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[FIXED] 2006 Buick Lacrosse Random Stall
3 years 6 months ago #43663
by Noah
"Ground cannot be checked with a 10mm socket"
[FIXED] 2006 Buick Lacrosse Random Stall was created by Noah
I had this car idling outside while I was working on other cars all week. The stall was so random and the car always started right back up, so it was difficult to reproduce and observe the symptoms.
The following is a summary of the diagnostic process that tool place over the course of several days last week.
2006 Buick Lacrosse Base 3800
Unregistered but sold, so no road test.
Shop has changed the ignition switch and ignition control module. The car currently has the original ICM reinstalled.
Symptoms: Engine idles well but when warmed up will suddenly stall.
No warning, no rough running, stick-in-the-spokes stop.
60psi fuel pressure at all times with a trusted gauge.
Always restarts on the first try and runs smooth until the next random stall event.
Longer run time results in more frequent stalls.
During the stall the tell tale lamps do not illuminate, for example; the charging system lamp, oil pressure warning, etc. do not illuminate.
40% of the time the check engine lamp will illuminate (as it should during a stall) but most of the time it does not.
Message center does stay alive and continues to display the odometer and the cluster remains back lit.
Service information explains that the PCM requests the illumination of these lamps via single wires class 2 communication.
During the stall communication between the scan tool and PCM is momentarily lost, and always regained at the press of a button.
It is observed that communication with the body control module is not lost during the stall. PIDs indicate that ignition switch voltage in position 2 and 3 do not change according to the BCM.
No codes are stored in any modules. (I was hoping for U codes to give me some direction)
This engine uses the old school GM bypass waste spark ignition system with 2 reluctor wheels on the balancer creating a 3x crank sensor signal and an 18x signal.
18x, 3x CKP& CMP data appears normal until communication is lost when the engine stalls.
When observed with a lab scope, the 18x CKP signal is a regular square wave and never lost when the car stalls.
Service information states that the engine will continue to run with the loss of the 3x CKP or 18x CKP, so no attempt was made to verify the 3x signal with the scope.
With Vantage MT2400 graphing multimeter, it is observed that during the stall power is momentarily lost at the ignition control module as the engine stalls. It is a fraction of a second glitch. I believe it would be virtually impossible to catch it live with a digital multimeter.
Top trace is ICM voltage feed, bottom is battery voltage.
This power is fed to the ignition control module via the Power Train Relay. This is also the power for the fuel injectors and the electronic throttle body.
The power is simultaneously lost to all of these components.
Power to the fuse that feeds the load side of the Power Train Relay in the same fuse box is not lost during the stall.
The relay was exchanged for the horn relay in the absence of a suitable break out to the test feed and control circuit with the relay installed and the car running.
A bypass relay was used to replace the Power Train Relay, but the car still eventually stalled.
The under hood fuse box was disassembled and inspected for terminal issues, and the harness was inspected for rubbing, chafing or modification.
At this point the car ran for 2 hours an I was sure I accidentally fixed it, until it stalled again.
With the PCM removed from the air cleaner housing, ignition 1, ignition 3, battery voltage and ground are monitored with Verus lab scope and it is observed that there are no drop outs in the power feeds during the stall.
When observing PCM control of the ground side driver for the power train relay at the PCM connector, it is clear that the PCM momentarily drops the ground to the control side of the Power Train Relay as the ICM loses its power feed and the car stalls.
Because the PCM powers and ground never faultered during the stall, I suspect the PCM is to blame for the intermittent stall as it heats up and fails to keep the power train relay energized, fails to communicate, fails to illuminate warning lamps on the cluster and fails to set any trouble codes.
After multiple attempts to complete the 30 minute anti theft relearn, the car started and ran from 3:30 to 6:30pm. I am satisfied that this one is a fix!
The following is a summary of the diagnostic process that tool place over the course of several days last week.
2006 Buick Lacrosse Base 3800
Unregistered but sold, so no road test.
Shop has changed the ignition switch and ignition control module. The car currently has the original ICM reinstalled.
Symptoms: Engine idles well but when warmed up will suddenly stall.
No warning, no rough running, stick-in-the-spokes stop.
60psi fuel pressure at all times with a trusted gauge.
Always restarts on the first try and runs smooth until the next random stall event.
Longer run time results in more frequent stalls.
During the stall the tell tale lamps do not illuminate, for example; the charging system lamp, oil pressure warning, etc. do not illuminate.
40% of the time the check engine lamp will illuminate (as it should during a stall) but most of the time it does not.
Message center does stay alive and continues to display the odometer and the cluster remains back lit.
Service information explains that the PCM requests the illumination of these lamps via single wires class 2 communication.
During the stall communication between the scan tool and PCM is momentarily lost, and always regained at the press of a button.
It is observed that communication with the body control module is not lost during the stall. PIDs indicate that ignition switch voltage in position 2 and 3 do not change according to the BCM.
No codes are stored in any modules. (I was hoping for U codes to give me some direction)
This engine uses the old school GM bypass waste spark ignition system with 2 reluctor wheels on the balancer creating a 3x crank sensor signal and an 18x signal.
18x, 3x CKP& CMP data appears normal until communication is lost when the engine stalls.
When observed with a lab scope, the 18x CKP signal is a regular square wave and never lost when the car stalls.
Service information states that the engine will continue to run with the loss of the 3x CKP or 18x CKP, so no attempt was made to verify the 3x signal with the scope.
With Vantage MT2400 graphing multimeter, it is observed that during the stall power is momentarily lost at the ignition control module as the engine stalls. It is a fraction of a second glitch. I believe it would be virtually impossible to catch it live with a digital multimeter.
Top trace is ICM voltage feed, bottom is battery voltage.
This power is fed to the ignition control module via the Power Train Relay. This is also the power for the fuel injectors and the electronic throttle body.
The power is simultaneously lost to all of these components.
Power to the fuse that feeds the load side of the Power Train Relay in the same fuse box is not lost during the stall.
The relay was exchanged for the horn relay in the absence of a suitable break out to the test feed and control circuit with the relay installed and the car running.
A bypass relay was used to replace the Power Train Relay, but the car still eventually stalled.
The under hood fuse box was disassembled and inspected for terminal issues, and the harness was inspected for rubbing, chafing or modification.
At this point the car ran for 2 hours an I was sure I accidentally fixed it, until it stalled again.
With the PCM removed from the air cleaner housing, ignition 1, ignition 3, battery voltage and ground are monitored with Verus lab scope and it is observed that there are no drop outs in the power feeds during the stall.
When observing PCM control of the ground side driver for the power train relay at the PCM connector, it is clear that the PCM momentarily drops the ground to the control side of the Power Train Relay as the ICM loses its power feed and the car stalls.
Because the PCM powers and ground never faultered during the stall, I suspect the PCM is to blame for the intermittent stall as it heats up and fails to keep the power train relay energized, fails to communicate, fails to illuminate warning lamps on the cluster and fails to set any trouble codes.
After multiple attempts to complete the 30 minute anti theft relearn, the car started and ran from 3:30 to 6:30pm. I am satisfied that this one is a fix!
"Ground cannot be checked with a 10mm socket"
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