89 Instrument Cluster question
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4th Gear
Joined: Feb 2018
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89 Instrument Cluster question
I'm working on building secondary display system for my 89. I have found the schematics on here and at batee.com but I don't see how it is figuring fuel mileage. I'm going to assume its probably calculating it in the ECM. Would it be better to try to hijack the sensor data like i'm doing for the rest of the instrument cluster or just use a serial connection through the odb1/aldl connection to query the ecm directly?
Team Owner
Joined: Jul 2004
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From: Hartford WI
I'm working on building secondary display system for my 89. I have found the schematics on here and at batee.com but I don't see how it is figuring fuel mileage. I'm going to assume its probably calculating it in the ECM. Would it be better to try to hijack the sensor data like i'm doing for the rest of the instrument cluster or just use a serial connection through the odb1/aldl connection to query the ecm directly?
Thread Starter
4th Gear
Joined: Feb 2018
Posts: 4
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Let me rephrase my problem. I said I assumed because I don't really care where exactly it does it at. I have no issues intercepting sensors that are coming directly to the instrument cluster as it is not that big of a problem to replace considering I already have it out and open fixing some issues that were there when I bought it. I'm not as comfortable with tagging onto a sensor directly tied to the ECM because I can't repair/replace it quite as easily. Do you think splitting off the sensor will cause problems with the ECM? I can get the data off the odb connection fine but I'm building this and using it as test bed for electronics and programming I am preparing for my 76. I would like to use as much raw sensor data as possible because that is what I will be using on the 76 but I don't want to cause issues with it running because that will throw all of my testing and debugging as well. I'm doing this in the 89 to make sure I have the responsiveness and stability I need for an instrument cluster while having the primary stock cluster to compare against and rely on in case of issues with my system.
Team Owner
Joined: Jul 2004
Posts: 28,459
Likes: 3,288
From: Hartford WI
Let me rephrase my problem. I said I assumed because I don't really care where exactly it does it at. I have no issues intercepting sensors that are coming directly to the instrument cluster as it is not that big of a problem to replace considering I already have it out and open fixing some issues that were there when I bought it. I'm not as comfortable with tagging onto a sensor directly tied to the ECM because I can't repair/replace it quite as easily. Do you think splitting off the sensor will cause problems with the ECM? I can get the data off the odb connection fine but I'm building this and using it as test bed for electronics and programming I am preparing for my 76. I would like to use as much raw sensor data as possible because that is what I will be using on the 76 but I don't want to cause issues with it running because that will throw all of my testing and debugging as well. I'm doing this in the 89 to make sure I have the responsiveness and stability I need for an instrument cluster while having the primary stock cluster to compare against and rely on in case of issues with my system.
Thread Starter
4th Gear
Joined: Feb 2018
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Team Owner
Joined: Jul 2004
Posts: 28,459
Likes: 3,288
From: Hartford WI
I don't think you should intercept the incoming (to the ECM) signal. Probably ok but I don't like to. OTOH, if it is outgoing from the ECM and doesn't feed back to the ECM, I can't see why not, assuming you have a schematic and not blindly poking wires.
Team Owner
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This is how I always thought MPG, IMPG etc were calculated. Bryan likely understands and might be able to provide information needed.
https://www.corvetteforum.com/forums...post1545449648
https://www.corvetteforum.com/forums...post1545449648
Thread Starter
4th Gear
Joined: Feb 2018
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That is interesting and quite different than what I thought it would be doing. I'm only going to passively pick up data off of the instrument clusters while keeping the systems as isolated as I can. I have the full schematic for the instrument cluster so I already know what I need to to pick the data up. I may end up with causing slightly off readings on the resistance gauges but that will be fine. Since I will be doing it in a much different way on the 76, I'm not even going to bother with any of the other sensors that don't feed to the cluster. Tach and speedo responsiveness are my main issue that I'm worried about. Trying to read to much data with one chip as well will be troublesome. I think the sensors that can be read from the instrument cluster will give me a good idea of the loading on the microprocessor.
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