1991 Corvette memcal/ecm problems
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Joined: May 2014
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From: Brentwood TN
1991 Corvette memcal/ecm problems
I am getting a 51 error code on my 91 Corvette auto Transmission convertible. I opened up the ecm and found a Hypertech Thermomaster chip. Thinking that this would be the likely culprit, I ordered a new one and installed it. I'm still getting the 51 error code. My next step, according to the service manual, would be installing a new ecm, but I'm wondering if it matters the orientation of the original memcal to the Hypertech chip:left to right or right to left. There appears to be 2 sides to the original memcal: the black side with the sticker and the "non sensing side", which is not black. What I am wondering is: does it matter which way the original memcal is attached to the Hypertech? Any help would be appreciated.
Racer
Joined: Apr 2018
Posts: 349
Likes: 55
I am getting a 51 error code on my 91 Corvette auto Transmission convertible. I opened up the ecm and found a Hypertech Thermomaster chip. Thinking that this would be the likely culprit, I ordered a new one and installed it. I'm still getting the 51 error code. My next step, according to the service manual, would be installing a new ecm, but I'm wondering if it matters the orientation of the original memcal to the Hypertech chip:left to right or right to left. There appears to be 2 sides to the original memcal: the black side with the sticker and the "non sensing side", which is not black. What I am wondering is: does it matter which way the original memcal is attached to the Hypertech? Any help would be appreciated.
Team Owner
Joined: Jul 2004
Posts: 28,431
Likes: 3,284
From: Hartford WI
I am getting a 51 error code on my 91 Corvette auto Transmission convertible. I opened up the ecm and found a Hypertech Thermomaster chip. Thinking that this would be the likely culprit, I ordered a new one and installed it. I'm still getting the 51 error code. My next step, according to the service manual, would be installing a new ecm, but I'm wondering if it matters the orientation of the original memcal to the Hypertech chip:left to right or right to left. There appears to be 2 sides to the original memcal: the black side with the sticker and the "non sensing side", which is not black. What I am wondering is: does it matter which way the original memcal is attached to the Hypertech? Any help would be appreciated.
I see that protrusion on the center "bar". It only goes in one way and if you force it, you are buying a new MEMCAL at best, ECM at worst.
Last edited by aklim; May 21, 2018 at 01:03 PM.
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Advanced
Joined: May 2014
Posts: 69
Likes: 1
From: Brentwood TN
Thread Starter
Advanced
Joined: May 2014
Posts: 69
Likes: 1
From: Brentwood TN
I think that my ECM is toast. My corvette started running rough. Not even limp mode anymore. Service Engine Soon light came on. Now it won't even throw a code. It was throwing code 51 before, but sometimes would not blink the end 12 code. I just bought another ECM. I sure hope that's the problem. I think I'll take JimLentz and aklim's advise and flush the Hypertech chip. It's the Thermomaster chip. It's suppose to run with a 160 degree thermostat, which I assume is what is in my '91. I think stock is 195. I bought this car with a Hypertech in it. Didn't know it until I opened her up. Wonder if that will affect things? Thanks for the help.
Racer
Joined: Apr 2018
Posts: 349
Likes: 55
I think that my ECM is toast. My corvette started running rough. Not even limp mode anymore. Service Engine Soon light came on. Now it won't even throw a code. It was throwing code 51 before, but sometimes would not blink the end 12 code. I just bought another ECM. I sure hope that's the problem. I think I'll take JimLentz and aklim's advise and flush the Hypertech chip. It's the Thermomaster chip. It's suppose to run with a 160 degree thermostat, which I assume is what is in my '91. I think stock is 195. I bought this car with a Hypertech in it. Didn't know it until I opened her up. Wonder if that will affect things? Thanks for the help.
For reference, with my ECM I can set the fan thresholds - I have it set to come on at 190, and stay on until it hits 170 (which it usually can't do unless its less than 50 out). There are several other variables that can control the fan, such as MPH threshold to turn the fan off, fan commanded on when AC is on, etc. This chip may have changed any number of those variables, but I doubt that those variables hampered the car in any way.
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Joined: May 2014
Posts: 69
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From: Brentwood TN
Just put in a new ECM with the old MEMCAL. Started right up. No Service Engine Soon light. Did not use the new Hypertech. I am very happy. I'm going to keep an eye on the temp reading, and I'm going to check my thermostat as per Blaster's instructions. Those stock MEMCAL's must be pretty tough. The old Thermomaster Hypertech was apparently not helping the engine stay cool, which I think is the thermomaster's purpose. The engine was routinely running hot in traffic during the summer months. I don't know if the new Hypertech would do any better. Not sure if I'm going to try it. Thanks everyone.
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Team Owner
Joined: Jul 2004
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From: Hartford WI
Sell the hyperJUNK to someone else and recoup some money. Put it towards an IR thermometer. HYPERJUNK turns the fans on at a lower temp is all. Remember that when you say "up to" it is meaningless. I promise you that I will give you "up to" a million bucks means the range of what you can expect runs from 0 through a million.
Also it is easier and cheaper than a dyno session. Cheap isn't good because it can't be and good isn't cheap because it can't and/or it doesn't need to be be
Also it is easier and cheaper than a dyno session. Cheap isn't good because it can't be and good isn't cheap because it can't and/or it doesn't need to be be