I have been using my megasquirt for a few months without problem then had to rebuild my engine. When I started it up for the first time it fired up and ran well but eventually stalled due to a vac hose off. When I went to start it again it wouldn't go. I found that pin 2 on one of the vb921s was burnt out, both leading coils were melted and the bolt which holds the ms case to the body was very hot.
I am using ms2 and I am only usuing it to run ignition and only leading which is cop with bosch coils.
At first I thought I had left an earth wire off somewhere but they are all ok includung the one that earths out the vb921 daughter board that is mounted on the outside of the ecu case.
Software seems ok and I still get cranking signal.

Can anyone shed any light on what might be going on?
Could my vbs be holding the coils to ground?
I am going to replace the vbs with bosch modules which should be more robust but I don't want to ruin new coils if the problem is still there.

Any help would be greatly appreciated. I realy want to run my new engine!
Paul

 

Still need help. Can't work out what went wrong.

 

Do you have spark output inverted? how are your vb921's wired?

 

Spark is going low (normal)

VBs are wired as per Jobros diagram minus the trailing.



From my limited understanding I need to work out if it is the VBs fault or if the ecu is giving the VBs the wrong signal. The ecu sends a 0V or 5V signal to the VB to ground the coil. At the moment the ecu out is reading 0.11V with the ignition on. I am assuming that the 5V part of the signal is to tell the VBs to ground the coil and 0V opens the circuit?

 

This is the "pullup" type circuit. With spark output normal, this should work fine, and should not cause the coils to charge.

The three LEDs should be on with the engine not running. Is this the case?

Ken

 

Yep all LEDs are on.

I think I will have to rewire my earth. There is no resistance then I tested it but something might be wrong with it. I can't see why it would have been trying to earth through the case but it certainly made the screw that holds the case to the car body very hot.

I have some of these new replacement VBs comming from Glens Garage and I will have to see if they help (with coils disconnected) I am guessing that a 12v led will do to indicate if the igniters are switching?