Good day,
If there are any GM techs here, perhaps you could tell me if I might be missing something. I can¹t seem to shake a +25% Long Term Fuel Trim issue that causes hesitation at low rpms and occasional random misfire and cyl 1 misfire codes. The fuel pressure at the rail with the key off is 58psi and
52 constant while running. Engine vac is steady between 18-19in Hg and a propane test on all intake/plenum gaskets, etc shows no leaks. I have checked and verfiied the IAC and EGR. Both O2 sensors have been replaced, the TPS and MAP were replaced replaced (TPS had a flat spot and the MAP pigtail needed replacement anyway). The plugs (all regapped to OE specs) were all replaced, new cap, rotor, coil and wires. There¹s no arcing when I kill the shop lights. I had an issue awhile back with a leaking fuel pressure regulator and slow/no starts. This was remedied with a replacement FPR. I am considering that there may be a stuck poppet injector that¹s leaking fuel into the cylinder causing the misfire but this theory isn¹t supported by my fuel pressure readings. The in-tank pump and screen have also been replaced within the last few months. Other than trying OEM wires, perhaps replacing the ignition control module or worst case, needing a new fuel spider, does anyone have any other ideas of what I might be missing? A ?tap test¹ of the ECU shows no change in fuel trim/hesitation. Water sprayed at the cap,wires shows no arc or stumble. The distributor is new as of maybe 6mo ago and the current problem didn¹t exist at that time so I don¹t think it¹s a bad gear.I¹m off to get a motorvac treatment at a local shop today in case one of the poppet springs is a gummed up or something.
Thanks and take care, Andrew.