2009 4.6 MPI bad fuel pump?

[Laxpro1376]

My 2009 Genesis 4.6 is starts on all 8 cylinders but once the car warms up and RPMs dip below 1000 it misfires and stalls out. I can cold start it and then drive until I have to stop at a light where it goes down into idle RPMs. I suspect my fuel pump could be the issue. Another thing I have seen it could be is the Idle Air Control valve. I have disconnected the fuel line from the fuel rail and it pumps when the car is turned on (before starting). But I would assume that from how it starts up right away. Next I would like to have a fuel gage reading as it stalls to see if fuel pressure dips as it starts to misfire and stall. I borrowed a fuel gauge from autozone but it came with threaded brass fittings and the fuel line in the Genesis fits in with an o-ring and two set screws, not threaded fittings. Has anyone here ever checked fuel pressure on a genesis that could lead me in the right direction? Has anyone experienced similar symptoms?

 

[joegr]

This certainly would not be a typical fuel pump failure. It is working fine when the engine needs a lot of fuel (cold start), but failing when when it needs very little fuel (warm idle)...
Why do you suspect the fuel pump for this?

 

[Laxpro1376]

This certainly would not be a typical fuel pump failure. It is working fine when the engine needs a lot of fuel (cold start), but failing when when it needs very little fuel (warm idle)...
Why do you suspect the fuel pump for this?

I guess I don’t know it’s the fuel pump, just my first thing to check. The car is a little down on power when it drives until it misfires and stalls at low rpm. The way it stalls it acts like the car is out of fuel. I think checking fuel pressure is a good place to start. It’s air, fuel, or spark. I’m starting by checking fuel.

 

[Laxpro1376]

Mainly the car stalls at a warm idle. I can start it up and leave it in park for a couple minutes and as soon as it tries to reduce RPM from 1000 to around 700 there are a 2-3 individual misfires and then the engine shakes and surges hard and stalls. I can start and drive right away just fine until it I come to a stop and idle while warm.

I’m leaning away from fuel pump and thinking more along the lines of:
O2 sensors
Crank position sensor
Idle air control valve
Failing ECM (yikes)
or any combination of the above

 

[Laxpro1376]

Finally took the car into a local import shop and they too suspect fuel pump. They did not have the adapter to measure fuel pressure when the car stalls but they can tell it is starving for fuel. Now I’m trying to locate a fuel pump for the car and I’m having trouble. Has anyone ever put an upgraded fuel pump in their gen sedan?

 

[mikec]

Fuel pumps often begin failing after they've warmed up a bit... thermal expansion causes parts to start jamming. The usual symptoms are:
1) normal operation when the fuel pump is stone-cold... like the first startup of the day.
2) after some time, when the pump is warming up, it begins to loose its ability to pump enough fuel to keep up with engine demands during acceleration or high-speed driving... but is able to keep up with low fuel demands such as idling.
3) as the pump wears/dies further, the ability to keep up with the engine's fuel appetite gets worse and worse and you find your car can idle but not accelerate or drive at any reasonable speed.

The OP's symptoms are exactly opposite this. Sometime debris in the fuel tank will block the fuel pickup. A gas cap with a jammed poppet valve lets too much vacuum accumulate in the fuel tank which makes it harder for the fuel pump to do its job... though that typically manifests as an inability to accelerate or maintain high engine power.

When the main engine computer (various names: ECU, PCM, ECM) starts going bad, one symptom can be normal operation on a stone-cold engine, stalling when coming to a stop sign or red traffic light about 10 minutes after startup, and then normal operation after 15 minutes or so. My 2009 did that a while ago. It'd stall once or twice a few miles from home... and then be perfectly fine for the rest of the drive. The dealer spent weeks trying to debug this. Mine threw several OBD-II codes, misfires on different cylinders error codes mostly.

If the dealer does replace the computer, make sure they do all software updates to it before you take the car. My dealer didn't initially... it was missing two TSBs and the symptoms of the first TSB reared their ugly head on my car days after the repair. Computers sitting in stockrooms aren't plugged into anything so they'll have whatever software version was "current" on the day they were manufactured... mine had the original 2009 software load.

Dealers also like to do a "throttle body cleaning" procedure. There are some skinny passages in there, especially related to the idle control stuff, so carbon buildup can screw things up. Hot idle needs less air (and less fuel) than cold idle so an idle control valve that's partially blocked will affect warm idle more. The dealer procedure isn't inexpensive... and it basically boils down to using fancy spray carburetor cleaner on any accessible interior part of the throttle body/intake manifold assembly.

The early Genesis models (maybe the later ones, I haven't read the service manuals for anything other than 2009s like my car) don't continuously monitor the crankshaft position sensor. If it's bad while the engine is trying to start - if the computer can see a few pulses from camshaft sensors without getting any crank pulses - it'll set the OBD-II code for the crankshaft position sensor. But once the engine is running, if the crankshaft position sensor doesn't output anything the computer simply gets confused and the engine stalls. And it likely won't restart either unless the sensor happens to fix itself.