roarpw Posted November 23, 2017 Report Share Posted November 23, 2017 Hi There, I have just rewired the entire body harness in my R33 GTst to a motorsport switch panel and bare essentials for racing. The issue im currently having amoung issues with the aim MXS dash.. The ecu is seeing/ reading low voltage copared woith the battery. The battery reads 12/ 13 volts depending on state of charge and and when the engine is running the battery is reading 13.5V... but the ecu is reading 12.1 / 12.2V with voltage sometime dropping lower in to the high 11.8/11.9V... I find it a bit strange but have a suspicion it may to do with an earth issue? Any insights would be appreciated. Quote Link to comment Share on other sites More sharing options...
Adamw Posted November 28, 2017 Report Share Posted November 28, 2017 Hello, sorry for the slow reply. Is this a plugin ECU or wire in? Quote Link to comment Share on other sites More sharing options...
roarpw Posted November 28, 2017 Author Report Share Posted November 28, 2017 all good, plug in ecu, r33 skyline GTst Quote Link to comment Share on other sites More sharing options...
roarpw Posted November 30, 2017 Author Report Share Posted November 30, 2017 anyone have any ideas what else may be causing the low voltage read at the ecu?? i have tested the power coming into the ecu and got 13.5V, power to aim dash 13.5V... i just dont understand how the ecu is seeing lower than 13.5V when the battery and everything else is reading correct?? Cheers Quote Link to comment Share on other sites More sharing options...
Adamw Posted November 30, 2017 Report Share Posted November 30, 2017 Can you put your voltmeter probes on pin 50 (main gnd) and pin 49 (main power) and tell us what voltage you get there compared to voltage displayed in VTS. Quote Link to comment Share on other sites More sharing options...
roarpw Posted December 1, 2017 Author Report Share Posted December 1, 2017 I will try this tonight and report back... i did get voltage to pin 50 on Wednesday with the multimeter grounded to battery / earth and that displayed 13.5V but i dont recall pin 49 as to whether or not i got a reading out of it. So i will try again. Quote Link to comment Share on other sites More sharing options...
roarpw Posted December 4, 2017 Author Report Share Posted December 4, 2017 I have found this difficult to determine whether or not i have the correct pins, what i have noticed i have applied the multimeter to what appears to be pins 50 and 59 and they have 13.5V but either nothing or no wire connected to pin 49 and no voltage at pin 60? Quote Link to comment Share on other sites More sharing options...
Adamw Posted December 4, 2017 Report Share Posted December 4, 2017 50 & 59 should give us an idea. So when you connect your mulitmeter across 50 & 59, you get 13.5V, what was the voltage showing in VTS at the time? Quote Link to comment Share on other sites More sharing options...
roarpw Posted December 7, 2017 Author Report Share Posted December 7, 2017 Hi Adam, i am still unsure i have the correct pins so i have attached a picture to make sure i am getting this right... in reference to the ecu plug picture attached when i ground the multimeter to the chassis i get 13-13.5v from Pin 50 (far rhs top row of plug) from the centre bolt as you look at it in the picture.. There is no wire on pin 49... on pin 59 with the multimeter ground to the chassis i get 13-13.5V, on pin 60 i get 0V... When i probe pin 50 and pin 60 together via the multimeter i get 13-13.5V... I had the car at a tuner yesterday and he seems to think that the with the ecu reading low voltage its causing the injector timing to slow down( he explained it similar to dwell??? due to the low voltage which is causing the car to run richer than normal... he has since taken some fuel out of the trim table to compensate but mention if i get this voltage issue sorted i will need to add the fuel back in? The VTS reads 11.4 volts currently whilst checking those pins explained above Quote Link to comment Share on other sites More sharing options...
Adamw Posted December 7, 2017 Report Share Posted December 7, 2017 49 & 50 are these two I think: Is that where you have been testing? Quote Link to comment Share on other sites More sharing options...
roarpw Posted December 7, 2017 Author Report Share Posted December 7, 2017 No I have been testing the opposite side of the plug? As I don't get any voltage out of any of those 4 pins at the end with the connector removed and ignition power on? Quote Link to comment Share on other sites More sharing options...
roarpw Posted December 7, 2017 Author Report Share Posted December 7, 2017 i have marked it out on the picture below... i will try the pins you have suggested again... Quote Link to comment Share on other sites More sharing options...
Adamw Posted December 7, 2017 Report Share Posted December 7, 2017 You need to do it with the ECU still connected. Poke something like a paper clip in through where the wire enters into the connector. This is often called "back probing". Watch this video from about 1:30 to see the technique. https://www.youtube.com/watch?v=g2ST8w_0w-Q Quote Link to comment Share on other sites More sharing options...
roarpw Posted December 7, 2017 Author Report Share Posted December 7, 2017 ok thanks, i think i have tested the pins you highlighted and i get 11.4V from pin 50 with the ground going to the chassis, and i will need to confirm this with the paper clip method but i got 6.3V with the ground going to pin 49 which i am not sure if that is correct or not? it doesnt sound right to me so i will try and get a paperclip in there... thanks, Andrew ok i have just back probed pin 49 and 50 with the multimeter and get 11.2/11.26V with VTS reading the same.... Quote Link to comment Share on other sites More sharing options...
roarpw Posted December 7, 2017 Author Report Share Posted December 7, 2017 voltage at battery at the same time is reading over 12.5v closer to 13V Quote Link to comment Share on other sites More sharing options...
Adamw Posted December 7, 2017 Report Share Posted December 7, 2017 Ok so the ECU is reporting the voltage it is being supplied correctly. So now you just need to fix the car so that it supplies the correct voltage... The first thing I would try is swap out the ECCS relay for known good or new one. They are probably the most common issue we see on Skylines. Quote Link to comment Share on other sites More sharing options...
roarpw Posted December 7, 2017 Author Report Share Posted December 7, 2017 Ok cool thanks I'll give that a go Quote Link to comment Share on other sites More sharing options...
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