82 New ECM Check Engine Light No Codes
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5th Gear
Joined: Apr 2019
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82 New ECM Check Engine Light No Codes
So a friend and myself are trying to get his brothers 1982 Corvette running. It had a bad ecm which we have replaced and the car started no problem but seems to be running rich. Possibly in some sort of limp mode? The check engine light is on, but we are not able to get it to flash any codes at all. Any ideas where to start?
Last edited by Craig4113; Apr 21, 2019 at 03:29 PM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
It should at the very least flash a code 12.....which is an operational "OK" code to let you know it is working.....either you have no power to this ECM or it too is bad......
Jebby
Jebby
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Disconnect the neg bat cable and see if there is any change.
Jebby
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Dr. Detroit
Joined: Mar 2012
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From: New Braunfels Texas
Safety Car
Joined: Nov 2005
Posts: 3,532
Likes: 1,185
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
Thanks Jebby. Well, there is a few things to look at, but first I want to know exactly what happens in what order. Does the CEL come ON even for a split second and then go OFF when you turn the key to the ON position or does it come ON and stay ON? If it stays ON, then without any further TS'ing you may have another bad ECM, but can be further determined below. The power is good going to the ECM because the CEL comes ON period. The light is controlled by the ECM and will not come ON without power to the ECM which is supplied by the 20 amp fuse in the battery compartment. If that fuse was bad/blown, you can crank the motor, you will have spark, but you will not have a CEL light or any fuel to the injectors since the pump will not come ON.
So, to further test the system, I would recommend that you disconnect the battery voltage to the ECM for about 10-20 seconds and then reconnect it, the 20 amp fuse can be pulled to do this vs. actually disconnecting the battery. This procedure will clear any faults period in the ECM that may be stored. Without grounding/shorting the Diag pins A/B, turn the key to ON position and see if the CEL comes ON and then goes OFF. If it does, then short pins A/B with your handy paperclip and see if you get the 12 flash code. If that works, start the motor and see if the CEL comes back ON. If not, your good to go, if it does, TS the codes that may come up "in order" first code first and so on. DO NOT randomly start TS a code and replace parts, that's not how that works. If multiple codes come up, it will display the lowest first followed by the next highest code.
If your CEL is ON all the time after all this and may be flashing, you are in "LIMP HOME" mode and it will run rather crappy and rich, but it will get you home...barely. Also, if you still have this same issue after doing this, it looks like you have another bad ECM which is not uncommon for an 82 ECM. I have seen several replaced before people have gotten a good one. IMO, it's a crap shoot on the old ECMs that are remans.
One last thing you can try is: with key OFF, disconnect the white connector on the ECM and then turn the key ON. Is the CEL light ON or OFF? If it's ON, you more than likely have a short to ground in circuit 419 and you will need to TS that with a meter. If CEL is OFF, turn key OFF, reconnect white connector. Turn key back ON back probe white connector pin #3 which is circuit 451 with a test light to ground. If you get code 12 you have an open in that circuit 451 and will have to TS it with a meter.
My last comment which should have been my first is... "If you don't have a 82 GM service manual, GET ONE, it's a MUST HAVE item. You can find them on eBay and see if you can get the original one with color diagrams vs a B/W copy. This manual is worth its weight in gold for a 38 year old car and has plenty of good troubleshooting charts. For ECM TSing, start in section 6E-15 and go from there. Good luck with your issue and post up "exactly" what happens.
If you can not find a manual, PM me.
So, to further test the system, I would recommend that you disconnect the battery voltage to the ECM for about 10-20 seconds and then reconnect it, the 20 amp fuse can be pulled to do this vs. actually disconnecting the battery. This procedure will clear any faults period in the ECM that may be stored. Without grounding/shorting the Diag pins A/B, turn the key to ON position and see if the CEL comes ON and then goes OFF. If it does, then short pins A/B with your handy paperclip and see if you get the 12 flash code. If that works, start the motor and see if the CEL comes back ON. If not, your good to go, if it does, TS the codes that may come up "in order" first code first and so on. DO NOT randomly start TS a code and replace parts, that's not how that works. If multiple codes come up, it will display the lowest first followed by the next highest code.
If your CEL is ON all the time after all this and may be flashing, you are in "LIMP HOME" mode and it will run rather crappy and rich, but it will get you home...barely. Also, if you still have this same issue after doing this, it looks like you have another bad ECM which is not uncommon for an 82 ECM. I have seen several replaced before people have gotten a good one. IMO, it's a crap shoot on the old ECMs that are remans.
One last thing you can try is: with key OFF, disconnect the white connector on the ECM and then turn the key ON. Is the CEL light ON or OFF? If it's ON, you more than likely have a short to ground in circuit 419 and you will need to TS that with a meter. If CEL is OFF, turn key OFF, reconnect white connector. Turn key back ON back probe white connector pin #3 which is circuit 451 with a test light to ground. If you get code 12 you have an open in that circuit 451 and will have to TS it with a meter.
My last comment which should have been my first is... "If you don't have a 82 GM service manual, GET ONE, it's a MUST HAVE item. You can find them on eBay and see if you can get the original one with color diagrams vs a B/W copy. This manual is worth its weight in gold for a 38 year old car and has plenty of good troubleshooting charts. For ECM TSing, start in section 6E-15 and go from there. Good luck with your issue and post up "exactly" what happens.
If you can not find a manual, PM me.
Last edited by Buccaneer; Apr 21, 2019 at 05:37 PM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Thanks Jebby. Well, there is a few things to look at, but first I want to know exactly what happens in what order. Does the CEL come ON even for a split second and then go OFF when you turn the key to the ON position or does it come ON and stay ON? If it stays ON, then without any further TS'ing you may have another bad ECM, but can be further determined below. The power is good going to the ECM because the CEL comes ON period. The light is controlled by the ECM and will not come ON without power to the ECM which is supplied by the 20 amp fuse in the battery compartment. If that fuse was bad/blown, you can crank the motor, you will have spark, but you will not have a CEL light or any fuel to the injectors since the pump will not come ON.
So, to further test the system, I would recommend that you disconnect the battery voltage to the ECM for about 10-20 seconds and then reconnect it, the 20 amp fuse can be pulled to do this vs. actually disconnecting the battery. This procedure will clear any faults period in the ECM that may be stored. Without grounding/shorting the Diag pins A/B, turn the key to ON position and see if the CEL comes ON and then goes OFF. If it does, then short pins A/B with your handy paperclip and see if you get the 12 flash code. If that works, start the motor and see if the CEL comes back ON. If not, your good to go, if it does, TS the codes that may come up "in order" first code first and so on. DO NOT randomly start TS a code and replace parts, that's not how that works. If multiple codes come up, it will display the lowest first followed by the next highest code.
If your CEL is ON all the time after all this and may be flashing, you are in "LIMP HOME" mode and it will run rather crappy and rich, but it will get you home...barely. Also, if you still have this same issue after doing this, it looks like you have another bad ECM which is not uncommon for an 82 ECM. I have seen several replaced before people have gotten a good one. IMO, it's a crap shoot on the old ECMs that are remans.
One last thing you can try is: with key OFF, disconnect the white connector on the ECM and then turn the key ON. Is the CEL light ON or OFF? If it's ON, you more than likely have a short to ground in circuit 419 and you will need to TS that with a meter. If CEL is OFF, turn key OFF, reconnect white connector. Turn key back ON back probe white connector pin #3 which is circuit 451 with a test light to ground. If you get code 12 you have an open in that circuit 451 and will have to TS it with a meter.
My last comment which should have been my first is... "If you don't have a 82 GM service manual, GET ONE, it's a MUST HAVE item. You can find them on eBay and see if you can get the original one with color diagrams vs a B/W copy. This manual is worth its weight in gold for a 38 year old car and has plenty of good troubleshooting charts. For ECM TSing, start in section 6E-15 and go from there. Good luck with your issue and post up "exactly" what happens. If you can not find a manual, PM me.
So, to further test the system, I would recommend that you disconnect the battery voltage to the ECM for about 10-20 seconds and then reconnect it, the 20 amp fuse can be pulled to do this vs. actually disconnecting the battery. This procedure will clear any faults period in the ECM that may be stored. Without grounding/shorting the Diag pins A/B, turn the key to ON position and see if the CEL comes ON and then goes OFF. If it does, then short pins A/B with your handy paperclip and see if you get the 12 flash code. If that works, start the motor and see if the CEL comes back ON. If not, your good to go, if it does, TS the codes that may come up "in order" first code first and so on. DO NOT randomly start TS a code and replace parts, that's not how that works. If multiple codes come up, it will display the lowest first followed by the next highest code.
If your CEL is ON all the time after all this and may be flashing, you are in "LIMP HOME" mode and it will run rather crappy and rich, but it will get you home...barely. Also, if you still have this same issue after doing this, it looks like you have another bad ECM which is not uncommon for an 82 ECM. I have seen several replaced before people have gotten a good one. IMO, it's a crap shoot on the old ECMs that are remans.
One last thing you can try is: with key OFF, disconnect the white connector on the ECM and then turn the key ON. Is the CEL light ON or OFF? If it's ON, you more than likely have a short to ground in circuit 419 and you will need to TS that with a meter. If CEL is OFF, turn key OFF, reconnect white connector. Turn key back ON back probe white connector pin #3 which is circuit 451 with a test light to ground. If you get code 12 you have an open in that circuit 451 and will have to TS it with a meter.
My last comment which should have been my first is... "If you don't have a 82 GM service manual, GET ONE, it's a MUST HAVE item. You can find them on eBay and see if you can get the original one with color diagrams vs a B/W copy. This manual is worth its weight in gold for a 38 year old car and has plenty of good troubleshooting charts. For ECM TSing, start in section 6E-15 and go from there. Good luck with your issue and post up "exactly" what happens.
If you can not find a manual, PM me.I probably knew all of this in the 80’s but have smoked myself retarded since then
Jebby
Safety Car
Joined: Nov 2005
Posts: 3,532
Likes: 1,185
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
You rule dude!
I probably knew all of this in the 80’s but have smoked myself retarded since then
Jebby
I probably knew all of this in the 80’s but have smoked myself retarded since then
Jebby
Burning Brakes
Joined: Sep 2013
Posts: 1,206
Likes: 365
From: The Motor City
If the ECM fuse (next to battery) is okay you probably blew the new ECM and/or eprom chip by installing it backwards. Expensive mistake. Ask me how I know. The Hypertech Streetrunner is an excellent replacement (and, smooths out the transmissions shift points).
Cruising
Joined: Dec 2017
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