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Ecu Constantly Powered

Josh

By Josh,
in Engines & Forced Induction

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Josh Grand Master

Josh

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Posted

I have an R34 GTT sedan running with an R32 RB26 in it(R32 engine loom was modded to suit an R34 body, not sure who did the work), controlled by a ViPEC plug and play to suit an R32, my issue, is that the ECU has constant power - I can connect to it thru my laptop with the key off and out of the ignition. This causes a few issues - ie running my battery flat... and it also has the effect of not performing the tachometer sweep and fuel pump prime when the key is inserted and turned to the on position as well as causing the the car to run on for a few seconds after being keyed off. It still starts and runs fine and NONE of the other items in the car - stereo/defis/boost controller stay on with the key off.

The tacho sweep and fuel prime issue are definitely caused by the constant power as the ecu cannot tell that it is being keyed on, since its already on and so will not perform these functions like its just been turned on - If cranked but not allowed enough time to start, when the key is returned to the on position from start, the pump primes and tacho sweeps like normal.....

There is a brown relay(not definite on what it's for) that is situated near the ecu under the kick panel on the passenger side, I have found that it has power to the switch/coil side all the time as even with the key off you can hear the relay click when plugged back in, which means whatever it is a relay for would be getting power all the time - perhaps the ecu. I think it IS for the ecu as when this relay is not plugged in I cannot connect to the ecu at all and the car won't start. Also when i remove the relay instead of turning the key off with the engine running, it shuts off immediately, thus fixing the running on issue, which I was sure WAS related to the constant power problem.

I've checked the plugs/wires etc for any obvious breaks/shorts but have come up with nothing so far. The problem here is the harness isn't in the best condition, but still functioned fine up until a couple of days ago.. - like I said before I'm not sure who did the work to join the two harnesses together.. I've had the good fortune of being able to compare voltage readings on my harness to an actual R32 GTR that works fine and found that mine had constant battery voltage at pins 49 & 59 with the key off, while the GTR did not, which is what originally led me to believe the ecu was on all the time.

At the moment I'm convinced i'm just going to have to check the whole harness and hopefully find something that doesnt look right.. this will be harder than it sounds due to the harness not being a single factory harness, but an very average amalgamation of two factory harness' :/ and not a lot ACTUALLY looking right anyway :P

Sorry about the long post, anybody else got any other ideas or come across something similar. Oh and the car had been running fine with this setup for around 12 months prior.

Josh

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_x_FiReStOrM_x_ Community Regular

_x_FiReStOrM_x_

Posted
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Sounds like you're close to the money with that relay. Start by tracing the switching side of the relay backwards. It'll have to go to an IGN relay or the IGN switch somewhere. See what you find. You'll need a good multimeter to check continuity. Check for dodgy taped-up wiring, that may be touching a 12V constant together with another wire.

Josh Grand Master

Josh

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I'm still wondering what the relay is exactly for, its not a normal relay, it has six pins, instead of the regular four, and going by the diagram on the relay itself two pairs of the pins are switches, the third pair being a coil... With it unplugged and the key switch in the on position, the fuel pump runs constantly, but no ecu power, with it THEN plugged in it does its normal tach sweep and pump prime for a few seconds. It must be the power relay for the ecu yeah?

Duncan Grand Master

Duncan

Posted
Posted

The ECU turns itself on and off using the ECCS relay. This gives it time to save settings etc before it turns off.

So...start by replacing the relay, maybe it has failed and is constantly on. Or even easier, replace the ECU with a known good one and check again because it could be a simple short internally

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