Code P0300, initial startup, engine stumbles hard and starts runs rough

JRLEONARD55

MEMBER
2007 CHRYSLER TOWN AND COUNTRY
3.8L
V6
2WD
AUTOMATIC
257,500 MILES

Until I give it gas and it will eventually smooth out. After a bit, the " Money Light " will come on, throwing a p0300 code it will run fine. I clear the code and start it again with no issues. It is the stumble start that causes trouble code, I can start up when cold and shut off and restart and no stumble and no money light. I can get away with this for a while but if it sits for any amount of time, it starts all over again. It's getting fuel, but I feel like fuel pressure bleeds off. I did fuel pressure test and it held at 50 PSI, but I didn't know specs at time it should be 58 + / - 5 I have thrown all kinds of parts at it, and most of them needed replaced. I believe it's the fuel regulator, does anybody have other ideas on what it could be?

1 Reply

AL514

MECHANIC
4,699 POSTS

Hello, you're correct on the fuel pressure spec 58psi +/-5psi. At idle if you raise the RPMs quickly the fuel pressure regulator should keep the fuel pressure up at the spec.The fuel regulator is part of the fuel pump, and the pump has a check valve that should hold the pressure up. So, the stumble is only at cold start up and the vehicle is fine the rest of the day? What parts have you changed so far? Have you done a fuel filter? It does sound like a fuel pressure issue. You could try leaving the fuel pressure gauge on the car overnight and see what the pressure is in the morning and what it gets to with the first two second prime at Key On and monitor the pressure while it's stumbling, since you only have that short period of time to catch this issue. That will tell you what's happening. I think since it smooths out after you rev it up it may be a volume issue more than a pressure issue.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/how-to-test-a-fuel-injector