help with GM E67 ECM on LS3...... troubleshooting
07-24-2023, 10:13 PM
#1
help with GM E67 ECM on LS3...... troubleshooting I'm out of ideas trying to find fault in ECM system.... engine ran great for years and then suddenly one day it immediately began to run rough and displayed several codes, everything from crank sensor to ECT. reference power bank faults.
I performed the normal troubleshooting such as checking for good grounds, quality of 5 volt reference circuit, removing all loads on the harness system and checking quality of wires under a load. All, we're good, Even the two grounds on each ECM under load when viewed on a scanner scope.
strange thing now is the crank sensor circuit is extremely sensitive when you move most any CKP wires in the harness... often just moving wires will cause the fuel pump to cycle on for three or seconds as it normally would on key ignition. when turning in ignition varios codes often trip, AAI check the faults and freeze data at time DTCs set, it sometimes shows inteal RPM of 1200 ish and/or temps much higher than what's indicated on dash. There is no damaged wires shorting, often just moving a wire slightly near another will start the pumps. I
Thinking this was likely a magnetic field on the CKP, I carefully inspected all wires without luck.
i don't believe problem is a sensor, as most indications are correct even with the false displaying. with the crank sensor wires hunting for a ground so much, I thought it was a bad ground somewhere in the system, but I have checked all grounds and their solid right back to the battery negative terminal even under a load such as a starter motor.
I expect that somehow I'm feeding bad power up that circuit that controls most of the faults displayed. not sure where to go next other than to run test wires directly to each sensor that's displayed faults to bypass any issues in the harness.
any suggestions? appreciate it. I'm in the Colorado springs area if anyone can recomend a guru for repairing this sort of problem
I performed the normal troubleshooting such as checking for good grounds, quality of 5 volt reference circuit, removing all loads on the harness system and checking quality of wires under a load. All, we're good, Even the two grounds on each ECM under load when viewed on a scanner scope.
strange thing now is the crank sensor circuit is extremely sensitive when you move most any CKP wires in the harness... often just moving wires will cause the fuel pump to cycle on for three or seconds as it normally would on key ignition. when turning in ignition varios codes often trip, AAI check the faults and freeze data at time DTCs set, it sometimes shows inteal RPM of 1200 ish and/or temps much higher than what's indicated on dash. There is no damaged wires shorting, often just moving a wire slightly near another will start the pumps. I
Thinking this was likely a magnetic field on the CKP, I carefully inspected all wires without luck.
i don't believe problem is a sensor, as most indications are correct even with the false displaying. with the crank sensor wires hunting for a ground so much, I thought it was a bad ground somewhere in the system, but I have checked all grounds and their solid right back to the battery negative terminal even under a load such as a starter motor.
I expect that somehow I'm feeding bad power up that circuit that controls most of the faults displayed. not sure where to go next other than to run test wires directly to each sensor that's displayed faults to bypass any issues in the harness.
any suggestions? appreciate it. I'm in the Colorado springs area if anyone can recomend a guru for repairing this sort of problem
07-25-2023, 08:20 AM
#3
I have 3 ECUs and all have same issue so not ECU which was my first conclusion as well.
It seems like a bad ground issue but all ECU grounds look good and test lest than .2 volts under load such as starter …..the ECU has 2 grounds and measured this voltage from bat terminal. . As the faults occasionally show DTCs for other sensors such as CMS and almost always ECT besides the ever present CKP, it indicates to me it’s likely a grounding issue but I can’t find it.
On key power up when faults occur immediately (engine not running) freeze data may indicate a RPM of about 1200 or ECT of 150F when engine is cold. So it’s seeing bad info as soon as power is supplied…….but other times there are no faults until engine runs for a while.
I know I am missing something likely obvious but I am out of ideas what it is.
It seems like a bad ground issue but all ECU grounds look good and test lest than .2 volts under load such as starter …..the ECU has 2 grounds and measured this voltage from bat terminal. . As the faults occasionally show DTCs for other sensors such as CMS and almost always ECT besides the ever present CKP, it indicates to me it’s likely a grounding issue but I can’t find it.
On key power up when faults occur immediately (engine not running) freeze data may indicate a RPM of about 1200 or ECT of 150F when engine is cold. So it’s seeing bad info as soon as power is supplied…….but other times there are no faults until engine runs for a while.
I know I am missing something likely obvious but I am out of ideas what it is.
07-25-2023, 08:00 PM
#4
Moderator
Instead of "checking grounds", I make temporary new grounds with a 10 gauge wire connected directly to the battery and with the other end connected to e.g. the ECU case, the firewall, the front core support, behind the dash, even the engine block.
However the sensitivity to movement of the harness suggests something else/additional is going on.
Hopefully you figure it out; please then give us an update.
However the sensitivity to movement of the harness suggests something else/additional is going on.
Hopefully you figure it out; please then give us an update.
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G Atsma (07-25-2023)
07-27-2023, 11:46 PM
#5
Thanks for advice….early on used jumper cables to add additional ground from bat to engine block, to no affect, Current faults remain CKP & ECT so I made basically a jumper to bypass harness and feed ECM directly to sensor, but no affect.
the Problem (and fault codes) occurs at ignition key on ( not start position) as I can view engine data snap shot at time the faults set. Almost always I see a high RPM and ECT even though engine is cold. I’m speculating that there is a bad ground that is not sinking the initial electrical power rush when key is turned on but both ECM grounds are less than .2V between them and the battery negative terminal under load. Also tried grounding ECM case without any affect.
occasionally, I don’t get any faults with key up or start and engine runs normal for a short term before faults reoccur and engine immediately runs poor…. This leads me to believe all sensors, injectors and ignition modules as well as ECM is fine….and problem lies in wiring.
open to all suggestions.
the Problem (and fault codes) occurs at ignition key on ( not start position) as I can view engine data snap shot at time the faults set. Almost always I see a high RPM and ECT even though engine is cold. I’m speculating that there is a bad ground that is not sinking the initial electrical power rush when key is turned on but both ECM grounds are less than .2V between them and the battery negative terminal under load. Also tried grounding ECM case without any affect.
occasionally, I don’t get any faults with key up or start and engine runs normal for a short term before faults reoccur and engine immediately runs poor…. This leads me to believe all sensors, injectors and ignition modules as well as ECM is fine….and problem lies in wiring.
open to all suggestions.