M4 Aux output 2 kills engine...

[NME308]

Hi Guys,
I have an early M4 motec with latest software (as of mid last year).
It is being used to control:
Ignition
Boost
Water Methanol
Data Logging

Aux ouptup 1 is setup for boost control with the motec 3 way valves and works fine.
The water methanol is being introduced under the carby via a Nitrous Oxide plate. We were attempting to use the main fuel map to give a fairly accurate mix, however investigation reveals the great big nitrous solenoid cannot be pulsed as fast as an EFI injector hence it is either on or off... i.e. as soon as the fuel map calls for any injection at all the solenoid is ON until the map calls for no injection at all!

Looking at the available features on the ecu Aux output 2 being programmed to 3 (aux table) setup as Pulse Width Modulated with 17hz seemed to be the goods. I programmed up a quick table with X axis being rpm and Y axis being MAP. Going to diagnostic mode and testing, the solenoid pulsed nicely and all appeared beautiful! Upon firing up the engine it ran like a busted sack of potatoes i.e. hardly idles, wont take throttle, poors fuel smoke, and the boost control solenoids pulsed full time. Now the water meth pump isn't even on at this stage and the injection isn't to start till 3000rpm and 167kpa MAP reading anyhow so it isn't suddenly flodding the engine with water meth. Checked the ecu sensors etc while running and all appeared to look normal, so we checked that the engine wasn't being flooded with fuel - which it wasn't. I switched from pump fuel tune to race fuel tune in desperation and instantly all is well! Immediatly I switched back to pump fuel tune and disabled Aux output 2 and engine runs perfectly again!

The nitrous solenoid is given constant 12v supply and earth side connects back to Aux output 2 wire on ecu to be switched as per programmed aux map.

Can anyone tell me I am doing something wrong/stupid please?

Cheers,
Jason

[NME308]

Well since its Easter and this forum has been super quiet I have had time to do a little more thinking...

With endless hours of searching this and the EFI University site I am wondering if it is possible that my settings in the Aux 2 Output parameters may be wrong (sort of...). I have a minimum duty cycle of 10 and max duty cycle of 90. Reading up on other peoples problems ect I get the impression the minimum duty cycle of 10 I have set could potentially see the solenoid active on startup at the 10% figure and not completely turned off at any time. While this in itself shouldn't cause my ecu to go crazy I am wondering if the .6 amps the Aux 2 can sink is way too low for the nitrous solenoid. Soooooooo while the setup worked fine in diagnostic mode maybe the solenoid being pulsed while in normal operation drags down the ecu??? As yet I havn't measured the amps the solenoid draws in operation.

We have the most important race meeting of our year coming up in a couple of days so I am not game to experiment on the car any further right now because frying the ecu would be disastrous!
I know we can operate happily enough with the water methanol just plain on or off as before so for this meeting I'll leave well enough alone.

Any knowledgeable people please edumicate me, I'm all ears!

Cheers,
Jason

[RossB]

With Minimum duty cycle set to 10 the valve will be running at a minimum of 10%, you may need to set this to 0. Check the resistance of the solenoid as it may exceed the current capabilities of the output. You may also need to adjust the frequency to get better control of the valve.