High RPM/WOT Miss!!!

[Mo95Talon]

1995 Talon TSi (fwd) - Starts and runs fine, occasionally between 5K - 7K rpms at WOT it feels like someone shut the key off minutely bad plugs, wires, coil? Has anyone had this problem before? Does a missfire on a 4-cylinder feel this violent? Thank you all.

 

[MrBoxx]

Is what you're describing like the car ran into a brick wall? If so, I'd say fuel cut. Check for boost leaks by doing a proper boost leak test.

If it's more of a random miss, what kind of spark plugs are you using and what are they gapped at?

 

[Mo95Talon]

It does feel rather dramatic. I use NGK 7131 BPR6ES gapped at .028. Can you explain the boost leak/fuel cut scenario, I am kinda lost. Thank you for the help (It did start doing this when it got cold).

 

[MrBoxx]

Here is a great FAQ on fuel cut, the common causes, and some solutions.

The short version is that when the MAS sees too much airflow, it cuts off the fuel supply to prevent damaging the motor. The majority of the time, this is caused by a boost leak or several. In colder weather, we see denser air charges, and this can also help contribute to it, as well as any boost creep that you may see. I know that my boost has risen at least 2psi since the weather turned chilly.

Try doing a boost leak test and see what you find. Get back to us with the results. Good luck.

 

[Mo95Talon]

Prior to testing for boost leaks, I tightened all hose clamps and adjusted all couplings. I did find one loose clamp on the hot side of the intercooler. Took it for a test drive and did not hit fuel cut at anytime (43 degrees outside).

Built my boost leak tester today, and found two small leaks coming from the BOV soft/hard adjustment nut (Greddy Type-RS) and from the BOV Intake Manifold vaccum line fitting (nut). I also heard bubbling noises from inside the Valve cover and did have pressure releasing out of the breather fitting (which I guess is typical after I researched it?).

I do have a few questions:

1.) How long is the system supposed to stay pressurized after you shut off the air compressor?

2.) Should the BOV release any pressure out of the piston? (Normal operation)

3.) Should the system pressurize quickly?

 

[Mo95Talon]

It was 28 degrees today and no problems. I am assuming I had a bad leak at the hot side of the intercooler (coupling) and the two small leaks at the BOV added to the cold weather probably helped me hit fuel cut. Thank you all for the help MrBoxx, I greatly appreciate it. I guess I will close this thread.