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Discussion Starter #1
I'm in need of a new ecu but I'm confused about which one I need. After searching some people have said that any 91-93 will work, others have said it has to have the same part number (mine is a 91 so it has MD159966), and still others have said it needs to have a matching E2T number. So which of these number do I need to match up?
 

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I just put a 93 ECU into my 91. The 91 was a 9966, the 93 was something else. Car runs better than ever. I did read that it might pull different timing at some point because of the CAS sensor differences??? I'm not sure thought.

-Evan
 

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There is one aspect of using 1991-1992 sensors with a 1993+ engine control unit (ECU), or 1993+ sensors with a 1991-1992 ECU that must be considered. Brian Geddes and Matt Jannusch (on the Team3S email list) pointed out that the two different types of sensor have different latency. Latency is the amount of time it takes the sensor to respond to the optical disk or vane and send a voltage change to the ECU. The ECU is programmed to accomodate the sensor latency. As determined from the AEM standalone engine management calibrations, the latency for the 1991-1992 sensors is 50 microseconds (us), or 0.050 millisecond (ms). The 1993 sensors have a 130 us latency (0.130 ms). What this means is that if you install the 1991-1992 optical pickup sensor and use a 1993+ ECU there will be more ignition timing advance than the ECU wants. If using 1993+ Hall effect sensors with a 1991-1992 ECU, there will less timing advance than what the ECU has determined is correct for the engine operating conditions. The AEM software allows a user to adjust the latency for the different types of sensor to assure the actual timing advance matches programmed advance.

This latency difference in sensor types causes a few degrees difference in timing at high rpm. For example, at 7000 rpm, a single degree of crank rotation takes place in 0.0238 ms (23.8 us); 7000 rpm = ~116.667 rps ==> ~8.57 ms/rev = 0.0238 ms/degree. There is a difference of 80 us between the two types of sensor, leading to a 3 to 4 degree difference in timing.
 

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Wow that is some good info. That's probably where the rumor about the 93's having a more aggressive tune came from. So if I'm understanding this right, a 93 will work, but is not the best idea. So for my 91 i should look for an ecu with MD159966. And the E2T number doesn't matter right?
 

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Correct, ET2 number does not matter and a 93 ecu will be fine for a normal car but if you plan on a lot of WOT runs the correct ecu is preferred.

I just called O'Reilly Auto Parts - Home and they sell the 91 ecu for $250 w/core.

Wow that is some good info. That's probably where the rumor about the 93's having a more aggressive tune came from. So if I'm understanding this right, a 93 will work, but is not the best idea. So for my 91 i should look for an ecu with MD159966. And the E2T number doesn't matter right?
 

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Discussion Starter #9
Correct, ET2 number does not matter and a 93 ecu will be fine for a normal car but if you plan on a lot of WOT runs the correct ecu is preferred.

I just called O'Reilly Auto Parts - Home and they sell the 91 ecu for $250 w/core.
Oh no kidding, I didn't think I could get an ecu from a auto parts store. I will have to check that out tomorrow. Thanks a lot.
 
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