540i hesitation/popping

[Tiger]

Sounds like the ICV valve... do the test.

[632 Regal]

I vote intake gasket leaks.

[jofusfarr]

This problem has boggled me. My 540 will hesitate briefly, with popping (in intake perhaps), upon initial acceleration (1-2k rpm).

I can't seem to duplicate the problem while it is in neutral.

Something also worth mentioning is when I first start the car, if I put it in reverse or drive (put load on engine) fairly quickly the idle may bog down and the engine may die completely.

Fuel pressure is around 40PSI. I'm going to test it with another pump because I think it should be a tad higher (possible variable error in gauge though).

MAF is clean.

I DO have some nice exhaust leaks before the 02 sensors.

Any ideas?

[jofusfarr]

I believe I've isolated the problem to fuel pressure.

I jumpered the pump (engine not running) and it held at 40PSI which is not enough to even push through the pressure regulator (I clamped the return line with no increase in pressure noted). While 40PSI is enough to run the engine, when slightly more fuel is required such as with acceleration, it will cause problems.

CAUSE: the pump, recently retrofitted check valve, or fuel filters.

I'll put the gauge right after the pump to rule out filters/check valve.

The pump was a cheap ebay one (not more than a few months old) that had been recommended by shogun here at some point. It had a weak or no internal check valve to begin with...I'd not be surprised if it is crap already.

[Tiger]

Ahh... you didn't tell us that before... we assumed everything factory.