Getting Random Misfire Code when driving on Highway or Higher speeds

[StrokerMax]

I’ve had an ongoing problem with getting a random misfire code while driving at higher speeds. The problem happens while under cruising conditions rather than hard acceleration and the car goes into limp mode and just starts stuttering.


If I turn the car off and back on then the problem goes away.


Yesterday I think my ignition control module (transistor) went bad. My car started misfiring and the problem wouldn’t go away with restarting the car and my tach was all over the place. I’m going to put in a new one tomorrow.


I just can’t figure out whats causing this . My ICM (Transistor) had less than 4000 miles on it when it went bad. My coil pack, plug wires, and spark plugs have about 4000 miles on them as well.


I’m running a lot of horsepower (Probably 500HP+) and the stock ignition is one of the few un-modified systems on my car. Is it possible that I should upgrade my ignition? Or could the problem be related to the location of my coil pack? Its mounted on the back of the block under the intake manifold.

My other thought is that this problem could be related to my CAS. I have a 1G CAS and have tried swapping it out and the problem still happens.

Would Enabling the cylinder misfire DTC check in ECMlink fix this possibly?


I bought this car 2 years ago and have since rebuilt the motor, tranny, and just about every system on the car. The prior owner hacked so many things on this car.


Any help is appreciated.

 

[jim95redgsx]

The 1G CAS is not compatible with the 2G ECU's misfire detection circuitry. This will show up as false misfires and the ECU will shut off the injector on the cylinder that it thinks is misfiring the most. It does this to prevent overheating the catalytic converter with too much unburned fuel and for emissions.

The ECU will only check for misfires after a 300 second, closed loop, highway cruise. It will not check for misfires at idle or WOT. Turning the key off and then back on will reset the ECU until it completes another 300 second drive cycle.

The solution is simple with ECMLink. Just uncheck the "cylinder misfire" box on the DTC's tab. This will disable misfire detection.

Your real misfire problem is different and is, most likely, being caused by the Power Transistor seeing that it is affecting the Tach reading as well.

Jim

 

[StrokerMax]

Thanks Jim! I will un-check the "cylinder misfire" box on the DTC's tab. Then replace my transistor.

 

[StrokerMax]

Okay So I put on my new transistor today. Started my car and it was running great (no more problem). Let it warm up for about 5 minutes and all of this sudden the tach drops to zero RPMS and it started mis-firing again.

I'm assuming I blew my new transistor somehow. Checked all my plug wires and everything is good.

I was reading that mounting these transistors is critical. Since I have a Magnus intake manifold and nothing is in its factory position, my transistor is mounted on the firewall. Its been there for about 3000 miles with no problems.

Could mounting of the transistor be my problem?

Either that I'm guessing its related to my coil pack

I swapped my CAS just to eliminate that... No difference.

Just ordered new MSD coils. Not sure what else could be causing my Transistor to blow

 

[smbgsx]

You ever figure this out? For what it's worth, I have a Magnus ITM as well. I mounted my transistor on the firewall, but I removed the paint where I mounted it then clear coated over the mounting bracket of the transistor and fastener, and sandwiched a ground strap between the bracket and firewall. I ran the strap to my engine block to ensure good ground, as it's my understanding that the factory ITM serves as a ground to the block when stock. But as you know there isn't a mounting location on the Magnus manifold.