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Old 08-12-2010, 11:13 AM   #1
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Default Low voltage while cranking

This is my average voltage while cranking: (~8.6-9.6v)
Name:  lowvoltagewhilecranking.png
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I'm certain it's the cause of the reset I was greeted with this morning too (as per the screenshot above)

It's the only thing that pisses me off now regarding my cars tune. My LC-1 can sometimes throw a low voltage error too from cranking if it dips below 9v.

Both are powered from the 12v ECU power connection on the main ECU loom and also grounded at the same point too. Both my LC-1 and MS are seeing the voltage drop while cranking.

For reference, the "power on" MS voltage is 11.8v, dips to ~8.6-9.6v while cranking and rises to 14.8v while the engine runs. I don't have anything on such as heaters/AC/radio etc while trying to crank.

What's the most robust fix for this issue and what cranking voltages are some of you guys seeing?
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Old 08-17-2010, 07:41 PM   #2
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Okay so today I logged another cold start after work and during cranking I got three kickback sounds and then the engine fired up. These kickback sounds are directly related to the voltage dropping off below 9v during cranking. (see the three dips in Battery Voltage during cranking)

Name:  Crankingvoltagedrop2.png
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How can I remedy this? I'm using a Westco dry cell battery from MX5parts.co.uk that is spec'd especially for the MX-5 and is less than 2 years old so I'm pretty much ruling out the battery.

Could my grounds be the issue? If so what about running a high quality ground directly from the battery and using this for the MS/LC-1 since they both require a minimum of 9v to operate?

If anyone could shed any light onto this, I'd be really grateful. It's literally the only thing that now pisses me off with my MS.
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Old 08-17-2010, 10:12 PM   #3
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My westco MX5 battery lasted 2 years. Primary reason is the car sat for 6 months without being driven. After that it was weeksos, and would only hold a shitty charge. It died again, and became pretty much unchargeable.

Find another 12V battery, remove (not jump) your westco, and connect the known good battery to the leads. Start car. Profit.

And perhaps I'm mistaken, but I don't know of any westco dry-cells. Mine was an AGM (Absorbed Glass Mat). "Dry Cells" are commonly referred to as 'flashlight batteries', and most usually come in sizes marked "9V", "AA", "AAA", "C", and "D"
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Old 08-18-2010, 05:44 AM   #4
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Sorry for my terminology, I mean dry as in not acid. It is a Glass Mat. It's this battery.

I do drive the car every day but the journeys are only 6 miles but the battery is never left for any length of time without daily running. Maybe a trickle charge is in order? I've had this issue ever since installing MS so maybe the OEM ECU is fine with a voltage drop below 9V but the MS simply can't handle it?

I have a spare battery that is fully charged so I'll try that one while my Westco trickle charges for a few days.

Hopefully I won't be back replying to this thread...

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Old 08-18-2010, 08:58 AM   #5
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If it solves your problem, please reply to this thread, and let us know about it.
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Old 08-20-2010, 08:39 AM   #6
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Just to add a spin on this. I investigated my install the other day and realised I'd wrongly wired my LC-1 into the 12v power of the OEM ECU supply along with the retro-fitted CAS 12v and also the MS 12v supply. That's alot to have hanging off a single thin gauge 12v supply so I relocated the LC-1 12v to the chunky blue heater core cable which is a proper 'switched' supply so it's off while cranking as per the LC-1 instructions.

I figured the LC-1 must be sapping some current during sensor warm-up and having the MS-1 sharing the same 12v supply is probably a bad idea. The engine started more smoothly this morning but it could just be blind luck and I didn't log it as I was in a rush

I'll update soon to see if it's cured my voltage drop while cranking.
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