p0300 code

kent ross
02-03-2018, 05:34 PM
This one is driving me crazy.
I only get the code when the car idles. I can drive for a week to work and back all highway 43 miles each way.
I replaced the intake madifold gasket, MAP sensor, Just replaced all spark plugs, Plug wires and coils. Still getting the same code.
Here is my Freeze Frame data:
All of the plugs looked the same
When this first started i did receive one MAF sensor error so I cleaned the Sensor with some MAF cleaner. I do not have any other error codes.
this is a GMC 2003 YukonXL 5.3 non flex with 145,000 miles.
Any help would be nice

02-03-2018, 08:29 PM
Welcome to AF. The Freeze Frame stuff is over my head. I'm sure someone with that experience will respond.

I will however suggest some mechanical stuff to check for.

Pull the Dist cap. While pushing down on the rotor, gently rotate the rotor back and forth. Absolutely no rotational play is allowed. Next check for side to side movement on the rotor and again no play is allowed.

Check fuel pressure.

Let us know what you find.

kent ross
02-03-2018, 09:05 PM
2003 doesn't have a distributor but I need to go rent a fuel pressure gauge. That keeps coming up as a possible cause.

Tech II
02-03-2018, 10:11 PM
Doesn't your scan tool show misfires per cylinder?

kent ross
02-04-2018, 09:02 AM
it does not. I have used two different scan tools same thing.

02-04-2018, 10:33 AM
Can you feel any engine roughness/ misfire? Dirty injectors are another possibility, maybe a couple of bottles of Chevron Techron. I see the freeze frame info came on in open loop, how does the fuel trim look in closed loop?

kent ross
02-04-2018, 04:23 PM
Live Data shows
this was driving around the block.

02-04-2018, 05:00 PM
Warmed up? Your trim is a little high, adding some fuel , but doesn't seem enough to cause the code. Have you checked fuel pressure? To add, rare, but extremely rough roads can cause 0300. Clear it see what happens. How does it run, though?

kent ross
02-06-2018, 05:48 PM
Rough idle but great on the highway. have not had time to get to the autoparts store to get a pressure gauge.

kent ross
02-08-2018, 08:29 PM
I got a fuel pressure gauge and with the key on I have 25 PSI, with the engine running I have 40 PSI. So from what I have read on other post and sites I should have nothing less than 50 PSI running and 54-60 Key on. Is that correct? If so then the fuel pump needs to be replaced?

02-08-2018, 09:19 PM
Those are the correct specs, pretty low, surprised the engine runs ok. Replace the fuel filter first.

Tech II
02-08-2018, 09:41 PM
Ditto, Max...

kent ross
02-17-2018, 02:57 PM
ordered a new fuel pump while waiting for it to come in this week the Yukon ran perfect until Friday and it started acting up again. I am in the middle of replacing the fuel pump. Will let you know how it goes.

kent ross
03-04-2018, 08:40 PM
not to keep you all hanging but with the rain and all. I got the fuel pump in and it helped a little. But after some on asked what type of air filter I had and if I had an oil one replace it with a paper one. So out of desperation I did. Well wouldn't know the engine code went away and the rough idle stopped. it has been over a week now and so far so good.

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