jumpbike Posted January 21, 2014 Share Posted January 21, 2014 Engine based topic only so a little off topic for mk4 people but might be of interest to many so here we go... Question: Does the ECU rely on the signal from speed sensor #1 for the auto to work properly or will it be fine with just the signal from speed sensor #2? Also, do both sensors have a direct affect on the speed limiter on a J-Spec ECU? Background is, I'm just going through the wiring diagrams while putting a J-Spec 2JZ-GTE engine and auto box in to a land cruiser. Now the land cruiser also used 2 speed signals in the same way the difference being the #1 sensor is after the transfer box, now anyone familiar with 4x4's will know that in H mode everything will be fine as both sensors will see the same speed BUT in L mode the ratio from input to output from the transfer box is reduced by around 2.4 or something so the #2 sensor will be seeing the speed out the auto box as before but the #1 sensor will be seeing a much reduced speed signal. Now the speedo will be fine as it uses the #1 signal so its accurate but the ECU will be seeing 2 different signals and the shifting may start having a fit. So back to my question, does the ECU need the signal from sensor #1 and if not will it flash the O/D light or something if not connected? Also when speed limit defenders are wired in do they usually intercept the signal from sensor #1 or #2? Finally is there any way sensor #2 can just be wired into both inputs, I know #1 uses 3 wires and #2 only 2 so not sure if the signal method is different or not. thanks, Quote Link to comment Share on other sites More sharing options...
jumpbike Posted January 22, 2014 Author Share Posted January 22, 2014 No auto experts? Quote Link to comment Share on other sites More sharing options...
Swampy442 Posted January 22, 2014 Share Posted January 22, 2014 No1 sensor is for the ECU, and number 2 is definitely for the speedo, whether the ECU uses both sensor signals before outputting to the speedo I don't know. Quote Link to comment Share on other sites More sharing options...
jumpbike Posted January 22, 2014 Author Share Posted January 22, 2014 the way I've been reading it is No. 2 sensor is the 2 wire one on the end of trans and controls the shifting only, No. 1 sensor is the one in the tail housing and has 3 wires and goes directly to the speedo and trip meter and then is outputted from there to the ECU, now apparently if the ECU does not see this signal it logs an error but im wondering if the engine light comes on because that would be annoying if I decide to just not connect this wire but is sensor No. 2 fails then there is no back up Quote Link to comment Share on other sites More sharing options...
Pedroby Posted January 22, 2014 Share Posted January 22, 2014 I am very interested in how your car will run! As you might face the same problems as I do atm. http://mkivsupra.net/vbb/showthread.php?302388-Auto-Shifting-problems-after-GTE-A-T-swap-solution-ABS-AEM-ECU-M-T Quote Link to comment Share on other sites More sharing options...
jumpbike Posted January 22, 2014 Author Share Posted January 22, 2014 I've got everywire that goes to the ECU that comes from the car and not the engine or box written down next to me, colours and what it does so I can join them all to the correct wires from the car, i'm more worried as I swapped the output shaft from the gearbox to the 4x4 one I've had most the insides of the auto box out on a table so hopefully it all still works! Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted January 22, 2014 Share Posted January 22, 2014 I think you will find it needs both. One is pre the gear train, one post, so the ecu expects X - Y RPM readings in a particular gear. If it sees daft, incorrect or not allowed readings it will "do things". For example it will stop the gearbox selecting 2 at 100 MPH. Quote Link to comment Share on other sites More sharing options...
jumpbike Posted January 22, 2014 Author Share Posted January 22, 2014 In that case there is 3 though, there is 1 at the very start that measures input speed, then 2 at the tail end, I think i'm just going to leave it and see what happens, worst case, i'll make a rectifier to covert sensor 2 to produce the same output that the input for sensor 1 expects and just use this sensor for both Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted January 22, 2014 Share Posted January 22, 2014 (edited) Even on an engine from a MANUAL gearbox car, if the Engine ECU doesn't receive the speed signal it throws an error code and the Engine Fault light comes on. How do I know? Because I've fitted a 2JZ in my Mk3 and presumed that feed would be irrelevant, being a Manual . . but it wasn't. I had to create a digital feed from the Mk3's mechanical speedo. Also - you obviously won't be able to create a signal for the input shaft speed from the output shaft, as the difference will vary depending on what gear you're in - as Chris explained, the Autobox actually uses that difference to decide what gear changes to do/allow. You need to appreciate that these are ELECTRONICALLY controlled Automatic Transmissions . . . if the computers don't get the right signals from the sensors, the Transmission won't work! Edited January 22, 2014 by Roger NE (see edit history) Quote Link to comment Share on other sites More sharing options...
jumpbike Posted January 23, 2014 Author Share Posted January 23, 2014 I think you are missing what I'm saying here, there are 2 speed sensors at the output end of the box, 1 compliments the input speed sensor by aiding with the shifting, the other goes to the speedo then goes to the ecu and is only used to help the shifting of the other 1 fails. I think the output signal from the 2 sensors varies slightly so can't just wire 1 into the other and I'm wondering if I just don't connect the wire between the speedo and the ecu, will I just get a code and/or a light - - - Updated - - - I think you are missing what I'm saying here, there are 2 speed sensors at the output end of the box, 1 compliments the input speed sensor by aiding with the shifting, the other goes to the speedo then goes to the ecu and is only used to help the shifting of the other 1 fails. I think the output signal from the 2 sensors varies slightly so can't just wire 1 into the other and I'm wondering if I just don't connect the wire between the speedo and the ecu, will I just get a code and/or a light Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted January 23, 2014 Share Posted January 23, 2014 I think you are missing what I'm saying here No I'm not ! You need the Input and Output shaft signals to make the Autobox change gear correctly . . And if the Speedo Drive Sensor output is NOT fed to the ECU, you get an Engine Fault light on the dash, even on a MANUAL car (as I just told you) Quote Link to comment Share on other sites More sharing options...
jumpbike Posted January 23, 2014 Author Share Posted January 23, 2014 But I never mentioned the input shaft sensor in the original post, that's a given that it would still be there Quote Link to comment Share on other sites More sharing options...
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