P0300 / Rough Idle / Gas Smell

[ComputernerdBD]

Hey everyone. Well I have that dreaded P0300 problem... I drove it a couple hundred miles yesterday (quite a bit of it on bumpy roads) and during the last 100 FEET when I hit a small bump all of a sudden the engine starts shaking, my check engine light starts flashing, RPMs are fluctuating and the lights are flickering. I limp it into my parking space and when I get out of the car I smell gas. I pull the code and find 1 active and 1 pending code: P0300. Nothing pointing to a particular cylinder. I just replaced the spark plugs in the spring and everything has been fine since then until now. I have tried unplugging coils 1-5 (can't get to 6 right now) individually but cannot find any change in how it is running. In fact it just throws P035* codes that way. I just bought an Actron U-Scan to try to get more info, but it shows no info in misfires. If anyone has any suggestions, any info would be appreciated. I am hoping I just have one or two bad coils somewhere. It runs like a pig right now. The misfire and shaking seems to show itself more at lower RPMs.

The coil packs are original. I find it shocking that it just happened after hitting a small dip in the road when I was driving on bumpy, poorly maintained city roads just an hour before and highways with bad bumps earlier that day. What could I be looking at? Should I just replace all of the coils now and see if that works? If not, what else are common issues? I have a 2007 with only 26,000 miles.

If anyone has any suggestions, any info would be appreciated. I am hoping I just have one or two bad coils somewhere. It runs like a pig right now. Thanks

 

[djthumper]

If you only have 26,000 miles why did you change the plugs? What kind of plugs to you put in? Our trucks seem to prefer the AC Delco.

 

[ComputernerdBD]

If you only have 26,000 miles why did you change the plugs? What kind of plugs to you put in? Our trucks seem to prefer the AC Delco.

I changed them to try to get better mileage. They are AC Delco 41-103.

 

[loondog33]

Did you attempt to gap the plugs? The spot of iridium is small and fragile. Attempting to gap with a disk tool will damage the iridium tip. Typically plugs are good for 100,000 miles, and I assume the same for coil packs.

As far as gas milage, it isn't getting any better than 18mpg in city, and that's hitting all green lights. I went from a 4 cylinder vw jetta, that I rarely spent $40 a week in gas, to this beast that $40 in gas gets me down the block a few times and back.

But I'll pay a few extra dollars for the piece of mind for the 4x4 and heavy frame suv, vs my old 3000lbs go kart. Plus, being 6 ft tall, it was hard on the back climbing in and out of little cars.

 

[djthumper]

I wouldn't just take the coil packs out but the plugs as well, if you are still smelling a strong fuel smell. Likely one of the plugs is not burning the fuel and that will likely be where your problem lies. Another likely suspect would be your injectors are partially clogged.

Your fuel mileage will probably benefit from cleaning the throttle body and resetting the PCM.

 

[ComputernerdBD]

I didn't try to gap the plugs, especially since they were already at where they were supposed to be. I checked back and I replaced those in April.

The throttle body was cleaned at the time I did the plugs. How can the injectors be tested?

 

[djthumper]

You can do a pressure test at the fuel rail with a tester that most parts stores have. To test the injectors you need noid lights to do that at the harness. Out here I just got use to periodically dump some injector cleaner into the tank.

 

[ComputernerdBD]

Took it to the dealer and they are finding hard misses on cylinders 1 and 2. Says possible intake/exhaust gaskets or something internal.... Wow

 

[djthumper]

How did they determine that? I am sure they plugged in the tech II. It would be nice if they showed you what they found.

 

[signalnc]

I'd switch around some coil packs see if the misfire follows them.


and I would not trust the dealer. not with a short answer like that

 

[ComputernerdBD]

I should have tried that... Maybe I should replace them all first

Maybe not considering that they just called me back and said it is a cylinder head and the cost is over $3000.....

 

[djthumper]

I think I would get a second opinion. I do trust the dealers. With only 26000 miles I find it very hard to believe.

 

[ComputernerdBD]

Doing that now. Got the car from the dealership earlier and drove it to another shop where I go often. They found the dealer's claims interesting also since it seems that all they want to do is sell a head when they can have a machine shop put new valves in it.

 

[signalnc]

I think you need to go get your truck back, buy two coil packs, or switch 1&2 with 3&4, see what happens. Also check the plugs.

 

[ComputernerdBD]

Unfortunately this time GM was right.... 1 and 2 had no compression. Not sure how it made it in that condition to the shop in that case...

Independent shop where I normally go to for both of my trucks confirmed it. It is something internal and not just something simple like a coil. They were pulling the valve cover to look further into it, but it may not need a head, just replacing the valves on the existing head. Hoping for a call early in the morning.

My big question with this whole thing is how this happened so suddenly at 26,000 miles?

 

[djthumper]

That I really have no idea.

 

[SmokeyMcBlazer]

Lack of use.

 

[KNBlazer]

Unfortunately this time GM was right.... 1 and 2 had no compression. Not sure how it made it in that condition to the shop in that case...

Independent shop where I normally go to for both of my trucks confirmed it. It is something internal and not just something simple like a coil. They were pulling the valve cover to look further into it, but it may not need a head, just replacing the valves on the existing head. Hoping for a call early in the morning.

My big question with this whole thing is how this happened so suddenly at 26,000 miles?

1 & 2 exh valves on mine were burnt, eventually head gasket gave way, random misfire, 3 weeks & 1k miles later, all good...

 

[KNBlazer]

Unfortunately this time GM was right.... 1 and 2 had no compression. Not sure how it made it in that condition to the shop in that case...

Independent shop where I normally go to for both of my trucks confirmed it. It is something internal and not just something simple like a coil. They were pulling the valve cover to look further into it, but it may not need a head, just replacing the valves on the existing head. Hoping for a call early in the morning.

My big question with this whole thing is how this happened so suddenly at 26,000 miles?

If you bought the truck new from the dealer, I would call Customer Service and "KINDLY" ask for assistance, I mean 26k miles!!!!!!

My truck gave out at 200k miles...

 

[The_Roadie]

3 weeks & 1k miles later, all good...

Plus a home equity loan and three weeks indentured servitude cleaning the shop's bathrooms with a toothbrush.

 

[ComputernerdBD]

Update: Shop removed the intake and valve cover and did a compression test. It was actually only cylinder 1 with the problem and it was a keeper and valve spring that needs to be replaced. Everything else looked fine. The head does not even need to be removed to fix it. Parts are on the way and the total cost is about 70-75% less than GM.

 

[KNBlazer]

Update: Shop removed the intake and valve cover and did a compression test. It was actually only cylinder 1 with the problem and it was a keeper and valve spring that needs to be replaced. Everything else looked fine. The head does not even need to be removed to fix it. Parts are on the way and the total cost is about 70-75% less than GM.

That's beyond great news.... how's your compression?

 

[djthumper]

I am glad to hear that it isn't as bad as initially thought.

 

[ComputernerdBD]

I was told that compression was around 200 for the other cylinders. Not sure what #1 was yet but they did another compression test today and it was fine. They finished the work this afternoon and I am told it runs like new. I will pick it up tomorrow. Thanks for all the tips.

Not as bad as $3100, but still a bit for an issue like this. It was less than a 1/3 of that... The issue was a valve spring all along...

 

[ComputernerdBD]

Got the truck back today and saw the damage firsthand. The valve spring was broken in two pieces and they also replaced the keeper. They did a great job with the repairs and even painted the valve cover and replaced the intake manifold/valve cover gaskets. The truck runs like new and even QUIETER than it was before the incident. The verdict is still out on this one but gas mileage also seems slightly improved. The valve didn't even drop into the cylinder which was really lucky.


Well I am not sure what to make of all this....... 26k miles and a valve spring breaks out of nowhere.

My opinion: I will never allow a GM dealer to touch either of my trucks again. That is one of the things I am taking from this incident. This high estimate and improper information was the very last straw for me with a long history of problems with multiple dealers. When the recall comes through for the power window switches again, is it possible to ask them to send me the part?