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.

 

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.

 

time to do a motor swap and call it done

 

I don't think so, not at this point after I spent all this money to change the head gasket. Any Other Ideas?

 

I would replace the fuel filter, PCV and then use Chevrons Techron injector cleaner for starters.

Check for:
-vacuum leaks.
-Front 02 sensors.
-leaking injectors.
-Make sure the head work was done correctly and the valves were not damaged. Check the compression.

 

PO300 is a common occurance for our cars. If the vehicle is not actually missing, I wouldn't worry about it too much.

 

The car is not actually missing. It runs fine. It worries me though that the SES light comes on blinking at highway speed. When I slow down it stops blinking but stays on. I never had any check engine light problems before the head and valve job. Should they have automatically done a head and valve job with the head gasket replacement? Is that standard?

 

Despite your diagnosis, the engine is in fact missing. Flashing CEL is never good nor should it be dismissed. You have ignition or fuel delivery problems. Most likely ignition, since the 5th Gen is notorious for that.

 

What kind of ignition problems? I haven't noticed an ignition problem. I just replaced all the plugs and the coils a few days ago but light came back on. This all started after the head and valve job. Is it standard to do a head and valve job while replacing the head gasket?

 

OP, do you experience any perofrmance problems... as in your car being slower?

 

It is advisable to do it.

 

It is a good idea.

The heads are machined to make sure they are true and not warped and with over 200,000 miles, replacing the valve guides and valve guide seals are a great/must idea and lapping the valves for a positive seal is the least minimum they should have done. And the max would be to replace all the valves and resurfaces the valve seats.

 

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, so it's not the fuel filter or injectors.
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 weird that all of a sudden my computer is spitting out codes for no reason.
What do you guys think?

 

do you have a rough idle 100% of the time, or occasionally?

 

Rough Idle %100 of the time and a lot more rough after 10-20 miles of driving.

 

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.

 

I am also experiencing that problem. I also have P1320 as well as P0300. The first time I got the P1320 is back to more than one years ago. Though I got the SES on, it runs fine. First thing I did was replacing all the spark plugs. After that, I tried with new ignition coils. But, still SES was on. I noticed some oil on the spark plug and replaced head valve cover gasket. But, it was no use. Like Ashvin's, mine is shaky on idle from time to time. Not so often, say, it's once in a week or less. Recently, I saw SES blinking and got P0300 too. It seems to happen when I speed up over 3000 rpm. In http://www.nicoclub.com/FSM/maxima/2000.5_Maxima/ec.pdf (page 380-), they say "Always drive vehicle at a safe speed." Yesterday, I also picked up my car for the mechanics and they inspected the wireset, spark plugs, ignition coils, injectors, etc. but didn't find out the cause. They said they possibly find the problem only when it misfires or run shaky. So, I left my car there for more inspection. Anyway, blinking SES does not seem to be in good condition. I hope they find out the cause in a few days.

 

Thats interesting. I got the same 0300 code and had oil in 2 of my spark plugs cylinders and i'm in the middle of ordering the new 04 valve cover and gasket. 120 bucks cheaper to get the 2004 valve cover. Its the same thing if you have the VQ35 max from 2002-03.

 

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.

 

You might want to have another mechanic, to at least do a Cylinder leak down test.

http://www.carcraft.com/techarticles/116_0406_cylinder_leakdown_tester/index.html

I have no practical experience on these engines, but I would look into the timing chain, the mechanic could have installed wrong when putting heads back or the chain is stretch/worn from the high mileage causing the cams to being out of time.

If all the rear cylinders that have the lower compression, it is a good chance the cams from that head were misalign go to EM-28 to EM-32 of the manual.

 

before you throw all this money into it, look into an engine swap with a used VQ35 with low miles.. better than having to put up with this crap for the rest of the car's life, you know? for all that money you spent on the head gasket, i'm sure you could do a swap for the same amount if not a little more

 

I got a P0300 code after changing spark plugs and coil packs. Now my car runs like shizz and I have no idea what's causing it. Anyone else have this issue?

 

^^^ i have the same problem

 

^^also have the same issue can someone chime in on this