mrl390 Posted March 17, 2011 Report Share Posted March 17, 2011 (edited) Well I spent a good but of yesterday afternoon with a guy I work with trying to diagnose why my cars idles so poor, misfires and starts hard every now and then. We checked just about everything we could with the scan tool. Checked the TPS, its fine. Checked the coil packs, they are fine. Its got new plugs and wires, PCV valve and new intake gaskets. Checked the pressure at the fuel rail and it is right in spec. Also opened each injector one by one with the scan tool so they all open. Im not sure if one may be hanging open or not tho. We are getting a rich reading on the LT fuel trim but short term isnt unusually high?? The computer is telling the engine to idle down correctly but it will only go as low as 900rpm when it calls for 800. So recap, running rich, idling poorly and intermittant hard start. Our thoughts on problems were either an injector stuck open, a bad O2 sensor, vacuum leak or carbon buildup in the IAC keeping it from closing all the way. What are your guy's thoughts? Of the above what sounds like it could be the problem or what else can you think of we are missing? 97 monte 3.4 dohc Edited March 17, 2011 by mrl390 Quote Link to comment Share on other sites More sharing options...
95 vert Posted March 18, 2011 Report Share Posted March 18, 2011 FPR leaking into the vac line? Def sounds like it has a vacuum leak. Quote Link to comment Share on other sites More sharing options...
AL Posted March 18, 2011 Report Share Posted March 18, 2011 (edited) FPR leaking into the vac line? Def sounds like it has a vacuum leak. A vacuum leak wouldnt cause long term fuel trims to rise, it would cause short term fuel trim to be close to +20-25% while the 02 sensor is reading lean... Edited March 18, 2011 by AL Quote Link to comment Share on other sites More sharing options...
mrl390 Posted March 18, 2011 Author Report Share Posted March 18, 2011 So does that completely rule out a vacuum leak then or just a leak to the FPR? It has correct fuel pressure at idle and under throttle as well as KOEO. I would assume that means the fuel delivery part is operating propery (pump, FPR as well as vacuum to the FPR). That leaves me with O2 sensor, IAC stuck open or a leaky injector. Is there any way to test if an injector is closing completely or do I need to remove it to check it? I forgot to mention that the scanner is calling the misfire random because many of the cylinders are reading a misfire but the majority of the counts were on cylinder 6 (20-25 counts when the other misfiring cylinders were reading like 4-5 counts at the most). From what I understand, cylinder 6 is the front right cylinder (left bank, rear cylinder). Quote Link to comment Share on other sites More sharing options...
mrl390 Posted March 18, 2011 Author Report Share Posted March 18, 2011 Update, I replaced the rear O2 sensor today and I cleaned the IAC. The IAC wasnt too dirty. Neither solved the problem. No change. Im really stumped here. Quote Link to comment Share on other sites More sharing options...
95 vert Posted March 19, 2011 Report Share Posted March 19, 2011 A vacuum leak wouldnt cause long term fuel trims to rise, it would cause short term fuel trim to be close to +20-25% while the 02 sensor is reading lean... A large enough leak would cause ST trims to max out and LT to rise. But that would be a massive leak. Idle being higher than PCM control would be a vacuum leak. FPR leak could imitate "leaky" injectors and cause trims to go negative. Hard starting and rough idle could be caused from a fuel leak into the vacuum line from the FPR. Quote Link to comment Share on other sites More sharing options...
mrl390 Posted March 19, 2011 Author Report Share Posted March 19, 2011 Should I be checking for fuel coming out of the FRP with the car running or can I just turn the key to on and prime the pump and check? I checked with the key on but not with the engine running. I assumed that if it were leaking, it would leak out as soon as the rails were pressurized. Its not leaking with the pump primed. Quote Link to comment Share on other sites More sharing options...
AL Posted March 19, 2011 Report Share Posted March 19, 2011 do it with it running Quote Link to comment Share on other sites More sharing options...
mrl390 Posted March 19, 2011 Author Report Share Posted March 19, 2011 I pulled the line real quick today with the car running. No fuel leaked out. Quote Link to comment Share on other sites More sharing options...
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