Lanos 1.5 hesitates when pushing throttle down

[MaXiMiZoR]

I just did the Rising Rate Fuel Pressure Regulator Mod a few months ago and now my car has developed a strange symptom.

At idle the engine sometimes shocks and seems to stall. This occurs once in a while, not very often.
When I push the throttle down, the engine hesitates too long to give more fuel and sometimes it seems like the throttle valve is all the way open (engine gets lots of air) but the engine doesn't get any more fuel and it shocks/holds in.
I already swapped the Malpassi RRFPR back to the original FPR but the symptoms stay.

Could this be symptoms of a worn-out fuel pump? Or is it an injector issue?

[benzino]

well follow it down the line:
you installed the RRFPR (did the problem occur as soon as it was installed, or when you fiddled with it a bit?)
maybe an incorrect setting put too much fuel into the engine>
which in turn might have fouled the spark plugs>
or maybe fouled the 02 sensor

or have you checked both ends of the vacuum hose going into the fpr?

[MaXiMiZoR]

well follow it down the line:
you installed the RRFPR (did the problem occur as soon as it was installed, or when you fiddled with it a bit?)
maybe an incorrect setting put too much fuel into the engine>
which in turn might have fouled the spark plugs>
or maybe fouled the 02 sensor

or have you checked both ends of the vacuum hose going into the fpr?

It's not as simple as that... Spark plugs look very good (grey-light brown). Lambda sensor reads okay with my codereader. Vacuum is okay.

[MMamdouh]

remove the RRFPR and see if the problem is cured... if it does then the RRFPR mode is not done correctly

MMamdouh

[MaXiMiZoR]

remove the RRFPR and see if the problem is cured... if it does then the RRFPR mode is not done correctly

MMamdouh

I already swapped the Malpassi RRFPR back to the original FPR but the symptoms stay. I guess my fuel pump is down...