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Thread: 1993 VR4 ECU into a 91 VR4?

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    Forum User Feedback Score 0 TKtw1nturb0's Avatar
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    1993 VR4 ECU into a 91 VR4?

    Is it possible or would the different CAS setups effect the compatibility? Reason I ask is this:



    This is my 91' VR4 ECU but I might have a spare 93' VR4 ECU. I'm thinking this is why my car has been having some weird problems.
    "It's only after we've lost everything that we're free to do anything"

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    It should work. The sensors are supposed to have a slightly different latency, but people report the change does not cause noticeable detrimental effects.

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    Forum User Feedback Score 1 (100%) lawdogg's Avatar
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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.
    Stealth 316 - CAS Conversion

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    Forum User Feedback Score 0 TKtw1nturb0's Avatar
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    Ok. Does the board look shot? Is it even worth trying to put in new caps?

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    Member verified Feedback Score 1 (100%) aaronatstate's Avatar
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    Quote Originally Posted by lawdogg View Post
    What Ryan quoted. I had to take out timing in the ECU when I did my Montero ECU swap to account for the latency difference. As soon as I pulled it out, all my knock issues went away.

    Granted I have 13t's and bigger injectors, and a higher compression ratio, but the latency difference DID affect my car.
    "Speed has never killed anyone, suddenly becoming stationary… that's what gets you." - Jeremy Clarkson


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    So what if you did this in reverse and put a 1991 ECU in a 1993? Would the latency difference cause engine knock?

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