Intermittent engine misfire with MSD

[puffinator]

I have a 6AL-6425 and a Blaster coil installed in a 85 Porsche Carrera. The Motronic is also in place so I can operate in either mode. In MSD mode with orange and black to the Blaster and the red and white to Bosch coil the car intermittently misfires and at each misfire the red light blinks off on the MSD unit. These misfires occur in the span of several seconds but not at any repeatable frequency.

If I move the high tension wire to the Bosch coil and disconnect the red and white wires the car runs fine.

Has anyone else experienced this problem and could help?

[Bob Kontak]

If I read your input correctly, you removed the primary wires (red and white) from the Bosch coil and then connected the secondary coil wire to the Bosch coil and it runs fine.

The primary signal to fire is really important. You have disconnected those wires from the (Bosch) coil - but your car runs fine?

[guru944]

Puffinator:

Does your setup have the MSD Tach adapter and diode wired within your setup?

These are critical in order to have the msd/motronic working properly...see below:

If, after installing an MSD Ignition Control, your ta*chometer, fuel pump relay or electronic fuel injection (in foreign vehicles) doesn’t operate correctly, your ap*plication may require a Tach Adapter. This is due to the trigger signal not being strong enough to trigger both the MSD and the factory’s components.There are a few Tach Adapters available and for more information see pages 152 and 153. Each Adapter is simple to wire in and will have your MSD and vehicle firing away in no time! If you are triggering an MSD Blaster, 5, 6, SCI, or 7 Series Ignition with its white wire or points terminal, you will need the PN 8910 Tach Adapter. The PN 8910 will correct the operation of most voltage-triggered tachometers or fuel injection systems that do not work directly off the tach output terminal of the MSD Ignition Unit.

go directly to MSD for details: Tach Adapter - 8910

Click on instructions Tab



This should help, Later...

[puffinator]

Thanks for responding Guru944 and Bob.

guru944 - I do not have one of the MSD tach adapters but I had North Hollywood Speedometers modify my tach to accept the MSD signal and it works fine. My fuel pump and fuel injection seem to be working fine.

bob - when I disconnect the red and white from the Bosch, I have then gone back to running on the Motronic system.