How many volts to start a MS1?

[dggt6]

Hello Guys,
I have been having trouble starting my MS1 car as there is no RPM signal and this is because the battery voltage has been dropping during cranking.
Could someone please tell me the minimum voltage MS1 requires to run?

I have replaced my old battery with a big new one with apparently little change.
I will have to investigate the current draw from my old Lucas starter motor.

Many thanks,
Doug

[dggt6]

Here is a photo of the log while cranking. The voltage drops during cranking then as soon as you let the key go, the volts pop up and you also get a "blip" on the RPM. You can see 2 "blips" on the graph of the RPM hitting about 535 RPM.
Thanks for any help,
Regards,

[keny]

Hi Doug Can you try using a second power supply, only to power the MS, when you operate the starter?

[jsmcortina]

Your datalog shows that the Megasquirt is alive and working.

Anything over about 7 volts should be enough. What is your tach input? Is the sensor ok? What has changed since it last worked.

James

[dggt6]

Thanks Kenny and James,
I have had another battery sitting in the car with just the Megasquirt plugged in but it did not give a reliable consistent solution. Perhaps this was never the problem as my cranking volts never got down to 7 where James says the MS should almost go???

Hi James, I had the car running (and starting) well on my MS1 up until 6 months ago when I started installing the fuel injection bits. Ever since then I have had persistant starting problem that did not get any better with a new battery.
I did have HUGE starting problems when I began this whole caper, but it went away after getting the proper plug leads, resistor plugs and other general light bulbs flicking on.
I am using a VR sensor and an EDIS unit
As with every other problem I have had, this one is not consistent and sometimes the engine will fire instantly. During tuning of the fuel map I have been attempting to start 10 times consectutively and it kicked each time! I have had it running for 20 mins at a time while I fiddle with the VE and Spark tables.

One of the many things I do not understand is why the Rpm is zero/dead whilst cranking, then blips up for 2 seconds when you release the key and the volts spring back up? I THINK the engine has fired a few times at this period, leading me towards the low voltage scenario.
I also must admit that I have never had a Trigger Log that looks like the ones on the web.

Many thanks again,
Doug

[dggt6]

Just been out to fiddle with the car and it would not start, of course.
I removed the power lead to the MS unit, checking to see if I had voltage whilst cranking. For some reason I cranked the engine with the wire OFF and the engine "kicked" but did not continue to run. Put the wire back and it started up!!!!! (and died because it was cold) It would not start again until I removed and replaced the MS power wire. It then started and kept running for 10 minutes.
It must be something in the way I have it wired up? Dodgy relay somewhere?????
Any thoughts?

Thanks,
Doug