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10/27/10 8:37pm - Original Message: '1981 ECM Code 15'
Almond81Vette
Former Member
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Stanley, NC - USA

Vette(s):
1981, dark blue w/carmel interior. 350 stock, auto tranny, Q-jet carb, ECM box

Joined: 8/9/2010
Posts: 91
  Hope all are doing well. My '81 is giving me a temporay check engine light about 2 minutes after start up and this come up to be a Code 13, Oxygen sensor but the light goes out in about a minute. But 5 minutes running the check engine light comes on and stays on and gives me a Code 15, Coolant Sensor.
   Once these codes pops up the carb starts to run rich and the vette does not run likes she should. Engine temp is fine, normal so not affecting the engine temp, just the carb.
   Thoughts, comments, suggestions? Waiting now to get the vette into the local shop to have him check it out if I cannot come up with solution. I have none of the meters to check the system as outlined in the '81 shop manual.
  Second question, has anyone of you with an '81 bypassed the ECM system completely? I know this means a different carb and vac dist and then address the transmission lock up switch, anything else? I average only 10 miles to the gallon running 93 octane so wondering if this swap out would improve fuel mileage.


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10/27/10 10:12pm - Reply: '1981 ECM Code 15'
yostusota
Former Member
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York, PA - USA

Vette(s):
1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top

Joined: 5/18/2010
Posts: 1518

Got to love the early cars and the fun stuff they do.  I would attack the coolant temp sensor first as that seems to be a hard code that doesn't go away and makes the car run bad..it comes out or never goes into closed loop and when your choke and idle kick down it runs fat..my guess is it never gets into closed loop..I have heard of people replacing the coolant sensor with a two wire style..give Larry a call at vette specialties he has them from what I remember..the O2 will need addessed also because it is being overwritten by the coolant sensor..do this after the coolant and recheck to see if it still gives you the code 13 again..It's not worth removing all the computer stuff.. at least I don't think it is...it really doesn't do all that much...

Make sure you have coolant in the car also as the sensor will not work if it is really low.
Rich


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10/27/10 10:22pm - Reply: '1981 ECM Code 15'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19449
You should not be getting an O2 sensor code when it's that cold..on a first start. That indicates to me that there is a problem with the O2 sensor. It may just be a loose connection, but it's more likely the sensor is failing. The O2 sensors don't really have any input on the fuel mixture or the timing until they get to operating temp(around 800*F). The ECM will not go into closed loop until the O2 starts reading/switching voltage.
I also think like Rich...the coolant sensor is most likely causing the bad running issue, more than the O2 sensor would.


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10/27/10 11:28pm - Reply: '1981 ECM Code 15'
yostusota
Former Member
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York, PA - USA

Vette(s):
1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top

Joined: 5/18/2010
Posts: 1518
I keep forgetting..no heaters duh..definetly bad connection or sensor.  I am used to the 20 second warm up and duty cycles..have to remember 1981....MC solenoids...
Rich


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