM engine speed signal switched from 0 -11.5 V without charging and 0 - 11.9 V when charging!
To summarize the above, an aftermarket ICM resulted in the PCM failing to drive the fuel injectors when the battery receives charge from either the alternator or external charger
The image below captures the stall event when the vehicle is started without charging, then a 14 V charge is applied to the battery
Based on the above the million-dollar questions are :
Why did the engine run when ICM switched engine speed signal from 0 - 6.5 V?
Why did the engine fail to run/stall when ICM switched engine speed signal from 0 - 7.5 V?
I guess we could settle for the fact that the aftermarket ICM was not “fit for purpose” which would appear to be true, but it would be nice to know why?
Unfortunately, the aftermarket ICM was returned to the parts supplier and therefore cannot be dismantled for investigation
Any feedback/theories would be most welcome as I am sure between us, we can crack it
Take care……Steve
We often receive several support requests where there is no logic behind how the vehicle is cured. (i.e., replace part “X” cured the problem)
The fact that replacing a component resolved the issue is great from a customer point of view but what about our perspective?
Can we learn something from the “fix” using post capture data or deep analysis of the failed component?
Most certainly we can but post fix data is a luxury and the time required to dismantle and further analyze failed parts is virtually non-existent
Below is one such example from our colleagues in the US; having chewed the fat for some days now we still cannot draw a conclusion as to why this vehicle demonstrated such symptoms:
Before I go on, a brief outline of how the engine management system is configured will help with interpretation of the included waveform
The vehicle below utilizes a PCM, Ignition control module (ICM), Crank sensor and Port injection
• The crank sensor reports engine speed to the ICM
• The ICM relays the engine speed signal to the PCM (@ twice the frequency of the original crank signal)
• The PCM then drives the injectors
• The ICM also incorporates an Ignition Diagnostic Monitor (IDM) signal and serves as a failure signal to the PCM in the event of an ignition fault (Similar to IGF signal for those that are familiar with Toyota)
I will lay the sequence of events out in bullet point form so as not to introduce any assumptions
Vehicle:
1994 Ford Ranger 2.3L, (4-Cylinder Petrol) Auto trans, Federal emissions, Dual-plug ignition system.
• Vehicle recovered to workshop as crank non-start
• Diagnosis confirmed loss of injector signal (i.e., no injector drive)
• Conclusion of diagnosis; Ignition control module (ICM) required (No engine speed signal to PCM)
• Customer authorized the replacement of ICM and a Timing belt (due to mileage)
• With the timing belt and ICM replaced (aftermarket ICM) the vehicle started and ran fine (N.B vehicle partially reassembled as alternator was not connected)
• Vehicle then fully reassembled and now starts and stalls
• Further diagnosis confirmed the stalling to be linked to battery voltage/charging
• Without charging, the ICM engine speed signal switched from approx. 0 - 6.5 V & engine runs OK
• With charging, the ICM engine speed signal switched from approx. 0 - 7.5 V & engine fails to run (no injector drive)
• With the alternator disconnected, engine runs fine, apply an external charger to the 12 V battery and the vehicle stalls (no injector drive)
• Replace the ICM for a genuine unit and the vehicle runs fine when charging (problem solved)
• The genuine ICM engine speed signal switched from 0 -11.5 V without charging and 0 - 11.9 V when charging!
To summarize the above, an aftermarket ICM resulted in the PCM failing to drive the fuel injectors when the battery receives charge from either the alternator or external charger
The image below captures the stall event when the vehicle is started without charging, then a 14 V charge is applied to the battery
- Image 1
Why did the engine run when ICM switched engine speed signal from 0 - 6.5 V?
Why did the engine fail to run/stall when ICM switched engine speed signal from 0 - 7.5 V?
I guess we could settle for the fact that the aftermarket ICM was not “fit for purpose” which would appear to be true, but it would be nice to know why?
Unfortunately, the aftermarket ICM was returned to the parts supplier and therefore cannot be dismantled for investigation
Any feedback/theories would be most welcome as I am sure between us, we can crack it
Take care……Steve
Re: A problem shared…….
Just theory. Common mode voltage? Charger / alternator superimposed noise? Thus no icm filtering?