Originally Posted by mitsuguy
I'd have to do some research into the throttle body, but I might be able to address the rich condition...
first off, is the car 100% stock?
secondly, what has made you look into this to start? you said it runs ok, - any symptoms whatsoever?
Thanks. Yes, 100% stock car. I began to look into it because I get an intermittent rear O2 sensor high voltage code on one bank which I think is unrelated as it seems to get set shortly after going through car washes though I can't figure out where the water is getting that is causing a short in that case. So that's what got me to finally just buy a working BT OBDII adapter/torque because I wanted to start logging everything to see if I could catch the voltage either creeping up or just suddenly spiking during a water event. I just happened to notice the high negative trims and started to try to diagnose it since it seems they are too low to be "normal" while not quite low enough yet to actually set rich codes.
As for symptoms, no, driving around is fine except for maybe a slight delay that occurs if I quickly put the pedal to the floor between the pedal going WOT and the car actually kicking into a lower gear and going. Normal driving around is fine as I would expect since the ECU is still able to lean out the mixture enough.
The fuel trims do normalize out depending on engine speed it seems, where at high engine speed the long term trims go back closer to zero but then shoot right back into low negatives when dropping back to idle. This does make me start thinking about causes that could be linked to vacuum but it's a returnless fuel system so there is no vacuum controlled fuel pressure regulator (it appears pressure is cam controlled where the cam directly runs a secondary pump faster or slower when the engine speed changes), and a vacuum leak would cause positive fuel trims and not negative ones unless I am thinking completely illogically about this.
Only other thing would be that my wife complains about the smell of gas from the exhaust particularly on cold starts but it is winter and I'm not sure if it is related to the trim or just normal. Leaking fuel injectors? Would it not be very unlucky to have leaking on both banks of approximately equal amounts? Maybe a badly leaking cold start injector could do it since it feeds into surge tank but I have never heard of a cold start injector going bad.
Any thoughts to bounce around would be appreciated.
I never really thought about the cold start injector until I wrote this post -- it does make sense in a lot of ways to fit into the puzzle. At high engine speed the amount of fuel coming from the cold start injector even if it is leaking or stuck open would be less of an issue for the air/fuel ratio than at idle. Fuel leaking from the cold start injector should affect all cylinders (obviously). It is also fuel that the ECU does not anticipate or monitor, so it would cause the air fuel sensors to see a rich condition and lean things out to compensate. Maybe I am just fooling myself though since this part is easy to get to and doesn't cost a lot.
So an additional two things to consider are:
1) Is it (relatively...) safe to remove the injector just to see if it is dribbling? I assume yes, if the engine is off - but I'm not sure if the fuel system is pressurized in the key on engine off condition - well I have the starter button. If the fuel system isn't pressurized before ignition is actually started then, well, removing it at that point would introduce a huge vacuum leak I guess I could have a rag handy to jam into the hole it leaves.
I imagine I could even remove it with everything off and just smell it or smell inside the hole, if it is leaking fuel I imagine it's going to stink like gas where it normally wouldn't.
2) If it comes to replacing it, am I better off *shudder* taking it to a shop to do so... I have not had to work on the fuel system on any car ever and I'm not even sure where to start when it comes to depressurizing things ahead of time and making sure that things go back together again properly to avoid some fire hazard type of DIY blunders.
-- With engine off after my wife got home from a drive, I watched the fuel rail pressure from the scanner readings... it was dropping 20Kpa every 15 or so seconds. I'm pretty sure in a returnless system that the pressure in the rail should stay there when the engine is off unless going through an injector.
I'm ordering a cold start injector cheap from a junker just to rule it out, no point in going through the trouble of disconnecting everything to test it just to have to do it again if I find it's bad.