P0300 Question

[libertybob]

Yesterday my wife was driving Libby and the MIL started flashing and the engine was losing power. She drove about 300 yards to a safe parking area and shut off the engine. I was right behind her in my truck so pulled over. We swapped vehicles. I started the engine (3.7l) and the MIL light was lit without flashing. I drove Libby home and all seemed normal. I pulled the codes P0300 multiple misfire, P0303 misfire # 3 cylinder and P0306 misfire on # 6 cylinder. I erased the codes and started the engine. The MIL light went out after starting as normal. I drove the vehicle around the block several times and no MIL. Since #3 and #6 cylinders are on opposite banks of the engine, I believe the misfire must have a common cause.

I had filled the gas tank about 15 miles earlier at a high volume gas station. Could there have been moisture in the gas that would cause a misfire? I have read that the relay might also be suspect. I have done a lot of reading about misfires last night and replacing parts without diagnosing the root cause seems common. I put 6000 miles on Libby since acquiring her and this is my first misfire. So, please help with your thoughts of how to identify the root cause.

 

[LibertyTC]

Ethanol fuels are a magnet to moisture. Water in fuel could cause misfire.
Try some of this quality stuff, at Walmart...
"Helps prevent phase separation by dispersing water throughout fuel as submicron-sized droplets that are safely eliminated while the engine operates"
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Link about Starbrite-Star Tron: Star Tron Enzyme Fuel Treatment Gas Additive Small Engine
For injector cleaning, I add Chevron Techron Concentrate also at Wallmart.
New vehicle to you= Generally a tune up check, spark plugs (use NGK as per under hood sticker gaped correctly) and coil pack inspection would be a good idea as well.
Jeep coils are hot, can eat the gap, so spark plugs every 25k miles are a good idea.

 

[Dave]

I had the same thing happen right after a long drive and then a fill-up. Got the random mis-fire code and then it went out after I started it a second time and never came back. Maybe something in the gas? I don't know. It was Sunoco.


I occasionally use Techron as TC does.


Dave

 

[CactusJacked]

Any time a misfire code pops up shortly after filling up at a gas station, first thing to suspect as the culprit is the gas. If the code doesn't come back, don't sweat it. But do avoid going to that gas station and see if it happens again.

 

[mightybeet]

its contagious!

 

[libertybob]

Follow up.....

Talked with my next door neighbor who is a Jeep mechanic. I told him about my misfire after filling up Libby. He said "just tell me you didn't fill up with *** gas." When I told him I had, he said garages in the area are finding problems with their gas. Guess the old saying that you get what you pay for is true. Cheap gas isn't always cheap. My mechanic buddy says moisture and carbon buildup are common problems with the gas I bought. Added a gas treatment to Libby and 30 miles after the incident no problems. If fact seems to be running better. Will be using brand name gas in the future.

Follow up: now make that 90 miles without misfires.