Ecm?
Thread Starter
Racer
Joined: Sep 2005
Posts: 304
Likes: 1
From: Carson City Nevada
Ecm?
Hi Guys, I have an interesting one. Testing my EGR solenoid on my 86, it doesn't do anything, no vacuum to the EGR. However, when I plug in my scanner, It magically starts functioning correctly. It's like it goes into diagnostic mode and all is well. The second I turn off the scanner, nothing again. The car also runs rough and comes up with the occasional 33 code and misses really bad when driving. I am thinking the ECM is no good, what do you think?
Race Director
Joined: Mar 2015
Posts: 15,926
Likes: 579
Not sure if this will help. But found this.
With the 86 cars,the green wire on the MAF connector needs to be checked.Check the connector and be sure it isnt broken.
Make sure there isnt a short in that wire.
Heres a list of things to check the tech should do before diangosing the fix ahead of time.I got this out of a book I have.
Clear codes and run the car...does code come back?
If YES,connect a digital voltmeter to the dark green wire at the MAF sensor.
Turn the ignition switch to "on" not start the car and note the voltage.
If near 0 volts,check the voltage at the termninal B12 at the ECM.
If theres 5 volts there,the ECM is good and you have a break or short in the dark green wire somewhere.If no 5 volts,and the connection is good there at the ECM,have them install a new or try a new ECM to see that fixes the problem.
(dont pay for it or take it if it doesnt)
Going back to the MAF test on the green wire,if there IS 5 volts on that wire,check the purple wire for 12 volts at the MAF with the engine running.
If theres 12 volts, the sensor is BAD.
If theres no 12 volts,apply 12 volts to the ALDL connector to terminal "G" on the purple wire to the MAF.
IS there now 12 volts at the MAF purpe wire?
If Yes,check the fuel pump fuse.If the fuse is OK,replace the oil pressure sending unit.
If No voltage,then check the wiring to the MAF power relay.If the wiring is good,replace the MAF power relay or recheck the connections there.
With the 86 cars,the green wire on the MAF connector needs to be checked.Check the connector and be sure it isnt broken.
Make sure there isnt a short in that wire.
Heres a list of things to check the tech should do before diangosing the fix ahead of time.I got this out of a book I have.
Clear codes and run the car...does code come back?
If YES,connect a digital voltmeter to the dark green wire at the MAF sensor.
Turn the ignition switch to "on" not start the car and note the voltage.
If near 0 volts,check the voltage at the termninal B12 at the ECM.
If theres 5 volts there,the ECM is good and you have a break or short in the dark green wire somewhere.If no 5 volts,and the connection is good there at the ECM,have them install a new or try a new ECM to see that fixes the problem.
(dont pay for it or take it if it doesnt)
Going back to the MAF test on the green wire,if there IS 5 volts on that wire,check the purple wire for 12 volts at the MAF with the engine running.
If theres 12 volts, the sensor is BAD.
If theres no 12 volts,apply 12 volts to the ALDL connector to terminal "G" on the purple wire to the MAF.
IS there now 12 volts at the MAF purpe wire?
If Yes,check the fuel pump fuse.If the fuse is OK,replace the oil pressure sending unit.
If No voltage,then check the wiring to the MAF power relay.If the wiring is good,replace the MAF power relay or recheck the connections there.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Depending on scanner you maybe be in aldl mode vs road test mode. ALDL mode ECM is in default operation, which can cover up some drivability concerns. Road test mode ECM is operating using the inputs from sensors. Do you have FSM? I think you need more diagnosis.
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 41
From: Baltimore, MD USA
Hi Guys, I have an interesting one. Testing my EGR solenoid on my 86, it doesn't do anything, no vacuum to the EGR. However, when I plug in my scanner, It magically starts functioning correctly. It's like it goes into diagnostic mode and all is well. The second I turn off the scanner, nothing again. The car also runs rough and comes up with the occasional 33 code and misses really bad when driving. I am thinking the ECM is no good, what do you think?
You can energize the egr solenoid by connecting Pin A to Pin B on the diagnostic connector and turning the ignition On. The egr solenoid should energize and the vacuum input path to the output path should be blocked.
Last edited by Hooked on Vettes; Sep 12, 2016 at 11:48 AM.
Thread Starter
Racer
Joined: Sep 2005
Posts: 304
Likes: 1
From: Carson City Nevada
Not sure if this will help. But found this.
With the 86 cars,the green wire on the MAF connector needs to be checked.Check the connector and be sure it isnt broken.
Make sure there isnt a short in that wire.
Heres a list of things to check the tech should do before diangosing the fix ahead of time.I got this out of a book I have.
Clear codes and run the car...does code come back?
If YES,connect a digital voltmeter to the dark green wire at the MAF sensor.
Turn the ignition switch to "on" not start the car and note the voltage.
If near 0 volts,check the voltage at the termninal B12 at the ECM.
If theres 5 volts there,the ECM is good and you have a break or short in the dark green wire somewhere.If no 5 volts,and the connection is good there at the ECM,have them install a new or try a new ECM to see that fixes the problem.
(dont pay for it or take it if it doesnt)
Going back to the MAF test on the green wire,if there IS 5 volts on that wire,check the purple wire for 12 volts at the MAF with the engine running.
If theres 12 volts, the sensor is BAD.
If theres no 12 volts,apply 12 volts to the ALDL connector to terminal "G" on the purple wire to the MAF.
IS there now 12 volts at the MAF purpe wire?
If Yes,check the fuel pump fuse.If the fuse is OK,replace the oil pressure sending unit.
If No voltage,then check the wiring to the MAF power relay.If the wiring is good,replace the MAF power relay or recheck the connections there.
With the 86 cars,the green wire on the MAF connector needs to be checked.Check the connector and be sure it isnt broken.
Make sure there isnt a short in that wire.
Heres a list of things to check the tech should do before diangosing the fix ahead of time.I got this out of a book I have.
Clear codes and run the car...does code come back?
If YES,connect a digital voltmeter to the dark green wire at the MAF sensor.
Turn the ignition switch to "on" not start the car and note the voltage.
If near 0 volts,check the voltage at the termninal B12 at the ECM.
If theres 5 volts there,the ECM is good and you have a break or short in the dark green wire somewhere.If no 5 volts,and the connection is good there at the ECM,have them install a new or try a new ECM to see that fixes the problem.
(dont pay for it or take it if it doesnt)
Going back to the MAF test on the green wire,if there IS 5 volts on that wire,check the purple wire for 12 volts at the MAF with the engine running.
If theres 12 volts, the sensor is BAD.
If theres no 12 volts,apply 12 volts to the ALDL connector to terminal "G" on the purple wire to the MAF.
IS there now 12 volts at the MAF purpe wire?
If Yes,check the fuel pump fuse.If the fuse is OK,replace the oil pressure sending unit.
If No voltage,then check the wiring to the MAF power relay.If the wiring is good,replace the MAF power relay or recheck the connections there.
Thread Starter
Racer
Joined: Sep 2005
Posts: 304
Likes: 1
From: Carson City Nevada
With the ignition on, engine not running, the egr solenoid should have no voltage on the control side of the solenoid. You should be able to blow thru the vacuum input to output path.
You can energize the egr solenoid by connecting Pin A to Pin B on the diagnostic connector and turning the ignition On. The egr solenoid should energize and the vacuum input path to the output path should be blocked.
You can energize the egr solenoid by connecting Pin A to Pin B on the diagnostic connector and turning the ignition On. The egr solenoid should energize and the vacuum input path to the output path should be blocked.
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