Tachometer going crazy then misfire codes??

[MilitaryTalon]

Alright I took my car to the track last night and it ran great but on the way home I was on the interstate and the RPM gauge went nuts then to 0. The car was still driving fine and the ECU is still reading RPM because my ECU+ is seeing it. About a mile after the gauge went dead I got a CEL and the car ran like ass. I checked the code and it was multiple random misfires (can't remember the number) I then cleared the code the tachometer started working again and all was well for about 20 miles then all over again.

Any suggestions?

 

[1990gsx1781]

coil pack

 

[MilitaryTalon]

The coil causing the misfires I understand but how would that be affecting my tach?

 

[slickers111]

I agree on the coils possibly misfiring, but as for the tach, I would check all the connections and wires. Otherwise I would have no idea.

 

[MilitaryTalon]

I have new plugs and wires in the car and all are securely connected. Can't figure this one out...

 

[90_GSX_DSM]

Couldn't this be the power transistor unit? I know that it deals with spark and I've read that it also gives a signal to the ecu about the rpm's. When I was troubleshooting why my rpm gauge didn't work this came up several times. Can anyone else confirm this? Hope this helps.

 

[MilitaryTalon]

Anyone know where to get a new power transistor? Is it a dealer item or would AutoZone or Kragen have it?

 

[90_GSX_DSM]

I'm thinking it's going to be a dealer item. Check in the haynes manual they show you how to test the power transistor with a multi-meter.

 

[MilitaryTalon]

Alright I replaced the power transistor unit and the coil and I am still having the same problem. The tach acts like it has a mind of it's own then misfireing like crazy. Can anyone tell me what to check next?

I was thinking maybe the cam sensor or crank sensor, does this sound relivant to anyone else? Please give me some feedback.

 

[MilitaryTalon]

Is there a way to test the cam sensor without an oscope?

 

[MilitaryTalon]

Anyone? I am at a stand still. Is there anyone out there with a suggestion?