P0300 Code on my workhorse engine

[Hazardman11]

My 6 liter workhorse on my class c jamboree has a misfire code P0300. It effects all cylinders. The gmc service thought it was a fuel pump and $1600 it was not. They then thought it was the injectors. Plugs, wires have been replaced. Silly me, feels like a simple fuel filter but they say it doesn’t have one (apparently in the fuel pump). I am 3500 miles from home and don’t think it will get me back without a solution as it’s running rough. Any thoughts?

Thanks!

Chris

[gjames50]

Originally Posted by Hazardman11

My 6 liter workhorse on my class c jamboree has a misfire code P0300. It effects all cylinders. The gmc service thought it was a fuel pump and $1600 it was not. They then thought it was the injectors. Plugs, wires have been replaced. Silly me, feels like a simple fuel filter but they say it doesn’t have one (apparently in the fuel pump). I am 3500 miles from home and don’t think it will get me back without a solution as it’s running rough. Any thoughts?

Thanks!

Chris

First you need to RUN away from the shop that you currently have working on it. They are not Diagnosing/Troubleshooting, they are SHOTGUNNING.

Take it to anyone who can actually troubleshoot and test. P0300 is not a specific enough error and will require actually checking and testing components and systems before you will find what is causing it.

For reference: https://www.fixdapp.com/blog/p0300-chevrolet/

For reference 2: https://www.gm-trucks.com/forums/top...-03-2500hd-60/

Literally could be almost anything.

[ArtJoyce]

+2 find a shop that can trouble shoot it. Your current shop is just switching out parts and charging you a lot of labor.

[Hazardman11]

Thanks a lot for the two links. Very informative. The shop was a GMC truck service center so I would hope they know what they are doing. The fact they couldn’t solve answers the the question I guess. They did a lot of what the links mention and even called GM headquarters for advice. We are traveling cross country and couldn’t hang out for days so after two days their final recommendation was to used high quality gas and add fuel injector cleaner.

I’ll try and schedule another shop further down the road. Bummer.

[catmandoo62]

what vehicle do you have.i do know some of the later ones did have the filter in the tank.

[vettenuts]

Does it misfire all the time, hot vs cold? Cruising vs accelerating?

[Hazardman11]

It varies but typically happened at higher speeds. I can feel it sputter. Sometimes the check engine light it solid and other times it flashes. Definitely not running right. I’m on the road heading home following a Criss country trip and it’s tough getting into a shop on short notice. I’m just driving and taking my chances. Using 93 gas with injector additive like the GMC shop suggested. Fingers crossed. It’s a 2006.

[Djfan]

P0300 is the worst code ever. Really, the manufacturer needs to hone this one in. It could literally be any one of about 25 things, ranging from a cheap, quick fix, to many thousands of dollars.

I know. I'm chasing one on my 2008 Suburban right now. I am about $450 into it, and no hope in sight. Super frustrated.

Get a qualified mechanic and be done with it.

Best wishes. I hope you win this soon.

[vettenuts]

The flashing light means it is currently misfiring, the solid light means a code has been set. What year is the coach?

[rikadoo]

I will offer my years of FORD drivability information, the code with ford states a Random misfire which can come from several sources, could be anything from slight cracks in cylinder heads allowing coolant to foul the spark plug to valve train. Some of the later models had in the computer software a system called “Mode 6” it gave the % of engine mis-fires as it relates to the firing order, i would look to see which cylinders had the highest rates of mis-fires an start my detective work from there. Many times i found the spark plug hole partialy filled with water which would cause the spark to arc down the side of the spark plug causing a mis fire, i dont know how GM is so the water in the plug hole may be moot, however random ignition misfires can be a hard one to diagnose. So something you can do is what i used to do BEFORE there was coil on plugs and mode 6, that was when we had spark plug wires, which were susceptible to leakage too. I would fill a spray bottle with water, then open the hood an sometimes i would remove the engine doghouse just to get a clear view, then you start the engine an spray the water on the spark plugs, if there is a boot issue it would start arcing causing a misfire, if at first it doesnt show up, let the engine get warmer then repeat. Generally speaking it such a sample test most “techs” are looking for a bigger problem, i found with gas engines stick to your basics 1st.
One more thing to know, gas engines in motorhomes wear out spark plugs WAY faster than cars do, they just have to work harder. So generally when a plug wears out you get a excessive gap for the arc to jump, and spark is lazy it will always go to the path of least resistance so if your boots are no longer soft an supple they can leak to ground alot easier than trying to bridge the gap in the cylinder with a fuel an air mixture under compression. All that said means this, when dealing with a random misfire establish a good base line first!!! Oh an if you have had a recient tune up, i cant TELL you how many times people have cracked a plug by not supporting the socket properly, which the spray bottle trick will find. Good luck
P.S. If you find you do have a cracked plug, replace the plug wire too even though its new cause once it leaks to ground it has a arc track that will continue to leak even though the plug was replaced.

[Djfan]

I just went to O'Reily's yesterday and checked the fuel pressure on my situation. It made it clear that the problem is fuel delivery (43 psi - 60 psi is the goal), so I am going to fix that.

Go check yours.

[Hazardman11]

I love this forum. You all are so helpful. I’m pretty good under the hood but this is more than I can handle. We are currently in Asheville (great place by the way) and I’m going to try and get an appointment in Nashville. Thank you very much.