New ECU Cold start issues

Technical Area Engine, Transmission, Exhaust etc
1

  1. My model of MX-5 is: __ NB 1.8VVT Montana

  2. I’m based near: __Hertfordshire

  3. I’m looking for technical help or recommendations on:

    Last year due to various reasons, faulty immobiliser issues etc… I fitted a ‘MS Labs MS3 Basic Plug and Play ECU For Mazda MX-5 NA NB - 01-05’.

    It has been to a garage to be tuned properly which they spent hours on, and yet the cold start is still not right, it’s hard to describe but it cranks and clunks, sounds rough. When its starts it run well with the only other issue being my revs drop to almost stall sometimes when I lift off the accelerator?

    Does anyone have any idea what’s going on :joy: ?

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Your mapping probably needs some adjustment to account for cold starts.

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Cold starts are the hardest to tune because you only get one cold start every 8 hours or so to test with. So you only have a few seconds to determine if you are rich or lean. In general this is the test procedure you want:

  1. Note down the ambient temp you are trying to start the car at.
  2. Attempt to start the car. While doing this, see if pressing the throttle pedal and opening the throttle plate helps the car start faster. If it does, that means you are rich, if it doesn’t that means you are lean(always assuming you have reasonable ignition timing)
  3. Now that you know if you are rich or lean, you can work on adjusting the bin for the temp you are at by adding/removing 10% fuel. Sadly…you have to wait another 8 hours to test again and make your next adjustment.

This procedure is for cranking pulse width. not for priming pulse. For example, this is my current cranking pulsewidth chart(temp is in Fahrenheit on this chart, not Celsius). It works of for me the most part aside from a couple temp bins that still need some finer tuning, and in general my priming pulsewidth could also do with a touch of tuning. This is not to say its suitable for your particular engine.

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If you want to know EXACTLY what is going on though, the best way is to pull your spark plugs directly after a start attempt and determine rich/lean that way…plug reading has always been the most reliable method….you certainly can’t depend on any air fuel reading you may get from a sensor during cranking after all, the sensor hasn’t had time to warm up properly.

2 Likes
4

Brilliant, thank you!

I’ll give it a go! I’ve never really played around with any of this before but I’m fairly determined I can crack it :joy:

Blind faith will prevail