High RPM Breakup/Stumble
 

Hey guys. My problem is that my car has a bad higher RPM stumble starting at about 3000 RPMs. It does it both on the street and sitting in my driveway. After stumbling, if I let off, it wants to die.

I took the plugs out and cleaned them with no change.

A little bit about the car:
S4 coupe, s5 block w/S4 intake, custom exhaust w/header and single cat, Taurus alt, omp blocked running premix 100:1, thats all I can think of thats relevant.

I just need an idea of where to start. Thanks.

Fuel filter, fuel pump (or wiring), fuel sock, fuel pressure, clogged primary injectors, primary injector plug(s) loose, dirty air filter, Pressure Sensor or TPS (TPS goes into full throttle position at 3000 rpm).

If the car behaves poorly while free reving then it's not a secondary injector issue. And is this an NA or turbo?

N/a

All the sensors and ECU are S4?

It's the injectors. The RPM where you experience the stumble confirms it as that's about where the secondaries start transitioning.

Pull your injectors and have them back flushed and tuned at RC Engineering or other like place.

He suggested that his problem occurs while in the driveway so that precludes the secondary injectors from the cause of his problem. Unless he placed the car under load situations ( unplugged and capped vacuum hose to Pressure Sensor and disconnected the TPS) the secondary injectors should not be the issue.

Correct.


I had the injectors overhauled about 3 years ago. They'll get done again regardless during this anyway.

I figured it was a fuel related issue anyway. I just wanted to be sure it wasn't a common thing with a simple solution.

ECU pins 3E and 3C will have 12 volts w/key to on if the injector plugs are secure. The Brown/Red wire at the Pressure Sensor should read 3.5 to 4 volts w/key to on. TPS should range from 1 volt at idle(fully warmed) to 4.5 volts or so on the Green/Red wire w/the plunger fully extended.