Nitrous solenoids being "pulsed" when key switched to on - Perth-WRX.com

rubberbudgie · #1 17-05-2010, 12:47 PM

As the subject says, when the ingition key is switched to on, the nitrous and fuel solenoids are being triggered for a brief moment causing a small amount of fuel and nitrous to be injected into the manifold which causes a nasty "pop" when you start the engine.

I'm using AUX8 (A34) to connect to the relay that controls the solenoids. I'm thinking it's got something to do with the polarity and output mode, when Polarity set to 0 output voltage is 3.3v and with it set to 1 output voltage is 0.1v but with either setting it still pulses the output briefly on power-up.

Thanks.

tuna · #2 17-05-2010, 01:18 PM

checked what circuit the relays are getting power from?

Rossco · #3 17-05-2010, 01:26 PM

I'd have thought you would have a manual switch to over ride the nitrous relay as a safety precaution?

Kind of like an arming switch, but separate to the ecu function switch.

If theres no power to the solenoid through the high current side of the relay (or you interrupt the circuit between the ecu & the relay) the solenoids cannot possible pulse, plus you have a hard wired way to kill the nitrous if there is a control issue.

If you used a parallel 4 pole switch (2 pairs of switched contacts), the ecu function switching & safety could be combined into the one switch.

mattmy99 · #4 17-05-2010, 02:13 PM

Are you sure it's the nitrous causing the pop? You seem to know what you're on about, so i dont doubt you've checked to see what's causing it... I'm just asking, as my motec causes "backfires" when i switch my car to "on" (without starting) also.

jungleboy · #5 17-05-2010, 11:18 PM

I recall something about the motec grounding some of the outputs on initial start-up. So if you are low side switching (Sink) a load it will momentarily switch and energise the load on start-up as you describe.

We noticed this on the UWA Motorsport car, which had a small cooling fan that would briefly start and then stop when we switched the ignition on. Basically the relay to switch the fan on was supplied with a fused 12V from the ignition switch and the negative side of the relay was connected to an output on the motec which when grounded would start the fan briefly.

From memory to rectify this you needed to high side switch (Source) the load (which not all the outputs will do) or rewire a relay so that grounding (Sinking) an output will not energise the load.

Bit of a pain.

rubberbudgie · #6 18-05-2010, 02:17 AM

Quote:

Originally Posted by Rossco

I'd have thought you would have a manual switch to over ride the nitrous relay as a safety precaution?

Kind of like an arming switch, but separate to the ecu function switch.

If theres no power to the solenoid through the high current side of the relay (or you interrupt the circuit between the ecu & the relay) the solenoids cannot possible pulse, plus you have a hard wired way to kill the nitrous if there is a control issue.

If you used a parallel 4 pole switch (2 pairs of switched contacts), the ecu function switching & safety could be combined into the one switch.

The DPST switch is an excellent idea and would be my preferred option except that the switches are those ignited brand missile switches that have the wanky LED inbuilt so I'm kind of stuck with it. And I was trying to avoid having to mount another switch but it's looking like the best option at the moment.

Quote:

Originally Posted by jungleboy

I recall something about the motec grounding some of the outputs on initial start-up. So if you are low side switching (Sink) a load it will momentarily switch and energise the load on start-up as you describe.

We noticed this on the UWA Motorsport car, which had a small cooling fan that would briefly start and then stop when we switched the ignition on. Basically the relay to switch the fan on was supplied with a fused 12V from the ignition switch and the negative side of the relay was connected to an output on the motec which when grounded would start the fan briefly.

From memory to rectify this you needed to high side switch (Source) the load (which not all the outputs will do) or rewire a relay so that grounding (Sinking) an output will not energise the load.

Bit of a pain.

You've hit the nail on the head. I think wiring the relay to ground and then setting the Motec to output=1 polarity=1 would work provided of course the AUX8 output supplies +12v. The M800 wiring diagram shows the outputs as being connected to the +12v rail so I'm guessing this should work fine. Only one way to find out I guess....

jungleboy · #7 18-05-2010, 09:17 AM

Note 4 on the M800 wiring diagram states AUX 1-2 and 5-8 can drive a grounded load, so your in luck.

Must be fun to drive with the nos! You going to take it down to the drags eventually?

rubberbudgie · #8 24-05-2010, 10:40 AM

Quote:

Originally Posted by jungleboy

Note 4 on the M800 wiring diagram states AUX 1-2 and 5-8 can drive a grounded load, so your in luck.

Must be fun to drive with the nos! You going to take it down to the drags eventually?

Yeah it's fun with the nos but I won't be taking it down the drags anytime soon, in my experience a car not properly set up for drag racing not to mention a driver not all that good at drag racing trying to do drag racing is a recipe for lots of $$$ being spent. That's not to say it will never happen of course.....

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