P0300 code, please help!

[Ashvin]

I just had the head gasket replaced on my 00 maxima with 217,000 miles. They also sent the heads to be machined. This had to be done twice because I guess they didn't do the heads right the first time and the car was running super rough. I took it back and they machined and adjusted the heads again and this time it was running smooth for about a week. But now I got the p0300 code all of a sudden. Is this something thats related to them changing the head gasket and machining the heads? or is it something different? I've already replaced 4 of the coils before, but this code is random multiple misfire so I don't know what to do. My spark plugs were changed right before the head gasket ordeal.
Modified by Ashvin at 8:34 AM 5/8/2009

[maxhopper]

Check here zerothread/230317

If that doesn't address your problem take it back where you had the head work done.

[Ashvin]

Thanks for the reply. I changed all the coils, and put in new Platinum spark plugs this weekend, but the light came back on. could it be that my fuel filter or injectors need to be changed so more fuel can get to the engine now that I have better compression? or do I need new heads? Could they have shaved them down too much? As you know the Fuel filter is in the gas tank so It has never been changed.

[maxhopper]

My guess would be that they took too much material off the head. If that is in fact the case, you will need new heads. I would also find out why they machined the heads in the first place. Were they warped? If they were warped what about the deck of the block, was it warped too?

[Ashvin]

Thanks for the reply. I changed all the coils, and put in new Platinum spark plugs this weekend, but the light came back on. could it be that my fuel filter or injectors need to be changed so more fuel can get to the engine now that I have better compression? or do I need new heads? Could they have shaved them down too much? As you know the Fuel filter is in the gas tank so It has never been changed.

[maxhopper]

You should not need new or bigger injectors. The people who did the head work screwed something up. I'd take it back and have them fix it.

[Ashvin]

So I should say that the car is not actually missing. Not that I can notice anyways, or that affects the performance. I does worry me though that SES light starts blinking at highway speeds and then stops blinking when I slow down. Should they have done a head and valve job automatically with the head gasket replacement? Is that standard? My engine never had a problem before.

[Ashvin]

I just picked up the car for the mechanics and they checked the compression and it was at 150 which they said where its exactly should be. Is that too low and causing the code? What should the compression be? They also said they pressure tested all the valves for leakage again and they are not leaking, and they checked the fuel pressure and it is fine.They told me despite the code there is no misfire. Let me say again the car is running great, with no performance problems that I can really notice except it's still a little shaky on idle, but not as the bad as the first time they did the head job. They said it must be my computer and that I should take it to a auto electric place for better diagnosis and scope the valves. I have never had a computer problem before, and it seems too weird that all of a sudden my computer is spitting out wrong codes for no reason.What do you guys think?

Modified by Ashvin at 6:49 AM 5/14/2009
Modified by Ashvin at 12:59 PM 5/15/2009

[Ashvin]

The new mechanic checked the compression himself. The front is 150 but the back is at 230! They didn't check the back. The whole thing has to be taken apart and the cams realigned and reset. The guy is willing to redo it so i guess I'm gonna have to give him a third chance.

[maxhopper]

Good deal! I'm glad they figured it out. It's good that the place is standing behind their work, and I think you're attitude about the ordeal will help getting it resolved. Be cool about it (stuff happens), but make sure that the problem gets fixed properly.

I would ask that they pull the back head off and inspect the valves, since the VQ is an interference engine; and the timing being misaligned can cause damage to the valves and/or pistons.

Be sure to get records of each visit, and see if they offers any kind of written warranty on their work.

My guess is that you will need a new head before it's all said and done. It is also standard that when replacing one head, you do both.

[Ashvin]

The first mechanic looked at the car again, after I told him that the electrical mechanic said the problem is not electrical and that he thinks the problem is the cams being out of time.He took the car somewhere else himself and had a "master mechanic" look at it. Now they say the problem is the rings can't handle the compression from the newly machined heads and there is too much compression for the bottom part of the engine. They say it is not fixable. They are refunding me all my money and said just to drive it till it eventually dies. He said it would just run rough with little power and burn gas, and that it could last a whole bunch more miles, but the point is he can't fix it.How long do you guys think it will last? I went in with a head gasket problem and ended up with a ruined engine. At least I'm getting my money back.

[maxhopper]

Personally, I'd be super pissed about it!

The problem is fixable, he just doesn't want to fix it. He needs to replace both heads, period.

It is good that you got your money back, but like you said, now you have a junk engine. I'd contact the better business bureau or an attorney. He's the one who ruined your engine. You went from a car that needed a head gasket to a car that needs heads or eventually an engine.

It's going to be hit and miss as far as how long your engine will keep running. Good luck!