Erratic tach + turning off

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vrtigo
MS/Extra Newbie
Posts: 16
Joined: Mon Oct 13, 2014 12:01 am

Erratic tach + turning off

Post by vrtigo »

Have had my MS1 working fine in the past, but after my latest engine swap, things are weird. Everything is the same, its just a new long block. The megasquirt is running in distributor mode, using a 4 tooth VR sensor, and the loom is wired into a factory ECU connector, and so is using the factory loom from there onwards.

The car starts and runs fine, but the RPM gauge in the car (getting signal strait from the factory location, ie the ignitor) when increasing RPM gradually indicated RPM reads what looks like twice as high as it should be, and starts to get very erratic. Eventually the MS cant handle it and shuts off completely, disconnecting from Tunerstudio and requiring an ignition reset. Sometimes this happens immediately with a decent throttle snap.

Swapping spark plugs didnt help, and they are definitely resistor type - NGK BCPR6E-IX.

The car runs and behaves perfectly fine when the stock ECU is plugged in, no problems at all, including the tach.

What could be the issue here?
Matt Cramer
Super MS/Extra'er
Posts: 17499
Joined: Thu Apr 16, 2009 8:08 pm

Re: Erratic tach + turning off

Post by Matt Cramer »

Please also post a data log.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
vrtigo
MS/Extra Newbie
Posts: 16
Joined: Mon Oct 13, 2014 12:01 am

Re: Erratic tach + turning off

Post by vrtigo »

I dont have access to the car right now, so have no log. Just after possibilities at this stage.
Matt Cramer
Super MS/Extra'er
Posts: 17499
Joined: Thu Apr 16, 2009 8:08 pm

Re: Erratic tach + turning off

Post by Matt Cramer »

If the VR sensor is wired to the ECU directly, try adjusting the VR trim pots.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
vrtigo
MS/Extra Newbie
Posts: 16
Joined: Mon Oct 13, 2014 12:01 am

Re: Erratic tach + turning off

Post by vrtigo »

Thanks, but do MS1 v2.2 have trim pots? If its a simple resistor, which one needs switching?
Matt Cramer
Super MS/Extra'er
Posts: 17499
Joined: Thu Apr 16, 2009 8:08 pm

Re: Erratic tach + turning off

Post by Matt Cramer »

V2.2s do not. I had missed that you were getting the tach signal from the ignitor. I'll need a data log to be able to offer any further advice. A tooth log from the Diagnostic menu might also help.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
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